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Marine sedimentation rate and bottom-water O2 concentration control organic carbon remineralization and sequestration across continental margins, but whether and how they shape microbiome architecture (the ultimate effector of all biogeochemical phenomena) across shelf and slope sediments is still unclear. Here we reveal distinct microbiome structures and functions, amidst comparable pore fluid chemistries, along 300 cm sediment horizons underlying the seasonal (shallow coastal; water depth: 31 m) and perennial (deep sea; water depths: 530 and 580 m) oxygen minimum zones (OMZs) of the Arabian Sea, situated across the western Indian margin. The sedimentary geomicrobiology was elucidated by analyzing metagenomes, metatranscriptomes, enrichment cultures, and depositional rates measured via radiocarbon and lead excess dating; the findings were then evaluated in light of the other geochemical data available for the cores. Along the perennial-OMZ sediment cores, microbial communities were dominated by Gammaproteobacteria and Alphaproteobacteria, but in the seasonal-OMZ core communities were dominated by Euryarchaeota and Firmicutes. As a perennial-OMZ signature, a cryptic methane production–consumption cycle was found to operate near the sediment surface, within the sulfate reduction zone; overall diversity, as well as the relative abundances of anaerobes requiring simple fatty acids (methanogens, anaerobic methane oxidizers, sulfate reducers, and acetogens), peaked in the topmost sediment layer and then declined via synchronized fluctuations until the sulfate–methane transition zone was reached. The microbiome profile was completely reversed in the seasonal-OMZ sediment horizon. In the perennial-OMZ sediments, deposited organic carbon was higher in concentration and rich in marine components that degrade readily to simple fatty acids; simultaneously, lower sedimentation rate afforded higher O2 exposure time for organic matter degradation despite perennial hypoxia in the bottom water. The resultant abundance of reduced carbon substrates eventually sustained multiple inter-competing microbial processes in the upper sediment layers. The entire geomicrobial scenario was opposite in the sediments of the seasonal OMZ. These findings create a microbiological baseline for understanding carbon–sulfur cycling in distinct depositional settings and water column oxygenation regimes across the continental margins.

Kinetics of thiosulfate oxidation, product and intermediate formation, and 34S fractionation, were studied for the members of Alphaproteobacteria Paracoccus sp. SMMA5 and Mesorhizobium thiogangeticum SJTT, the Betaproteobacteria member Pusillimonas ginsengisoli SBO3, and the Acidithiobacillia member Thermithiobacillus sp. SMMA2, during chemolithoautotrophic growth in minimal salts media supplemented with 20 mM thiosulfate. The two Alphaproteobacteria oxidized thiosulfate directly to sulfate, progressively enriching the end-product with 34S; Δ34Sthiosulfate-sulfate values recorded at the end of the two processes (when no thiosulfate was oxidized any further) were −2.9‰ and −3.5‰, respectively. Pusillimonas ginsengisoli SBO3 and Thermithiobacillus sp. SMMA2, on the other hand, oxidized thiosulfate to sulfate via tetrathionate intermediate formation, with progressive 34S enrichment in the end-product sulfate throughout the incubation period; Δ34Sthiosulfate-sulfate, at the end of the two processes (when no further oxidation took place), reached −3.5‰ and −3.8‰, respectively. Based on similar 34S fractionation patterns recorded previously during thiosulfate oxidation by strains of Paracoccus pantotrophus, Advenella kashmirensis and Hydrogenovibrio crunogenus, it was concluded that progressive reverse fractionation, enriching the end-product sulfate with 34S, could be a characteristic signature of bacterial thiosulfate oxidation.

Marine sedimentation rate and bottom-water O2 concentration control the remineralization/sequestration of organic carbon across continental margins; but whether/how they shape microbiome architecture (the ultimate effector of all biogeochemical phenomena), across shelf/slope sediments, is unknown. Here we reveal distinct microbiome structures and functions, amidst comparable pore-fluid chemistries, along ~3 m sediment-horizons underlying the seasonal (shallow coastal) and perennial (deep sea) oxygen minimum zones (OMZs) of the Arabian Sea, situated across the western-Indian margin (water-depths: 31 m and, 530 and 580 m, respectively). Along the perennial- and seasonal-OMZ sediment-cores microbial communities were predominated by Gammaproteobacteria/Alphaproteobacteria and Euryarchaeota/Firmicutes respectively. As a perennial-OMZ signature, a cryptic methane production-consumption cycle was found to operate near the sediment-surface; overall diversity, as well as the relative abundances of simple-fatty-acids-requiring anaerobes (methanogens, anaerobic methane-oxidizers, sulfate-reducers and acetogens), peaked in the topmost sediment-layer and then declined via synchronized fluctuations until the sulfate-methane transition zone was reached. The entire microbiome profile was reverse in the seasonal-OMZ sediment-horizon. We discerned that in the perennial-OMZ sediments organic carbon deposited was higher in concentration, and marine components-rich, so it potentially degraded readily to simple fatty acids; lower sedimentation rate afforded higher O2 exposure time for organic matter degradation despite perennial hypoxia in the bottom-water; thus, the resultant abundance of reduced metabolites sustained multiple inter-competing microbial processes in the upper sediment-layers. Remarkably, the whole geomicrobial scenario was opposite in the sediments of the seasonal/shallow-water OMZ. Our findings create a microbiological baseline for understanding carbon-sulfur cycling across distinct marine depositional settings and water-colum n oxygenation regimes.

