| Quorum Sensing(QS)is one of the key factors involved in the density balance,biophysical functions and response for environment stress in microbial community.Bacteriophages have been regarded as the natural enemies of bacteria,and thought to be the most important biological factor in keeping bacterial community balance.It is a very interesting thing to explore the mechanism of quorum sensing system involved into bacteriophage resistance of bacteria.In this study,a novel quorum-sensing-regulated antiphage defense mechanism in Escherichia coli BW25113 and T4 phage has been reported.The main points are concluded below:1.We confirmed that LsrB was the natural receptor for AI-2.The results showed that lsrB deficient strains did not respond to the addition of AI-2,meanwhile its sensitivity towards T4 phage was increased by 21%.2.Two new mechanisms of QS-II involved into T4 phage resistance in E.coli have been illustrated in our study.Firstly,our results showed that the activation of QS-II reduced the numbers of T4 receptor on the cell surface and then lead to reduction of phage adsorption rate up to 19%.The expression of phage-receptor encoding genes,such as ompC,waaA,waaQ were decreased by 40%,35% and 20%,respectively.It have showed AI-2 mediate metabolism to enhance phage resistance,and leads to a downregulation of genes related to host-basic metabolism.The expression of genes such as csrA,ptsG,ptsH,ptsI were decreased by 50%.We proposed two mechanisms serve to protect E.coli under conditions of high risk of infection,and decreased infection by T4 phage 26%.3.We also demonstrated that the activation of QS-II by signals AI-2 did not bring any changes at transcriptional levels for genes of hns,leuO and casE which are involved in the CRISPR system.In this paper,we found that E.coli utilize AI-2 to reduce infection by T4 phage.This is,to our knowledge,the first example of AI-2 regulated antiphage defense mechanism.Our research investigated QS-II is an important determinant of phage-host interactions.On the basis of our finding in the E.coli-T4 model system,we hypothesize that an important perspective for molecular mechanisms that coordinate phage-host interactions and QS. |
