Abstract: Objective: The purpose of this study was to explore the role of the global transcriptional regulator CodY in the oxidative stress response in Listeria monocytogenes. Methods: Oxidative stress tolerance and antioxidant parameters (CAT, SOD and GSH) were compared between the wild-type strain EGDe and the isogenic CodY deletion strain EGDeDcodY at the mid-logarithmic growth stage (OD600 nm= 0.65) under H2O2 stress. Genomic template stability (GTS) of the two strains was compared by random amplified polymorphic DNA (RAPD) method and the transcriptional expression of the genes encoding antioxidants and those involved in SOS response were assessed by real-time PCR. Results: 1) The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of H2O2 against EGDeDcodY were about twice higher than against EGDe, and the diameter of inhibition zone of EGDeDcodY was significantly greater than that of EGDe when the concentration of H2O2 was over 20 mmol/L (P ≤ 0.01); 2) The growth of EGDeDcodY was completely inhibited by 200 mmol/L H2O2, while it just slightly slowed down the growth of EGDe; 3) H2O2-induced oxidative stress decreased CAT activity in both EGDe and EGDeDcodY, but did not significantly alter the transcription level of this enzyme. SOD activity was not changed significantly, but its mRNA expression presented significant differences between the two strains (P ≤ 0.001). Notably, the general trend of transcription and concentration level of GSH in the two strains was almost same, which decreased markedly and then increased slightly with increasing H2O2 exposure time. Moreover, the transcription level of GSH in EGDeDcodY was always lower than that in EGDe (P ≤ 0.01); 4) GTS of EGDe and EGDeDcodY were 93.1% and 80.0%, respectively. In addition, the expressions of recA, lexA, recR, lmo1302, and lmo1975, which are important for SOS response, were significantly inhibited in EGDeDcodY (P ≤ 0.001), while the expressions of recA, lmo1302 and lmo1975 in EGDe were activated. Conclusion: The deletion of CodY can reduce bacterial oxidative stress tolerance, growth rate and GSH content as well as GTS and inhibit SOS response-related gene expressions, corroborating that CodY plays an important role in the oxidative stress response in Listeria monocytogenes.

Key words: Listeria monocytogenes; CodY; oxidative stress; SOS response