Abstract
Helicobacter pylori
strains show both geographic and disease-associated allelic variation. We investigated the diversity present in two genes,
babA
and
babB
, which are members of a paralogous family of outer membrane proteins. Eleven family members within a single
H. pylori
strain, predicted to encode proteins with substantial N- and C-terminal similarity to each other, were classified as
babA
paralogues. In their central regions, most are less than 54% related to one another. Examining the
babA
and
babB
central regions in 42
H. pylori
strains from different geographic locales, we identified five different allele groups of
babA
(AD1 to AD5) and three different allele groups of
babB
(BD1 to BD3). Phylogenetic analysis revealed that the allelic groupings of
babA
and
babB
are independent of one another and that, for both, geographic variation is present. Analysis of synonymous and nonsynonymous substitutions in these regions showed that
babA
is more diverse, implying an earlier origin than that of the same region of
babB
, but that the
babA
diversity region may have more functional constraints. Although recombination has been central to the evolution of both genes, with
babA
and
babB
showing low mean compatibility scores and homoplasy ratios of 0.71 and 0.67, respectively, recombination is not sufficient to obscure evidence of clonal descent. Despite the involvement of
babA
in binding to the host blood group antigen Lewis B, neither the presence of different
babA
allele groups nor that of different
babB
allele groups is a determining factor in Lewis B binding of
H. pylori
strains.