Arcobacteraceae: genome adaptation and genome size reduction in species isolated from animals and human demonstrated by comparative genome analysis

The Arcobacteraceae bacterial family includes Gram-negative species previously belonging to Campylobacteraceae. Part of these species are considered foodborne pathogens, and are present on different foods and animals. Arcobacter butzleri and Arcobacter cryaerophilus are the two most isolated species form human clinical samples, and have been isolated from food of animal origin, including chicken and pork. The different abilities of the Arcobacteraceae to survive in various hosts and environmental conditions suggest an evolutionary pressure linked to genome adaptation. The different physiological and genomic characteristics of Arcobacteraceae species led to the proposal to create new genera, which is however criticized for the lack of discriminatory features and biological/clinical relevance. The aim of this study was Arcobacteraceae pangenome evaluation in order to characterize possible relationships between 20 validly described species. The analyses have been conducted on type strains genomes obtained by Illumina sequencing. These species were included in different groups considering the isolation sources and information present in literature. The use of different bioinformatics tools enabled the obtainment of information about pangenome partitions (Roary, Panaroo, PPanGGOLiN) and gene classes (EggNOG). The results do not support the proposed division into different genera of the Arcobacteraceae family showing pangenome partitions (core genes) like Campylobacter genus. A smaller genome size of the animal related species was observed suggesting an evolutionary adaptation of these species to hosts. Moreover, the gene class compositions in animal and human-associated species showed a higher percentage of virulence-related gene classes such as cell motility genes. Some orthologues like MotA/TolQ/ExbB proton channel family (TonB-related; virulence functions), were positively correlated to the animals related species suggesting a specific function of different orthologues. The genome analysis identified the presence of specific genes linked to different species groups. A division into pathogenic and non-pathogenic species is suggested, supporting future research on food safety and public health.