The marine cyanobacterium Trichodesmium has a remarkable ability to interact with and utilize air... more The marine cyanobacterium Trichodesmium has a remarkable ability to interact with and utilize airborne dust as a nutrient source. However, dust may adversely affect Trichodesmium through buoyancy loss and exposure to toxic metals. Our study explored the effect of desert dust on buoyancy and mortality of natural Red Sea puff-shaped Trichodesmium thiebautii. Sinking velocities and ability of individual colonies to stay afloat with increasing dust loads were studied in sedimentation chambers. Low dust loads of up to˜400 ng per colony did not impact initial sinking velocity and colonies remained afloat in the chamber. Above this threshold, sinking velocity increased linearly with the colony dust load at a slope matching prediction based on Stoke's law. The potential toxicity of dust was assessed with regards to metal dissolution kinetics, differentiating between rapidly released metals that may impact surface blooms and gradually released metals that may impact dust-centering colonies. Incubations with increasing dust concentrations revealed colony demise, but the observed lethal dose far exceeded dust concentrations measured in coastal and open ocean systems. Removal of toxic particles as a mechanism to reduce toxicity was explored using SEM-EDX imaging of colonies incubated with Cu-minerals, yet observations did not support this pathway. Combining our current and former experiments, we suggest that in natural settings the nutritional benefits gained by Trichodesmium via dust collection outweigh the risks of buoyancy loss and toxicity. Our data and concepts feed into the growing recognition of the significance of dust for Trichodesmium's ecology and subsequently to ocean productivity.
Trichodesmium, a globally important, N2-fixing and colony-forming cyanobacterium employs multiple... more Trichodesmium, a globally important, N2-fixing and colony-forming cyanobacterium employs multiple pathways for acquiring nutrients from air-borne dust, including the active collection of dust particles. Once concentrated within the colony core, dust can supply Trichodesmium with the limiting nutrients iron (Fe) and phosphorus (P). Studying particle collection by natural colonies, we recently documented a preference for Fe-rich over Fe-free particles. In this follow-up study we examined if colonies selectively collect P-rich particles. Over an entire bloom season, we incubated ~1 200 Trichodesmium colonies from the Red Sea with P-free CaCO3, P-coated CaCO 3 and dust. We utilized three discrete parameters to characterize the colony-particle interactions and integrated them to an index that describes the particle collection behavior over time. Colonies were found to preferably interact, center and retain P-coated CaCO3 in comparison to P-free CaCO3, suggesting that Trichodesmium can optimize its P-acquisition by selecting P-rich particles. In both current and former studies, colonies clearly favored dust over all other particles tested, while nutrient-free particles were barely collected or retained, indicating that Trichodesmium senses the particle composition and preferably collects nutrient-rich particles. This unique ability contributes to Trichodesmium's current ecological success and may assist it to flourish in future warmer oceans.
Highlights Natural Trichodesmium colonies collect and maintain dust within their colony core Usin... more Highlights Natural Trichodesmium colonies collect and maintain dust within their colony core Using synthetic particles we tested if colonies select the particles they collect Colonies selectively collect and retain nutrientrich over nutrient-free particles Selective collection of particles optimizes their nutrient acquisition from dust
Dust is an important iron (Fe) source to the ocean, but its utilization by phytoplankton is const... more Dust is an important iron (Fe) source to the ocean, but its utilization by phytoplankton is constrained by rapid sinking and slow dissolution dust-bound iron (dust-Fe). Colonies of the globally important cyanobacterium, Trichodesmium, overcome these constraints by efficient dust capturing and active dust-Fe dissolution. In this study we examined the ability of Trichodesmium colonies to maximize their Fe supply from dust by selectively collecting Fe-rich particles. Testing for selectivity in particle collection, we supplied~600 individual colonies, collected on multiple days from the Gulf of Aqaba, with natural dust and silica minerals that were either cleaned of or coated with Fe. Using a stereoscope, we counted the number of particles retained by each colony shortly after addition and following 24 h incubation with particles, and documented translocation of particles to the colony core. We observed a strong preference for Fe-rich particles over Fe-free particles in all tested parameters. Moreover, some colonies discarded the Fe-free particles they initially collected. The preferred collection of Fe-rich particles and disposal of Fe-free particles suggest that Trichodesmium can sense Fe and selectively choose Fe-rich dust particles. This ability assists Trichodesmium obtain Fe from dust and facilitate its growth and subsequent contribution to nutrient cycling and productivity in the ocean.
תקציר בעברית: בשל הצפי לגידול האוכלוסייה ולהתרחבות הגודש בכבישים צפויות להחמיר גם ההשפעות הסביבתי... more תקציר בעברית: בשל הצפי לגידול האוכלוסייה ולהתרחבות הגודש בכבישים צפויות להחמיר גם ההשפעות הסביבתיות של ענף התחבורה בישראל. לשם התמודדות עם שינויים אלה יש לצמצם משמעותית את הנסועה הפרטית. אחד מכלי המדיניות שיוצרים שינוי בביקוש לנסיעות הוא עבודה מרחוק, המאפשרת לעובדים להימנע מנסיעות באזורי ביקוש ובשעות השיא. מאמר זה סוקר את הידע הקיים בנושא מדיניות עבודה מרחוק, את ההשלכות האפשריות של יישום מדיניות זו בישראל בכלל, ולנוכח השפעות מגפת הקורונה (COVID-19) בפרט. לעבודה מרחוק יש פוטנציאל לתועלת משקית רבה, כגון חיסכון בעלויות החיצוניות מהנסועה, הגדלת הפריון והעלאת פרודוקטיביות העובדים, חיזוק הפריפריה, צמצום פערים מגדריים והנגשת שוק העבודה לאוכלוסיות מוחלשות. עם זאת, עבודה מרחוק יוצרת גם אתגרים לא מעטים: ניהוליים, טכנולוגיים, חברתיים ונוספים. שיעור העובדים מרחוק בישראל נמוך משמעותית ביחס למערב, אך נמצא במגמת עלייה במגזר הפרטי. לעומת זאת, הסכמי השכר במגזר הציבורי אינם מאפשרים עבודה מרחוק מלבד במקרים בודדים. דו"ח ועדת מומחים שפורסם לאחרונה ממליץ לממשלת ישראל לקדם תוכנית לאומית לעידוד עבודה מרחוק, שתכלול הצבת יעדים כמותיים לעבודה מרחוק במשק, תמיכה בתוכניות פיילוט ומתן תמריצים למגזרים השונים. מגפת הקורונה חשפה עובדים ומעסיקים רבים במשק לאפשרות של עבודה מרחוק, וזו הפכה לאחד הסממנים הבולטים של התקופה ויושמה לראשונה במגוון ענפים במשק, לרבות המגזר הציבורי. נראה כי להתנסות לא מתוכננת זו תהיה השפעה גם בתום תקופת המשבר על מיסוד והטמעה של עבודה מרחוק במשק הישראלי, וייתכן שבתנאים מסוימים אף על היקף הגודש בכבישים. יש לזכור כי בחלק גדול מהמשק בוצע מעבר חירום לא מתוכנן לעבודה מרחוק, ללא הכשרה מתאימה לעובדים ולמנהלים, ללא תיעוד ובקרה נאותה הנדרשים מפיילוט שמופעל במצב שגרה, וללא שימוש במרכזי תעסוקה משותפים המותאמים לעבודה מרחוק. למרות זאת, המשבר יצר הזדמנות חשובה לקידום עבודה מרחוק בישראל ולזיהוי פרקטיקות אפקטיביות לעבודה מהבית. התובנות שעולות כיום ושימשיכו להצטבר בעקבותיו יאפשרו למקבלי ההחלטות לקדם ולמסד הסדרי עבודה גמישים במשק הישראלי גם לאחריו. English Abstract: The projected population growth and the expansion of traffic congestion, are expected to exacerbate the environmental impacts of the transportation sector in Israel. To deal with these changes, the mileage of private transportation must be significantly reduced. Teleworking (telecommuting) is one of the policy tools that can alter road travel demand, by allowing employees to avoid travelling in peak hours and in high demand areas. This paper reviews the existing knowledge on teleworking policy, the possible consequences of implementing this policy in Israel in general, and in light of the COVID-19 pandemic effects in particular. Teleworking has a great potential for economic and social benefits, such as transportation externalities saving, increasing productivity, strengthening the periphery areas, reducing gender inequality and making the labor market accessible to underprivileged populations. However, teleworking also creates quite a few challenges: administrative, technological, social and more. The rate of teleworking in Israel was significantly lower than in western countries, but is now on the rise in the private sector. In contrast, public sector employment contracts prohibit teleworking, except in very few specific cases. A recently published expert opinion report recommends that the Israeli government promotes a national plan to encourage teleworking, which will include setting quantitative targets for teleworking, supporting pilot programs and providing incentives to the various sectors. The COVID-19 pandemic has exposed many employees and employers to the possibility of working remotely, which has become one of this period's prominent features and was implemented for the first time in a variety of sectors and industries, including the public sector. It seems that this unplanned natural experiment will also have a positive effect on the institutionalization and assimilation of teleworking in the Israeli economy, beyond the pandemic, and under certain conditions even on the extent of traffic congestion. It should be noted that in a large part of the labor market, an unplanned emergency transition to teleworking has occurred, without proper training, documentation and proper control required from a pilot program in routine conditions, and without the use of hubs, adapted for teleworking. Despite this, the crisis has created an important opportunity to promote teleworking in Israel and to identify effective practices for working from home. The insights that arise today and will continue to accumulate in its wake, will enable decision-makers to promote and establish flexible working arrangements in the Israeli economy after the pandemic.
