Diverse Thermophilic Anaerobes from Indian Hot Springs Exhibit High Potential for Bioenergy Production from Lignocellulosic Biomass

Thermophilic anaerobic bacteria are crucial for degrading lignocellulosic biomass and producing biofuels under high-temperature, oxygen-limited conditions, presenting industrial relevance. However, their diversity and function from Indian hot springs remain underexplored. In this study, water and sediment samples were collected from ten geographically distinct Indian hot springs (25–85°C), and physicochemical parameters were measured to characterise environmental heterogeneity. Enrichments were performed using cellulose, xylan, neutral detergent fibre, and lignin, which demonstrated significant hydrogen production, primarily at thermophilic temperatures (55–85°C). Using anaerobic roll bottle isolation and redundancy reduction by RFLP, 83 distinct strains were obtained. Phylogenetic analysis of the 16S rRNA gene identified 19 species across 13 genera and 9 bacterial families, including Caldibacillus , Caloramator , Clostridium , Thermoanaerobacterium , and Sporanaerobium . Numerous strains exhibited notable cellulase, xylanase, and esterase activities on untreated rice and wheat straw. Distinct strain-level variations were noted in enzyme activities and metabolite profiles. Isolates produced high yields of ethanol, hydrogen, and volatile fatty acids, including acetic, butyric, and propionic acids. Notably, strains of Caldibacillus thermoamylovorans , Thermoanaerobacter wiegelii , and Thermoanaerobacterium spp. showed promise for consolidated bioprocessing applications. This represents the first comprehensive systematic study of lignocellulolytic thermophilic anaerobes from Indian geothermal ecosystems, highlighting their ecological diversity and significant potential for bioenergy production from agricultural residues.