The ecology of aerobic microorganisms is never explored in marine oxygen minimum zone (OMZ) sediments. Here we reveal aerobic bacterial communities along ∼3 m sediment-horizons of the eastern Arabian Sea OMZ. Sulfide-containing sediment-cores retrieved from 530 mbsl (meters beneath the sea-level) and 580 mbsl were explored at 15–30 cm intervals, using metagenomics, pure-culture-isolation, genomics and metatranscriptomics. Genes for aerobic respiration, and oxidation of methane/ammonia/alcohols/thiosulfate/sulfite/organosulfur-compounds, were detected in the metagenomes from all 25 sediment-samples explored. Most probable numbers for aerobic chemolithoautotrophs and chemoorganoheterotrophs at individual sample-sites were up to 1.1 × 107 (g sediment)-1. The sediment-sample collected from 275 cmbsf (centimeters beneath the seafloor) of the 530-mbsl-core yielded many such obligately aerobic isolates belonging to Cereibacter, Guyparkeria, Halomonas, Methylophaga, Pseudomonas and Sulfitobacter which died upon anaerobic incubation, despite being provided with all possible electron acceptors and fermentative substrates. High percentages of metatranscriptomic reads from the 275 cmbsf sediment-sample, and metagenomic reads from all 25 sediment-samples, matched the isolates’ genomic sequences including those for aerobic metabolisms, genetic/environmental information processing and cell division, thereby illustrating the bacteria's in-situ activity, and ubiquity across the sediment-horizons, respectively. The findings hold critical implications for organic carbon sequestration/remineralization, and inorganic compounds oxidation, within the sediment realm of global marine OMZs., Aerobic microorganisms in marine oxygen minimum zone sediment.

Geomicrobiology of sulfur–boron-dominated, neutral-pH hydrothermal systems was revealed in a Trans-Himalayan spring named Lotus Pond, located at 4436 m, in Puga Valley, Ladakh (India), where water boils at 85°C. Water sampled along Lotus Pond’s outflow (vent to an adjacent river called Rulang), representing an 85–14°C gradient, had high microbial diversity and boron/chloride/sodium/sulfate/thiosulfate concentration; potassium/silicon/sulfide/sulfite was moderately abundant, whereas cesium/lithium small but definite. Majority of the bacterial genera identified in the 85–72°C samples have no laboratory-growth reported at >45°C, and some of those mesophiles were culturable. Sulfur-species concentration and isotope-ratio along the hydrothermal gradient, together with the distribution of genera having sulfur-oxidizing members, indicated chemolithotrophic activities in the 85–72°C sites. While biodiversity increased in the vent-to-river trajectory all-day, maximum rise was invariably between the vent (85–81°C) and the 78–72°C site; below 72°C, diversity increased gradually. Biodiversity of the vent-water exhibited diurnal fluxes relatable to the sub-surface-processes-driven temporal fluxes in physicochemical properties of the discharge. Snow-melts infiltrating (via tectonic faults) the ~160°C geothermal reservoir located within the breccia, at ~450 m depth, apparently transport mesophilic microbes into the thermal waters. As these micro-organisms emanate with the vent-water, some remain alive, illustrating that natural bacterial populations are more heat-resilient than their laboratory counterparts.

