The road not taken: Could stress-specific mutations lead to different evolutionary paths?

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.