N-acylhomoserine lactone-degrading Bacillus strains isolated from aquaculture animals

Infections caused by antibiotic-resistant pathogenic bacteria can cause considerable losses in aquaculture. Many aquaculture pathogens regulate the expression of virulence genes through quorum sensing, bacterial cell-to-cell communication with small signal molecules. N-acyl homoserine lactones (AHLs) are the most extensively studied class of quorum sensing signals. AHL-degrading enrichment cultures were previously isolated from the intestinal tract of healthy aquaculture animals and found to increase the survival of fish and shrimp larvae. In this study, we isolated Gram-positive spore-forming strains from AHL-degrading enrichment cultures originating from whiteleg shrimp and European sea bass. Five selected isolates showed good AHL degradation abilities in a nutrient-rich background, simulating the presence of high levels of other nutrients as is the case in a gastrointestinal environment. Indeed, degradation rates between 0.7 and 0.9 mg l(-1) h(-1) were observed in Luria-Bertani medium supplemented with 5 mg l(-1) N-hexanoyl-L-homoserine lactone. The selected isolates were confirmed to belong to the genus Bacillus by 16S rDNA sequencing and might be interesting novel biocontrol strains for use in aquaculture. (C) 2010 Elsevier B.V. All rights reserved.