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

Escherichia coli hemolysin, also termed alpha-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 sigma factor RpoS, and the small RNA DsrA, which is known to inhibit H-NS function and to stimulate RpoS synthesis. During growth at 30 degrees C, DsrA overexpression increased ehxA transcription in the wild type but not in an hns deletion mutant. During growth at 37 degrees 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 sigma factor is essential for ehxCABD operon expression.