תקציר בעברית: בשל הצפי לגידול האוכלוסייה ולהתרחבות הגודש בכבישים צפויות להחמיר גם ההשפעות הסביבתי... more תקציר בעברית: בשל הצפי לגידול האוכלוסייה ולהתרחבות הגודש בכבישים צפויות להחמיר גם ההשפעות הסביבתיות של ענף התחבורה בישראל. לשם התמודדות עם שינויים אלה יש לצמצם משמעותית את הנסועה הפרטית. אחד מכלי המדיניות שיוצרים שינוי בביקוש לנסיעות הוא עבודה מרחוק, המאפשרת לעובדים להימנע מנסיעות באזורי ביקוש ובשעות השיא. מאמר זה סוקר את הידע הקיים בנושא מדיניות עבודה מרחוק, את ההשלכות האפשריות של יישום מדיניות זו בישראל בכלל, ולנוכח השפעות מגפת הקורונה (COVID-19) בפרט. לעבודה מרחוק יש פוטנציאל לתועלת משקית רבה, כגון חיסכון בעלויות החיצוניות מהנסועה, הגדלת הפריון והעלאת פרודוקטיביות העובדים, חיזוק הפריפריה, צמצום פערים מגדריים והנגשת שוק העבודה לאוכלוסיות מוחלשות. עם זאת, עבודה מרחוק יוצרת גם אתגרים לא מעטים: ניהוליים, טכנולוגיים, חברתיים ונוספים. שיעור העובדים מרחוק בישראל נמוך משמעותית ביחס למערב, אך נמצא במגמת עלייה במגזר הפרטי. לעומת זאת, הסכמי השכר במגזר הציבורי אינם מאפשרים עבודה מרחוק מלבד במקרים בודדים. דו"ח ועדת מומחים שפורסם לאחרונה ממליץ לממשלת ישראל לקדם תוכנית לאומית לעידוד עבודה מרחוק, שתכלול הצבת יעדים כמותיים לעבודה מרחוק במשק, תמיכה בתוכניות פיילוט ומתן תמריצים למגזרים השונים. מגפת הקורונה חשפה עובדים ומעסיקים רבים במשק לאפשרות של עבודה מרחוק, וזו הפכה לאחד הסממנים הבולטים של התקופה ויושמה לראשונה במגוון ענפים במשק, לרבות המגזר הציבורי. נראה כי להתנסות לא מתוכננת זו תהיה השפעה גם בתום תקופת המשבר על מיסוד והטמעה של עבודה מרחוק במשק הישראלי, וייתכן שבתנאים מסוימים אף על היקף הגודש בכבישים. יש לזכור כי בחלק גדול מהמשק בוצע מעבר חירום לא מתוכנן לעבודה מרחוק, ללא הכשרה מתאימה לעובדים ולמנהלים, ללא תיעוד ובקרה נאותה הנדרשים מפיילוט שמופעל במצב שגרה, וללא שימוש במרכזי תעסוקה משותפים המותאמים לעבודה מרחוק. למרות זאת, המשבר יצר הזדמנות חשובה לקידום עבודה מרחוק בישראל ולזיהוי פרקטיקות אפקטיביות לעבודה מהבית. התובנות שעולות כיום ושימשיכו להצטבר בעקבותיו יאפשרו למקבלי ההחלטות לקדם ולמסד הסדרי עבודה גמישים במשק הישראלי גם לאחריו. English Abstract: The projected population growth and the expansion of traffic congestion, are expected to exacerbate the environmental impacts of the transportation sector in Israel. To deal with these changes, the mileage of private transportation must be significantly reduced. Teleworking (telecommuting) is one of the policy tools that can alter road travel demand, by allowing employees to avoid travelling in peak hours and in high demand areas. This paper reviews the existing knowledge on teleworking policy, the possible consequences of implementing this policy in Israel in general, and in light of the COVID-19 pandemic effects in particular. Teleworking has a great potential for economic and social benefits, such as transportation externalities saving, increasing productivity, strengthening the periphery areas, reducing gender inequality and making the labor market accessible to underprivileged populations. However, teleworking also creates quite a few challenges: administrative, technological, social and more. The rate of teleworking in Israel was significantly lower than in western countries, but is now on the rise in the private sector. In contrast, public sector employment contracts prohibit teleworking, except in very few specific cases. A recently published expert opinion report recommends that the Israeli government promotes a national plan to encourage teleworking, which will include setting quantitative targets for teleworking, supporting pilot programs and providing incentives to the various sectors. The COVID-19 pandemic has exposed many employees and employers to the possibility of working remotely, which has become one of this period's prominent features and was implemented for the first time in a variety of sectors and industries, including the public sector. It seems that this unplanned natural experiment will also have a positive effect on the institutionalization and assimilation of teleworking in the Israeli economy, beyond the pandemic, and under certain conditions even on the extent of traffic congestion. It should be noted that in a large part of the labor market, an unplanned emergency transition to teleworking has occurred, without proper training, documentation and proper control required from a pilot program in routine conditions, and without the use of hubs, adapted for teleworking. Despite this, the crisis has created an important opportunity to promote teleworking in Israel and to identify effective practices for working from home. The insights that arise today and will continue to accumulate in its wake, will enable decision-makers to promote and establish flexible working arrangements in the Israeli economy after the pandemic.
