Abstract
The Pasteurellaceae 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 Pasteurellaceae family, aiming at determining its phylogenetic position, antimicrobial susceptibility profile, and identifying putative virulence factors. In silico 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 Pasteurellaceae 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, ompA, ompH) and colonization (exbD, fur, galU, galE, lpxA, lpxC, and kdsA) of the host and a cytolethal distending toxin (cdt), 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 Pasteurellaceae family, designated as Mergibacter gen. nov., with Mergibacter septicus sp. nov. as the type species. The type strain is Mergibacter septicus A25201T (=DSM 112696).
Highlights
The family Pasteurellaceae is the only member of the order Pasteurellales in the class Gammaproteobacteria (Christensen et al, 2014)
A preliminary taxonomic identification of the isolates was performed by amplification and sequencing of a portion of bacterial housekeeping gene the 16S rRNA, indicating an exact match of these five isolates with sequences of the Bisgaard taxon 40 from the Pasteurellaceae family [i.e., AY172732.1 (Christensen et al, 2003b); MG735704.1 (Knowles et al, 2019)]
They indicate that Bisgaard taxon 40, closely related to the Gallibacterium genus, warrants classification as a new genus within the Pasteurellaceae family, and it was renamed as Mergibacter with the type species M. septicus A25201 (DSM 112696; CP054053)
Summary
The family Pasteurellaceae is the only member of the order Pasteurellales in the class Gammaproteobacteria (Christensen et al, 2014). Members of the family Pasteurellaceae have been isolated from mucosal membranes of the alimentary, respiratory, and reproductive tracts of healthy and diseased vertebrates (Christensen et al, 2003b). Important avian pathogens are included in the Pasteurellaceae family with a broad clinical presentation that ranges from acute septicemia to chronic and localized infections, leading to significant morbidity and mortality in domestic and wild birds (Christensen et al, 2014). The Bisgaard taxa represent a group of unclassified members of the Pasteurellaceae family isolated from several orders of birds and rodents with and without the disease (Christensen et al, 2003b, 2014). With the advent of following nextgeneration sequencing (NGS) technologies, further taxonomic efforts established more definite classification for numerous
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