Rapid Evolutionary Characteristics of P1 and T5 Infection in E. coli Strains

Abstract

The emergence of superbug has once again thrust century-old phage into the spotlight as a hot research topic. While the "phage display" technology has enabled targeted evolution of viruses, the successful application of phage remains uncertain due to their replicative and mutative nature, as well as the complexity of phage-bacteria interactions and evolutionary mechanisms. In this study, we used two rapidly evolving phages, P1 and T5, along with 18 types of E. coli strains, as representatives to explore the evolutionary characteristics of phage-infected bacteria. Our findings confirm that the evolutionary of phages and their hosts is a co-evolutionary process, resembling an "arms race", after the early rapid evolution of P1 and T5, the host range expands to infect different E. coli strains, but continued rapid evolution reaches a certain stage where P1, T5, and E. coli strains all experience a fitness cost, and the host range no longer expands. Three new findings in this study differ from previous studies. Firstly, although E. coli strains were not infected in the same way, there was no statistically significant difference between P1 and T5 infection in different E. coli strains at different evolutionary stages. Secondly, 11 types of E. coli strains that had been infected by T5 during co-evolution all showed E. coli tolerant plaques on the medium at the fifth stage of evolution, whether they had been infected by T5 at that stage of evolution, and at the sixth stage of evolution, all of these tolerant plaques disappeared again. Thirdly, after the fitness cost of the co-evolutionary process had already occurred, although the host range of P1 and T5 no longer continued to expand, the types of E. coli strains infected by P1 and T5 at the same evolutionary stage did not decrease in focus with the continued prolongation of the co-evolutionary time, but instead showed a gradual incremental trend. This study provides experimental evidence for the resolution of phage-bacteria co-evolutionary mechanism and new ideas for phagotherapy strategies for the superbug.