Statistical optimization of medium constituents and conditions for improved antimicrobial compound production by marine Streptomyces sp. JRG-04

A recently isolated Streptomyces sp. JRG-04 from a mangrove estuary was identified as a producer of a broad-spectrum antimicrobial compound against various pathogens, including multidrug resistant (MDR) pathogens, with no cytotoxic effect on H9C2 cells. In this study, the concentrations of various nutrient factors and culture conditions were optimized by both classical and statistical methods for an improved titer of the antimicrobial compound production. Among nutrient factors, carbon and nitrogen sources such as maltose and yeast extract stimulated the production of the antimicrobial compound with the highest titer. The production medium, with a pH 7.5 at 28°C, promoted increased antimicrobial compound production. All non-statistically optimized nutrients and environmental conditions were used for subsequent statistical optimization using a Plackett-Burman design (PBD) and response surface methodology (RSM). Maltose, yeast extract and the inorganic salt NH4Cl were found to be significant components for antimicrobial compound production by the PBD method. Interactions between important variables were evaluated using central composite design (CCD) of response surface methodology. The final optimized medium (L-1) contained: 10 g maltose, 2.9 g Na2HPO4, 2.3 g KH2PO4, 1 g NH4Cl, 0.5 g MgSO4×7H2O, 0.002 g FeSO4, 0.5 g CaCO3, 5.25 g yeast extract and trace elements in 5.0 mL salt solution (0.1 g ZnSO4×7H2O, 0.3 g H3BO3, 0.2 g COCl2×6H2O, 0.03 g MnCl2 4H2O, 0.03 g Na2MO4×2H2O, 0.02 g NiCl2×6H2O, 0.01 g CuCl2×2H2O). The medium provided an overall 42.8% increase in antibiotic activity when compared to the unoptimized medium, from 140.57±0.80 to 210.33±0.57 U/mL