Highlights Natural Trichodesmium colonies collect and maintain dust within their colony core Usin... more Highlights Natural Trichodesmium colonies collect and maintain dust within their colony core Using synthetic particles we tested if colonies select the particles they collect Colonies selectively collect and retain nutrientrich over nutrient-free particles Selective collection of particles optimizes their nutrient acquisition from dust
תקציר בעברית: בשל הצפי לגידול האוכלוסייה ולהתרחבות הגודש בכבישים צפויות להחמיר גם ההשפעות הסביבתי... more תקציר בעברית: בשל הצפי לגידול האוכלוסייה ולהתרחבות הגודש בכבישים צפויות להחמיר גם ההשפעות הסביבתיות של ענף התחבורה בישראל. לשם התמודדות עם שינויים אלה יש לצמצם משמעותית את הנסועה הפרטית. אחד מכלי המדיניות שיוצרים שינוי בביקוש לנסיעות הוא עבודה מרחוק, המאפשרת לעובדים להימנע מנסיעות באזורי ביקוש ובשעות השיא. מאמר זה סוקר את הידע הקיים בנושא מדיניות עבודה מרחוק, את ההשלכות האפשריות של יישום מדיניות זו בישראל בכלל, ולנוכח השפעות מגפת הקורונה (COVID-19) בפרט. לעבודה מרחוק יש פוטנציאל לתועלת משקית רבה, כגון חיסכון בעלויות החיצוניות מהנסועה, הגדלת הפריון והעלאת פרודוקטיביות העובדים, חיזוק הפריפריה, צמצום פערים מגדריים והנגשת שוק העבודה לאוכלוסיות מוחלשות. עם זאת, עבודה מרחוק יוצרת גם אתגרים לא מעטים: ניהוליים, טכנולוגיים, חברתיים ונוספים. שיעור העובדים מרחוק בישראל נמוך משמעותית ביחס למערב, אך נמצא במגמת עלייה במגזר הפרטי. לעומת זאת, הסכמי השכר במגזר הציבורי אינם מאפשרים עבודה מרחוק מלבד במקרים בודדים. דו"ח ועדת מומחים שפורסם לאחרונה ממליץ לממשלת ישראל לקדם תוכנית לאומית לעידוד עבודה מרחוק, שתכלול הצבת יעדים כמותיים לעבודה מרחוק במשק, תמיכה בתוכניות פיילוט ומתן תמריצים למגזרים השונים. מגפת הקורונה חשפה עובדים ומעסיקים רבים במשק לאפשרות של עבודה מרחוק, וזו הפכה לאחד הסממנים הבולטים של התקופה ויושמה לראשונה במגוון ענפים במשק, לרבות המגזר הציבורי. נראה כי להתנסות לא מתוכננת זו תהיה השפעה גם בתום תקופת המשבר על מיסוד והטמעה של עבודה מרחוק במשק הישראלי, וייתכן שבתנאים מסוימים אף על היקף הגודש בכבישים. יש לזכור כי בחלק גדול מהמשק בוצע מעבר חירום לא מתוכנן לעבודה מרחוק, ללא הכשרה מתאימה לעובדים ולמנהלים, ללא תיעוד ובקרה נאותה הנדרשים מפיילוט שמופעל במצב שגרה, וללא שימוש במרכזי תעסוקה משותפים המותאמים לעבודה מרחוק. למרות זאת, המשבר יצר הזדמנות חשובה לקידום עבודה מרחוק בישראל ולזיהוי פרקטיקות אפקטיביות לעבודה מהבית. התובנות שעולות כיום ושימשיכו להצטבר בעקבותיו יאפשרו למקבלי ההחלטות לקדם ולמסד הסדרי עבודה גמישים במשק הישראלי גם לאחריו. English Abstract: The projected population growth and the expansion of traffic congestion, are expected to exacerbate the environmental impacts of the transportation sector in Israel. To deal with these changes, the mileage of private transportation must be significantly reduced. Teleworking (telecommuting) is one of the policy tools that can alter road travel demand, by allowing employees to avoid travelling in peak hours and in high demand areas. This paper reviews the existing knowledge on teleworking policy, the possible consequences of implementing this policy in Israel in general, and in light of the COVID-19 pandemic effects in particular. Teleworking has a great potential for economic and social benefits, such as transportation externalities saving, increasing productivity, strengthening the periphery areas, reducing gender inequality and making the labor market accessible to underprivileged populations. However, teleworking also creates quite a few challenges: administrative, technological, social and more. The rate of teleworking in Israel was significantly lower than in western countries, but is now on the rise in the private sector. In contrast, public sector employment contracts prohibit teleworking, except in very few specific cases. A recently published expert opinion report recommends that the Israeli government promotes a national plan to encourage teleworking, which will include setting quantitative targets for teleworking, supporting pilot programs and providing incentives to the various sectors. The COVID-19 pandemic has exposed many employees and employers to the possibility of working remotely, which has become one of this period's prominent features and was implemented for the first time in a variety of sectors and industries, including the public sector. It seems that this unplanned natural experiment will also have a positive effect on the institutionalization and assimilation of teleworking in the Israeli economy, beyond the pandemic, and under certain conditions even on the extent of traffic congestion. It should be noted that in a large part of the labor market, an unplanned emergency transition to teleworking has occurred, without proper training, documentation and proper control required from a pilot program in routine conditions, and without the use of hubs, adapted for teleworking. Despite this, the crisis has created an important opportunity to promote teleworking in Israel and to identify effective practices for working from home. The insights that arise today and will continue to accumulate in its wake, will enable decision-makers to promote and establish flexible working arrangements in the Israeli economy after the pandemic.
Bio-Enhanced Dust Dissolution Fe-quotas and growth rates we calculated the Fe requirements of the... more Bio-Enhanced Dust Dissolution Fe-quotas and growth rates we calculated the Fe requirements of the colonies under Felimited and Fe-replete conditions. The calculated dissolved Fe supply from dust retained within colonies can fulfill the Fe requirements of slow growing Fe-limited colonies, but cannot support fast growth and/or higher cellular Fe quotas. We conclude that despite these bio-dissolution mechanisms, dust-Fe availability to Trichodesmium is low and propose that it employs additional mechanisms to actively mine Fe from dust.
Dust is an important iron (Fe) source to the ocean, but its utilization by phytoplankton is const... more Dust is an important iron (Fe) source to the ocean, but its utilization by phytoplankton is constrained by rapid sinking and slow dissolution dust-bound iron (dust-Fe). Colonies of the globally important cyanobacterium, Trichodesmium, overcome these constraints by efficient dust capturing and active dust-Fe dissolution. In this study we examined the ability of Trichodesmium colonies to maximize their Fe supply from dust by selectively collecting Fe-rich particles. Testing for selectivity in particle collection, we supplied ~600 individual colonies, collected on multiple days from the Gulf of Aqaba, with natural dust and silica minerals that were either cleaned of or coated with Fe. Using a stereoscope, we counted the number of particles retained by each colony shortly after addition and following 24 h incubation with particles, and documented translocation of particles to the colony core. We observed a strong preference for Fe-rich particles over Fe-free particles in all tested para...
The Middle East is one of the regions in the world where relatively high concentrations of atmosp... more The Middle East is one of the regions in the world where relatively high concentrations of atmospheric particulate matter (PM) have been detected frequently. It has been suggested that PM levels in the Middle East are present at levels that lead to adverse health effects and to poor visibility. In the current study, we summarize results published by our group over the last decade and introduce new data which demonstrate the extent of trans-boundary PM transport, and the fact that synoptic conditions control its chemical and mineralogical composition and might also affect its toxicity.
