Journal of Experimental Marine Biology and Ecology, 2011
Enhanced or reduced pCO 2 (partial pressure of CO 2) may affect the photosynthetic performance of... more Enhanced or reduced pCO 2 (partial pressure of CO 2) may affect the photosynthetic performance of marine microalgae since changes in pCO 2 can influence the activity of carbon concentrating mechanisms, modulate cellular RuBisCO levels or alter carbon uptake efficiency. In the present study we compared the photophysiology of the Antarctic diatom Chaetoceros brevis at two pCO 2 extremes: 750 ppmv (2× ambient) and 190 ppmv (0.5× ambient) CO 2. Cultures were acclimated to four irradiance regimes: two regimes simulating deep or shallow vertical mixing, and two regimes mimicking limiting and saturating stable water column conditions. Then, growth rate, pigmentation, RuBisCO large subunit expression, RuBisCO activity, photosynthesis vs irradiance curves, effective quantum yield of PSII (F v /F m), and POC were measured. The four irradiance regimes induced a suite of photophysiological responses, ranging from low light acclimation to efficient photoprotection. Growth was reduced under the low constant and the deep mixing regime, compared to the shallow mixing and the stable saturating regime. Low stable irradiance resulted in higher light harvesting pigment concentrations, lower RuBisCO activity and a lower light saturation point (E k) compared to the other irradiance regimes. Highest RuBisCO activity as well as P max levels was measured in the shallow mixing regime, which received the highest total daily light dose. Photoprotection by xanthophyll cycling was observed under all irradiance regimes except the low stable irradiance regime, and xanthophyll cycle pool sizes were higher under the dynamic irradiance regimes. For the fluctuating irradiance regimes, F v /F m was hardly affected by previous excess irradiance exposure, suggesting minimal PSII damage. No significant differences between the two pCO 2 levels were found, with respect to growth, pigment content and composition, photosynthesis, photoprotection and RuBisCO activity, for all four irradiance regimes. Thus, within the range tested, pCO 2 does not significantly affect the photophysiological performance of C. brevis.
Photolithotrophs are divided between those that use water as their electron
donor (Cyanobacteria ... more Photolithotrophs are divided between those that use water as their electron donor (Cyanobacteria and the photosynthetic eukaryotes) and those that use a different electron donor (the anoxygenic photolithotrophs, all of themBacteria). Photolithotrophs with themost reduced genomes have more genes than do the corresponding chemoorganotrophs, and the fastest-growing photolithotrophs have significantly lower specific growth rates than the fastest-growing chemoorganotrophs. Slower growth results from diversion of resources into the photosynthetic apparatus, which accounts for about half of the cell protein. There are inherent dangers in (especially oxygenic) photosynthesis, including the formation of reactive oxygen species (ROS) and blue light sensitivity of the water spitting apparatus. The extent to which photolithotrophs incur greater DNA damage and repair, and faster protein turnover with increased rRNA requirement, needs further investigation. A related source of environmental damage is ultraviolet B (UVB) radiation (280–320 nm), whose flux at the Earth’s surface decreased as oxygen (and ozone) increased in the atmosphere. This oxygenation led to the requirements of defence againstROS, and decreasing availability to organisms of combined (non-dinitrogen) nitrogen and ferrous iron, and (indirectly) phosphorus, in the oxygenated biosphere. Differential codon usage in the genome and, especially, the proteome can lead to economies in the use of potentially growth-limiting elements
Atmospheric levels of carbon dioxide (CO2) and nitric oxide (NO) have been on the rise ever since... more Atmospheric levels of carbon dioxide (CO2) and nitric oxide (NO) have been on the rise ever since the beginning of industrialisation. A significant fraction of this increase can be attributed to the emissions from stationary sources such as thermal power plants and steel plants. While there has been an impetus in recent times towards sequestration of these greenhouse gases at source, current technologies are not commercially viable. In this context, microalgae-mediated CO2 capture and utilization has attracted attention, although several technological challenges remain to be addressed. Importantly, this process will require algal strains that grow fast and are tolerant to high light, temperature and flue gases. The majority of the reported algal strains fail in at least one of these requirements. On account of this, we have isolated two novel green algal strains, which have been identified as Asterarcys quadricellulare and Chlorella sorokiniana, from water bodies that are located in and around a steel plant in India. These are relatively fast-growing strains with specific growth rates of up to 0.06 h− 1 and 0.1 h− 1, respectively. Furthermore, these strains can tolerate high temperatures of up to 43 °C, high light intensity and high CO2 and NO levels. When exposed to high CO2 levels, 55–71% of the dry cell weight comprised of carbohydrates. Additionally, exposure to NO gas along with CO2 led to an enhanced lipid accumulation of 44%–46% of dry biomass. The high lipid content makes these strains valuable feedstock in biodiesel production, and the high carbohydrate content makes the lipid extracted biomass an attractive source of carbon for biochemical conversion to ethanol. We believe that these strains are promising and ready to be tested with real flue gases under outdoor conditions.
