Metagenomic analysis of geothermal water reservoir sites exploring carbohydrate-related thermozymes

Hot springs are geothermally heated underground water that create a natural habitat for diverse thermophilic microorganisms. The study presents a comprehensive investigation of microbial diversity and functional potential of four thermal water reservoirs of 55 to 98 °C temperature range, located in Tattapani geothermal field of Chhattisgarh, India, by using culture-independent metagenome sequencing approach. The MG-RAST taxonomic profiling of metagenome samples revealed the predominance of bacterial domains (94.8 to 98.2%), followed by archaea (1.1 to 4.8%), eukaryota (0.1 to 0.5%), and viruses (0.04 to 0.09%). The quality filtered reads (42.1 to 68.1 million) were assembled into 66 to 330 thousand non-redundant contigs (>200 bp length) in the four metagenome samples. The functional annotation using CAZy database identified a total of 4083 putative genes with functional domains involved in catalysis of carbohydrate degradation or modification or synthesis of glycosidic bonds. The study detected many novel biocatalysts associated with hydrolysis of lignocellulosic biomass polymers- cellulose, hemicellulose, lignin, and pectin. Metagenome assembly and catalytic functions of two metagenomic contigs, encoding β-glucosidase, and xylanase, were experimentally validated. The findings emphasized these geothermal water reservoir sites as the repository of biocatalyst-encoding genes of carbohydrate-related and lignocellulosic biomass processing significance.