Differential expression of catalases in Vibrio parahaemolyticus under various stress conditions.

Among antioxidant enzymes, catalases protect microorganisms by degrading hydrogen peroxide under oxidative stress. In this study, the activities of at least four Vibrio parahaemolyticus catalases (Kat1 to Kat4) were differentially detected during different growth stages and under various stress conditions using zymographic analysis. Our results showed that only Kat2 is stable at 55 °C. Kat1 and Kat2 respond to hydrogen peroxide during the early stationary and exponential growth phases, respectively and the response decreases upon entering the stationary phase. Kat3 and Kat4 are bifunctional, exhibiting both catalase and peroxidase activities and are only expressed during the stationary phase, under starvation or under stress at pH 5.5. Our study also shows that expression of Kat3 and Kat4 depends on RpoS. We confirm that both monofunctional and bifunctional catalases are expressed and function differentially under various stresses to contribute total catalase activities for the survival of V. parahaemolyticus. A comparative genomic study among Vibrio species revealed that only V. parahaemolyticus contains two copies of genes that encode monofunctional and bifunctional catalases. We propose that both types of catalases, whether evolved or acquired horizontally through long-term evolution, may play crucial protective roles in V. parahaemolyticus in response to environmental fluctuations.
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