Rhodoglobus galactosidasius sp. nov., a psychrophilic Actinomycetota producing a cold-active β-galactosidase isolated from Cape Hallett, Antarctica

Abstract

A novel psychrophilic member of the phylum Actinomycetota , designated strain CPHL_1 T , was isolated from the shoreline of Cape Hallett, Antarctica. Cells were Gram-positive, aerobic, non-motile, non-spore-forming rods (0.7–1.0 µm in length) with orange to yellow pigmentation. Optimal growth occurred at 15 °C, pH 8.0, with NaCl tolerance up to 3% (w/v). Strain CPHL_1 T exhibited cytosolic cold-active β-galactosidase activity, with an optimum at 15 °C and pH 7.0 and formed non-adherent biofilms. Phylogenetic analysis based on 16S rRNA gene sequence placed the strain within the genus Rhodoglobus , showing high similarity to Rhodoglobus vestalii LV3 T (99.4%) and Rhodoglobus aureus CMS 81y T (97.6%). Chemotaxonomic characteristics, including the predominance of anteiso-C 15 : 0 , anteiso-C 17 : 0 and iso-C 16 : 0 fatty acids, the presence of MK-11, MK-10 and MK-12 as the major respiratory quinones, and genomic G+C content of 60%, further supported its assignment to the genus Rhodoglobus . Whole-genome comparisons revealed clear taxonomic distinction, with strain CPHL_1 T sharing 88.9% average nucleotide identity (ANI) and 38.3% digital DNA–DNA hybridization (dDDH) values with R. aureus , and 81.7% ANI and 25.1% dDDH with R. vestalii , confirming its status as a novel species. Phylogenetic analysis revealed that the β-galactosidases from these Rhodoglobus strains form a well-supported clade with high sequence similarity. Based on these data, a novel species is proposed: Rhodoglobus galactosidasius sp. nov. (type strain CPHL_1 T =ITEM 19986 T =KCTC 59592 T ). Genomic analyses also highlighted its biosynthetic potential for specialized metabolites, consistent with the recognized metabolic diversity of the genus.