The rise and fall of mutator bacteria

Bacteria with elevated mutation rates are frequently found among natural is olates. This is probably because of their ability to generate genetic varia bility, the substrate for natural selection. However, such high mutation ra tes can lead to the loss of vital functions. The evolution of bacterial pop ulations may happen through alternating periods of high and low mutation ra tes. The cost and benefits of high mutation rates in the course of bacteria l adaptive evolution are reviewed.