Novel Thermophilic Thermobaculum Strains From High-altitude Geothermal Springs in Tajikistan

Novel thermophilic bacterial strains belonging to the genus Thermobaculum were isolated from geothermal springs in the Tamdykul and Khodja-Obi-Garm districts of Tajikistan, located at elevations of 2,198 m and 1,835 m, respectively. Samples collected from these environments at temperatures of 64°C (pH 7.4) and 93°C (pH 8.5) contained obligately aerobic, nonspore-forming, rod-shaped bacteria that formed pink colonies on R2A agar. The isolates, designated T41p and KhOGp, grew at temperatures ranging from 55 to 80°C and pH 5.0–10.0. Phylogenetic analysis based on 16S rRNA gene sequences placed the isolates in the genus Thermobaculum , revealing 94.2% sequence similarity to Thermobaculum terrenum , the only previously described species in this genus. Preliminary genome sequencing revealed a genome size of 3.0 Mb, a G + C content of 51.6 mol%, and genome completeness exceeding 97%. Average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values of 89.6% and 36.6%, respectively, supported their classification as a distinct species of Thermobaculum . The isolates exhibited strong hydrolytic activity at 65°C, including the degradation of cellulose, casein, and starch, as well as the production of enzymes such as esterase-lipase (C8), β-galactosidase, and α-glucosidase. These results highlight the biotechnological potential of thermophilic microorganisms inhabiting the geothermal environments of Tajikistan and represent the first report of culturable thermophilic bacterial isolates from this region.