Regulation Of AI-2on Biological Functions Of Riemerella Anatipestifer

Riemerella anatipestifer (RA) infection is a contagious disease of various animals including ducks,goose, turkeys and so on, which has been named as Pasterurella anatipestifer disease and Infectiousserositis. RA infection is one of the major diseases endangering the duck industry, causing severeeconomic losses due to high mortality and growth retardation. Bacteria have been regarded as monadwhich has no connection with other organisms and surrounding environment. However, quorum sensing(QS) has been reported in most species of bacteria, LuxS/AI-2type of QS is shared by bothGram-positive and Gram-negative bacteria. Bacteria use AI-2to communicate between interspeciescells and regulate physiological behaviors such as biofilm formation, virulence-related gene expressionand so on. This study mainly includes five parts as described below:1. Detection of AI-2in the RA culturesIn this study, V.harveyi BB170bioassay had been developed to determine the production of AI-2inthe cultural supernatant of34RA strains. The results showed that no AI-2was produced by all of the34RA strains.2. Internalization of AI-2in RA and the effect of AI-2on the growth rate of RAIn this study, the commercial AI-2was added to the RA culture and V.harveyi BB170bioassay wasused to detect AI-2at different growth phase to verify whether RA could internalize AI-2. The growthrate of RA was determined after addition of AI-2to investigate the influence. The results demonstratedthat RA could internalize AI-2and added AI-2could not change the growth rate of RA, which provide asolid basis for future research of QS in RA.3. Effect of AI-2on biofilm formation and the associated gene transcriptionIn this study, we studied the effect of AI-2on biofilm formation of RA through crystal violetstaning, and the effect of AI-2on transcriptional level of related genes using real-time PCR. The resultsdemonstrated that AI-2could inhibit biofilm formation of strain CH3and the inhibition wasconcentration-dependent. Moreover, AI-2down-regulated the transcriptional levels of most detectedgenes.4. Effect of AI-2on adherence to and invasion of Vero cells and transcriptional level of related genesof RAIn this study, different concentrations of AI-2were added to verify whether the abilities ofadherence and invasion of CH3was affected. The effect of AI-2on transcriptional levels ofvirulence-related and metabolism-related genes of RA was also investigated. The results suggested thataddition of AI-2affected the abilities of bacterial adherence and invasion to the cells, as well as thetranscriptional levels of selected genes.5. Identification of the mtan gene of RA on the biosynthesis of AI-2In this study, the pfs gene deleted Avian Pathogenic Escherichia coli (APEC) mutant strain DE17-△pfs was constructed and the mtan gene of CH3was transformed into this mutant strain. As a result, this combinant strain could produce AI-2, which suggested that mtan gene of RA could be able toparticipate in biosynthesis of AI-2. This finding will help to future researches of mtan gene of RA.