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Title: ALLELIC VARIATION WITHIN HELICOBACTER PYLORI BABA AND BABB

Author
item PRIDE, DAVID - VANDERBILT UNIVERSITY
item Meinersmann, Richard - Rick
item BLASER, MARTIN - VANDERBILT UNIVERSITY

Submitted to: Infection and Immunity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2000
Publication Date: 2/1/2001
Citation: PRIDE, D.T., MEINERSMANN, R.J., BLASER, M.J. ALLELIC VARIATION WITHIN HELICOBACTER PYLORI BABA AND BABB. INFECTION AND IMMUNITY. 2001.

Interpretive Summary: Helicobacter pylori is the species of bacteria that causes stomach ulcers in people. It is closely related to Campylobacter, a group of bacteria of agricultural concern because of food-borne illnesses. H. pylori is a very diverse species, as are the Campylobacters. H. pylori is a good model for studying the generation of diversity because it apparently uses a mechanism common with Campylobacter but to a much more exaggerated extent. Generation of diversity can best be understood in terms of evolutionary analysis. In this investigation, a family of genes that probably have a single origin, was studied using methods designed to deduce the ancestry of a group of genes based on how the sequences most likely changed over the generations. It was found that H. pylori may promote the formation of diversity not only by exchange of fragments of DNA between different lineages, but also between variants of the gene that exist within a single organism. Despite the tremendous variability, lines of descent of the organism could be determined that correlated with the geographic location the organism was obtained from. This study will help to improve our models for studying the evolution of bacteria so that we can make better predictions of the source of organisms with such apparent large amount of DNA sharing and better predict how new variants of the organism may develop.

Technical Abstract: Helicobacter pylori strains show both geographic and disease-associated allelic variation. We investigated the diversity present in 2 genes, babA and babB, which are members of a paralogous family of outer membrane proteins. Eleven family members, predicted to encode proteins with substantial N and C-terminal similarity to each other, were classified as babA paralogues. In their central regions, none are more 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 (AD1-AD5) of babA, and three different allele groups (BD1-BD3) of babB. 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 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 scoresm and homoplasy ratios of 0.71 and 0.67, respectively, recombination is not sufficient to obscure evidence of clonal descent.