Revisiting the taxonomic and genomic repertoire of the family Colwelliaceae with three new species

Background Colwelliaceae is a bacterial family that inhabits diverse marine environments, including low-temperature, high-salinity, high-pressure, and symbiotic environments with marine organisms. Although cold-adaptation mechanisms have been reported in some species, comparative genomic evaluations of the entire family are lacking. In this study, we conducted phylogenetic reassessment of the Colwelliaceae family, followed by a comparative analysis of genes associated with cold adaptation. Result Phylogenetic tree and Average Amino-acid Identity (AAI) analyses incorporating 10 additional genomes, including seven newly added genomes and three genomes representing novel species, revealed that the previously recognized 24 genera were resolved into 32 distinct genera. Two additional genera were established to accommodate the three novel species. Comparative analyses of cold adaptation-related proteins showed that cold shock proteins (Csps) formed two Colwelliaceae -specific clades independent of the Escherichia coli Csp clade, although the Csp phylogeny alone was not associated with growth temperature. Some cold-growing strains formed clusters based on fatty acid composition;, however, they did not explain the cold-growing characteristics. Genes, related to compatible solutes did not consistently explain low-temperature growth, and compatible solute-related genes showed no family-wide patterns associated with cold adaptation. These findings demonstrate that cold adaptation in the Colwelliaceae is associated with lineage-specific combinations of genomic features, including cold-shock proteins, compatible-solute metabolism, and membrane-associated functions. Conclusion By integrating comprehensive phylogenetic reconstruction, AAI-based taxonomic analysis, comparative genomics, and phenotypic associations with growth at low temperatures, this study elucidated the genomic basis of cold adaptation across Colwelliaceae and provided a refined framework for understanding the relationship between evolutionary diversification and cold tolerance in this family.