Inhibition of luminescence and virulence in the black tiger prawn (Penaeusmonodon) pathogen Vibrio harveyi by intercellular signal antagonists

Expression of luminescence in the Penaeus monodon pathogen Vibrio harveyi i s regulated by an intercellular quorum sensing mechanism involving the synt hesis and detection of two signaling molecules, one of which is N-hydroxy b utanoyl-L-homoserine lactone and the other of which is uncharacterized. Ind irect evidence has suggested that virulence, associated with a toxic extrac ellular protein, and luminescence in V; harveyi are coregulated. In this st udy the effects of an acylated homoserine lactone antagonist produced by th e marine alga Delisea pulchra on luminescence and toxin production in a vir ulent strain of V. harveyi were analyzed. Luminescence and toxin production were both inhibited by the signal antagonist at concentrations that had no impact on growth. Toxin production was found to be prematurely induced in V. harveyi cultures incubated in a 10% conditioned medium. Additionally, a significant reduction in the toxicity of concentrated supernatant extracts from V. harveyi cultures incubated in the presence of the signal antagonist , as measured by in vivo toxicity assays in mice and parwns, was observed. These results suggest that intercellular signaling antagonists have potenti al utility in the control of V. harveyi prawn infections.