Abstract The importance of algae-derived biofuels has been
highlighted by the current problems as... more Abstract The importance of algae-derived biofuels has been highlighted by the current problems associated with fossil fuels. Considerable past research has shown that limiting nutrients such as nitrogen and phosphorus increases the cellular lipid content in microalgae. However, limiting the supply of nutrients results in decreased biomass, which in turn decreases the overall lipid productivity of cultures. Therefore, nutrient limitation has been a subject of dispute as to whether it will benefit biofuel production on an industrial scale. Our research explores the physiological changes a cell undergoes when exposed to nitrogen and phosphorus limitations, both individually and in combination, and also examines the biotechnological aspects of manipulating N and P in order to increase cellular lipids, by analyzing the lipid production. We show that nitrogen starvation and also nitrogen plus phosphorus starvation combined have a more profound effect on the physiology and macromolecular pools of Chlamydomonas reinhardtii than does phosphorus starvation alone. The photosynthetic performance of C. reinhardtii underwent drastic changes under nitrogen starvation, but remained relatively unaffected under phosphorus starvation. The neutral lipid concentration per cell was at least 2.4-fold higher in all the nutrient-starved groups than the nutrient-replete controls, but the protein level per cell was lower in the nitrogen-starved groups. Overall, nitrogen starvation has a more dramatic effect on the physiology and neutral lipids and protein levels of C. reinhardtii than phosphorus starvation. However, the level of total lipids per volume of culture obtained was similar among nutrient-replete and all of the nutrient-starved groups. We conclude that combined nitrogen and phosphorus starvation does not likely benefit biofuel production in terms of enhanced lipid or biomass production
The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversi... more The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversity, with thousands of tonnes of urea in order to stimulate algal blooms and sequester carbon is flawed for multiple reasons. Urea is preferentially used as a nitrogen source by some cyanobacteria and dinoflagellates, many of which are neutrally or positively buoyant. Biological pumps to the deep sea are classically leaky, and the inefficient burial of new biomass makes the estimation of a net loss of carbon from the atmosphere questionable at best. The potential for growth of toxic dinoflagellates is also high, as many grow well on urea and some even increase their toxicity when grown on urea. Many toxic dinoflagellates form cysts which can settle to the sediment and germinate in subsequent years, forming new blooms even without further fertilization. If large-scale blooms do occur, it is likely that they will contribute to hypoxia in the bottom waters upon decomposition. Lastly, urea production requires fossil fuel usage, further limiting the potential for net carbon sequestration. The environmental and economic impacts are potentially great and need to be rigorously assessed.
Abstract The extent of enhanced post-illumination respiration (EPIR) has been investigated in a n... more Abstract The extent of enhanced post-illumination respiration (EPIR) has been investigated in a number of microalgae. Respiration rates, as determined by O 2 consumption, were enhanced (in all but one case) by 50–140% following pre-exposure to high photon flux ...
... However, the Lowry assay may overestimate (Berges et al. ... In most of the phytoplankton stu... more ... However, the Lowry assay may overestimate (Berges et al. ... In most of the phytoplankton studies cited here, the orcinol and Lowry methods were used ... a much greater range of RNA-specific protein synthesis rates than of growth rates in this interspecies comparison involving nine ...
The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversi... more The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversity, with thousands of tonnes of urea in order to stimulate algal blooms and sequester carbon is flawed for multiple reasons. Urea is preferentially used as a nitrogen source by some cyanobacteria and dinoflagellates, many of which are neutrally or positively buoyant. Biological pumps to the deep sea are classically leaky, and the inefficient burial of new biomass makes the estimation of a net loss of carbon from the atmosphere questionable at best. The potential for growth of toxic dinoflagellates is also high, as many grow well on urea and some even increase their toxicity when grown on urea. Many toxic dinoflagellates form cysts which can settle to the sediment and germinate in subsequent years, forming new blooms even without further fertilization. If large-scale blooms do occur, it is likely that they will contribute to hypoxia in the bottom waters upon decomposition. Lastly, urea production requires fossil fuel usage, further limiting the potential for net carbon sequestration. The environmental and economic impacts are potentially great and need to be rigorously assessed.
The major fatty acids in a Dunaliella sp. isolated from an Antarctic hypersaline lake were 18:3o9... more The major fatty acids in a Dunaliella sp. isolated from an Antarctic hypersaline lake were 18:3o93, 16:0 and 16:4o93, which together accounted for 72 75% of the total fatty acids in the cells. The fatty acid composition was modified by varying the salinity in the growth medium. With salinity increasing from 0.4 M to 4 M NaC1 in the cultures, the proportion of total saturated and monounsaturated fatty acids increased, while total polyunsaturated fatty acids decreased. All the ~o3 fatty acids showed negative trends to salinity. Total polyunsaturated fatty acid content was ca 10% higher in the low salinity culture. The results obtained suggest that increasing salinity in the growth medium increases the degree of fatty acid saturation and, hence, reduces the fluidity and permeability of the microalgal membranes. ,
Canadian Journal of Botany-revue Canadienne De Botanique, 2005
Inorganic phosphate (P i ) plays a central role in cellular energy transduction. As a consequence... more Inorganic phosphate (P i ) plays a central role in cellular energy transduction. As a consequence, limitation of growth by phosphate availability can have an important impact on various aspects of metabolism. Since carbon acquisition via CO 2 -concentrating mechanisms (CCMs) in most microalgae is an active process, requiring ATP, it might be expected that phosphate limitation could have an indirect regulatory influence on CCM activity. We grew the green alga Chlorella emersonii Shihira et Krauss in semicontinuous or continuous cultures in nutrient-replete conditions or with orthophosphate as the limiting nutrient. CCM activity was down-regulated by P limitation. K 0.5 (dissolved inorganic carbon) values increased from approximately 4.5 µmol·L -1 in cells growing at close to maximal rates to >12 µmol·L -1 in cells growing at 0.2 d -1 . Maximal rates of photosynthesis decreased by approximately half over the same range of growth rates. Direct measurements of CCM activity showed that internal CO 2 : external CO 2 ratio was markedly decreased under P limitation, and concurrent measurements of stable carbon isotope discrimination were consistent with decreased CCM activity in the P-limited cells.
