Abstract
Quorum sensing (QS) is a cell density dependent process that enables bacteria to communicate with each other based on the production, secretion and sensing of the auto-inducer molecules and then subsequently regulate virulence associated gene expression. Interrupting quorum sensing may represent a novel alternative approach to combat bacterial pathogen. Several bacteria can produce quorum quenching (QQ) enzymes. However, the role of QQ bacteria in shaping the microbiota and the level of N-acyl-homoserine lactones (AHLs, a prevalent type of QS molecules) producing bacteria remains largely unknown. The objective of this study was to examine the presence of AHLs in the fish intestine and investigate the modulation of gut microbiota and its effect on Aeromonas hydrophila level by a QQ enzyme producing probiotic Bacillus sp. QSI-1. AHLs were found in fish gut content and were confirmed in Aeromonas species using Chromobacterium violaceum CV026 and Agrobacterium tumefaciens AT 136 (pZLR4) as reporter strains. We demonstrated that the composition of fish gut microbiota was affected by quenching bacteria QSI-1, and the percentage of A. hydrophila was decreased significantly. Taken together, these results provide valuable insights into QQ enzyme producing probiotics can modulate the microbiota structure and decrease the percentage of AHL-producing pathogenic bacteria in the gut. These data strongly suggest that QQ probiotics may serve as non-antibiotic feed additive in aquaculture to control bacterial diseases.
Highlights
The fish gastrointestinal (GI) tract is a complex ecosystem that always possessing a diverse bacterial community in a balanced relationship with each other, and some of the bacteria likely provide beneficial effects to the host (Wu et al, 2012b)
Using the weightedUniFrac metric, principal component analysis (PCA) and principal co-ordinates analysis (PCoA) plots were calculated from weighted UniFrac distances for the evaluation of the community composition, the results demonstrates a clear separation between each groups (Figures 5A,B), and suggesting that there is clear dissimilarity between the gut microbiota fed with or without QSI-1 supplemented diet
The fish intestine houses a dense and diverse microbial community, studies on fish gut microbiota have been reported by some researchers (Wu et al, 2013; Li et al, 2014; Kashinskaya et al, 2015; Gajardo et al, 2016), the gut microbiota is critical to health, and the microorganisms in the gut use chemical communication to coordinate and synchronize gene expression via the quorum-sensing regulatory pathway
Summary
The fish gastrointestinal (GI) tract is a complex ecosystem that always possessing a diverse bacterial community in a balanced relationship with each other, and some of the bacteria likely provide beneficial effects to the host (Wu et al, 2012b). The freshwater fish intestinal microbiota tends to be dominated by members of the genera such as Aeromonas, Acinetobacter, Lactococcus, Flavobacterium and Pseudomonas, representatives of the QSI-1 Modulate Gut Microbiota family Enterobacteriaceae, and obligate anaerobic bacteria of the genera Clostridium, Bacteroides, and Fusobacterium. Among these bacteria, their population is influenced by the metabolites and the effectors that promote species stability, adaptation, and survival in the gut (Ye et al, 2014; Kashinskaya et al, 2015). Acyl-homoserine lactones (AHLs) are considered to be intraspecies signaling molecules in Gramnegative bacteria (Bandara et al, 2012), it has been shown that between bacteria using these molecules to communicate with other species (Riedel et al, 2001; Ryan and Dow, 2008; Giaouris et al, 2015)
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