The Molecular Mechanism Of Effection Of Stx2-Encoding Phage ?Min27 Lysogenization On Host Escherichia Coli

E.coli O157 is an important food-borne pathogens in which one of the main virulence factors is Shiga toxin(Stx)and the phages encoding Stx is known as Stx phages.The lysogen of Stx phages could make the host bacteria producing Stx and enhance their pathogenicity.In addition,what is the interaction between the lysogen of Stx phages and the host bacteria is not quite clear.Stx2-encoding phage ?Min27 was adopted for the project on the basis of previous research in our lab to attempt to reveal the mutual regulation between the lysogen of Stx2 phages and the host,and provide some theoretical basis for preventing and controlling Shiga toxin-producing Escherichia coli especially E.coli O157.The main results were as follows:We compared the protein expression profiles of the host MG1655 and lysogens by 2-dimensional electrophoresis.Four different genes identified were all related to Fe/S subunit production,namely,nfuA,fdoH,sdhB,and ftnA.To explore the role of nfuA in the biology of Stx prophage lysogeny,gene knockout experiments and phage lysogenic conversion were performed.The inactivation of nfuA caused the prophage to enter its lytic life cycle,especially under an iron-depleted condition.A similar activity was also detected in the Escherichia coli O157:H7 strain from which the Stx phage Min 27 was originally isolated.NfuA might be the positive regulator of genes controlling lysogenic cycle such as cI,cII and cIII since their transcriptional level was significantly reduced in nfuA deletion mutant as shown by qRT-PCR.We conclude that NfuA is essential for maintenance of Stx phage lysogeny in host's genetic reservoir under iron deficient condition.In another motility experiment,to explore the role of fliA,fliD,fliE and flhDC relevant to motility in the biology of Stx prophage lysogeny,gene knockout experiments and phage lysogenic conversion were performed.The motility of wild strain,the mutants,the complemented strains and the lysogens were detected.And the changes of expression of the other genes involved in motility between wild strain and the lysogens before and after flhDC deletion by qRT-PCR were analyzed.The results showed that fliA and fliD gene together participated the regulation for flagella motility and flhDC gene could affect the motility of the lysogened strain by phage.It provided the theory basis for the further research on the mutual regulation between phage lysogenization and host genes.