Journal of Photochemistry and Photobiology B-biology, 2006
Cultures of the marine diatoms Phaeodactylum tricornutum and Chaetoceros muelleri were grown in f... more Cultures of the marine diatoms Phaeodactylum tricornutum and Chaetoceros muelleri were grown in f/2 medium supplied with either nitrate (N-Nt), ammonium (N-Am) or urea (N-Ur) as the nitrogen (N) source at the same final N concentration (0.88 mM). Exponential growth phase cultures of the two diatoms were exposed to four different light regimes for 2 days: (UVAR) PAR (60 lmol quanta m À2 s À1 ) plus 8.22 W m À2 (unweighted) UVAR; (high UVBR) PAR (60 lmol quanta m À2 s À1 ) plus 1.04 W m À2 (unweighted) UVBR plus 13.73 W m À2 (unweighted) UVAR; (low UVBR) PAR (60 lmol quanta m À2 s À1 ) plus 0.19 W m À2 (unweighted) UVBR plus 2.76 W m À2 (unweighted) UVAR and (PAR) PAR (60 lmol quanta m À2 s À1 ) alone (control). No significant effects of N source on the growth rates of the two diatoms were detected. The maximum effective quantum yield of PSII, UPSII e-max , and the initial slope of the light curve, a, of P. tricornutum and C. muelleri were all inhibited, whereas I k was somewhat increased, as a consequence of 2 days of exposure to all the UVR treatments. Multiple factor ANOVA revealed that all the major fatty acids, both in P. tricornutum and C. muelleri, were influenced more strongly by N source than by UVR. The composition of saturated fatty acids (SFA), monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) in P. tricornutum and C. muelleri exhibited almost the same pattern of variation with N source and UVR. The maximum value of SFA was found in the N-Am treatment, that of MUFA in the N-Nt treatment and for PUFA in the N-Ur treatment irrespective of the UV radiation. On the other hand, the impact of UVR resulted in an increase of PUFA and a reduction of SFA both in P. tricornutum and C. muelleri under all N sources.
The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversi... more The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversity, with thousands of tonnes of urea in order to stimulate algal blooms and sequester carbon is flawed for multiple reasons. Urea is preferentially used as a nitrogen source by some cyanobacteria and dinoflagellates, many of which are neutrally or positively buoyant. Biological pumps to the deep sea are classically leaky, and the inefficient burial of new biomass makes the estimation of a net loss of carbon from the atmosphere questionable at best. The potential for growth of toxic dinoflagellates is also high, as many grow well on urea and some even increase their toxicity when grown on urea. Many toxic dinoflagellates form cysts which can settle to the sediment and germinate in subsequent years, forming new blooms even without further fertilization. If large-scale blooms do occur, it is likely that they will contribute to hypoxia in the bottom waters upon decomposition. Lastly, urea production requires fossil fuel usage, further limiting the potential for net carbon sequestration. The environmental and economic impacts are potentially great and need to be rigorously assessed.
Abstract The extent of enhanced post-illumination respiration (EPIR) has been investigated in a n... more Abstract The extent of enhanced post-illumination respiration (EPIR) has been investigated in a number of microalgae. Respiration rates, as determined by O 2 consumption, were enhanced (in all but one case) by 50–140% following pre-exposure to high photon flux ...
Canadian Journal of Botany-revue Canadienne De Botanique, 2005
Most of the algae and cyanobacteria that have been critically examined express a carbon-concentra... more Most of the algae and cyanobacteria that have been critically examined express a carbon-concentrating mechanism (CCM) when grown at, or below, the current atmospheric CO 2 concentration. This paper considers algae that appear to lack a CCM. Critical examination of the evidence on which the presence or absence of a CCM is decided shows that more information is frequently needed before the criteria can be fully applied. Examples are the pathways of glycolate metabolism in nongreen algae, and the 13 C/ 12 C discrimination shown by form ID Rubisco in vitro. The available evidence suggests that the algae lacking CCMs are some terrestrial green microalgae, some florideophyte freshwater red macroalgae, and a number of florideophyte red macroalgae from the supralittoral, littoral, and sublittoral, and almost all of the freshwater chrysophytes and synurophytes examined. Certain environmental, biochemical, and biophysical factors may permit the occurrence of algae lacking CCMs. The absence of CCMs is presumably the plesiomorphic (i.e., ancestral) condition in cyanobacteria (and algae?).
At least 95% of the organic carbon in cyanobacteria and algae has been fixed as CO2 by Rubisco. T... more At least 95% of the organic carbon in cyanobacteria and algae has been fixed as CO2 by Rubisco. The kinetic properties of Rubisco are such that even the genetic variants with the highest CO2:O2 selectivity would show limited CO2 fixation and significant oxygenase activity if CO2 and O2 fluxes into cells are driven solely by diffusion. This is especially the case for submerged algae with low gas diffusion coefficients relative to diffusion boundary layer thicknesses. There is evidence from gas exchange properties and intracellular inorganic concentration that inorganic carbon concentrating mechanisms (CCMs) function in all cyanobacteria and many algae. CCMs can, in theory, operate through three categories of mechanism: the first mechanism is active transport of HCO-3 and/or CO2 across membranes, the second is CO2 pumping by a biochemical mechanism analogous to C4 and CAM (Crassulacean Acid Metabolism) pathways in higher land plants, and the third mechanism involves active transport of H+ producing an acid compartment supplied with HCO-3, which generates a high (equilibrium) CO2 concentration that supplies CO2 to Rubisco in a nearby more alkaline compartment. Most evidence favors the first mechanism as being responsible for CCM activity in algae. The CO2 (and HCO-3) permeability of membranes is crucial in defining the extent of inorganic C leakage from CCMs, and the functioning of diffusive CO2 supply to Rubisco from the medium. Like carbonic anhydrases, CCMs, are probably polyphyletic.
