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 degrees C, pH 7.0, in the presence of 0% (w/v) NaCl. StrainHSW-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 15731T (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 104150T 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 (C18:1 omega 7c and/or C18:1 omega 6c), 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.