Regulation of the Shiga-like toxin II operon in Escherichia coli

Abstract

Investigations of the regulation of the bacteriophage-encoded Shiga-like toxin II (SLT-II) in Escherichia coli demonstrated that bacteriophages exhibit a regulatory impact on toxin production by two mechanisms. Firstly, replication of the toxin-converting bacteriophages brings about an increase in toxin production due to concomitant multiplication of toxin gene copies. Secondly, an influence of a phage-encoded regulatory molecule was demonstrated by using low-copy-number plasmid pADR-28, carrying a translational gene fusion between the promoter and proximal portion of slt-IIA and the structural gene for bacterial alkaline phosphatase (phoA). PhoA activity, reflecting the slt-II promoter activity, was significantly enhanced in E. coli strains which had been lysogenized with an SLT-I-or SLT-II-converting bacteriophage (H-19B or 933W, respectively) or bacteriophage. Both mechanisms are dependent on bacteriophage induction and hence are recA dependent. Moreover, the study revealed that the DNA-binding protein H-NS has a regulatory impact on both bacteriophage-mediated SLT-II synthesis and the activity of the slt-II promoter of plasmid pADR-28. While a slight impact of growth temperature on SLT-II expression was observed, no impact of either osmolarity, pH, oxygen tension, acetates, iron level, or utilized carbon source could be demonstrated.

Aeromonas hydrophilafrom marketed mullet (Mugil cephalus) in Egypt: PCR characterization ofβ-lactam resistance and virulence genes

“…The observation that none of the studied A. hydrophila isolates contain stx2 gene warrants further investigations. However, this might be linked to the fact that stx2 gene is carried on bacteriophages, which itself exhibits a regulatory impact on stx2 production (Muhldorfer et al 1996). It is also plausible to assume that the stx2 gene locus might be disrupted due to the acquisition of other colocalized genes.…”

“…The inability of A. hydrophila to encode both stx2 and bla SHV remains puzzling, and definitely generalizing this observation requires investigating more bacterial isolates. While stx2 is carried on a bacteriophage (Muhldorfer et al 1996), bla SHV is plasmid mediated (Tzouvelekis and Bonomo 1999). Therefore, we assume that this 'coabsence' association is not due to lack of acquisition of a single plasmid or phage.…”

Genotypic characterization to identify markers associated with putative hypervirulence in Swedish Escherichia coli O157:H7 cattle strains

“…The authors also determined that this was because of genetic differences in the prophages carrying the VT2 genes from the different lineages. The transcriptional activating factor Q is known to act as regulator in the induced prophage and has a positive regulatory impact on the vtx 2 operon (Muhldorfer et al 1996). Zhang et al (2010) were able to demonstrate that lineage II strains carry VT2 prophages where the transcriptional activator Q (upstream of vtx 2 ) is replaced by a pphA (serine ⁄ threonine phosphatase) homologue, whereas lineage I and linage I ⁄ II (clade 8) have intact Q genes.…”

The Pasteurella multocida toxin is encoded within a lysogenic bacteriophage

“…Toxin production is induced during the lytic cycle as a result of increased toxin gene copy number and/or increasing toxin transcription from phage promoters that are repressed during lysogeny. In particular, the phage-mediated regulation of Stx1 expression is well established (Muhldorfer et al, 1996;Wagner et al, 2002). The possibility that PMT expression is regulated by the phage life cycle has not been investigated, although the toxin is known to be expressed in vitro in the absence of phage induction by DNA-damaging agents.…”