Genetic dissection of Helicobacter pylori AddAB role in homologous recombination

Abstract

Helicobacter pylori infects the stomach of about half of the world's human population, frequently causing chronic inflammation at the origin of several gastric pathologies. One of the most remarkable characteristics of the species is its remarkable genomic plasticity in which homologous recombination (HR) plays a critical role. Here, we analyzed the role of the H. pylori homologue of the AddAB recombination protein. Bioinformatics analysis of the proteins unveils the similarities and differences of the H. pylori AddAB complex with respect to the RecBCD and AddAB complexes from Escherichia coli and Bacillus subtilis, respectively. Helicobacter pylori mutants lacking functional addB or/and addA show the same level of sensitivity to DNA-damaging agents such as UV or irradiation and of deficiency in intrachromosomal RecA-dependent HR. Epistasis analyses of both DNA repair and HR phenotypes, using double and triple recombination mutants, demonstrate that, in H. pylori, AddAB and RecOR complexes define two separate presynaptic pathways with little functional overlap. However, neither of these complexes participates in the RecA-dependent process of transformation of these naturally competent bacteria.

Change Is Good: Variations in Common Biological Mechanisms in the Epsilonproteobacterial GeneraCampylobacterandHelicobacter

“…Interestingly, disruption of the RecOR pathway does not appear to impair recombination after natural transformation, which suggests that RecOR-mediated recombination initiation may be subject to substrate specificity and may function primarily in types of DNA repair other than that of non-dsDNA breaks (399). This hypothesis is supported by subsequent findings indicating that the RecOR and AddAB recombination initiation pathways have little overlap in function and that disruption of the RecOR pathway has a greater impact than inactivation of AddAB on survival after UV irradiation (398). At this time, it is not clear whether C. jejuni also employs the RecOR pathway in a similar manner; however, a putative recO gene has been annotated in at least one C. jejuni genome (J. J. Gilbreath and D. S. Merrell, unpublished observation).…”

A Recombination Puzzle Solved: Role for New DNA Repair Systems in Helicobacter pylori Diversity/Persistence

“…For example, recA mutants were much more sensitive to UV or Gamma radiation than the recB or recO single mutants, and were similar to the recBO double mutant [68][69][70]. The recA mutants completely lost the ability to undergo natural transformation [68][69][70]. The intra-genomic recombination frequency of the recA mutant was also much lower than that of the recR or recB single mutants [68,71].…”

“…Among the mutants of DNA recombination and repair genes, recA mutants displayed the most severe phenotypes. For example, recA mutants were much more sensitive to UV or Gamma radiation than the recB or recO single mutants, and were similar to the recBO double mutant [68][69][70]. The recA mutants completely lost the ability to undergo natural transformation [68][69][70].…”

“…Furthermore, by using the highly conserved AddB nuclease motif "GRIDRID" in BLAST search, HP1089 was identified as the putative AddB homolog [69]. Now it is accepted that HP1553 and HP1089 are termed addA and addB respectively in H. pylori with a reminder that previous recB [20,68,70,92] was the equivalent of addA [69,71,93]. Both genes addA and addB are present in 56 H. pylori clinical isolates from around the world [94]; thus they are considered core genes that are not strain variable.…”

“…Regarding the role of H. pylori AddA in DNA recombination during natural transformation, conflicting results were reported from different studies. The addA (note: it was named recB in certain references) mutant showed enhanced [68,70], decreased [20,71,92], or no change [27,69] in transformation frequency. Indeed, a high degree of variability (>100-fold) in transformation frequency in H. pylori was observed between different strains and different experiments.…”