Comparative genomic analyses of four novel Ramlibacter species and the cellulose-degrading properties of Ramlibacter cellulosilyticus sp. nov.

In this study, four novel bacterial strains, USB13^T, AW1^T, GTP1^T, and HM2^T, were isolated from various environments in Busan and Jeju Island, Republic of Korea. The 16S rRNA sequencing results indicated that the four novel strains belong to the genus Ramlibacter. All four strains were tested for their potential cellulolytic properties, where strain USB13^T was identified as the only novel bacterium and the first within its genus to show cellulolytic activity. When tested, the highest activities of endoglucanase, exoglucanase, β-glucosidase, and filter paper cellulase (FPCase) were 1.91 IU/mL, 1.77 IU/mL, 0.76 IU/mL, and 1.12 IU/mL, respectively at pH 6.0. Comparisons of draft whole genome sequences (WGS) were also made using average nucleotide identity, digital DNA-DNA hybridization values, and average amino acid identity values, while whole genome comparison was visualized using the BLAST Ring Image Generator. The G + C contents of the strains ranged from 67.9 to 69.9%, while genome sizes ranged from 4.31 to 6.15 Mbp. Based on polyphasic evidence, the novel strains represent four new species within the genus Ramlibacter, for which the names Ramlibacter cellulosilyticus sp. nov. (type strain, USB13^T = KACC 21656^T = NBRC 114839^T) Ramlibacter aurantiacus sp. nov. (type strain, AW1^T = KACC 21544^T = NBRC 114862^T), Ramlibacter albus sp. nov. (type strain, GTP1^T = KACC 21702^T = NBRC 114488^T), and Ramlibacter pallidus sp. nov. (type strain, HM2^T = KCTC 82557^T = NBRC 114489^T) are proposed.