Coevolution Between Pseudomonas Fluorescens W-6 And Its Cold-active Siphoviridae Phage VW-6S

The process of one group evolution interacts with other groups evolution is called coevolution.Coevolution is ubiquitous in nature.The bacteria-bacteriophage system is the model for studying coevolution.Phages play important roles in environmental food web processes,biogeochemical cycles,gene transfer,and the structure and diversity of prokaryotes.Siphoviridae phage is the largest family of tailed phages.At present,the research on coevolution of bacteria-phage system mainly focuses on Podoviridae and Myoviridae phages and their hosts.However,the coevolution of bacteria-Siphoviridae phages in low cold environment was unknown.In this study,Pseudomonas fluorescens W-6 and its Siphoviridae phage VW-6S,isolated from the water samples of Napahai plateau wetland,were used to analyze genome,coevolution model,kinetics of host and bacteriophage,and partial genes change during coevolution.Firstly,the homology comparisons of 13 spacer sequences of CRISPR structure of host W-6 and phage VW-6S genome sequences were carried out using DNAMAN software.It was concluded that the spacer sequences 1,2,8 and12 were homologous to the VW-6S genome.The identities are relatively high,reaching 65%,77%,73%and 65%,respectively.It was deduced that the VW-6S spacer sequences may be obtained through the CRISPR system.The homologous comparison and phylogenetic analysis of the proteins were performed.Studies on the coevolution of Pseudomonas fluorescens W-6 and its cold-active Siphoviridae phage VW-6S showed that in the early course of coevolution?P₁^P₂?,the infectivity of other phages to the host strain showed a decreasing trend,and the coevolutionary kinetics conformed to the ARD model,and then the coevolution model belongs to the GFG model.At the later course,the phage infectivity to the host is a nonlinear trajectory,then is a fluctuating evolutionary dynamic,obeys the FSD model,and belongs to the MA model.Finally,sequencing analysis of phage VW-6S tail fiber protein,head-tail connector and cell wall hydrolyzing enzyme showed that phage gene mutations associated with infection are more rapid during coevolution,such as gp28,so the tail fiber protein Gp28 may be the main adsorption site.This study preliminarily revealed the coevolution of Pseudomonas fluorescens W-6 and its cold-active Siphoviridae phage VW-6S.It provides a basis for further elucidating the reaction of bacteria and phages.