Canadian Journal of Botany-revue Canadienne De Botanique, 1998
Most microalgae possess a mechanism for actively transporting inorganic carbon that concentrates ... more Most microalgae possess a mechanism for actively transporting inorganic carbon that concentrates CO 2 at the active site of the carbon fixing enzyme ribulose bisphosphate carboxylase-oxygenase (Rubisco). This review considers the effects of environmental factors on the capacity and activity of microalgal CO 2 -concentrating mechanisms. Limitation of energy supply by light availability decreases the rate of inorganic carbon transport and cells grown under light-limited conditions have a reduced capacity for CO 2 accumulation. Phosphorus limitation also reduces the capacity of algal cells to accumulate CO 2 , whereas both the rate of supply of nitrogen and the form in which it is made available interact in various complex ways with carbon utilization. The potential role of other nutrients in modulating inorganic carbon transport is also discussed. The capacity of algae for carbon accumulation is also affected by CO 2 supply, which, in turn, is a function of the interactions between ionic strength of the growth medium, pH, cell density in culture, aeration rate, and inorganic carbon concentration in the medium. The effects of these interacting parameters are discussed, together with an assessment of the possible roles and significance of CO 2 -concentrating mechanisms to microalgae in marine and freshwater ecosystems.
Rapid light curves (RLCs), based on pulse amplitude modulated (PAM) fluorometry, were used to inv... more Rapid light curves (RLCs), based on pulse amplitude modulated (PAM) fluorometry, were used to investigate the spatio-temporal variability in photosynthesis versus irradiance parameters (a, I k and P max ) and the F v /F m ratio of the seagrass Zostera tasmanica (formerly Heterozostera tasmanica). Spatial variation was examined across scales ranging from within a leaf (cms) to across the bed (ms), using a nested analysis of covariance sampling design. Overall, significant variation was identified at all scales examined, excluding the largest scale (area). Patterns of variability differed among individual parameters; however a high percentage of the variation was consistently assigned to the covariates, age (within and between leaves) for all parameters, except P max .
Journal of Experimental Marine Biology and Ecology, 2011
Enhanced or reduced pCO 2 (partial pressure of CO 2) may affect the photosynthetic performance of... more Enhanced or reduced pCO 2 (partial pressure of CO 2) may affect the photosynthetic performance of marine microalgae since changes in pCO 2 can influence the activity of carbon concentrating mechanisms, modulate cellular RuBisCO levels or alter carbon uptake efficiency. In the present study we compared the photophysiology of the Antarctic diatom Chaetoceros brevis at two pCO 2 extremes: 750 ppmv (2× ambient) and 190 ppmv (0.5× ambient) CO 2. Cultures were acclimated to four irradiance regimes: two regimes simulating deep or shallow vertical mixing, and two regimes mimicking limiting and saturating stable water column conditions. Then, growth rate, pigmentation, RuBisCO large subunit expression, RuBisCO activity, photosynthesis vs irradiance curves, effective quantum yield of PSII (F v /F m), and POC were measured. The four irradiance regimes induced a suite of photophysiological responses, ranging from low light acclimation to efficient photoprotection. Growth was reduced under the low constant and the deep mixing regime, compared to the shallow mixing and the stable saturating regime. Low stable irradiance resulted in higher light harvesting pigment concentrations, lower RuBisCO activity and a lower light saturation point (E k) compared to the other irradiance regimes. Highest RuBisCO activity as well as P max levels was measured in the shallow mixing regime, which received the highest total daily light dose. Photoprotection by xanthophyll cycling was observed under all irradiance regimes except the low stable irradiance regime, and xanthophyll cycle pool sizes were higher under the dynamic irradiance regimes. For the fluctuating irradiance regimes, F v /F m was hardly affected by previous excess irradiance exposure, suggesting minimal PSII damage. No significant differences between the two pCO 2 levels were found, with respect to growth, pigment content and composition, photosynthesis, photoprotection and RuBisCO activity, for all four irradiance regimes. Thus, within the range tested, pCO 2 does not significantly affect the photophysiological performance of C. brevis.
