Genome-Based Classification and Phylogenetic Revision of the Family Colwelliaceae with Proposals for New Genera and Species

Lee Min Seo ^1,2 Sung-Hyun Yang ¹ Yun Jae Kim ¹ Yeong-Jun Park ^1,3 Mi-Jeong Park ^1* Kae Kyoung Kwon ^1,3

• ¹ Korea Institute of Ocean Science and Technology (KIOST), Busan, Republic of Korea
• ² Hannam University, Daejeon, Republic of Korea
• ³ University of Science and Technology, Daejeon, Republic of Korea

Psychrophilic marine bacteria of the family Colwelliaceae have attracted considerable industrial interest. However, their phylogenetic positions remain ambiguous when classified solely based on 16S rRNA gene sequences. In this study, we aimed to characterize four novel species belonging to this family, but limitations of traditional classification methods hindered accurate taxonomic placement. To address this, we employed a taxogenomic approach to clarify phylogenetic relationships within Colwelliaceae and determine the positions of the newly isolated species. Genomic indices including ANI, dDDH, and AAI were compared across all available genomes. By applying a repetitive clustering and evaluation strategy, we defined genus-level AAI thresholds specific to Colwelliaceae, which ranged from 74.07% to 75.11%. Using this framework, we re-evaluated 47 species including four novel species and proposed 18 new genera, expanding the previously recognized 6 genera to 24 genera. The four novel species were assigned to three of these new genera. Our results provide a comprehensive revision of Colwelliaceae taxonomy and offer a refined classification system grounded in genome-based metrics.