Effect Of Extracellular Antigen Of E.coli Nissle 1917(EcN) On P1 Infection

Phage P1 is a widely used transduction tool in bacteria and has important application value in bacterial gene knockout.It is a lysogenic bacteriophage that exists in bacteria in the form of a single copy plasmid during the proto-lytic cycle.After entering the cleavage cycle,the host cell molecular machine was used to synthesize the required substances,and the host genome DNA was packaged into its protein capsid to form a progeny phage.Bacteriophage P1 can recognize a variety of bacteria,but can not infect some strains with polysaccharide capsule on the cell surface.In addition,the infection site of phage P1 has not been found so far,which is an obstacle to expand the scope of application of phage P1.In order to find out the infection site of Escherichia coli infected by phage P1,E.coli Nissle 1917 was selected as the experimental strain.P1 can not form phagocytic plaque on Ec N,and the serotype of Ec N is O6::K5::H1,which can express K antigen and O antigen covering on the cell surface.So we constructed gene mutants of K antigen and O antigen and then infected them with P1,but we found that P1 can still not lyse these strains.During the experiment,we found that Ec N and its mutant strains can not be broken down by P1,yet Ec N can be used as the receptor strain of P1 phage transduction,that is,P1 can transfer packaged DNA to Ec N.So we constructed ZK126?rec A::Kan as the donor strain of P1,and transduced rec A::Kan to Ec N wildtype and its K antigen and O antigen mutants.The results showed that the transduction efficiency of K antigen mutant was significantly higher than that of other strains,indicating that K antigen on the cell surface would hinder the contact between P1 and its recognition site.In addition,the double mutant Ec N?kfi A?waa G::Cm had the highest transduction efficiency,indicating that O antigen is also a factor of P1 infection with EcN.