Abstract
Organisms often encounter stressful conditions, some of which damage their DNA. In response, some organisms show a high expression of error-prone DNA repair machinery, causing a temporary increase in the genome-wide mutation rate. Although we now have a detailed map of the molecular mechanisms underlying such stress-induced mutagenesis (SIM), it has been hotly debated whether SIM alters evolutionary dynamics. Key to this controversy is our poor understanding about which stresses increase mutagenesis and their long-term consequences for adaptation. In a new study with Escherichia coli, Maharjan and Ferenci show that while only some nutritional stresses (phosphorous and carbon limitation) increase total mutation rates, each stress generates a unique spectrum of mutations. Their results suggest the potential for specific stresses to shape evolutionary dynamics and highlight the necessity for explicit tests of the long-term evolutionary impacts of SIM.
Highlights
A large body of work demonstrates stress-induced mutagenesis (SIM)—a transient increase in mutation rates under stresses such as antibiotic exposure or starvation—via specific pathways that are typically suppressed under rapid growth [5,6]
E. coli strains lacking mismatch repair pathway (MMR) genes show distinct mutation spectra [9,10], indicating that the suppression of MMR induced by stress may have a similar effect
Maharjan and Ferenci found that stress-induced mutation spectra were stress-specific, and that only some stresses were associated with increased mutation rates
Summary
A large body of work demonstrates stress-induced mutagenesis (SIM)—a transient increase in mutation rates under stresses such as antibiotic exposure or starvation—via specific pathways that are typically suppressed under rapid growth [5,6]. Analysis of single genes suggest that SIM can alter the mutation spectrum [8]—the relative frequency of different types of mutations (e.g., base pair substitutions or large insertion sequences)—determining the available set of mutations upon which natural selection can act. E. coli strains lacking MMR genes show distinct mutation spectra [9,10], indicating that the suppression of MMR induced by stress may have a similar effect.
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