Extreme ecosystems such as hot springs are of great interest as a source of novel extremophilic species, enzymes, metabolic functions for survival and biotechnological products. India harbors hundreds of hot springs, the majority of which are not yet explored and require comprehensive studies to unravel their unknown and untapped phylogenetic and functional diversity. The aim of this study was to perform a large-scale metagenomic analysis of three major hot springs located in central India namely, Badi Anhoni, Chhoti Anhoni, and Tattapani at two geographically distinct regions (Anhoni and Tattapani), to uncover the resident microbial community and their metabolic traits. Samples were collected from seven distinct sites of the three hot spring locations with temperature ranging from 43.5 to 98°C. The 16S rRNA gene amplicon sequencing of V3 hypervariable region and shotgun metagenome sequencing uncovered a unique taxonomic and metabolic diversity of the resident thermophilic microbial community in these hot springs. Genes associated with hydrocarbon degradation pathways, such as benzoate, xylene, toluene, and benzene were observed to be abundant in the Anhoni hot springs (43.5–55°C), dominated by Pseudomonas stutzeri and Acidovorax sp., suggesting the presence of chemoorganotrophic thermophilic community with the ability to utilize complex hydrocarbons as a source of energy. A high abundance of genes belonging to methane metabolism pathway was observed at Chhoti Anhoni hot spring, where methane is reported to constitute >80% of all the emitted gases, which was marked by the high abundance of Methylococcus capsulatus. The Tattapani hot spring, with a high-temperature range (61.5–98°C), displayed a lower microbial diversity and was primarily dominated by a nitrate-reducing archaeal species Pyrobaculum aerophilum. A higher abundance of cell metabolism pathways essential for the microbial survival in extreme conditions was observed at Tattapani. Taken together, the results of this study reveal a novel consortium of microbes, genes, and pathways associated with the hot spring environment.
Ophiolites are on-land remnants of oceanic lithosphere, and most of the more extensive ophiolites apparently formed above a subduction zone, a tectonic setting known as a suprasubduction-zone setting. Thin sheets of high-grade metamorphic rocks, known as metamorphic soles, crop out structurally beneath many suprasubduction-zone ophiolites. Such rocks may have formed during the inception of subduction beneath young and hot oceanic lithosphere. Disagreement exists as to whether suprasubduction-zone ophiolites are emplaced over the same subduction zone over which they once formed or over a later one. High-grade metamorphic rocks (blocks-in-mélange and coherent sheets) from the Franciscan Complex may represent a metamorphic sole beneath the suprasubduction-zone Coast Range ophiolite. Trace-element and isotopic data indicate that the Franciscan high-grade metamorphic rocks formed in a suprasubduction-zone envi ronment, requiring the existence of a pre-Franciscan sub duction zone, whereas later-subducted, lower-grade oceanic rocks are of mid-ocean-ridge or oceanic-island basalt affi ni ties. The Coast Range ophiolite and Franciscan high-grade rock protoliths formed over a pre-Franciscan subduction zone that may have dipped westward. The high-grade Franciscan rocks were metamorphosed at the inception of east-dipping subduction beneath the Coast Range ophiolite, and the ophiolite was subsequently emplaced over this later subduction zone. Suprasubduction-zone protolith signatures have been obtained for other metamorphic soles beneath suprasubduction-zone ophiolites, suggesting that our proposed model of suprasubduction-zone ophiolite generation over one subduction zone and emplacement over a second one may be globally applicable. Regional geology suggests that this dual subduction-zone model may also apply to suprasubduction-zone ophiolites with midocean-ridge and/or oceanic-island basalt soles.Generation of ophiolite over first subduction zone and emplacement over a later one.
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