Photolithotrophs are divided between those that use water as their electron
donor (Cyanobacteria ... more Photolithotrophs are divided between those that use water as their electron donor (Cyanobacteria and the photosynthetic eukaryotes) and those that use a different electron donor (the anoxygenic photolithotrophs, all of themBacteria). Photolithotrophs with themost reduced genomes have more genes than do the corresponding chemoorganotrophs, and the fastest-growing photolithotrophs have significantly lower specific growth rates than the fastest-growing chemoorganotrophs. Slower growth results from diversion of resources into the photosynthetic apparatus, which accounts for about half of the cell protein. There are inherent dangers in (especially oxygenic) photosynthesis, including the formation of reactive oxygen species (ROS) and blue light sensitivity of the water spitting apparatus. The extent to which photolithotrophs incur greater DNA damage and repair, and faster protein turnover with increased rRNA requirement, needs further investigation. A related source of environmental damage is ultraviolet B (UVB) radiation (280–320 nm), whose flux at the Earth’s surface decreased as oxygen (and ozone) increased in the atmosphere. This oxygenation led to the requirements of defence againstROS, and decreasing availability to organisms of combined (non-dinitrogen) nitrogen and ferrous iron, and (indirectly) phosphorus, in the oxygenated biosphere. Differential codon usage in the genome and, especially, the proteome can lead to economies in the use of potentially growth-limiting elements
Atmospheric levels of carbon dioxide (CO2) and nitric oxide (NO) have been on the rise ever since... more Atmospheric levels of carbon dioxide (CO2) and nitric oxide (NO) have been on the rise ever since the beginning of industrialisation. A significant fraction of this increase can be attributed to the emissions from stationary sources such as thermal power plants and steel plants. While there has been an impetus in recent times towards sequestration of these greenhouse gases at source, current technologies are not commercially viable. In this context, microalgae-mediated CO2 capture and utilization has attracted attention, although several technological challenges remain to be addressed. Importantly, this process will require algal strains that grow fast and are tolerant to high light, temperature and flue gases. The majority of the reported algal strains fail in at least one of these requirements. On account of this, we have isolated two novel green algal strains, which have been identified as Asterarcys quadricellulare and Chlorella sorokiniana, from water bodies that are located in and around a steel plant in India. These are relatively fast-growing strains with specific growth rates of up to 0.06 h− 1 and 0.1 h− 1, respectively. Furthermore, these strains can tolerate high temperatures of up to 43 °C, high light intensity and high CO2 and NO levels. When exposed to high CO2 levels, 55–71% of the dry cell weight comprised of carbohydrates. Additionally, exposure to NO gas along with CO2 led to an enhanced lipid accumulation of 44%–46% of dry biomass. The high lipid content makes these strains valuable feedstock in biodiesel production, and the high carbohydrate content makes the lipid extracted biomass an attractive source of carbon for biochemical conversion to ethanol. We believe that these strains are promising and ready to be tested with real flue gases under outdoor conditions.
Abstract The importance of algae-derived biofuels has been
highlighted by the current problems as... more Abstract The importance of algae-derived biofuels has been highlighted by the current problems associated with fossil fuels. Considerable past research has shown that limiting nutrients such as nitrogen and phosphorus increases the cellular lipid content in microalgae. However, limiting the supply of nutrients results in decreased biomass, which in turn decreases the overall lipid productivity of cultures. Therefore, nutrient limitation has been a subject of dispute as to whether it will benefit biofuel production on an industrial scale. Our research explores the physiological changes a cell undergoes when exposed to nitrogen and phosphorus limitations, both individually and in combination, and also examines the biotechnological aspects of manipulating N and P in order to increase cellular lipids, by analyzing the lipid production. We show that nitrogen starvation and also nitrogen plus phosphorus starvation combined have a more profound effect on the physiology and macromolecular pools of Chlamydomonas reinhardtii than does phosphorus starvation alone. The photosynthetic performance of C. reinhardtii underwent drastic changes under nitrogen starvation, but remained relatively unaffected under phosphorus starvation. The neutral lipid concentration per cell was at least 2.4-fold higher in all the nutrient-starved groups than the nutrient-replete controls, but the protein level per cell was lower in the nitrogen-starved groups. Overall, nitrogen starvation has a more dramatic effect on the physiology and neutral lipids and protein levels of C. reinhardtii than phosphorus starvation. However, the level of total lipids per volume of culture obtained was similar among nutrient-replete and all of the nutrient-starved groups. We conclude that combined nitrogen and phosphorus starvation does not likely benefit biofuel production in terms of enhanced lipid or biomass production
The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversi... more The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversity, with thousands of tonnes of urea in order to stimulate algal blooms and sequester carbon is flawed for multiple reasons. Urea is preferentially used as a nitrogen source by some cyanobacteria and dinoflagellates, many of which are neutrally or positively buoyant. Biological pumps to the deep sea are classically leaky, and the inefficient burial of new biomass makes the estimation of a net loss of carbon from the atmosphere questionable at best. The potential for growth of toxic dinoflagellates is also high, as many grow well on urea and some even increase their toxicity when grown on urea. Many toxic dinoflagellates form cysts which can settle to the sediment and germinate in subsequent years, forming new blooms even without further fertilization. If large-scale blooms do occur, it is likely that they will contribute to hypoxia in the bottom waters upon decomposition. Lastly, urea production requires fossil fuel usage, further limiting the potential for net carbon sequestration. The environmental and economic impacts are potentially great and need to be rigorously assessed.
Abstract The extent of enhanced post-illumination respiration (EPIR) has been investigated in a n... more Abstract The extent of enhanced post-illumination respiration (EPIR) has been investigated in a number of microalgae. Respiration rates, as determined by O 2 consumption, were enhanced (in all but one case) by 50–140% following pre-exposure to high photon flux ...
... However, the Lowry assay may overestimate (Berges et al. ... In most of the phytoplankton stu... more ... However, the Lowry assay may overestimate (Berges et al. ... In most of the phytoplankton studies cited here, the orcinol and Lowry methods were used ... a much greater range of RNA-specific protein synthesis rates than of growth rates in this interspecies comparison involving nine ...
