Escherichia coli Gene Expression Responsive to Levels of the Response Regulator EvgA

Abstract

ABSTRACT To investigate the function of the EvgA response regulator, we compared the genome-wide transcription profile of EvgA-overexpressing and EvgA-lacking Escherichia coli strains by oligonucleotide microarrays. The microarray measurements allowed the identification of at least 37 EvgA-activated genes, including acid resistance-related genes gadABC and hdeAB , efflux pump genes yhiUV and emrK , and 21 genes with unknown function. EvgA overexpression conferred acid resistance to exponentially growing cells. This acid resistance was abolished by deletion of ydeP , ydeO , or yhiE , which was induced by EvgA overexpression. These results suggest that ydeP , ydeO , and yhiE are novel genes related to acid resistance and that EvgA regulates several acid resistance genes. Furthermore, the deletion of yhiE completely abolished acid resistance in stationary-phase cells, suggesting that YhiE plays a critical role in stationary-phase acid resistance. The multidrug resistance in an acrB deletion mutant caused by EvgA overexpression was completely abolished by deletion of yhiUV , while the emrKY deletion had no effect on the increase in resistance by EvgA overexpression. In addition, EvgA overexpression did not confer resistance in a tolC -deficient strain. These results suggest that YhiUV induced by EvgA overexpression is functionally associated with TolC and contributes to multidrug resistance.