Abstract
Quorum sensing (QS) is closely associated with the production of multiple virulence factors in bacterial pathogens. N-acyl homoserine lactones (AHLs) are important QS signal molecules that modulate the virulence of gram-negative pathogenic bacteria. Enzymatic degradation of AHLs to interrupt QS, termed quorum quenching (QQ), has been considered a novel strategy for reduction of pathogenicity and prevention of bacterial disease. However, the low expression levels of QQ proteins in the original host bacteria has affected the applications of these proteins. Previously, we identified a novel marine QQ enzyme, named MomL, with high activity and promising biocontrol function. In this study, we linked the target fragment momL to pNCMO2, which provided a basis for the first heterologous expression of MomL in the antifungal and anti-gram-positive-bacteria biocontrol strain Bacillus brevis, and obtaining the recombinant strain named BbMomL. The QQ activity of BbMomL was confirmed using a series of bioassays. BbMomL could not only degrade the exogenous signal molecule C6-HSL, but also the AHL signal molecules produced by the gram-negative pathogens Pectobacterium carotovorum subsp. carotovorum (Pcc) and Pseudomonas aeruginosa PAO1. In addition, BbMomL significantly reduced the secretion of pathogenic factors and the pathogenicity of Pcc and P. aeruginosa PAO1. We tested the biocontrol function of BbMomL for prevention of plant diseases in vitro. The result indicates that BbMomL has a broad antibacterial spectrum. Compared with wild-type B. brevis, BbMomL not only inhibited fungi and gram-positive bacterial pathogens but also considerably inhibited gram-negative bacterial pathogens. Moreover, the Bacillus brevis expression system has good application prospects and is an ideal host for expression and secretion of foreign proteins.
Highlights
Microbial quorum sensing (QS), known as self-induction, is a self-sensing system in which microorganisms perceive population density by diffusion of secreted small molecules between cells, and these small molecules regulate the expression of a series of genes [1].The pathogenicity of many pathogens is mediated by the Quorum sensing (QS) systems
By conduction signal molecule degradation experiments and in vitro detection of the control of plant soft rot by the recombinant strain BbMomL, we found that the recombinant strain BbMomL can effectively degrade the acyl homoserine lactones (AHLs) molecules produced by pathogenic bacteria, block the QS system and reduce the pathogenicity of the bacteria
Upon verification of the degradation of the signal molecules produced by P. aeruginosa PAO1 by different protein components, we found that the degradation efficiency of the 0–20% ammonium sulfate component toward the AHL signal molecule was only 20%
Summary
Microbial quorum sensing (QS), known as self-induction, is a self-sensing system in which microorganisms perceive population density by diffusion of secreted small molecules (self-inducers) between cells, and these small molecules regulate the expression of a series of genes [1]. The pathogenicity of many pathogens is mediated by the QS systems. Mar. Drugs 2019, 17, 128; doi:10.3390/md17020128 www.mdpi.com/journal/marinedrugs. Mar. Drugs 2018, 16, x carotovorum subsp. Carotovorum (Pcc) can cause a soft rot of various plants, such as carrot and [2,3]; and stewartii subsp Drugs 2018, 16, x carotovorum subsp. carotovorum (Pcc) can cause a soft rot of various plants, such as carrot and [2,3]; and stewartii subsp
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