Iron acquisition presents a significant challenge to many microorganisms in aquatic environments.... more Iron acquisition presents a significant challenge to many microorganisms in aquatic environments. Poor solubility in oxygenated waters favors the formation of mineral phase iron. However, the bioavailability of this fraction is poorly understood. This work addresses how cyanobacteria, photosynthetic aquatic microbes, access this relatively abundant pool of iron. Using a model cyanobacterium, this study identifies an active biological mechanism that enhances ferrihydrite dissolution, highlighting a significant biological component to mineral phase iron bioavailability in aquatic environments.
Numerous studies have demonstrated that elevated concentrations of suspended atmospheric particul... more Numerous studies have demonstrated that elevated concentrations of suspended atmospheric particulate matter (PM) are associated with adverse health effects. In order to minimize the adverse public health effects of atmospheric PM by exposure management, there is a need for a greater understanding of the toxic mechanisms and the components that are liable for the toxic effects. The aim of this study was to utilize bioassay techniques to investigate these aspects. For this purpose a reporter panel of 9 genetically engineered bacterial (Escherichia coli) strains was composed. Each panel member was designed to report on a different stress condition with a measurable light signal produced by the luciferase enzyme. Toxic mechanisms and components were studied using six anthropogenic PM source samples, including two vehicle combustion particles, three coal fly ash (CFA) samples and an urban dust sample. The most prominent outcome of the panel exposure results were broad panel responses observed for two of the CFA samples, indicating oxidative stress, respiration inhibition and iron deficiency. These responses were relieved when the samples were treated with EDTA, a non-specific metal chelator, suggesting the involvement of metals in the observed effects. Bioavailability analysis of the samples suggests that chromium was related to the toxic responses induced by two of the CFA samples. Oxidative stress was also observed in several samples of ambient atmospheric aerosols and excess metal toxicity in an urban dust sample collected in a parking lot. The reporter panel approach, as demonstrated in this study, has the potential of providing novel insights as to the mechanisms of atmospheric PM toxicity. Furthermore, combining the panel's results with bioavailability data can enlighten about the role of different PM components in the observed toxicity.
Iron (Fe) bioavailability, as determined by its sources, sinks, solubility and speciation, places... more Iron (Fe) bioavailability, as determined by its sources, sinks, solubility and speciation, places severe environmental constraints on microorganisms in aquatic environments. Cyanobacteria are a widespread group of aquatic, photosynthetic microorganisms with especially high iron requirements. While iron exists predominantly in particulate form, little is known about its bioavailability to cyanobacteria. Some cyanobacteria secrete iron solubilizing ligands called siderophores, yet many environmentally relevant strains do not have this ability. This work explores the bioavailability of amorphous synthetic Fe-oxides (ferrihydrite) to the non-siderophore producing, unicellular cyanobacterium, Synechocystis sp PCC 6803. Iron uptake assays with 55 ferrihydrite established dissolution as a critical prerequisite for iron transport. Dissolution assays with the iron binding ligand, desferrioxamine B, demonstrated that Synechocystis 6803 enhances ferrihydrite dissolution, exerting siderophore-independent biological influence on ferrihydrite bioavailability. Dissolution mechanisms were studied using a range of experimental conditions; both cell-particle physical proximity and cellular electron flow were shown to be important determinants of bio-dissolution by Synechocystis 6803. Finally, the effects of ferrihydrite stability on bio-dissolution rates and cell physiology were measured, integrating biological and chemical aspects of ferrihydrite bioavailability. Collectively, these findings demonstrate that Synechocystis 6803 actively dissolves ferrihydrite, highlighting a significant biological component to mineral phase iron bioavailability in aquatic environments. ; Tel. 972-2-6585205; Fax 972-2-6584425. † These authors contributed equally to this work.
< A new bacterial bioassay for toxicity of particulate air pollution is presented. < Bioassay res... more < A new bacterial bioassay for toxicity of particulate air pollution is presented. < Bioassay responses indicating toxicity were observed for several PM samples. < These responses suggest oxidative stress, respiration inhibition and Fe deficiency. < A metal chelating treatment of the samples relieved the bioassay's responses. < Bioavailability analysis suggested that Cr was related to these toxic responses. a b s t r a c t Numerous studies have demonstrated that elevated concentrations of suspended atmospheric particulate matter (PM) are associated with adverse health effects. In order to minimize the adverse public health effects of atmospheric PM by exposure management, there is a need for a greater understanding of the toxic mechanisms and the components that are responsible for the toxic effects. The aim of this study was to utilize bioassay techniques to investigate these aspects. For this purpose a reporter panel of 9 genetically engineered bacterial (Escherichia coli) strains was composed. Each panel member was designed to report on a different stress condition with a measurable light signal produced by the luciferase enzyme. Toxic mechanisms and components were studied using six anthropogenic PM source samples, including two vehicle combustion particles, three coal fly ash (CFA) samples and an urban dust sample. The most prominent outcome of the panel exposure results were broad panel responses observed for two of the CFA samples, indicating oxidative stress, respiration inhibition and iron deficiency. These responses were relieved when the samples were treated with EDTA, a non-specific metal chelator, suggesting the involvement of metals in the observed effects. Bioavailability analysis of the samples suggests that chromium was related to the toxic responses induced by two of the CFA samples. Oxidative stress was also observed in several samples of ambient atmospheric aerosols and excess metal toxicity in an urban dust sample collected in a parking lot. The reporter panel approach, as demonstrated in this study, has the potential of providing novel insights as to the mechanisms of atmospheric PM toxicity. Furthermore, combining the panel's results with bioavailability data can enlighten about the role of different PM components in the observed toxicity.
Iron (Fe) bioavailability, as determined by its sources, sinks, solubility and speciation, places... more Iron (Fe) bioavailability, as determined by its sources, sinks, solubility and speciation, places severe envi-ronmental constraints on microorganisms in aquatic environments. Cyanobacteria are a widespread group of aquatic, photosynthetic microorganisms with especially high iron requirements. While iron exists predominantly in particulate form, little is known about its bioavailability to cyanobacteria. Some cya-nobacteria secrete iron solubilizing ligands called siderophores, yet many environmentally relevant strains do not have this ability. This work explores the bioavailability of amorphous synthetic Fe-oxides (ferrihydrite) to the non-siderophore producing, uni-cellular cyanobacterium, Synechocystis sp PCC 6803. Iron uptake assays with 55 ferrihydrite estab-lished dissolution as a critical prerequisite for iron transport. Dissolution assays with the iron binding ligand, desferrioxamine B, demonstrated that Syne-chocystis 6803 enhances ferrihydrite dissolution, exerting siderophore-independent biological influ-ence on ferrihydrite bioavailability. Dissolution mechanisms were studied using a range of experi-mental conditions; both cell-particle physical proximity and cellular electron flow were shown to be important determinants of bio-dissolution by Syne-chocystis 6803. Finally, the effects of ferrihydrite stability on bio-dissolution rates and cell physiology were measured, integrating biological and chemical aspects of ferrihydrite bioavailability. Collectively, these findings demonstrate that Synechocystis 6803 actively dissolves ferrihydrite, highlighting a signifi-cant biological component to mineral phase iron bioavailability in aquatic environments.
