Familial Reclassification Within Order and Proposal of Four Novel Species.

The order consists of three families (, and ), many members of which are important pathogenic and beneficial bacteria. Previous classifications of members within order have relied heavily on 16S rRNA gene sequences, leading to taxonomic ambiguities at the familial level. With the advancement of sequencing technologies, an increasing number of whole-genome sequences have been available, providing an opportunity to revisit the taxonomy of families in . In this study, we revisited the taxonomy of by focusing on family-level reclassification based on phylogenomic frameworks. A total of 218 genome sequences, including 217 strains from and 1 from (used as an outgroup), were collected for phylogenetic analysis. Phylogenetic relationships were inferred based on UBCG (up-to-date bacterial core gene) approach using 92 core genes and a concatenated protein phylogeney based on 227 single-copy orthologous proteins. Additionally, genomic similarity metrics, including average nucleotide identity (ANI), digital DNA-DNA hybridization (dDDH), average amino acid identity (AAI) and core-proteome average amino acid identity (cpAAI), were employed to assess the taxonomy of order . Our results support the proposal of one novel family and the reassignment of six genera across different families within , emphasizing the need for a refined family-level taxonomy. In addition, four novel species belonging to the family were also confirmed. This study provides an updated familial framework for , laying a robust foundation for future detailed taxonomic revisions at the genus and species levels.