Abstract
BackgroundExtensive genetic diversity and rapid allelic diversification are characteristics of the human gastric pathogen Helicobacter pylori, and are believed to contribute to its ability to cause chronic infections. Both a high mutation rate and frequent imports of short fragments of exogenous DNA during mixed infections play important roles in generating this allelic diversity. In this study, we used a genetic approach to investigate the roles of nucleotide excision repair (NER) pathway components in H. pylori mutation and recombination.ResultsInactivation of any of the four uvr genes strongly increased the susceptibility of H. pylori to DNA damage by ultraviolet light. Inactivation of uvrA and uvrB significantly decreased mutation frequencies whereas only the uvrA deficient mutant exhibited a significant decrease of the recombination frequency after natural transformation. A uvrC mutant did not show significant changes in mutation or recombination rates; however, inactivation of uvrC promoted the incorporation of significantly longer fragments of donor DNA (2.2-fold increase) into the recipient chromosome. A deletion of uvrD induced a hyper-recombinational phenotype.ConclusionsOur data suggest that the NER system has multiple functions in the genetic diversification of H. pylori, by contributing to its high mutation rate, and by controlling the incorporation of imported DNA fragments after natural transformation.
Highlights
Extensive genetic diversity and rapid allelic diversification are characteristics of the human gastric pathogen Helicobacter pylori, and are believed to contribute to its ability to cause chronic infections
Characterization of H. pylori nucleotide excision repair (NER) mutants and their susceptibility to UV light-induced cell damage To investigate how the NER system contributes to genetic diversification in H. pylori, we individually inactivated the NER genes in H. pylori strain 26695 by either allelic disruption with a kanamycin resistance cassette, a chloramphenicol resistance conferring cassette, or by quasi-complete replacement with a kanamycin resistance
Since the components of the NER system participate in repairing damage caused by UV radiation in many different organisms [15], we first investigated the sensitivity of the diverse NER mutant strains against UV light
Summary
Extensive genetic diversity and rapid allelic diversification are characteristics of the human gastric pathogen Helicobacter pylori, and are believed to contribute to its ability to cause chronic infections. Both a high mutation rate and frequent imports of short fragments of exogenous DNA during mixed infections play important roles in generating this allelic diversity. We have previously described an in vitro system that allows us to measure mutation and transformation frequencies in H. pylori wild type strains and isogenic gene knock-out mutants, as well as the length of the donor DNA fragments imported into the recipient chromosome after transformation [12]. The inactivation of mutY in H. pylori did not completely abrogate the formation of ISR, suggesting that additional mechanisms might contribute to ISR generation
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