Allelic diversity among Helicobacter pylori outer membrane protein genes homB and homA generated by recombination

Recombination is one of the main mechanisms contributing to Helicobacter pylori genomic variability. homB and homA are paralogous genes coding for H. pylori outer membrane proteins (OMPs). Both genes display allelic variation yielded by polymorphisms of the genes' middle regions, with six different alleles. This study used bioinformatic and statistical analyses to evaluate whether the allelic diversity of homB and homA is generated by recombination. A detailed molecular analysis of the most prevalent homB allelic variant was also performed to establish its molecular profile. The two most prevalent homB and homA allelic variants resulted from interallelic homologous recombination between the rarest allelic variants of each gene, with a crossover point localized in the middle of the genes, containing the allelic region. Molecular analysis of the most prevalent homB allele revealed a geographic partition among Western and East Asian strains, more noticeable for the 5' and 3' homB regions than for the middle allelic regions. In conclusion, the diversity of the 5' and 3' homB regions reflect the strains' geographical origin, and variants likely occur via the accumulation of single nucleotide polymorphisms. On the other hand, homologous recombination seems to play an important role in the diversification of the highly polymorphic homB and homA allele-defining regions, where the most prevalent alleles worldwide result from genomic exchange between the rarest variants of each gene, suggesting that the resulting combinations confer biological advantages to H. pylori. This phenomenon illustrates an evolutionary scenario in which recombination appears to be associated with ecological success.