QUORUM QUENCHING Enterobacter STRAINS IMPROVE SHRIMP SURVIVAL DURING Vibrio INFECTION

Shrimp aquaculture is the fastest growing area of animal protein production. Shrimp are prone to the infectious diseases due to high-density cultivation in shrimp ponds. Acute hepatopancreatic necrosis disease (AHPND), aka Early Mortality Syndrome (EMS), is a severe bacterial shrimp disease caused by virulent strains of Vibrio harboring a plasmid encoding a pir-like toxin. This bacteria-produced toxin is a major pathogenicity factor that causes tissue destruction in shrimp intestines. Repressing expression of pathogenicity factors, e.g. pir-like toxin, is a promising approach for prevention of the disease outbreaks.

Frequently, expression of bacterial pathogenicity factors depends on the population density of the pathogen, which is regulated via quorum sensing mechanisms. Interruption of bacterial quorum sensing signaling, e.g. quorum quenching, may be valuable anti-infection strategy. In order to explore potential applications of quorum quenching in aquaculture, we engineered Enterobacter Ag1, a strain of enteric bacteria that is able to survive in the seawater and to colonize shrimp intestine, to reduce quorum sensing molecules concentration to reduce the likelihood of conversion of Vibrio into a pathogenic state.

Here we show (Fig.1):

• shrimp feed Ag1, expressing enzyme AidH that disrupts Vibrio autoinducer-1, had reduced mortality (25 to 55%) relative to controls
• shrimp feed Ag1, over-expressing lsr operon to reduce autoinducer-2 levels, had reductions in mortality ranging from 31 to 55% relative to controls.

Correspondingly, expression of pir-like toxin in shrimp intestines decreased in both cases by more than 2 fold (Fig. 2). We propose that the reduction in shrimp mortality is directly related to lower toxin production.

These results indicate that quorum-quenching by probiotic bacteria may be an effective means to control bacterial diseases in aquaculture. Our approach may considerably reduce if not eliminate the use of antibiotics and chemicals in aquaculture and provide a more sustainable solution to disease control and enhanced productivity.