Polyphosphate kinase 1-coding gene (ppk1) is involved in the oxidative stress resistance in uropathogenic Escherichia coli by modulating the expression of katG and katE genes
Objective 
To investigate the role and the mechanism of ppk1 gene (coding for polyphosphate kinase 1) in oxidative stress resistance in uropathogenic Escherichia coli (UPEC). 
 
 
Methods 
Mutant strains with ppk1-deletion (△pk1) and complemented strains (△pk1-C) were constructed based on the UPEC strain CFT073. A comparative analysis was conducted to analyze survival rates of CFT073, △pk1 and △pk1-C strains at different time points while they were under oxidative stress. Differences in protein expression between CFT073 and △pk1 strains were analyzed using mass spectrometric analysis. Differences between CFT073 and △pk1 strains in expression of katG and katE genes were analyzed using real-time quantitative RT-PCR. 
 
 
Results 
The survival rate of △pk1 strains was lower than that of CFT073 strains at every time point, while the survival rate of △pk1-C strains was basically the same as that of CFT073 strains. Gel image analysis and mass spectrometric analysis revealed that six proteins were down-regulated and one was up-regulated in △pk1 strains as compared with those in CFT073 strains. Expression of the catalase-coding genes katG and katE in △pk1 strains were respectively (20.5±8.2)% and (20.9±6.9)% of those in CFT073 strains (P<0.05). 
 
 
Conclusion 
The ppk1 gene plays an important role in oxidative stress resistance in UPEC by modulating the expression of catalase-coding genes katG and katE. 
 
 
Key words: 
Urinary tract infection; Escherichia coli; Polyphosphate kinase 1; Oxidative stress