Background: Microbial tolerance to different environmental stresses is of importance for efficient production ofbiofuels and biochemical.Such traits are often improved by evolutionary engineering approaches including mutagen-induced mutagenesis and successive passage.In contrast to these approaches which generate mutations in rapidly growing cells, recent research showed that mutations could be generated in non-dividing cells under stressful but non-lethal conditions, leading to the birth of the theory of stress-induced mutagenesis (SIM).A molecular mechanism of SIM has been elucidated to be mutagenic repair of DNA breaks.This inspired us to develop a synthetic SIM module to simulate the mutagenic cellular response so as to accelerate microbial adaptive evolution for an improved stress tolerance.