In vivo effects of single or combined N-acyl homoserine lactone quorum sensing signals on the performance of Macrobrachium rosenbergii larvae

Three experiments, each of 8-days, were conducted to evaluate the effects of (5) N-acyl homoserine lactone (AHL) either alone or in combination on the development and survival of Macrobrachium rosenbergii larvae. Experiment 1 was carried out as preliminary trial to confirm whether AHL mixture added daily at 1 mg/L concentration could have any negative effect on the larval performance. In experiment 2, it was verified whether the negative effect on the larvae was due to individual AHL or their interactions and experiment 3 was carried out to determine the critical threshold dose of AHL mixture. Results revealed that AHL mixture added daily at 1 mg/L concentration significantly (P < 0.01) reduced the development and survival of the larvae. Except for C4-HST, there was no significant effect (P > 0.05) of any of the AHL molecules added individually at 1 mg/L concentration on the development and survival of the prawn larvae. The AHL molecule C4-HST significantly (P < 0.01) reduced the larval stage index (LSI) and survival of prawn larvae by about 9.1 and 8.7%, respectively. In contrast, the AHL mixture added daily at 1 mg/L concentration significantly (P < 0.01) reduced the LSI and survival of the larvae by 12 and 41%, respectively. Thus the poor development and low survival of the larvae is probably due to the interaction of different AHL molecules which could have instigated the production of various virulence factors in micro-organisms associated with the larvae. Using the AHL mixture, the dose response relationship with respect to the performance of the larvae showed that the development of the larvae was already negatively affected by adding the mixture to a final concentration of 0.125 mg/L while at that concentration, the survival was still unaffected. This indicate that the standing microbial communities associated with the prawn larvae can become virulent when a quorum or critical threshold level is reached through the daily addition of the AHL mixture at a concentration of 0.125 mg/L.