Recombination, diversity and allele sharing of infectivity proteins between Bartonella species from rodents

The alpha-Proteobacterium Bartonella is a common parasite of voles and mice, giving rise to short-lived (4 weeks to 2 months) infections. Here, we report high sequence diversity in genes of the VirB/VirD type IV secretion system (T4SS), amongst Bartonella from natural rodent populations in NE Poland. The VirB5 protein is predicted to consist of three conserved alpha helices separated by loops of variable length which include numerous indels. The C-terminal domain includes repeat stretches of KEK residues, reflecting underlying homopolymeric stretches of adenine residues. A total of 16 variants of VirB5, associated with host identity, but not bacterial taxon, were identified from 22 Bartonella isolates. One was clearly a recombinant from two others, another included an insertion of two KEK repeats. The virB5 gene appears to evolve via both mutation and recombination, as well as slippage mediated insertion/deletion events. The recombinational units are thought to be relatively short, as there was no evidence of linkage disequilibrium between virB5 and the bepA locus only 5.5 kb distant. The diversity of virB5 is assumed to be related to immunological role of this protein in Bartonella infections; diversity of virB5 may assist persistence of Bartonella in the rodent population, despite the relatively short (3-4 weeks) duration of individual infections. It is clear from the distribution of virB5 and bepA alleles that recombination within and between clades is widespread, and frequently crosses the boundaries of conventionally recognised Bartonella species.