Papers by Cathrine S Manohar
Background: A wealth of microbial eukaryotes is adapted to life in oxygen-deficient marine enviro... more Background: A wealth of microbial eukaryotes is adapted to life in oxygen-deficient marine environments. Evidence is accumulating that some of these eukaryotes survive anoxia by employing dissimilatory nitrate reduction, a strategy that otherwise is widespread in prokaryotes. Here, we report on the anaerobic nitrate metabolism of the fungus Aspergillus terreus (isolate An-4) that was obtained from sediment in the seasonal oxygen minimum zone in the Arabian Sea, a globally important site of oceanic nitrogen loss and nitrous oxide emission. Results: Axenic incubations of An-4 in the presence and absence of oxygen and nitrate revealed that this fungal isolate is capable of dissimilatory nitrate reduction to ammonium under anoxic conditions. A 15 N-labeling experiment proved that An-4 produced and excreted ammonium through nitrate reduction at a rate of up to 175 nmol 15 NH 4 + g -1 protein h -1 . The products of dissimilatory nitrate reduction were ammonium (83%), nitrous oxide (15.5%), and nitrite (1.5%), while dinitrogen production was not observed. The process led to substantial cellular ATP production and biomass growth and also occurred when ammonium was added to suppress nitrate assimilation, stressing the dissimilatory nature of nitrate reduction. Interestingly, An-4 used intracellular nitrate stores (up to 6-8 μmol NO 3 g -1 protein) for dissimilatory nitrate reduction.
Oxygen minimum zone a b s t r a c t Denitrification is a microbial process during which nitrate o... more Oxygen minimum zone a b s t r a c t Denitrification is a microbial process during which nitrate or nitrite is reduced under anaerobic condition to gaseous nitrogen. The Arabian Sea contains one of the major pelagic denitrification zones and in addition to this, denitrification also takes places along the continental shelf. Prokaryotic microorganisms were considered to be the only players in this process. However recent studies have shown that higher microeukaryotes such as fungi can also adapt to anaerobic mode of respiration and reduce nitrate to harmful green house gases such as NO and N 2 O. In this study we examined the distribution and biomass of fungi in the sediments of the seasonal anoxic region off Goa from two stations. The sampling was carried out in five different periods from October 2005, when dissolved oxygen levels were near zero in bottom waters to March 2006. We isolated mycelial fungi, thraustochytrids and yeasts. Species of Aspergillus and thraustochytrids were dominant. Fungi were isolated under aerobic, as well as anaerobic conditions from different seasons. Four isolates were examined for their denitrification activity. Two cultures obtained from the anoxic sediments showed better growth under anaerobic condition than the other two cultures that were isolated from oxic sediments. Our preliminary results suggest that several species of fungi can grow under oxygen deficient conditions and participate in denitrification processes. j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / m y c r e s m y c o l o g i c a l r e s e a r c h 1 1 3 ( 2 0 0 9 ) 1 0 0 -1 0 9 0953-7562/$ -see front matter ª
Facultative anaerobe fungus Goa Marine Morphological dimorphism Phylogeny a b s t r a c t A funga... more Facultative anaerobe fungus Goa Marine Morphological dimorphism Phylogeny a b s t r a c t A fungal culture (FCAS11) was isolated from coastal sediments of the Arabian Sea during the anoxic season. Multigene phylogenetic analyses confidentially place the organism as a novel species within the recently defined class Tritirachiomycetes, subphylum Pucciniomycotina, phylum Basidiomycota. We named the new species Tritirachium candoliense and provide the first description of a member of this class from a marine environment. DNA sequences and morphological characters distinguish T. candoliense from previously described Tritirachium species. Its growth characteristics, morphology, and ultrastructural features showed that under anoxic conditions the species grows slowly and produces mainly hyphae with only few blastoconidia. Electron microscopy revealed differences when the culture was exposed to anoxic stress. Notable ultrastructural changes occur for example in mitochondrial cristae, irregularly shaped fat globules and the presence of intracellular membrane invaginations. We assume that the growth characteristics and substrate utilization patterns are an adaptation to its source location, the seasonally anoxic environment of the Arabian Sea.
Studies on the molecular diversity of the micro-eukaryotic community have shown that fungi occupy... more Studies on the molecular diversity of the micro-eukaryotic community have shown that fungi occupy a central position in a large number of marine habitats. Environmental surveys using molecular tools have shown the presence of fungi from a large number of marine habitats such as deep-sea habitats, pelagic waters, coastal regions, hydrothermal vent ecosystem, anoxic habitats, and icecold regions. This is of interest to a variety of research disciplines like ecology, evolution, biogeochemistry, and biotechnology. In this review, we have summarized how molecular tools have helped to broaden our understanding of the fungal diversity in various marine habitats.
In order to study fungal diversity in oxygen minimum zones of the Arabian Sea, we analyzed 1440 c... more In order to study fungal diversity in oxygen minimum zones of the Arabian Sea, we analyzed 1440 cloned small subunit rRNA gene (18S rRNA gene) sequences obtained from environmental samples using three different PCR primer sets. Restriction fragment length polymorphism (RFLP) analyses yielded 549 distinct RFLP patterns, 268 of which could be assigned to fungi (Dikarya and zygomycetes) after sequence analyses. The remaining 281 RFLP patterns represented a variety of nonfungal taxa, even when using putatively fungal-specific primers. A substantial number of fungal sequences were closely related to environmental sequences from a range of other anoxic marine habitats, but distantly related to known sequences of described fungi. Community similarity analyses suggested distinctively different structures of fungal communities from normoxic sites, seasonally anoxic sites and permanently anoxic sites, suggesting different adaptation strategies of fungal communities to prevailing oxygen conditions. Additionally, we obtained 26 fungal cultures from the study sites, most of which were closely related (4 97% sequence similarity) to well-described Dikarya. This indicates that standard cultivation mainly produces more of what is already known. However, two of these cultures were highly divergent to known sequences and seem to represent novel fungal groups on high taxonomic levels. Interestingly, none of the cultured isolates is identical to any of the environmental sequences obtained. Our study demonstrates the importance of a multiple-primer approach combined with cultivation to obtain deeper insights into the true fungal diversity in environmental samples and to enable adequate intersample comparisons of fungal communities.
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Papers by Cathrine S Manohar