Flounder Intestinal Vibrio Quorum Sensing System And Its Signaling Molecules, Degradation Of The Isolation Of Strains

Quorum sensing is a signal sensing system by which bacteria monitor the density of their population. Bacteria can secret the chemical signal molecules, and the signal molecules diffuse from inner cell to outer cell, bacteria can sense the density of cells and alter gene expression when the signals accumulate to a minimal threshold level, the progress is called quorum sensing. A number of quorum sensing systems have been found in Gram-positive and in Gram-negative bacteria, which control the expression of multiple genes. Some pathogenic species belonging to the Vibrionaceae family have been shown to regulate virulence through a complicated network of quorum-sensing systems.In this study, three kinds of N-acylhomoserine lactone (AHL) signal molecules were detected in Vibrio ichthyoenteri DA3,a pathogen of cultured turbot (Scophthalmus maximus), with the Agrobacterium tumefaciens reporter strain KYC55 (pJZ372)(pJZ384)(pJZ410).Because these three AHL signal molecules can not be detected by the Chromobacterium violaceum CV026, we can speculate that they may have a longer N-acyl side chain or special side chain groups, for example, the hydroxyl side chain group.The characterization of these molecules is still unknown, needed to be analyzed by HPLC-MS for further research. DA3 produced AHLs during the whole growth phase and the level of AHLs increased, accompanied by the increase of cell population density. DA3 was also shown to have autoinducer 2 (AI-2) activities. The level of AI-2 activity in DA3 increased rapidly at the log phase of growth, and kept the high level till the stationary phase. The coding sequence for a luxS-like gene of DA3 was obtained showing a maximum similarity of 99.6% to that of V. scophthalmi. A mutation in luxS produced no detectable AI-2 activity, but did not result in noticeable changes in growth rate, biofilm formation and virulence of V. ichthyoenteri to turbot, implying that luxS may not play a significant role in regulating the virulence gene expression in this bacterium or that different signal systems need to be inactivated at once in order to decrease virulence.V. ichthyoenteri DA3 as well as the type strain LMG19664T did not produce any Cholerae autoinducer 1 (CAI-1) activity.It's reported that AHL-mediated quorum sensing system of Vibrio bacteria participate in the regulation of virulence, such as V. harveyi, V. anguillarum and so on, so interference with AHL-mediated quorum sensing system is a new anti-infective strategies.The research shows that AiiA enzyme, produced by Bacillus strains, can inactivate AHLs by hydrolyzing the acetyl chain, amino homoserine lactone ring of the ester bond or the lactone bond of AHLs.37 strains of Bacillus spp isolated from natural seawater were screened for their AHL degrading ability in this study, and 5 strains were proved to possess the greater AHL degrading ability.This is the first report of quorum-sensing systems in V. ichthyoenteri.