The marine cyanobacterium Trichodesmium has a remarkable ability to interact with and utilize air... more The marine cyanobacterium Trichodesmium has a remarkable ability to interact with and utilize airborne dust as a nutrient source. However, dust may adversely affect Trichodesmium through buoyancy loss and exposure to toxic metals. Our study explored the effect of desert dust on buoyancy and mortality of natural Red Sea puff-shaped Trichodesmium thiebautii. Sinking velocities and ability of individual colonies to stay afloat with increasing dust loads were studied in sedimentation chambers. Low dust loads of up to˜400 ng per colony did not impact initial sinking velocity and colonies remained afloat in the chamber. Above this threshold, sinking velocity increased linearly with the colony dust load at a slope matching prediction based on Stoke's law. The potential toxicity of dust was assessed with regards to metal dissolution kinetics, differentiating between rapidly released metals that may impact surface blooms and gradually released metals that may impact dust-centering colonies. Incubations with increasing dust concentrations revealed colony demise, but the observed lethal dose far exceeded dust concentrations measured in coastal and open ocean systems. Removal of toxic particles as a mechanism to reduce toxicity was explored using SEM-EDX imaging of colonies incubated with Cu-minerals, yet observations did not support this pathway. Combining our current and former experiments, we suggest that in natural settings the nutritional benefits gained by Trichodesmium via dust collection outweigh the risks of buoyancy loss and toxicity. Our data and concepts feed into the growing recognition of the significance of dust for Trichodesmium's ecology and subsequently to ocean productivity.
Trichodesmium, a globally important, N2-fixing and colony-forming cyanobacterium employs multiple... more Trichodesmium, a globally important, N2-fixing and colony-forming cyanobacterium employs multiple pathways for acquiring nutrients from air-borne dust, including the active collection of dust particles. Once concentrated within the colony core, dust can supply Trichodesmium with the limiting nutrients iron (Fe) and phosphorus (P). Studying particle collection by natural colonies, we recently documented a preference for Fe-rich over Fe-free particles. In this follow-up study we examined if colonies selectively collect P-rich particles. Over an entire bloom season, we incubated ~1 200 Trichodesmium colonies from the Red Sea with P-free CaCO3, P-coated CaCO 3 and dust. We utilized three discrete parameters to characterize the colony-particle interactions and integrated them to an index that describes the particle collection behavior over time. Colonies were found to preferably interact, center and retain P-coated CaCO3 in comparison to P-free CaCO3, suggesting that Trichodesmium can optimize its P-acquisition by selecting P-rich particles. In both current and former studies, colonies clearly favored dust over all other particles tested, while nutrient-free particles were barely collected or retained, indicating that Trichodesmium senses the particle composition and preferably collects nutrient-rich particles. This unique ability contributes to Trichodesmium's current ecological success and may assist it to flourish in future warmer oceans.
Highlights Natural Trichodesmium colonies collect and maintain dust within their colony core Usin... more Highlights Natural Trichodesmium colonies collect and maintain dust within their colony core Using synthetic particles we tested if colonies select the particles they collect Colonies selectively collect and retain nutrientrich over nutrient-free particles Selective collection of particles optimizes their nutrient acquisition from dust
Dust is an important iron (Fe) source to the ocean, but its utilization by phytoplankton is const... more Dust is an important iron (Fe) source to the ocean, but its utilization by phytoplankton is constrained by rapid sinking and slow dissolution dust-bound iron (dust-Fe). Colonies of the globally important cyanobacterium, Trichodesmium, overcome these constraints by efficient dust capturing and active dust-Fe dissolution. In this study we examined the ability of Trichodesmium colonies to maximize their Fe supply from dust by selectively collecting Fe-rich particles. Testing for selectivity in particle collection, we supplied~600 individual colonies, collected on multiple days from the Gulf of Aqaba, with natural dust and silica minerals that were either cleaned of or coated with Fe. Using a stereoscope, we counted the number of particles retained by each colony shortly after addition and following 24 h incubation with particles, and documented translocation of particles to the colony core. We observed a strong preference for Fe-rich particles over Fe-free particles in all tested parameters. Moreover, some colonies discarded the Fe-free particles they initially collected. The preferred collection of Fe-rich particles and disposal of Fe-free particles suggest that Trichodesmium can sense Fe and selectively choose Fe-rich dust particles. This ability assists Trichodesmium obtain Fe from dust and facilitate its growth and subsequent contribution to nutrient cycling and productivity in the ocean.
תקציר בעברית: בשל הצפי לגידול האוכלוסייה ולהתרחבות הגודש בכבישים צפויות להחמיר גם ההשפעות הסביבתי... more תקציר בעברית: בשל הצפי לגידול האוכלוסייה ולהתרחבות הגודש בכבישים צפויות להחמיר גם ההשפעות הסביבתיות של ענף התחבורה בישראל. לשם התמודדות עם שינויים אלה יש לצמצם משמעותית את הנסועה הפרטית. אחד מכלי המדיניות שיוצרים שינוי בביקוש לנסיעות הוא עבודה מרחוק, המאפשרת לעובדים להימנע מנסיעות באזורי ביקוש ובשעות השיא. מאמר זה סוקר את הידע הקיים בנושא מדיניות עבודה מרחוק, את ההשלכות האפשריות של יישום מדיניות זו בישראל בכלל, ולנוכח השפעות מגפת הקורונה (COVID-19) בפרט. לעבודה מרחוק יש פוטנציאל לתועלת משקית רבה, כגון חיסכון בעלויות החיצוניות מהנסועה, הגדלת הפריון והעלאת פרודוקטיביות העובדים, חיזוק הפריפריה, צמצום פערים מגדריים והנגשת שוק העבודה לאוכלוסיות מוחלשות. עם זאת, עבודה מרחוק יוצרת גם אתגרים לא מעטים: ניהוליים, טכנולוגיים, חברתיים ונוספים. שיעור העובדים מרחוק בישראל נמוך משמעותית ביחס למערב, אך נמצא במגמת עלייה במגזר הפרטי. לעומת זאת, הסכמי השכר במגזר הציבורי אינם מאפשרים עבודה מרחוק מלבד במקרים בודדים. דו"ח ועדת מומחים שפורסם לאחרונה ממליץ לממשלת ישראל לקדם תוכנית לאומית לעידוד עבודה מרחוק, שתכלול הצבת יעדים כמותיים לעבודה מרחוק במשק, תמיכה בתוכניות פיילוט ומתן תמריצים למגזרים השונים. מגפת הקורונה חשפה עובדים ומעסיקים רבים במשק לאפשרות של עבודה מרחוק, וזו הפכה לאחד הסממנים הבולטים של התקופה ויושמה לראשונה במגוון ענפים במשק, לרבות המגזר הציבורי. נראה כי להתנסות לא מתוכננת זו תהיה השפעה גם בתום תקופת המשבר על מיסוד והטמעה של עבודה מרחוק במשק הישראלי, וייתכן שבתנאים מסוימים אף על היקף הגודש בכבישים. יש לזכור כי בחלק גדול מהמשק בוצע מעבר חירום לא מתוכנן לעבודה מרחוק, ללא הכשרה מתאימה לעובדים ולמנהלים, ללא תיעוד ובקרה נאותה הנדרשים מפיילוט שמופעל במצב שגרה, וללא שימוש במרכזי תעסוקה משותפים המותאמים לעבודה מרחוק. למרות זאת, המשבר יצר הזדמנות חשובה לקידום עבודה מרחוק בישראל ולזיהוי פרקטיקות אפקטיביות לעבודה מהבית. התובנות שעולות כיום ושימשיכו להצטבר בעקבותיו יאפשרו למקבלי ההחלטות לקדם ולמסד הסדרי עבודה גמישים במשק הישראלי גם לאחריו. English Abstract: The projected population growth and the expansion of traffic congestion, are expected to exacerbate the environmental impacts of the transportation sector in Israel. To deal with these changes, the mileage of private transportation must be significantly reduced. Teleworking (telecommuting) is one of the policy tools that can alter road travel demand, by allowing employees to avoid travelling in peak hours and in high demand areas. This paper reviews the existing knowledge on teleworking policy, the possible consequences of implementing this policy in Israel in general, and in light of the COVID-19 pandemic effects in particular. Teleworking has a great potential for economic and social benefits, such as transportation externalities saving, increasing productivity, strengthening the periphery areas, reducing gender inequality and making the labor market accessible to underprivileged populations. However, teleworking also creates quite a few challenges: administrative, technological, social and more. The rate of teleworking in Israel was significantly lower than in western countries, but is now on the rise in the private sector. In contrast, public sector employment contracts prohibit teleworking, except in very few specific cases. A recently published expert opinion report recommends that the Israeli government promotes a national plan to encourage teleworking, which will include setting quantitative targets for teleworking, supporting pilot programs and providing incentives to the various sectors. The COVID-19 pandemic has exposed many employees and employers to the possibility of working remotely, which has become one of this period's prominent features and was implemented for the first time in a variety of sectors and industries, including the public sector. It seems that this unplanned natural experiment will also have a positive effect on the institutionalization and assimilation of teleworking in the Israeli economy, beyond the pandemic, and under certain conditions even on the extent of traffic congestion. It should be noted that in a large part of the labor market, an unplanned emergency transition to teleworking has occurred, without proper training, documentation and proper control required from a pilot program in routine conditions, and without the use of hubs, adapted for teleworking. Despite this, the crisis has created an important opportunity to promote teleworking in Israel and to identify effective practices for working from home. The insights that arise today and will continue to accumulate in its wake, will enable decision-makers to promote and establish flexible working arrangements in the Israeli economy after the pandemic.
