Transcription of the Subtilase Cytotoxin Gene in Shiga Toxin-Producing Escherichia coli Is Dependent on and .

Certain foodborne Shiga toxin-producing (STEC) strains carry genes encoding the subtilase cytotoxin (SubAB). Although the mode of action of SubAB is under intensive investigation, information about the regulation of gene expression is currently not available. In this study, we investigated the regulation of the chromosomal gene in laboratory strain DH5α and STEC O113:H21 strain TS18/08 using a luciferase reporter gene assay. Special emphasis was given to the role of the global regulatory protein genes and in promoter activity. Subsequently, quantitative real-time PCR was performed to analyze the expression of Shiga toxin 2a (Stx2a), SubAB1, and cytolethal distending toxin V (Cdt-V) genes in STEC strain TS18/08 and its isogenic and deletion mutants. The deletion of led to a significant increase of up to 2-fold in expression, especially in the late growth phase, in both strains. However, deletion of showed different effects on the promoter activity during the early and late exponential growth phases in both strains. Furthermore, upregulation of and was demonstrated in and deletion mutants in TS18/08. These data showed that the expression of , , and is integrated in the regulatory network of global regulators Hfq and H-NS in Shiga toxin-producing (STEC) strains are responsible for outbreaks of foodborne diseases, such as hemorrhagic colitis and the hemolytic uremic syndrome. The pathogenicity of those strains can be attributed to, among other factors, the production of toxins. Recently, the subtilase cytotoxin was detected in locus of enterocyte effacement (LEE)-negative STEC, and it was confirmed that it contributes to the cytotoxicity of those STEC strains. Although the mode of action of SubAB1 is under intensive investigation, the regulation of gene expression is currently not known. The global regulatory proteins H-NS and Hfq have impact on many cellular processes and have been described to regulate virulence factors as well. Here, we investigate the role of and in expression of as well as and in an laboratory strain as well as in wild-type STEC strain TS18/08.