Engineering Synthetic Multistress Tolerance in Escherichia coli by Using a Deinococcal Response Regulator, DR1558

Cellular robustness is an important trait for industrial microbes, because the microbial strains are exposed to a multitude of different stresses during industrial processes, such as fermentation. Thus, engineering robustness in an organism in order to push the strains toward maximizing yield has become a significant topic of research. We introduced the deinococcal response regulator DR1558 intoEscherichia coli (strainEc -1558), thereby conferring tolerance to hydrogen peroxide (H2 O2 ). The reactive oxygen species (ROS) level in strainEc -1558 was reduced due to the increased KatE catalase activity. Among four regulators of the oxidative-stress response, OxyR, RpoS, SoxS, and Fur, we found that the expression ofrpoS increased inEc -1558, and we confirmed this increase by Western blot analysis. Electrophoretic mobility shift assays showed that DR1558 bound to therpoS promoter. Because the alternative sigma factor RpoS regulates various stress resistance-related genes, we performed stress survival analysis using anrpoS mutant strain.Ec -1558 was able to tolerate a low pH, a high temperature, and high NaCl concentrations in addition to H2 O2 , and the multistress tolerance phenotype disappeared in the absence ofrpoS . Microarray analysis clearly showed that a variety of stress-responsive genes that are directly or indirectly controlled by RpoS were upregulated in strainEc -1558. These findings, taken together, indicate that the multistress tolerance conferred by DR1558 is likely routed through RpoS. In the present study, we propose a novel strategy of employing an exogenous response regulator from polyextremophiles for strain improvement.