Quorum Quenching Properties and Probiotic Potentials of Intestinal Associated Bacteria in Asian Sea Bass .

Quorum quenching (QQ), the enzymatic degradation of -acyl homoserine lactones (AHLs), has been suggested as a promising strategy to control bacterial diseases. In this study, 10 AHL-degrading bacteria isolated from the intestine of barramundi were identified by 16S rDNA sequencing. They were able to degrade both short and long-chain AHLs associated with several pathogenic species (spp.) in fish, including -[(RS)-3-Hydroxybutyryl]-l-homoserine lactone (3-oh-C-HSL), -Hexanoyl-l-homoserine lactone (C-HSL), -(β-Ketocaproyl)-l-homoserine lactone (3-oxo-C-HSL), -(3-Oxodecanoyl)-l-homoserine lactone (3-oxo-C-HSL), -(3-Oxotetradecanoyl)-l-homoserine lactone (3-oxo-C-HSL). Five QQ isolates (QQIs) belonging to the and genera, showed high capacity to degrade both synthetic AHLs as well as natural AHLs produced by and using the well-diffusion method and thin-layer chromatography (TLC). The genes responsible for QQ activity, including , and were also detected. Analysis of the amino acid sequences from the predicted lactonases revealed the presence of the conserved motif HxHxDH. The selected isolates were further characterized in terms of their probiotic potentials in vitro. Based on our scoring system, QQ1 and QQ2 exhibited suitable probiotic characteristics, including the production of spore and exoenzymes, resistance to bile salts and pH, high potential to adhere on mucus, appropriate growth abilities, safety to barramundi, and sensitivity to antibiotics. These isolates, therefore, constitute new QQ probiotics that could be used to control vibriosis in .