Here we present high-resolution biogeochemical study using nitrogen/carbon isotope ratio measurement and molecular proxies from a sediment core (length = 2.9 m) collected from the center (588 mbsl; Lat: 16049.88’N and Long: 710 58.55’ E) of the oxygen minimum zone off west coast of India. The core archives the depositional record covering 1.114 to 12.025 ky BP. The concentrations of total organic carbon (TOC) and total nitrogen (TN) range from 0.7 to 4.9 wt% and 0.068 to 0.5 wt % respectively. TOC and TN show parallel trends and the TOC/TN ratio varies within a narrow range of 8 to 11.5. The δ13C values range from -20.5‰ to -21.9‰ (V-PDB). The TOC/TN and δ13C suggest typical marine organic matter source. This observation is also further supported by the n-alkane distribution pattern where the dominance of nC21 to nC24 and the absence of odd alkane dominance over even suggest predominantly marine organic source. The δ15N profile shows a steady increase from 5.7‰ at 203 cmbsf (5.5 ky BP) to 7.5‰ at 2 cmbsf (~1ky BP) suggesting gradual increase in denitrification possibly liked to reduced ventilation in the Arabian Sea, whereas, between 5.5 to 12 ky BP, the δ15N values show marked fluctuations (5.2 to 7.1‰) possibly indicating variable level of oxygenation which in turn controlled the extent of denitrification. Possible influence of diagenesis (microbial degradation of organic matter) on the δ15N values also need to be investigated for a better understanding of the water column processes.

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.

Metabolically-active obligate aerobes are unheard-of in tightly-anoxic environments. Present culture-independent and culture-dependent investigations revealed aerobic microbial communities along two, ~3-meter-long sediment-cores underlying the eastern Arabian Sea oxygen minimum zone, where high H2S disallows O2influx from the water-column. While genes for aerobic respiration byaa3-/cbb3-type cytochrome-coxidases and cytochrome-bdubiquinol oxidase, and aerobic oxidation of methane/ammonia/alcohols/thiosulfate/sulfite/organosulfur-compounds, were present across the cores, so were live aerobic, sulfur-chemolithoautotrophs and chemoorganoheterotrophs. The 8820-years-old, highly–sulfidic, methane-containing sediment-sample from 275 cmbsf of 530 mbsl yielded many such obligately-aerobic bacterial-isolates that died upon anaerobic incubation with alternative electron-acceptors/fermentative-substrates. Several metatranscriptomic reads from this sediment-sample matched aerobic-respiration-/oxidase-reaction-/transcription-/translation-/DNA-replication-/membrane-transport-/cell-division-related genes of the obligately-aerobic isolates, thereby corroborating their active aerobic metabolic-statusin situ. Metagenomic and metatranscriptomic detection of perchlorate-/chlorate-reduction genes, plus anaerobic growth of an obligately-aerobicHalothiobacillusisolate in the presence of perchlorate and perchlorate-reducing-consortia, suggested that cryptic O2produced by perchlorate-respirers could be sustaining obligately-aerobes in this environment.

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 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.

Little is known about life in the boron-rich hot springs of Trans-Himalayas. Here, we explore the geomicrobiology of a 4438-m-high spring which emanates ~70 °C-water from a boratic microbialite called Shivlinga. Due to low atmospheric pressure, the vent-water is close to boiling point so can entropically destabilize biomacromolecular systems. Starting from the vent, Shivlinga’s geomicrobiology was revealed along the thermal gradients of an outflow-channel and a progressively-drying mineral matrix that has no running water; ecosystem constraints were then considered in relation to those of entropically comparable environments. The spring-water chemistry and sinter mineralogy were dominated by borates, sodium, thiosulfate, sulfate, sulfite, sulfide, bicarbonate, and other macromolecule-stabilizing (kosmotropic) substances. Microbial diversity was high along both of the hydrothermal gradients. Bacteria, Eukarya and Archaea constituted >98%, ~1% and Shivlinga’s microbiome, respectively. Temperature constrained the biodiversity at ~50 °C and ~60 °C, but not below 46 °C. Along each thermal gradient, in the vent-to-apron trajectory, communities were dominated by Aquificae/Deinococcus-Thermus, then Chlorobi/Chloroflexi/Cyanobacteria, and finally Bacteroidetes/Proteobacteria/Firmicutes. Interestingly, sites of >45 °C were inhabited by phylogenetic relatives of taxa for which laboratory growth is not known at >45 °C. Shivlinga’s geomicrobiology highlights the possibility that the system’s kosmotrope-dominated chemistry mitigates against the biomacromolecule-disordering effects of its thermal water.

