A paradigm for direct stress-induced mutation in prokaryotes

Area of Science:

• Microbiology
• Genetics
• Evolutionary Biology

Background:

• Environmental stresses can induce bacterial hypermutation, increasing beneficial variant generation.
• Hypermutators typically arise from mismatch repair gene (MMR) inactivation or error-prone polymerases.
• Helicobacter pylori lacks canonical hypermutation mechanisms but has high intrinsic mutation rates.

Purpose of the Study:

• To investigate stress-induced mutagenesis in Helicobacter pylori.
• To determine if reactive oxygen and nitrogen species trigger transient mutagenesis.
• To explore alternative mechanisms of stress adaptation in H. pylori.

Main Methods:

• Exposure of H. pylori strains to reactive oxygen species (ROS) and reactive nitrogen species (RNS).
• Quantification of spontaneous point mutations, deletions between direct repeats, and intergenomic recombination rates.
• Analysis to determine if observed mutations involve selection for hypermutator phenotypes.

Main Results:

• Exposure to ROS and RNS directly elevated mutation rates, including deletions and recombination.
• These mutagenic effects were transient and did not result in the selection of hypermutator strains.
• H. pylori contains direct repeats in gene rearrangement-prone regions, suggesting targeted mutation pathways.

Conclusions:

• Helicobacter pylori employs a transient, targeted mutagenesis mechanism in response to environmental stress.
• This stress-induced mutagenesis avoids the fitness costs associated with fixed hypermutation.
• This represents a novel paradigm for bacterial adaptation under selective pressures.