Plasmids Derived from Lambdoid Bacteriophages as Models for Studying Replication of Mobile Genetic Elements Responsible for the Production of Shiga Toxins by Pathogenic Escherichia coli Strains

Abstract

Background: Genes encoding Shiga toxins in pathogenic Escherichia coli strains (Shiga toxin-producing E. coli, STEC) are located on lambdoid prophages. However, studies on the replication of these phages were not reported to date. Methods: Plasmids derived from Shiga toxin-converting phages were constructed, introduced into wild-type E. coli strain and studied using methods of molecular genetics. Results: The studied replicons behaved similarly to plasmids derived from bacteriophage lambda, and DNA sequence analysis revealed their high level of homology to the lambda replication region. Nevertheless, contrary to lambda and two of six tested plasmids, four tested replicons were able to replicate in the E. coli dnaA46 mutant. Specific nucleotide differences, causing amino acid substitutions relative to wild-type lambda O and P proteins, appeared to be responsible for this phenotype. Conclusions: We conclude that replicons of phages bearing Shiga toxin genes are functionally similar to that of bacteriophage lambda, however, some of them have important differences which influence replication regulation. Furthermore, our results may suggest that there are newly discovered molecular interactions in the DNA replication regulation of lambda and lambdoid phages. Hence, plasmids derived from lambdoid phages appear to be convenient models to study the replication of Shiga toxin-converting bacteriophages. Copyright (C) 2009 S. Karger AG, Basel