Coevolution Analysis Of Pseudomonas Fluorescens And Its Bacteriophage Based On Resequencing Technique

Bacteria-phage antagonistic co-evolution is a key driver of molecular evolution and plays a key role in maintaining microbial diversity.For a long time,the endless co-evolutionary process has led to the formation of a complex offensive and defensive mechanism between bacteriophage and bacteria.In this study,the 20th cycle of co-evolution of cold-active Pseudomonas fluores-cens W-6 and its Siphoviridae phage VW6S were used as research materials to monitor the changes of phage infectivity/host resistance during co-evolution,carried out the preliminary analysis of the host prophage and the resequencing analysis of host and phage weight during co-evolution and the study of some gene changes during co-evolution.It was found that the phage's infectivity to the host showed a decreasing trend in the early stage of coevolution(P₂₁-P₂₈),the co-evolution dynamics followed the ARD model and the evolutionary model is the GFG model during the co-evolution of P.fluorescens W-6 and Siphoviridae phage VW6S.The co-evolution is a non-linear trajectory in the later stage,which is the fluctuated evolutionary dynamics,and it follows the FSD model and is the MA model.Preliminary analysis of the cold-active Pseudomonas fluorescens W-6 prophage revealed that there is more than one prophage in the host genome,of which the 67,326bp prophage sequence has the highest homology with the phage VW6S and contains its adsorption element gp28.Host resequencing analysis at different periods showed that the host produced 226 mutations during co-evolution,involving 47 genes,of which host-specific protein genes mutations were up to 43%,tail fiber protein genes mutations were 15%,and cleavage-related genes were 8%,and both are located on the prophage.PCR amplification experiments further verified that there are indeed many mutations in these three genes,indicating that the prophage plays an important role in the host's resistance to phage.Resequencing analysis of phage weight in different periods showed that the changes in the phage genome during co-evolution mainly occurred in the tail fiber protein gene gp28,while the other tail fiber protein gene gp27 did not change,and the cleavage-related genes endolysin and holin were also basically unchanged.In the process of phage adsorption to the host,gp28 is an important adsorption element.Therefore,it is speculated that the adsorption process may be the main“battlefield”of phage VW6S and P.fluorescens W-6 against evolution.This study revealed the co-evolution rules between P.fluorescens W-6 and Siphoviridae phage VW6S,and describes the changes in the genomes of the host and phage genome during the co-evolution,and preliminary analysis of the prophage was also carried.It laid a foundation for further elucidating the law of co-evolution of bacteriophage-bacteria resistance and the offensive and defensive mechanism.