תקציר בעברית: בשל הצפי לגידול האוכלוסייה ולהתרחבות הגודש בכבישים צפויות להחמיר גם ההשפעות הסביבתי... more תקציר בעברית: בשל הצפי לגידול האוכלוסייה ולהתרחבות הגודש בכבישים צפויות להחמיר גם ההשפעות הסביבתיות של ענף התחבורה בישראל. לשם התמודדות עם שינויים אלה יש לצמצם משמעותית את הנסועה הפרטית. אחד מכלי המדיניות שיוצרים שינוי בביקוש לנסיעות הוא עבודה מרחוק, המאפשרת לעובדים להימנע מנסיעות באזורי ביקוש ובשעות השיא. מאמר זה סוקר את הידע הקיים בנושא מדיניות עבודה מרחוק, את ההשלכות האפשריות של יישום מדיניות זו בישראל בכלל, ולנוכח השפעות מגפת הקורונה (COVID-19) בפרט. לעבודה מרחוק יש פוטנציאל לתועלת משקית רבה, כגון חיסכון בעלויות החיצוניות מהנסועה, הגדלת הפריון והעלאת פרודוקטיביות העובדים, חיזוק הפריפריה, צמצום פערים מגדריים והנגשת שוק העבודה לאוכלוסיות מוחלשות. עם זאת, עבודה מרחוק יוצרת גם אתגרים לא מעטים: ניהוליים, טכנולוגיים, חברתיים ונוספים. שיעור העובדים מרחוק בישראל נמוך משמעותית ביחס למערב, אך נמצא במגמת עלייה במגזר הפרטי. לעומת זאת, הסכמי השכר במגזר הציבורי אינם מאפשרים עבודה מרחוק מלבד במקרים בודדים. דו"ח ועדת מומחים שפורסם לאחרונה ממליץ לממשלת ישראל לקדם תוכנית לאומית לעידוד עבודה מרחוק, שתכלול הצבת יעדים כמותיים לעבודה מרחוק במשק, תמיכה בתוכניות פיילוט ומתן תמריצים למגזרים השונים. מגפת הקורונה חשפה עובדים ומעסיקים רבים במשק לאפשרות של עבודה מרחוק, וזו הפכה לאחד הסממנים הבולטים של התקופה ויושמה לראשונה במגוון ענפים במשק, לרבות המגזר הציבורי. נראה כי להתנסות לא מתוכננת זו תהיה השפעה גם בתום תקופת המשבר על מיסוד והטמעה של עבודה מרחוק במשק הישראלי, וייתכן שבתנאים מסוימים אף על היקף הגודש בכבישים. יש לזכור כי בחלק גדול מהמשק בוצע מעבר חירום לא מתוכנן לעבודה מרחוק, ללא הכשרה מתאימה לעובדים ולמנהלים, ללא תיעוד ובקרה נאותה הנדרשים מפיילוט שמופעל במצב שגרה, וללא שימוש במרכזי תעסוקה משותפים המותאמים לעבודה מרחוק. למרות זאת, המשבר יצר הזדמנות חשובה לקידום עבודה מרחוק בישראל ולזיהוי פרקטיקות אפקטיביות לעבודה מהבית. התובנות שעולות כיום ושימשיכו להצטבר בעקבותיו יאפשרו למקבלי ההחלטות לקדם ולמסד הסדרי עבודה גמישים במשק הישראלי גם לאחריו. English Abstract: The projected population growth and the expansion of traffic congestion, are expected to exacerbate the environmental impacts of the transportation sector in Israel. To deal with these changes, the mileage of private transportation must be significantly reduced. Teleworking (telecommuting) is one of the policy tools that can alter road travel demand, by allowing employees to avoid travelling in peak hours and in high demand areas. This paper reviews the existing knowledge on teleworking policy, the possible consequences of implementing this policy in Israel in general, and in light of the COVID-19 pandemic effects in particular. Teleworking has a great potential for economic and social benefits, such as transportation externalities saving, increasing productivity, strengthening the periphery areas, reducing gender inequality and making the labor market accessible to underprivileged populations. However, teleworking also creates quite a few challenges: administrative, technological, social and more. The rate of teleworking in Israel was significantly lower than in western countries, but is now on the rise in the private sector. In contrast, public sector employment contracts prohibit teleworking, except in very few specific cases. A recently published expert opinion report recommends that the Israeli government promotes a national plan to encourage teleworking, which will include setting quantitative targets for teleworking, supporting pilot programs and providing incentives to the various sectors. The COVID-19 pandemic has exposed many employees and employers to the possibility of working remotely, which has become one of this period's prominent features and was implemented for the first time in a variety of sectors and industries, including the public sector. It seems that this unplanned natural experiment will also have a positive effect on the institutionalization and assimilation of teleworking in the Israeli economy, beyond the pandemic, and under certain conditions even on the extent of traffic congestion. It should be noted that in a large part of the labor market, an unplanned emergency transition to teleworking has occurred, without proper training, documentation and proper control required from a pilot program in routine conditions, and without the use of hubs, adapted for teleworking. Despite this, the crisis has created an important opportunity to promote teleworking in Israel and to identify effective practices for working from home. The insights that arise today and will continue to accumulate in its wake, will enable decision-makers to promote and establish flexible working arrangements in the Israeli economy after the pandemic.
