REGULATION OF THE SHIGA-LIKE TOXIN-II OPERON IN ESCHERICHIA-COLI

Investigations of the regulation of the bacteriophage encoded Shiga-li ke toxin II (SLT-II) in Escherichia coli demonstrated that bacteriopha ges exhibit a regulatory impact on toxin production by two mechanisms. Firstly, replication of the toxin-converting bacteriophages brings ab out an increase in toxin production due to concomitant multiplication of toxin gene copies. Secondly, an influence of a phage-encoded regula tory molecule was demonstrated by using low-copy-number plasmid pADR-2 8, carrying a translational gene fusion between the promoter and proxi mal portion of slt-IIA and the structural gene for bacterial alkaline phosphatase (phoA). PhoA activity, reflecting the slt-II promoter acti vity, was significantly enhanced in E. coli strains which had been lys ogenized with an SLT-I- or SLT-II-converting bacteriophage (H-19B or 9 33W, respectively) or bacteriophage lambda. Both mechanisms are depend ent 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 activi ty 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 ei ther osmolarity, pH, oxygen tension, acetates, iron level, or utilized carbon source could be demonstrated.