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Geomicrobiologies of the hot springs of Chumathang and Panamik (located in the Indus and Nubra valleys of eastern and northern Ladakh, respectively) were revealed and compared with the Lotus Pond spring of Puga Valley (eastern Ladakh), which is known for its mineralogical and ecological peculiarities. Physicochemically, the vent-waters of the explored springs, Chumathang_01, Panamik_01 and Panamik_02, were distinct from Lotus Pond, with wide variations in boron, chloride, lithium, magnesium and potassium concentrations. Their microbiomes encompassed several unique constituents, but resembled Lotus Pond in being highly diversified and bacterial-mesophiles-dominated. Higher diversities of thermophilic archaea were detected in Chumathang_01 compared to Panamik_01 or Panamik_02. Statistical analysis of the geochemical and microbiological data highlighted the overall uniqueness of Lotus Pond, the constraint imposed by high temperature on the diversity of most bacterial groups, and the potential role of in-situ geochemicals in helping mesophilic bacteria inhabit the high-temperature environments. While the microbiome architecture of the 86°C Chumathang_01 (having the highest bacterial species count) closely resembled that of the geochemically similar 78°C Panamik_01, both the biomes were apparently shaped by temperature and pH. In contrast, the distinctive geochemistry of the 81°C Lotus Pond was apparently instrumental in sustaining a microbiome similar to that of the cooler (70°C) Panamik_02. [ABSTRACT FROM AUTHOR]

To explore the potential role of tetrathionate in the sulfur cycle of marine sediments, population ecology of microorganisms capable of metabolizing this polythionate was revealed at 15-30 cm resolution along two, ~ 3-m-long, cores collected from 530 and 580 meters below the sea level, off India's west coast, within the oxygen minimum zone (OMZ) of the Arabian Sea. Metagenome analysis along the two sediment-cores revealed widespread occurrence of genes involved in microbial formation, oxidation, and reduction of tetrathionate; high diversity and relative-abundance was also detected for bacteria that are known to render these metabolisms in vitro. Results of slurry-incubation of the sediment-samples in thiosulfate- or tetrathionate-containing microbial growth media, data obtained via pure-culture isolation, and finally metatranscriptome analyses, corroborated the in situ functionality of tetrathionate-forming, oxidizing, and reducing microorganisms. Geochemical analyses revealed the presence of up to 11.1 μM thiosulfate along the two cores, except a few sample-sites near the sediment-surface. Thiosulfate oxidation by chemolithotrophic bacteria prevalent in situ is the apparent source of tetrathionate in this ecosystem. However, potential abiotic origin of the polythionate can neither be ruled out nor confirmed from the geochemical information currently available for this territory. Tetrathionate, in turn, can be either oxidized to sulfate (via oxidation by the chemolithotrophs present) or reduced back to thiosulfate (via respiration by native bacteria). Up to 2.01 mM sulfide present in the sediment-cores may also reduce tetrathionate abiotically to thiosulfate and elemental sulfur. As tetrathionate was not detected in situ, high microbiological and geochemical reactivity of this polythionate was hypothesized to be instrumental in its cryptic status as a central sulfur cycle intermediate. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]