Evaluation of pyocyanin toxicity in various life stages of Penaeus monodon and in nitrifying bacterial consortia for their safe application in recirculating aquaculture systems (RAS) to abrogate pathogenic vibrios

Pyocyanin has recently been recognized as antimicrobial agent in aquaculture industry, an alternative to antibiotics, as it accorded higher level inhibitory effect on aquaculture pathogens. As pyocyanin-induced toxicity is a major concern, this study has been undertaken to evaluate the toxicity of purified pyocyanin and to determine the LC50 value for its safe application in aquaculture. The dose-dependent pyocyanin-induced toxicity was tested on various life stages of P. monodon such as nauplius, zoea, mysis and post-larva as well as on nitrifying bacterial consortia used in aquaculture in order to fix the concentration limits to the animal rearing systems. The study revealed that pyocyanin was a potential inhibitory compound to V. harveyi, bacteriostatic at 5 mg L-1 and bactericidal at 10 mg L-1. The LC50 values of pyocyanin at various life stages of P. monodon were higher than the concentration required to abrogate pathogenic V. harveyi. Moreover, pyocyanin did not inhibit nitrification, specifically of nitrifying bacterial consortia used for activating nitrifying bioreactors, at different salinities, suggesting its potential application in recirculating aquaculture systems to control pathogenic vibrios.