Highlights Natural Trichodesmium colonies collect and maintain dust within their colony core Usin... more Highlights Natural Trichodesmium colonies collect and maintain dust within their colony core Using synthetic particles we tested if colonies select the particles they collect Colonies selectively collect and retain nutrientrich over nutrient-free particles Selective collection of particles optimizes their nutrient acquisition from dust
תקציר בעברית: בשל הצפי לגידול האוכלוסייה ולהתרחבות הגודש בכבישים צפויות להחמיר גם ההשפעות הסביבתי... more תקציר בעברית: בשל הצפי לגידול האוכלוסייה ולהתרחבות הגודש בכבישים צפויות להחמיר גם ההשפעות הסביבתיות של ענף התחבורה בישראל. לשם התמודדות עם שינויים אלה יש לצמצם משמעותית את הנסועה הפרטית. אחד מכלי המדיניות שיוצרים שינוי בביקוש לנסיעות הוא עבודה מרחוק, המאפשרת לעובדים להימנע מנסיעות באזורי ביקוש ובשעות השיא. מאמר זה סוקר את הידע הקיים בנושא מדיניות עבודה מרחוק, את ההשלכות האפשריות של יישום מדיניות זו בישראל בכלל, ולנוכח השפעות מגפת הקורונה (COVID-19) בפרט. לעבודה מרחוק יש פוטנציאל לתועלת משקית רבה, כגון חיסכון בעלויות החיצוניות מהנסועה, הגדלת הפריון והעלאת פרודוקטיביות העובדים, חיזוק הפריפריה, צמצום פערים מגדריים והנגשת שוק העבודה לאוכלוסיות מוחלשות. עם זאת, עבודה מרחוק יוצרת גם אתגרים לא מעטים: ניהוליים, טכנולוגיים, חברתיים ונוספים. שיעור העובדים מרחוק בישראל נמוך משמעותית ביחס למערב, אך נמצא במגמת עלייה במגזר הפרטי. לעומת זאת, הסכמי השכר במגזר הציבורי אינם מאפשרים עבודה מרחוק מלבד במקרים בודדים. דו"ח ועדת מומחים שפורסם לאחרונה ממליץ לממשלת ישראל לקדם תוכנית לאומית לעידוד עבודה מרחוק, שתכלול הצבת יעדים כמותיים לעבודה מרחוק במשק, תמיכה בתוכניות פיילוט ומתן תמריצים למגזרים השונים. מגפת הקורונה חשפה עובדים ומעסיקים רבים במשק לאפשרות של עבודה מרחוק, וזו הפכה לאחד הסממנים הבולטים של התקופה ויושמה לראשונה במגוון ענפים במשק, לרבות המגזר הציבורי. נראה כי להתנסות לא מתוכננת זו תהיה השפעה גם בתום תקופת המשבר על מיסוד והטמעה של עבודה מרחוק במשק הישראלי, וייתכן שבתנאים מסוימים אף על היקף הגודש בכבישים. יש לזכור כי בחלק גדול מהמשק בוצע מעבר חירום לא מתוכנן לעבודה מרחוק, ללא הכשרה מתאימה לעובדים ולמנהלים, ללא תיעוד ובקרה נאותה הנדרשים מפיילוט שמופעל במצב שגרה, וללא שימוש במרכזי תעסוקה משותפים המותאמים לעבודה מרחוק. למרות זאת, המשבר יצר הזדמנות חשובה לקידום עבודה מרחוק בישראל ולזיהוי פרקטיקות אפקטיביות לעבודה מהבית. התובנות שעולות כיום ושימשיכו להצטבר בעקבותיו יאפשרו למקבלי ההחלטות לקדם ולמסד הסדרי עבודה גמישים במשק הישראלי גם לאחריו. English Abstract: The projected population growth and the expansion of traffic congestion, are expected to exacerbate the environmental impacts of the transportation sector in Israel. To deal with these changes, the mileage of private transportation must be significantly reduced. Teleworking (telecommuting) is one of the policy tools that can alter road travel demand, by allowing employees to avoid travelling in peak hours and in high demand areas. This paper reviews the existing knowledge on teleworking policy, the possible consequences of implementing this policy in Israel in general, and in light of the COVID-19 pandemic effects in particular. Teleworking has a great potential for economic and social benefits, such as transportation externalities saving, increasing productivity, strengthening the periphery areas, reducing gender inequality and making the labor market accessible to underprivileged populations. However, teleworking also creates quite a few challenges: administrative, technological, social and more. The rate of teleworking in Israel was significantly lower than in western countries, but is now on the rise in the private sector. In contrast, public sector employment contracts prohibit teleworking, except in very few specific cases. A recently published expert opinion report recommends that the Israeli government promotes a national plan to encourage teleworking, which will include setting quantitative targets for teleworking, supporting pilot programs and providing incentives to the various sectors. The COVID-19 pandemic has exposed many employees and employers to the possibility of working remotely, which has become one of this period's prominent features and was implemented for the first time in a variety of sectors and industries, including the public sector. It seems that this unplanned natural experiment will also have a positive effect on the institutionalization and assimilation of teleworking in the Israeli economy, beyond the pandemic, and under certain conditions even on the extent of traffic congestion. It should be noted that in a large part of the labor market, an unplanned emergency transition to teleworking has occurred, without proper training, documentation and proper control required from a pilot program in routine conditions, and without the use of hubs, adapted for teleworking. Despite this, the crisis has created an important opportunity to promote teleworking in Israel and to identify effective practices for working from home. The insights that arise today and will continue to accumulate in its wake, will enable decision-makers to promote and establish flexible working arrangements in the Israeli economy after the pandemic.
Bio-Enhanced Dust Dissolution Fe-quotas and growth rates we calculated the Fe requirements of the... more Bio-Enhanced Dust Dissolution Fe-quotas and growth rates we calculated the Fe requirements of the colonies under Felimited and Fe-replete conditions. The calculated dissolved Fe supply from dust retained within colonies can fulfill the Fe requirements of slow growing Fe-limited colonies, but cannot support fast growth and/or higher cellular Fe quotas. We conclude that despite these bio-dissolution mechanisms, dust-Fe availability to Trichodesmium is low and propose that it employs additional mechanisms to actively mine Fe from dust.
Dust is an important iron (Fe) source to the ocean, but its utilization by phytoplankton is const... more Dust is an important iron (Fe) source to the ocean, but its utilization by phytoplankton is constrained by rapid sinking and slow dissolution dust-bound iron (dust-Fe). Colonies of the globally important cyanobacterium, Trichodesmium, overcome these constraints by efficient dust capturing and active dust-Fe dissolution. In this study we examined the ability of Trichodesmium colonies to maximize their Fe supply from dust by selectively collecting Fe-rich particles. Testing for selectivity in particle collection, we supplied ~600 individual colonies, collected on multiple days from the Gulf of Aqaba, with natural dust and silica minerals that were either cleaned of or coated with Fe. Using a stereoscope, we counted the number of particles retained by each colony shortly after addition and following 24 h incubation with particles, and documented translocation of particles to the colony core. We observed a strong preference for Fe-rich particles over Fe-free particles in all tested para...
The Middle East is one of the regions in the world where relatively high concentrations of atmosp... more The Middle East is one of the regions in the world where relatively high concentrations of atmospheric particulate matter (PM) have been detected frequently. It has been suggested that PM levels in the Middle East are present at levels that lead to adverse health effects and to poor visibility. In the current study, we summarize results published by our group over the last decade and introduce new data which demonstrate the extent of trans-boundary PM transport, and the fact that synoptic conditions control its chemical and mineralogical composition and might also affect its toxicity.
