Hsp33 confers bleach resistance by protecting elongation factor Tu against oxidative degradation in Vibrio cholerae

The redox-regulated chaperone Hsp33 protects bacteria specifically against stress conditions that cause oxidative protein unfolding, such as treatment with bleach or exposure to peroxide at elevated temperatures. To gain insight into the mechanism by which expression of Hsp33 confers resistance to oxidative protein unfolding conditions, we made use of Vibrio cholerae strain O395 lacking the Hsp33 gene hslO. We found that this strain, which is exquisitely bleach-sensitive, displays a temperature-sensitive (ts) phenotype during aerobic growth, implying that V. cholerae suffers from oxidative heat stress when cultivated at 43 degrees C. We utilized this phenotype to select for Escherichia coli genes that rescue the ts phenotype of V. cholerae hslO when overexpressed. We discovered that expression of a single protein, the elongation factor EF-Tu, was sufficient to rescue both the ts and bleach-sensitive phenotypes of V. cholerae ?hslO. In vivo studies revealed that V. cholerae EF-Tu is highly sensitive to oxidative protein degradation in the absence of Hsp33, indicating that EF-Tu is a vital chaperone substrate of Hsp33 in V. cholerae. These results suggest an essential client protein model for Hsp33's chaperone action in Vibrio in which stabilization of a single oxidative stress-sensitive protein is sufficient to enhance the oxidative stress resistance of the whole organism.