Continental shelves are the major sites for organic carbon burial and sulfate reduction. Organic carbon degradation and sulfidization along continental shelves are expected to play a significant role in global carbon-sulfur-iron (C–S–Fe) cycles. Here we report sediment pore-water chemistry and iron-sulfur speciation in two short cores SSK-42/9 and 10 collected off Malvan from the seasonally hypoxic shelf region off the west coast of India (WCI) at water depths of 30 and 13 m respectively. Concentration profiles of pore-water SO42−, NH4+, DIC, ΣHS− and depth-integrated sulfate reduction rates (JSO4) suggest a variable influence of sedimentation rates, the composition of organic matter (marine and terrestrial) and anaerobic oxidation of methane (AOM) on the pore-fluid chemistry. Chromium reducible sulfur (CRS) and organic-bound sulfur (OBS) are the detectable solid-phase sulfur species in the studied sediment cores. Sulfur content and isotope ratios of chromium reducible sulfur (CRS) and organic-bound sulfur (OBS) phases produced via HS−/Sx2− pathways (sulfidization and sulfurization) show contrasting profiles in SSK42/9 and 10, apparently influenced by the availability of reactive iron, the relative significance of early and late diagenetic processes, source of OBS (detritus of marine origin and sulfurized organic molecules) and diffusion of ΣHS− produced via AOM across the SMTZ. The marked influence of AOM-driven sulfate reduction and the diffusion of isotopically enriched hydrogen sulfide across the sulfate-methane transition zone (SMTZ) is apparent from the δ34SCRS profiles in SSK-42/10. Sediment TOC/TS ratios recorded in this study are significantly less than that of average modern marine surface sediments (2.8:1) underlying oxygenated water and this is attributed to the enhanced sulfidization and burial of iron-sulfur minerals in the seasonally hypoxic regions. Since the inner shelf of WCI experiences seasonal alternation from normoxia to hypoxia which may have a profound influence on the benthic community structure, nature, and depth of bioturbation/bioirrigation, we propose that the impact of these processes need to be studied at a significantly higher resolution for better understanding C–S–Fe biogeochemical cycle.

Biogeochemistry of oxygen minimum zone (OMZ) sediments, which are characterized by high input of labile organic matter, have crucial bearings on the benthic biota, gas and metal fluxes across the sediment-water interface, and carbon-sulfur cycling. Here we couple pore-fluid chemistry and comprehensive microbial diversity data to reveal the sedimentary carbon-sulfur cycle across a water-depth transect covering the entire thickness of eastern Arabian Sea OMZ, off the west coast of India. Geochemical data show remarkable increase in average total organic carbon content and aerial sulfate reduction rate (JSO42−) in the sediments of the OMZ center coupled with shallowing of sulfate methane transition zone and hydrogen sulfide and ammonium build–up. Total bacterial diversity, including those of complex organic matter degraders, fermentative and exoelectrogenic bacteria, and sulfate-reducers (that utilize only simple carbon compounds) were also found to be highest in the same region. The above findings indicate that higher organic carbon sequestration from the water-columns (apparently due to lower benthic consumption, biodegradation and biotransformation) and greater bioavailability of simple organic carbon compounds (apparently produced by fermetative microflora of the sediments) are instrumental in intensifying the carbon-sulfur cycle in the sediments of the OMZ center.

Background The purpose of the present study was to examine the differential effect of core stability exercise training and conventional physiotherapy regime on altered postural control parameters in patients with chronic low back pain (CLBP). As heterogeneity in CLBP population moderates the effect of intervention on outcomes, in this study, interventions approaches were used based on sub-groups of CLBP. Methods This was an allocation concealed, blinded, sequential and pragmatic control trial. Three groups of participants were investigated during postural perturbations: 1) CLBP patients with movement impairment (n = 15, MI group) randomized to conventional physiotherapy regime 2) fifteen CLBP patients with control impairment randomized to core stability group (CI group) and 3) fifteen healthy controls (HC). Results The MI group did not show any significant changes in postural control parameters after the intervention period however they improved significantly in disability scores and fear avoidance belief questionnaire work score (P < 0.05). The CI group showed significant improvements in Fx, Fz, and My variables (p < 0.013, p < 0.006, and p < 0.002 respectively with larger effect sizes: Hedges's g > 0.8) after 8 weeks of core stability exercises for the adjusted p values. Postural control parameters of HC group were analyzed independently with pre and post postural control parameters of CI and MI group. This revealed the significant improvements in postural control parameters in CI group compared to MI group indicating the specific adaptation to the core stability exercises in CI group. Though the disability scores were reduced significantly in CI and MI groups (p < 0.001), the post intervention scores between groups were not found significant (p < 0.288). Twenty percentage absolute risk reduction in flare-up rates during intervention was found in CI group (95% CI: 0.69-0.98). Conclusions In this study core stability exercise group demonstrated significant improvements after intervention in ground reaction forces (Fz, Mz; g > 0.8) indicating changes in load transfer patterns during perturbation similar to HC group. Trial registration UTRN095032158-06012009423714