A paradigm for direct stress-induced mutation in prokaryotes.
Environmental stresses may lead to selection for hypermutator bacterial cells, which have an increased chance of generating beneficial variants. With stress removal, cost of mutation exceeds the fitness advantage, selecting against hypermutators. Hypermutators arise through several mechanisms, including inactivation of mismatch repair genes (MMR) or induction of error-prone polymerases. Helicobacter pylori may provide an alternative mechanism of stress-induced mutagenesis, since it lacks the MMR genes and error-prone polymerases found in other bacterial species, and possesses an endogenously high mutation frequency. In this study, we expose H. pylori strains to reactive oxygen species and reactive nitrogen species, stressors found in their natural environment. These exposures directly resulted in elevated rates of spontaneous point mutation, deletion between direct repeats, and intergenomic recombination. We demonstrate that these effects are transient and do not involve selection for hypermutator strains. That H. pylori possesses direct repeats in regions where potential gene rearrangements can occur suggests a mechanism for targeted mutation in response to stress that avoids the deleterious fitness costs of fixed hypermutation. These studies provide a new paradigm for adaptation under increased selective pressures that may be present in other prokaryotes.
Kang
Josephine M
JM
Department of Medicine, New York University School of Medicine, 550 First Ave., New York, NY 10016, USA. kangm01@med.nyu.edu
Iovine
Nicole M
NM
Blaser
Martin J
MJ
D004249:DNA Damage / Q000187:drug effects; D004269:DNA, Bacterial / Q000737:chemistry / Q000187:drug effects / Q000235:genetics; D017353:Gene Deletion; D016480:Helicobacter pylori / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D016296:Mutagenesis / Q000187:drug effects; D009154:Mutation / Q000235:genetics*; D018384:Oxidative Stress / Q000187:drug effects / Q000235:genetics*; D026361:Reactive Nitrogen Species / Q000378:metabolism / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000378:metabolism / Q000494:pharmacology
D004269:DNA, Bacterial; D026361:Reactive Nitrogen Species; D017382:Reactive Oxygen Species