Escherichia coli exhibits a very high level of genetic diversity. Studies have shown that prophages (i.e. the phages whose genetic materials incorporated into the bacterial genome) make up a large portion of E. coli strain-specific genes and are found to be able to facilitate E. coli to expand its niche among different animal host species. E. coli strains were also reported to be persistent in the natural environment even in the absence of fecal input, and on the basis of previous studies with model strains, we hypothesized that prophage-mediated genetic event may play a role in the transition process of E. coli from animal hosts to the natural environment. Through induction and reinfection, prophages can mediate the horizontal gene transfer (HGT) among different strains. Howeve...[ Read more ]

Escherichia coli exhibits a very high level of genetic diversity. Studies have shown that prophages (i.e. the phages whose genetic materials incorporated into the bacterial genome) make up a large portion of E. coli strain-specific genes and are found to be able to facilitate E. coli to expand its niche among different animal host species. E. coli strains were also reported to be persistent in the natural environment even in the absence of fecal input, and on the basis of previous studies with model strains, we hypothesized that prophage-mediated genetic event may play a role in the transition process of E. coli from animal hosts to the natural environment. Through induction and reinfection, prophages can mediate the horizontal gene transfer (HGT) among different strains. However, the effective range of such prophage-mediated HGT within E. coli population is still unknown due to the inadequate information about the infection specificity of lysogenic phages. In this study, we investigated the interactions between lysogenic phages and their E. coli hosts, particularly in the aspects of the infection specificity and the ecophysiological fitness they may confer to their hosts. The lysogenic infection specificity was better characterized from strain level by determining the host range of prophages induced from E. coli isolated from seawater. Our results indicated that lysogenic phage infection is actually specific and exhibited certain infection patterns, suggesting that the range of prophage-mediated HGT within E. coli population is limited. Also, by comparing the ecophysiological difference between a pair of wild type and lysogenic fecal original E. coli strains, we found that prophages can greatly change the phenotype and enhance the survivability of E. coli in marine environment, which provided a new model to elucidate how E. coli may become adapted to the natural environment.