RpoS, H-NS, and DsrA influence EHEC hemolysin operon (ehxCABD) transcription in Escherichia coli O157:H7 strain EDL933

Abstract

Escherichia coli hemolysin, also termed α-hemolysin, is a virulence factor for extraintestinal E. coli. Hemolysin operon (hlyCABD) transcription is inhibited by the nucleoid-associated protein, H-NS. This inhibition is stronger at lower growth temperature. This study investigated transcription of the homologous EHEC hemolysin (enterohemolysin) operon (ehxCABD) in EHEC O157:H7 strain EDL933. We examined the influence of H-NS, the σ factor RpoS, and the small RNA DsrA, which is known to inhibit H-NS function and to stimulate RpoS synthesis. During growth at 30 °C, DsrA overexpression increased ehxA transcription in the wild type but not in an hns deletion mutant. During growth at 37 °C, DsrA overexpression increased ehxA transcription independent of hns genotype. This indicates that DsrA influences ehxCABD operon transcription by two different routes, one (at lower temperature) at least partially dependent on H-NS, and one (at higher temperature) independent of H-NS. An rpoS deletion mutant expressed nondetectable levels of ehxA mRNA regardless of growth temperature or DsrA overexpression, indicating that the RpoS σ factor is essential for ehxCABD operon expression. © 2008 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.