Abstract
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.
Highlights
Extremophilic microorganisms are known to survive in diverse extreme conditions, such as high or low temperatures, high salinity, acidic and alkaline pH-values, and high radiation (Mirete et al, 2016)
Water samples were collected from two sites at Chhoti Anhoni region, (i) sample from a depth of ∼1 m from the surface of the hot spring which had a temperature of 43.5◦C, and (ii) sample from the free flowing water of the outlet of a borehole which was among the several boreholes drilled at Chhoti Anhoni site and was labeled as CAP (Chhoti Anhoni Petroleum)
The hot springs of Anhoni and Tattapani are located in the margins of Gondwana coalfields of India and have been reported as important geothermal resources (Pandey and Negi, 1995)
Summary
Extremophilic microorganisms are known to survive in diverse extreme conditions, such as high or low temperatures, high salinity, acidic and alkaline pH-values, and high radiation (Mirete et al, 2016) Among these extremophilic microbes, thermophiles, and hyper-thermophiles have the ability to survive in environments with very high temperature such as in hot springs, with the help of enzymes that remain catalytically active under such conditions. A time point metagenomic study carried out for 3 years in three alkaline hot springs of Yellowstone National Park (44– 75◦C) showed variations in the resident bacterial population at the three sites which had different temperatures. The elemental analysis of these hot springs revealed elevated levels of sodium, chloride and fluoride, and absence of iron, cobalt, silver, and other heavy metals. No significant correlation has been observed between the microbial diversity and geochemical characteristics of the hot springs in the above-mentioned studies
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