Genetic Variability Determinants ofHelicobacter pylori:Influence of Clinical Background and Geographic Origin of Isolates

Abstract

Helicobacter pylori has an unusual pattern of genetic variation, which complicates research on this organism. To gain a better understanding of the forces behind this phenomenon, the extent to which recombination and single point mutations affect genetic variability in H. pylori was quantified and the influence of both geographical distance and clinical background were assessed. Site-directed restriction-endonuclease digestion of 2 gene fragments was performed on 168 isolates from Montreal and Berlin. Allelic diversity was found to be much higher for H. pylori than for other bacterial species. This finding is consistent with those of previous studies on H. pylori that were conducted using other techniques. However, nucleotide diversity was within the range reported for other bacterial species. Phylogenetic analysis found no grouping of strains with clinical background or geographical origin. Recombination at a rate that resulted in linkage equilibrium within genes can explain these observations.

Type V Protein Secretion Pathway: the Autotransporter Story

“…800-bp central region, termed the "mid-region," which covers a large portion of the p55 subdomain coding area, and the "signal region," which encompasses the distal region of the signal sequence and a small part of the p33 subdomain. The remainder of the p33 subdomain is relatively well conserved between alleles (14, 15), although there is evidence of recombination (170,471).…”

Crystal structure of the Helicobacter pylori vacuolating toxin p55 domain

“…Diversification in these surface-exposed regions of VacA may have been driven by immune selective pressures. Recombination occurs commonly in H. pylori (32,33), but m1/m2 chimeras are only rarely identified (35). This suggests that H. pylori strains with intact m1 or m2 VacA sequences have favorable functional properties and, thus, have a selective advantage compared with strains containing chimeric m1/m2 sequences (36)(37)(38).…”

“…Analysis of H. pylori strains isolated from unrelated humans indicates a high level of genetic diversity among vacA alleles (32)(33)(34)(35). Although frequent recombination events have eliminated phylogenetic structure from the 5Ј region of vacA alleles (32,33), phylogenetic analysis of sequences from a vacA midregion (located within p55, Fig.…”

“…Although frequent recombination events have eliminated phylogenetic structure from the 5Ј region of vacA alleles (32,33), phylogenetic analysis of sequences from a vacA midregion (located within p55, Fig. 1a) indicates the existence of two large families of sequences, termed m1 and m2 (34,35).…”

Two Different Families ofhopQAlleles inHelicobacter pylori

“…When H. pylori strains isolated from unrelated humans are compared, each isolate is genetically unique, with a level of relatedness among most orthologous sequences ranging from about 90 to 99% nucleotide identity (1,4,21,24,42,49). This diversity is the consequence of numerous point mutations, combined with a very high rate of intraspecies genetic recombination (11,24,49,55). In addition, certain genes are present in some H. pylori strains but absent from others (3,6,13,45).…”