Introduction: Recirculating aquaculture system (RAS) are nowadays considered to be particularly resource-efficient and sustainable. The biofilter of a RAS is a key element for the water treatment, since it removes byproducts originated during the fish production . A proper balance of the microbial community maintains safe levels of these residual compounds. An imbalance in the microbial community of the system results in poor water quality, which causes stress to the fish physiological system. In the worst cases this situation results in a disease outbreak. New strategies for disease prevention contributes to the development of a safe and sustainable aquaculture production.
Aim: The objective of the present work is the selection of microorganisms to enhance the biofiltration system in a RAS, and investigate its capacity to reduce the abundance of pathogens in the system.
Methods: Samples were obtained from the biofilter of a freshwater RAS with reared Clarias gariepinus. Different bacterial colonies were isolated and biochemically characterized . Isolates with interesting metabolic profiles were selected and tested for biofilm formation ability, quorum sensing activity and antagonistic effect against seven potentially pathogenic bacteria. Two bacterial candidates were tested for its capacity of inhibiting Escherichia Coli and enhancing water quality inside small scale in vitro biofilters , which consisted on bottles containing bioballs and water that simulated a RAS effluent. During a four-day trial, the abundance of R5, R28 and E. Coli were calculated and water samples analyzed for physicochemical parameters.
Results: Two strains , namely R28 and R5, showed a strong inhibition of the growth from Staphylococcus aureus and Pseudomonas veronii . R28 was able to catalyze phosphate, glucose, casein, gelatin, cellulose and reduce nitrate. R5 had an antagonistic effect on the growth of Vibrio anguilarum , Aeromonas hydrophila and E. Coli, and could reduce nitrate and catalyze another five compounds. Results of the four-day trial showed how R5 colonizes the bioballs and water while preventing E. Coli to increase in abundance. R28 did not perform as efficiently as R5 in controlling the growth of E. Coli.
Conclusions: The two candidates had essential functional traits with the potential to control the overgrowth of some potentially pathogenic bacteria. They also had advantageous biotechnological and functional characteristics for the future development of probiotics which could be used at the production sector.