The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversi... more The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversity, with thousands of tonnes of urea in order to stimulate algal blooms and sequester carbon is flawed for multiple reasons. Urea is preferentially used as a nitrogen source by some cyanobacteria and dinoflagellates, many of which are neutrally or positively buoyant. Biological pumps to the deep sea are classically leaky, and the inefficient burial of new biomass makes the estimation of a net loss of carbon from the atmosphere questionable at best. The potential for growth of toxic dinoflagellates is also high, as many grow well on urea and some even increase their toxicity when grown on urea. Many toxic dinoflagellates form cysts which can settle to the sediment and germinate in subsequent years, forming new blooms even without further fertilization. If large-scale blooms do occur, it is likely that they will contribute to hypoxia in the bottom waters upon decomposition. Lastly, urea production requires fossil fuel usage, further limiting the potential for net carbon sequestration. The environmental and economic impacts are potentially great and need to be rigorously assessed.
The major fatty acids in a Dunaliella sp. isolated from an Antarctic hypersaline lake were 18:3o9... more The major fatty acids in a Dunaliella sp. isolated from an Antarctic hypersaline lake were 18:3o93, 16:0 and 16:4o93, which together accounted for 72 75% of the total fatty acids in the cells. The fatty acid composition was modified by varying the salinity in the growth medium. With salinity increasing from 0.4 M to 4 M NaC1 in the cultures, the proportion of total saturated and monounsaturated fatty acids increased, while total polyunsaturated fatty acids decreased. All the ~o3 fatty acids showed negative trends to salinity. Total polyunsaturated fatty acid content was ca 10% higher in the low salinity culture. The results obtained suggest that increasing salinity in the growth medium increases the degree of fatty acid saturation and, hence, reduces the fluidity and permeability of the microalgal membranes. ,
Canadian Journal of Botany-revue Canadienne De Botanique, 2005
Inorganic phosphate (P i ) plays a central role in cellular energy transduction. As a consequence... more Inorganic phosphate (P i ) plays a central role in cellular energy transduction. As a consequence, limitation of growth by phosphate availability can have an important impact on various aspects of metabolism. Since carbon acquisition via CO 2 -concentrating mechanisms (CCMs) in most microalgae is an active process, requiring ATP, it might be expected that phosphate limitation could have an indirect regulatory influence on CCM activity. We grew the green alga Chlorella emersonii Shihira et Krauss in semicontinuous or continuous cultures in nutrient-replete conditions or with orthophosphate as the limiting nutrient. CCM activity was down-regulated by P limitation. K 0.5 (dissolved inorganic carbon) values increased from approximately 4.5 µmol·L -1 in cells growing at close to maximal rates to >12 µmol·L -1 in cells growing at 0.2 d -1 . Maximal rates of photosynthesis decreased by approximately half over the same range of growth rates. Direct measurements of CCM activity showed that internal CO 2 : external CO 2 ratio was markedly decreased under P limitation, and concurrent measurements of stable carbon isotope discrimination were consistent with decreased CCM activity in the P-limited cells.
Journal of Photochemistry and Photobiology B-biology, 2006
Cultures of the marine diatoms Phaeodactylum tricornutum and Chaetoceros muelleri were grown in f... more Cultures of the marine diatoms Phaeodactylum tricornutum and Chaetoceros muelleri were grown in f/2 medium supplied with either nitrate (N-Nt), ammonium (N-Am) or urea (N-Ur) as the nitrogen (N) source at the same final N concentration (0.88 mM). Exponential growth phase cultures of the two diatoms were exposed to four different light regimes for 2 days: (UVAR) PAR (60 lmol quanta m À2 s À1 ) plus 8.22 W m À2 (unweighted) UVAR; (high UVBR) PAR (60 lmol quanta m À2 s À1 ) plus 1.04 W m À2 (unweighted) UVBR plus 13.73 W m À2 (unweighted) UVAR; (low UVBR) PAR (60 lmol quanta m À2 s À1 ) plus 0.19 W m À2 (unweighted) UVBR plus 2.76 W m À2 (unweighted) UVAR and (PAR) PAR (60 lmol quanta m À2 s À1 ) alone (control). No significant effects of N source on the growth rates of the two diatoms were detected. The maximum effective quantum yield of PSII, UPSII e-max , and the initial slope of the light curve, a, of P. tricornutum and C. muelleri were all inhibited, whereas I k was somewhat increased, as a consequence of 2 days of exposure to all the UVR treatments. Multiple factor ANOVA revealed that all the major fatty acids, both in P. tricornutum and C. muelleri, were influenced more strongly by N source than by UVR. The composition of saturated fatty acids (SFA), monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) in P. tricornutum and C. muelleri exhibited almost the same pattern of variation with N source and UVR. The maximum value of SFA was found in the N-Am treatment, that of MUFA in the N-Nt treatment and for PUFA in the N-Ur treatment irrespective of the UV radiation. On the other hand, the impact of UVR resulted in an increase of PUFA and a reduction of SFA both in P. tricornutum and C. muelleri under all N sources.
The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversi... more The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversity, with thousands of tonnes of urea in order to stimulate algal blooms and sequester carbon is flawed for multiple reasons. Urea is preferentially used as a nitrogen source by some cyanobacteria and dinoflagellates, many of which are neutrally or positively buoyant. Biological pumps to the deep sea are classically leaky, and the inefficient burial of new biomass makes the estimation of a net loss of carbon from the atmosphere questionable at best. The potential for growth of toxic dinoflagellates is also high, as many grow well on urea and some even increase their toxicity when grown on urea. Many toxic dinoflagellates form cysts which can settle to the sediment and germinate in subsequent years, forming new blooms even without further fertilization. If large-scale blooms do occur, it is likely that they will contribute to hypoxia in the bottom waters upon decomposition. Lastly, urea production requires fossil fuel usage, further limiting the potential for net carbon sequestration. The environmental and economic impacts are potentially great and need to be rigorously assessed.
