Optimization of medium for the production of a novel aquaculture probiotic, streptomyces sp. a1 using central composite design of response surface methodology

A strain, Streptomyces sp. A1 isolated from shrimp pond sediments has been identified as an aquaculture probiotic antagonistic to pathogenic Vibrio harveyi V7. In the present study, the different carbon and nitrogen sources and growth factors in a mineral base medium were optimized for enhanced biomass production and antagonistic activity, following response surface methodology (RSM). Accordingly, the minimum and maximum limits of the selected variables were determined and a set of fifty experiments programmed employing central composite design CCD of RSM for the final optimization. The response surface plots of biomass production showed similar pattern with that of antagonistic activity, which indicated a correlation between the biomass and antagonism. The optimum concentrations of the carbon and nitrogen source, and growth factors for both biomass and antagonistic activity were starch (14.62 g/1), casein (0.93 g/1), NaCl (15.6 g/1), DL-α-alanine (0.233 g/1), and vitamin B₆ (0.023 g/1).