Role for a Phage Promoter in Shiga Toxin 2 Expression from a Pathogenic Escherichia coli Strain

Open Access
Publisher Website
Google Scholar
Abstract
Shiga toxins (Stxs), encoded by the stxA andstxB genes, are important contributors to the virulence ofEscherichia coli O157:H7 and other Stx-producing E. coli (STEC) strains. The stxA and stxBgenes in STEC strains are located on the genomes of resident prophages of the λ family immediately downstream of the phage late promoters (p R′). The phage-encoded Q proteins modify RNA polymerase initiating transcription at the cognatep R′ promoter which creates transcription complexes that transcend a transcription terminator immediately downstream of p R′ as well as terminator kilobases distal to p R′. To test if this Q-directed processive transcription plays a role instx 2 AB expression, we constructed a mutant prophage in an O157:H7 clinical isolate from whichp R′ and part of Q were deleted but which has an intact pStx, the previously describedstx 2 AB-associated promoter. We report that production of significant levels of Stx2 in this O157:H7 isolate depends on the p R′ promoter. Since transcription initiating at p R′ ultimately requires activation of the phage lytic cascade, expression ofstx 2 AB in STEC depends primarily on prophage induction. By showing this central role for the prophage instx 2 AB expression, our findings contradict the prevailing assumption that phages serve merely as agents for virulence gene transfer.