RpoS acts as a global repressor of virulence gene expression in Escherichia coli O104:H4 and enteroaggregative E. coli
In 2011, in Germany, Escherichia coli O104:H4 caused the enterohemorrhagic E. coli (EHEC) outbreak with the highest incidence rate of hemolytic uremic syndrome. This pathogen carries an exceptionally potent combination of EHEC- and enteroaggregative E. coli (EAEC)-specific virulence factors. Here, we identified an E. coli O104:H4 isolate that carried a single nucleotide polymorphism (SNP) in the start codon (ATG>ATA) of rpoS, encoding the alternative sigma factor S. The rpoS ATG>ATA SNP was associated with enhanced EAEC-specific virulence gene expression. Deletion of rpoS in E. coli O104:H4 Dstx2 and typical EAEC resulted in a similar effect. Both rpoS ATG>ATA and DrpoS strains exhibited stronger virulence-related phenotypes in comparison to wild type. Using promoter-reporter gene fusions, we demonstrated that wild-type RpoS repressed aggR, encoding the main regulator of EAEC virulence. In summary, our work demonstrates that RpoS acts as a global repressor of E. coli O104:H4 virulence, primarily through an AggR-dependent mechanism. Overall design: We performed strand specific RNA-seq with total RNA isolated from E. coli O104:H4 wild type and rpoS ATG>ATA grown under standard laboratory conditions (LB medium; 37oC; 180 rpm) to logarithmic growth phase (log; OD600 = 0.4- 0.5) and to transition to stationary phase (transition; OD600 = 3.0-3.4). Three biological replicates per strain were included. DESeq2 analysis based on the reads mapped to the E. coli O104:H4 genome was performed to identify examples of differential gene expression.