Comparative Genomics Analyses Support the Reclassification of Bisgaard Taxon 40 as gen. nov., With sp. nov. as Type Species: Novel Insights Into the Phylogeny and Virulence Factors of a e Family Member Associated With Mortality Events in Seabirds.

The family has been associated with fatal diseases in numerous avian species. Several new taxa within this family, including Bisgaard taxon 40, have been recently described in wild birds, but their genomic characteristics and pathogenicity are not well understood. We isolated Bisgaard taxon 40 from four species of seabirds, including one sampled during a mass, multi-species mortality event in Florida, United States. Here, we present a comprehensive phenotypic and genetic characterization of Bisgaard taxon 40 and comparative genomic analysis with reference strains from the family, aiming at determining its phylogenetic position, antimicrobial susceptibility profile, and identifying putative virulence factors. multilocus sequence-based and whole-genome-based phylogenetic analysis clustered all Bisgaard taxon 40 strains together on a distinct branch separated from the other members of the family, indicating that Bisgaard taxon 40 could represent a new genus. These findings were further supported by protein similarity analyses using the concatenation of 31 conserved proteins and other taxonomic approaches such as the percentage of conserved protein test. Additionally, several putative virulence factors were identified, including those associated with adhesion (capsule, , ) and colonization (, , , , , , and ) of the host and a cytolethal distending toxin (), which may have played a role in disease development leading to the mortality event. Considerably low minimum inhibitory concentrations (MICs) were found for all the drugs tested, in concordance with the absence of antimicrobial resistance genes in these genomes. The novel findings of this study highlight genomic and phenotypic characteristics of this bacterium, providing insights into genome evolution and pathogenicity. We propose a reclassification of these organisms within the family, designated as gen. nov., with sp. nov. as the type species. The type strain is A25201 (=DSM 112696).