Comprehensive genomic and phenotypic characterization of thermophilic bacterium Sinimarinibacterium thermocellulolyticum sp. nov. HSW-8T, a cellulase-producing bacterium isolated from hot spring water in South Korea

A thermophilic cellulase-producing bacterium, strain HSW-8^T, isolated from hot spring waters in South Korea, was subjected to a taxonomic analysis. Cells of strain HSW-8^T were gram-stain-negative, facultatively anaerobic, rod-shaped, with optimum growth at 45 °C, pH 7.0, in the presence of 0% (w/v) NaCl. Strain HSW-8^T showed the highest 16S rRNA gene sequence similarity to Sinimarinibacterium flocculans NH6-24^T (97.52%), followed by Fontimonas thermophila DSM 23609^T (96.97%), Solimonas flava CW-KD 4^T (95.24%), and Solimonas variicoloris DSM 15731^T (95.18%). Based on 16S rRNA phylogeny, strain HSW-8^T is phylogenetically closely related to Fontimonas thermophila DSM 23609^T and Sinimarinibacterium flocculans DSM 104150^T and could be distinguished from the type species based on their phenotypic properties. The genome length of strain HSW-8^T was 3.32 Mbp with a 67.33% G + C content. The average nucleotide identity and digital DNA–DNA hybridization values between strain HSW-8^T and its closely related type strains were 75.4–83.2 and 20.2–26.2%, respectively. Summed feature 8 (C_18:1ω7c and/or C_18:1ω6c), C_16:0, and iso-C_16:0 identified the major fatty acids (> 10%). Phosphatidylglycerol and phosphatidylethanolamine were demonstrated as the major polar lipids while the respiratory quinone is ubiquinone-8. Strain HSW-8^T exhibited multiple adaptations for survival at high temperatures, including diverse potential motility mechanisms and toxin-antitoxin systems, as evidenced by both phenotypic characteristics and genomic analysis. Based on genotypic and phenotypic features, strain HSW-8^T (= KCTC 92765^T = GDMCC 1.4313^T) represents a novel Sinimarinibacterium species, in which the name Sinimarinibacterium thermocellulolyticum sp. nov. is proposed.