Abstract The extent of enhanced post-illumination respiration (EPIR) has been investigated in a n... more Abstract The extent of enhanced post-illumination respiration (EPIR) has been investigated in a number of microalgae. Respiration rates, as determined by O 2 consumption, were enhanced (in all but one case) by 50–140% following pre-exposure to high photon flux ...
Canadian Journal of Botany-revue Canadienne De Botanique, 2005
Most of the algae and cyanobacteria that have been critically examined express a carbon-concentra... more Most of the algae and cyanobacteria that have been critically examined express a carbon-concentrating mechanism (CCM) when grown at, or below, the current atmospheric CO 2 concentration. This paper considers algae that appear to lack a CCM. Critical examination of the evidence on which the presence or absence of a CCM is decided shows that more information is frequently needed before the criteria can be fully applied. Examples are the pathways of glycolate metabolism in nongreen algae, and the 13 C/ 12 C discrimination shown by form ID Rubisco in vitro. The available evidence suggests that the algae lacking CCMs are some terrestrial green microalgae, some florideophyte freshwater red macroalgae, and a number of florideophyte red macroalgae from the supralittoral, littoral, and sublittoral, and almost all of the freshwater chrysophytes and synurophytes examined. Certain environmental, biochemical, and biophysical factors may permit the occurrence of algae lacking CCMs. The absence of CCMs is presumably the plesiomorphic (i.e., ancestral) condition in cyanobacteria (and algae?).
At least 95% of the organic carbon in cyanobacteria and algae has been fixed as CO2 by Rubisco. T... more At least 95% of the organic carbon in cyanobacteria and algae has been fixed as CO2 by Rubisco. The kinetic properties of Rubisco are such that even the genetic variants with the highest CO2:O2 selectivity would show limited CO2 fixation and significant oxygenase activity if CO2 and O2 fluxes into cells are driven solely by diffusion. This is especially the case for submerged algae with low gas diffusion coefficients relative to diffusion boundary layer thicknesses. There is evidence from gas exchange properties and intracellular inorganic concentration that inorganic carbon concentrating mechanisms (CCMs) function in all cyanobacteria and many algae. CCMs can, in theory, operate through three categories of mechanism: the first mechanism is active transport of HCO-3 and/or CO2 across membranes, the second is CO2 pumping by a biochemical mechanism analogous to C4 and CAM (Crassulacean Acid Metabolism) pathways in higher land plants, and the third mechanism involves active transport of H+ producing an acid compartment supplied with HCO-3, which generates a high (equilibrium) CO2 concentration that supplies CO2 to Rubisco in a nearby more alkaline compartment. Most evidence favors the first mechanism as being responsible for CCM activity in algae. The CO2 (and HCO-3) permeability of membranes is crucial in defining the extent of inorganic C leakage from CCMs, and the functioning of diffusive CO2 supply to Rubisco from the medium. Like carbonic anhydrases, CCMs, are probably polyphyletic.
Canadian Journal of Botany-revue Canadienne De Botanique, 1998
Most microalgae possess a mechanism for actively transporting inorganic carbon that concentrates ... more Most microalgae possess a mechanism for actively transporting inorganic carbon that concentrates CO 2 at the active site of the carbon fixing enzyme ribulose bisphosphate carboxylase-oxygenase (Rubisco). This review considers the effects of environmental factors on the capacity and activity of microalgal CO 2 -concentrating mechanisms. Limitation of energy supply by light availability decreases the rate of inorganic carbon transport and cells grown under light-limited conditions have a reduced capacity for CO 2 accumulation. Phosphorus limitation also reduces the capacity of algal cells to accumulate CO 2 , whereas both the rate of supply of nitrogen and the form in which it is made available interact in various complex ways with carbon utilization. The potential role of other nutrients in modulating inorganic carbon transport is also discussed. The capacity of algae for carbon accumulation is also affected by CO 2 supply, which, in turn, is a function of the interactions between ionic strength of the growth medium, pH, cell density in culture, aeration rate, and inorganic carbon concentration in the medium. The effects of these interacting parameters are discussed, together with an assessment of the possible roles and significance of CO 2 -concentrating mechanisms to microalgae in marine and freshwater ecosystems.
Rapid light curves (RLCs), based on pulse amplitude modulated (PAM) fluorometry, were used to inv... more Rapid light curves (RLCs), based on pulse amplitude modulated (PAM) fluorometry, were used to investigate the spatio-temporal variability in photosynthesis versus irradiance parameters (a, I k and P max ) and the F v /F m ratio of the seagrass Zostera tasmanica (formerly Heterozostera tasmanica). Spatial variation was examined across scales ranging from within a leaf (cms) to across the bed (ms), using a nested analysis of covariance sampling design. Overall, significant variation was identified at all scales examined, excluding the largest scale (area). Patterns of variability differed among individual parameters; however a high percentage of the variation was consistently assigned to the covariates, age (within and between leaves) for all parameters, except P max .
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donor (Cyanobacteria and the photosynthetic eukaryotes) and those that use a
different electron donor (the anoxygenic photolithotrophs, all of themBacteria).
