Study On Isolation,Biological And Genome Of Plague Phage From Plague Focus Of Wild Plague In Heqing

ObjectiveThis project aims to investigate whether there are plague phage in the plague focus in Heqing Country.We wonder what are the characteristics of these phage,how these characteristics are related to the Yersinia pestis strains of Heqing,and what role does it play in the micro-ecology of plague and how it affects the plague.Methods1.We select Xinhua Town,a new plague epidemic site in Heqing,Yunnan Province,as a survey point in 2017.Rodents were collected by traps and cages,and mouse intestinal specimens were collected for plague phage isolation.2.The plague phage was isolated and purified by double-layer plate,and proliferated,and phage samples satisfying the conditions were obtained by concentration;3.The optimal growth temperature of the obtained phage was determined,and the morphology was observe by electron microscope,as well as the cleavage spectrum and other general biological characteristics were determined.4.The DNA was extracted with X phage DNA kit and sequenced,and the obtained plague phage genome was subjected to bioinformatics analysis.Results1.354 adult rat samples were collected from four natural villages(Named Machang,Xiaomachang,Heini Shao and Anle)in Heqing County,Yunnan Province.Two strains of plague phage were isolated,which named HQ67 and HQ 1032.Both two phages belong to the muscle tail phage,the head has a regular Icosahedronl structure and the tail is longer.The plaque is round and has a sharp edge with a diameter of 1-1.5 nm.The optimum growth temperature is 37?,with special cracking characteristics,only the plague bacteria are lysed,and the other strains are not lysed.3.The genome size of the two phage genomes is about 34 kb,and the GC content is between 51.46%and 52.24%.The number of annotated genes is 39,the number of HQ67 annotated genes is 39,and the number of HQ103 annotated genes is 46.The nucleotides of the two phage have 97.5%homology.The two phage genomes were compared with the gene pool in two pairs:Only L-413C has 96.4%homology with HQ67 nucleotides and 96.6%homology with HQ 103 nucleotides.Other phage have no homology with the two phages.The Blast alignment in the genome showed that the two phage genes were similar to the E.coli strain.And the phylogenetic tree analysis found that the three phage of HQ 103,HQ67 and L-413C were in the same branch of the phylogenetic tree,and the latter two strains were in the same small branch.ConclusionThis study showed that there was a distribution of plague phage in the plague foci of Heqing voles.The isolated phage was a muscle tail phage,and its lytic plague was temperature-dependent,that is,within a certain range,its cleavage rate increased with temperature.High and enhanced,suggesting that this phage has a biological barrier to Y.pestis in animals,and in the environment this phage can coexist with Yersinia pestis.From the genomic point of view,the two phage isolated this time are new plague phage,and its deeper biological significance and the relationship with the genetic evolution of Yersinia in nature are worthy of further discussion.