Study On Foreign AHL's Effect On The Quorum Sensing System Of M.tianshanesne And The Function Of Root Colonization

Quorum-sensing is the regulation of gene expression in response to fluctuations in cell-population density and allows populations of bacteria to synchronize group behaviors. Quorum-sensing systems can be divided into two paradigmatic classes: LuxI/LuxR-type quorum-sensing systems in Gram-negative bacteria which produce aryl-homoserine lactone (AHL) autoinducers, and oligopeptide/two-component-type quorum-sensing ciruits in Gram-positive bacteria which produce autoinducing peptide (AIP) autoinducers. AHL and AIP autoinducers are species-specific signaling molecular for intraspecies communications and AI-2 serves as a universal signal molecule for interspecies communications. The N-acyl homoserine lactone is known as the signal molecule of most gram-negative organisms that can regulate diverse physiological functions. And the QS system plays a critical role in the rhizobia symbiotic process.In order to study the foreign AHL's effect on mrtI expression, we isolated forty strains of rhizobia from field. We use the mrtI-lacZ transcriptional fusion to test the supernatant of the strains. It was found that there are four strains that can induce the mrtI-lacZ expression and the more the supernatant was the more lacZ expressed. We extracted the AHLs from the supernatant and subjected to TLC detection by which we found that comparing with M.tianshanesne there were one to four AHLs of the strains have the same mobility. Base on this fact we think they may have the same AHLs and it explains why the foreign AHLs can influence the expression of mrtI. The comparison of gene sequence also supports this.The experiments of root hair adherence show that the strains that have the approximate QS system can impact each other's ability of root hair adherence. These data provide some evidence that quorum sensing plays a critical role in root colonization process. These stains can also adhere on the root hair of each other's host plant either. That made some theoretics reference on the internality mechanism of corss-inocunation by different rhizobia and expands sthe application of rhizobia. Meanwhile the competitive root colonization shows that quorum sensing plays a critical role in the M. tianshanense symbiotic process.