Photolithotrophs with themost reduced genomes have more genes than do the
corresponding chemoorganotrophs, and the fastest-growing photolithotrophs
have significantly lower specific growth rates than the fastest-growing chemoorganotrophs.
Slower growth results from diversion of resources into the
photosynthetic apparatus, which accounts for about half of the cell protein.
There are inherent dangers in (especially oxygenic) photosynthesis, including
the formation of reactive oxygen species (ROS) and blue light sensitivity of the
water spitting apparatus. The extent to which photolithotrophs incur greater
DNA damage and repair, and faster protein turnover with increased rRNA
requirement, needs further investigation. A related source of environmental
damage is ultraviolet B (UVB) radiation (280–320 nm), whose flux at the
Earth’s surface decreased as oxygen (and ozone) increased in the atmosphere.
This oxygenation led to the requirements of defence againstROS, and decreasing
availability to organisms of combined (non-dinitrogen) nitrogen and ferrous
iron, and (indirectly) phosphorus, in the oxygenated biosphere. Differential
codon usage in the genome and, especially, the proteome can lead to economies
in the use of potentially growth-limiting elements
highlighted by the current problems associated with fossil
fuels. Considerable past research has shown that limiting nutrients
such as nitrogen and phosphorus increases the cellular
lipid content in microalgae. However, limiting the supply of
nutrients results in decreased biomass, which in turn decreases
the overall lipid productivity of cultures. Therefore, nutrient
limitation has been a subject of dispute as to whether it will
benefit biofuel production on an industrial scale. Our research
explores the physiological changes a cell undergoes when
exposed to nitrogen and phosphorus limitations, both individually
and in combination, and also examines the biotechnological
aspects of manipulating N and P in order to increase
cellular lipids, by analyzing the lipid production. We show
that nitrogen starvation and also nitrogen plus phosphorus
starvation combined have a more profound effect on the physiology
and macromolecular pools of Chlamydomonas
reinhardtii than does phosphorus starvation alone. The photosynthetic
performance of C. reinhardtii underwent drastic
changes under nitrogen starvation, but remained relatively unaffected
under phosphorus starvation. The neutral lipid concentration
per cell was at least 2.4-fold higher in all the
nutrient-starved groups than the nutrient-replete controls, but
the protein level per cell was lower in the nitrogen-starved
groups. Overall, nitrogen starvation has a more dramatic effect
on the physiology and neutral lipids and protein levels of
C. reinhardtii than phosphorus starvation. However, the level
of total lipids per volume of culture obtained was similar
among nutrient-replete and all of the nutrient-starved groups.
We conclude that combined nitrogen and phosphorus starvation
does not likely benefit biofuel production in terms of
enhanced lipid or biomass production
donor (Cyanobacteria and the photosynthetic eukaryotes) and those that use a
different electron donor (the anoxygenic photolithotrophs, all of themBacteria).
Photolithotrophs with themost reduced genomes have more genes than do the
corresponding chemoorganotrophs, and the fastest-growing photolithotrophs
have significantly lower specific growth rates than the fastest-growing chemoorganotrophs.
Slower growth results from diversion of resources into the
photosynthetic apparatus, which accounts for about half of the cell protein.
There are inherent dangers in (especially oxygenic) photosynthesis, including
the formation of reactive oxygen species (ROS) and blue light sensitivity of the
water spitting apparatus. The extent to which photolithotrophs incur greater
DNA damage and repair, and faster protein turnover with increased rRNA
requirement, needs further investigation. A related source of environmental
damage is ultraviolet B (UVB) radiation (280–320 nm), whose flux at the
Earth’s surface decreased as oxygen (and ozone) increased in the atmosphere.
This oxygenation led to the requirements of defence againstROS, and decreasing
availability to organisms of combined (non-dinitrogen) nitrogen and ferrous
iron, and (indirectly) phosphorus, in the oxygenated biosphere. Differential
codon usage in the genome and, especially, the proteome can lead to economies
in the use of potentially growth-limiting elements
highlighted by the current problems associated with fossil
fuels. Considerable past research has shown that limiting nutrients
such as nitrogen and phosphorus increases the cellular
lipid content in microalgae. However, limiting the supply of
nutrients results in decreased biomass, which in turn decreases
the overall lipid productivity of cultures. Therefore, nutrient
limitation has been a subject of dispute as to whether it will
benefit biofuel production on an industrial scale. Our research
explores the physiological changes a cell undergoes when
exposed to nitrogen and phosphorus limitations, both individually
and in combination, and also examines the biotechnological
aspects of manipulating N and P in order to increase
cellular lipids, by analyzing the lipid production. We show
that nitrogen starvation and also nitrogen plus phosphorus
starvation combined have a more profound effect on the physiology
and macromolecular pools of Chlamydomonas
reinhardtii than does phosphorus starvation alone. The photosynthetic
performance of C. reinhardtii underwent drastic
changes under nitrogen starvation, but remained relatively unaffected
under phosphorus starvation. The neutral lipid concentration
per cell was at least 2.4-fold higher in all the
nutrient-starved groups than the nutrient-replete controls, but
the protein level per cell was lower in the nitrogen-starved
groups. Overall, nitrogen starvation has a more dramatic effect
on the physiology and neutral lipids and protein levels of
C. reinhardtii than phosphorus starvation. However, the level
of total lipids per volume of culture obtained was similar
among nutrient-replete and all of the nutrient-starved groups.
We conclude that combined nitrogen and phosphorus starvation
does not likely benefit biofuel production in terms of
enhanced lipid or biomass production