Iron acquisition presents a significant challenge to many microorganisms in aquatic environments.... more Iron acquisition presents a significant challenge to many microorganisms in aquatic environments. Poor solubility in oxygenated waters favors the formation of mineral phase iron. However, the bioavailability of this fraction is poorly understood. This work addresses how cyanobacteria, photosynthetic aquatic microbes, access this relatively abundant pool of iron. Using a model cyanobacterium, this study identifies an active biological mechanism that enhances ferrihydrite dissolution, highlighting a significant biological component to mineral phase iron bioavailability in aquatic environments.
Numerous studies have demonstrated that elevated concentrations of suspended atmospheric particul... more Numerous studies have demonstrated that elevated concentrations of suspended atmospheric particulate matter (PM) are associated with adverse health effects. In order to minimize the adverse public health effects of atmospheric PM by exposure management, there is a need for a greater understanding of the toxic mechanisms and the components that are liable for the toxic effects. The aim of this study was to utilize bioassay techniques to investigate these aspects. For this purpose a reporter panel of 9 genetically engineered bacterial (Escherichia coli) strains was composed. Each panel member was designed to report on a different stress condition with a measurable light signal produced by the luciferase enzyme. Toxic mechanisms and components were studied using six anthropogenic PM source samples, including two vehicle combustion particles, three coal fly ash (CFA) samples and an urban dust sample. The most prominent outcome of the panel exposure results were broad panel responses observed for two of the CFA samples, indicating oxidative stress, respiration inhibition and iron deficiency. These responses were relieved when the samples were treated with EDTA, a non-specific metal chelator, suggesting the involvement of metals in the observed effects. Bioavailability analysis of the samples suggests that chromium was related to the toxic responses induced by two of the CFA samples. Oxidative stress was also observed in several samples of ambient atmospheric aerosols and excess metal toxicity in an urban dust sample collected in a parking lot. The reporter panel approach, as demonstrated in this study, has the potential of providing novel insights as to the mechanisms of atmospheric PM toxicity. Furthermore, combining the panel's results with bioavailability data can enlighten about the role of different PM components in the observed toxicity.
Iron (Fe) bioavailability, as determined by its sources, sinks, solubility and speciation, places... more Iron (Fe) bioavailability, as determined by its sources, sinks, solubility and speciation, places severe environmental constraints on microorganisms in aquatic environments. Cyanobacteria are a widespread group of aquatic, photosynthetic microorganisms with especially high iron requirements. While iron exists predominantly in particulate form, little is known about its bioavailability to cyanobacteria. Some cyanobacteria secrete iron solubilizing ligands called siderophores, yet many environmentally relevant strains do not have this ability. This work explores the bioavailability of amorphous synthetic Fe-oxides (ferrihydrite) to the non-siderophore producing, unicellular cyanobacterium, Synechocystis sp PCC 6803. Iron uptake assays with 55 ferrihydrite established dissolution as a critical prerequisite for iron transport. Dissolution assays with the iron binding ligand, desferrioxamine B, demonstrated that Synechocystis 6803 enhances ferrihydrite dissolution, exerting siderophore-independent biological influence on ferrihydrite bioavailability. Dissolution mechanisms were studied using a range of experimental conditions; both cell-particle physical proximity and cellular electron flow were shown to be important determinants of bio-dissolution by Synechocystis 6803. Finally, the effects of ferrihydrite stability on bio-dissolution rates and cell physiology were measured, integrating biological and chemical aspects of ferrihydrite bioavailability. Collectively, these findings demonstrate that Synechocystis 6803 actively dissolves ferrihydrite, highlighting a significant biological component to mineral phase iron bioavailability in aquatic environments. ; Tel. 972-2-6585205; Fax 972-2-6584425. † These authors contributed equally to this work.
< A new bacterial bioassay for toxicity of particulate air pollution is presented. < Bioassay res... more < A new bacterial bioassay for toxicity of particulate air pollution is presented. < Bioassay responses indicating toxicity were observed for several PM samples. < These responses suggest oxidative stress, respiration inhibition and Fe deficiency. < A metal chelating treatment of the samples relieved the bioassay's responses. < Bioavailability analysis suggested that Cr was related to these toxic responses. a b s t r a c t Numerous studies have demonstrated that elevated concentrations of suspended atmospheric particulate matter (PM) are associated with adverse health effects. In order to minimize the adverse public health effects of atmospheric PM by exposure management, there is a need for a greater understanding of the toxic mechanisms and the components that are responsible for the toxic effects. The aim of this study was to utilize bioassay techniques to investigate these aspects. For this purpose a reporter panel of 9 genetically engineered bacterial (Escherichia coli) strains was composed. Each panel member was designed to report on a different stress condition with a measurable light signal produced by the luciferase enzyme. Toxic mechanisms and components were studied using six anthropogenic PM source samples, including two vehicle combustion particles, three coal fly ash (CFA) samples and an urban dust sample. The most prominent outcome of the panel exposure results were broad panel responses observed for two of the CFA samples, indicating oxidative stress, respiration inhibition and iron deficiency. These responses were relieved when the samples were treated with EDTA, a non-specific metal chelator, suggesting the involvement of metals in the observed effects. Bioavailability analysis of the samples suggests that chromium was related to the toxic responses induced by two of the CFA samples. Oxidative stress was also observed in several samples of ambient atmospheric aerosols and excess metal toxicity in an urban dust sample collected in a parking lot. The reporter panel approach, as demonstrated in this study, has the potential of providing novel insights as to the mechanisms of atmospheric PM toxicity. Furthermore, combining the panel's results with bioavailability data can enlighten about the role of different PM components in the observed toxicity.
Iron (Fe) bioavailability, as determined by its sources, sinks, solubility and speciation, places... more Iron (Fe) bioavailability, as determined by its sources, sinks, solubility and speciation, places severe envi-ronmental constraints on microorganisms in aquatic environments. Cyanobacteria are a widespread group of aquatic, photosynthetic microorganisms with especially high iron requirements. While iron exists predominantly in particulate form, little is known about its bioavailability to cyanobacteria. Some cya-nobacteria secrete iron solubilizing ligands called siderophores, yet many environmentally relevant strains do not have this ability. This work explores the bioavailability of amorphous synthetic Fe-oxides (ferrihydrite) to the non-siderophore producing, uni-cellular cyanobacterium, Synechocystis sp PCC 6803. Iron uptake assays with 55 ferrihydrite estab-lished dissolution as a critical prerequisite for iron transport. Dissolution assays with the iron binding ligand, desferrioxamine B, demonstrated that Syne-chocystis 6803 enhances ferrihydrite dissolution, exerting siderophore-independent biological influ-ence on ferrihydrite bioavailability. Dissolution mechanisms were studied using a range of experi-mental conditions; both cell-particle physical proximity and cellular electron flow were shown to be important determinants of bio-dissolution by Syne-chocystis 6803. Finally, the effects of ferrihydrite stability on bio-dissolution rates and cell physiology were measured, integrating biological and chemical aspects of ferrihydrite bioavailability. Collectively, these findings demonstrate that Synechocystis 6803 actively dissolves ferrihydrite, highlighting a signifi-cant biological component to mineral phase iron bioavailability in aquatic environments.
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Papers by Nivi Kessler