Phylogenetic analyses and nitrate-reducing activity of fungal cultures isolated from the permanent, oceanic oxygen minimum zone of the Arabian Sea

Reports on the active role of fungi as denitrifiers in terrestrial ecosystems have stimulated an interest in the study of the role of fungi in oxygen-deficient marine systems. In this study, the culturable diversity of fungi was investigated from 4 stations within the permanent, oceanic, oxygen minimum zone of the Arabian Sea. The isolated cultures grouped within the 2 major fungal phyla Ascomycota and Basidiomycota; diversity estimates in the stations sampled indicated that the diversity of the oxygen-depleted environments is less than that of mangrove regions and deep-sea habitats. Phylogenetic analyses of 18S rRNA sequences revealed a few divergent isolates that clustered with environmental sequences previously obtained by others. This is significant, as these isolates represent phylotypes that so far were known only from metagenomic studies and are of phylogenetic importance. Nitrate reduction activity, the first step in the denitrification process, was recorded for isolates under simulated anoxic, deep-sea conditions showing ecological significance of fungi in the oxygen-depleted habitats. This report increases our understanding of fungal diversity in unique, poorly studied habitats and underlines the importance of fungi in the oxygen-depleted environments.

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Carbon processing at the deep-sea floor of the Arabian Sea oxygen minimum zone: A tracer approach

Journal of Sea Research ◽

10.1016/j.seares.2013.01.002 ◽

2013 ◽

Vol 78 ◽

pp. 45-58 ◽

Cited By ~ 11

Author(s):

Lara Pozzato ◽

Dick van Oevelen ◽

Leon Moodley ◽

Karline Soetaert ◽

Jack J. Middelburg

Keyword(s):

Deep Sea ◽

Arabian Sea ◽

Oxygen Minimum Zone ◽

Sea Floor ◽

Minimum Zone ◽

Carbon Processing ◽

Oxygen Minimum

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Cryptic role of tetrathionate in the sulfur cycle: A study from Arabian Sea oxygen minimum zone sediments

10.1101/686469 ◽

2019 ◽

Author(s):

Subhrangshu Mandal ◽

Sabyasachi Bhattacharya ◽

Chayan Roy ◽

Moidu Jameela Rameez ◽

Jagannath Sarkar ◽

...

Keyword(s):

Arabian Sea ◽

Potential Role ◽

Sediment Cores ◽

Oxygen Minimum Zone ◽

Sulfur Cycle ◽

Metagenome Analysis ◽

Minimum Zone ◽

Oxygen Minimum

ABSTRACTTo explore the potential role of tetrathionate in the sulfur cycle of marine sediments, the population ecology of tetrathionate-forming, oxidizing, and respiring microorganisms was revealed at 15-30 cm resolution along two, ∼3-m-long, cores collected from 530- and 580-mbsl water-depths of Arabian Sea, off India’s west coast, within the oxygen minimum zone (OMZ). Metagenome analysis along the two sediment-cores revealed widespread occurrence of the structural genes that govern these metabolisms; high diversity and relative-abundance was also detected for the bacteria known to render these processes. Slurry-incubation of the sediment-samples, pure-culture isolation, and metatranscriptome analysis, corroborated thein situfunctionality of all the three metabolic-types. Geochemical analyses revealed thiosulfate (0-11.1 μM), pyrite (0.05-1.09 wt %), iron (9232-17234 ppm) and manganese (71-172 ppm) along the two sediment-cores. Pyrites (via abiotic reaction with MnO2) and thiosulfate (via oxidation by chemolithotrophic bacteria prevalentin situ) are apparently the main sources of tetrathionate in this ecosystem. Tetrathionate, in turn, can be either converted to sulfate (via oxidation by the chemolithotrophs present) or reduced back to thiosulfate (via respiration by native bacteria); 0-2.01 mM sulfide present in the sediment-cores may also reduce tetrathionate abiotically to thiosulfate and elemental sulfur. Notably tetrathionate was not detectedin situ- high microbiological and geochemical reactivity of this polythionate is apparently instrumental in the cryptic nature of its potential role as a central sulfur cycle intermediate. Biogeochemical roles of this polythionate, albeit revealed here in the context of OMZ sediments, may well extend to the sulfur cycles of other geomicrobiologically-distinct marine sediment horizons.

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Cryptic role of tetrathionate in the sulfur cycle: A study from Arabian Sea oxygen minimum zone sediments

10.5194/bg-2019-248 ◽

2019 ◽

Author(s):

Subhrangshu Mandal ◽

Sabyasachi Bhattacharya ◽

Chayan Roy ◽

Moidu Jameela Rameez ◽

Jagannath Sarkar ◽

...

Keyword(s):

Arabian Sea ◽

Potential Role ◽

Sediment Cores ◽

Oxygen Minimum Zone ◽

Sulfur Cycle ◽

Metagenome Analysis ◽

Minimum Zone ◽

Oxygen Minimum

Abstract. To explore the potential role of tetrathionate in the sulfur cycle of marine sediments, the population ecology of tetrathionate-forming, oxidizing, and respiring microorganisms was revealed at 15–30 cm resolution along two, ~ 3-m-long, cores collected from 530- and 580-mbsl water-depths of Arabian Sea, off India’s west coast, within the oxygen minimum zone (OMZ). Metagenome analysis along the two sediment-cores revealed widespread occurrence of the structural genes that govern these metabolisms; high diversity and relative-abundance was also detected for the bacteria known to render these processes. Slurry-incubation of the sediment-samples, pure-culture isolation, and metatranscriptome analysis, corroborated the in situ functionality of all the three metabolic-types. Geochemical analyses revealed thiosulfate (0–11.1 µM), pyrite (0.05–1.09 wt %), iron (9232–17234 ppm) and manganese (71–172 ppm) along the two sediment-cores. Pyrites (via abiotic reaction with MnO2) and thiosulfate (via oxidation by chemolithotrophic bacteria prevalent in situ) are apparently the main sources of tetrathionate in this ecosystem. Tetrathionate, in turn, can be either converted to sulfate (via oxidation by the chemolithotrophs present) or reduced back to thiosulfate (via respiration by native bacteria); 0–2.01 mM sulfide present in the sediment-cores may also reduce tetrathionate abiotically to thiosulfate and elemental sulfur. Notably tetrathionate was not detected in situ – high microbiological and geochemical reactivity of this polythionate is apparently instrumental in the cryptic nature of its potential role as a central sulfur cycle intermediate. Biogeochemical roles of this polythionate, albeit revealed here in the context of OMZ sediments, may well extend to the sulfur cycles of other geomicrobiologically-distinct marine sediment horizons.

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