Optimization of cultivation medium for enhanced production of antifungal metabolites by Streptomyces hygroscopicus

• Production of apple bitter rot antagonists by Streptomyces hygroscopicus was analysed.
• The best carbon and nitrogen sources for medium preparation were defined.
• Quantities of glycerol, yeast extract and phosphorus were optimized using response surface methodology.
• Obtained results were confirmed in planta on artificially inoculated apple fruits.

Antifungal potential of Streptomyces hygroscopicus metabolites was tested against the isolates of Colletotrichum spp., obtained from rotten apple fruits. Experimental factorial design and response surface methodology were employed to optimize medium composition and enhance antifungal components productivity by S. hygroscopicus. Results of optimization suggest that the optimal medium composition is (g/L): glycerol (13.92), yeast extract (5.00), phosphates (0.63), CaCO3, (3.0), NaCl, (3.0), MgSO4, (0.5). Further research was performed to validate the obtained results and confirm their applicability in planta on artificially inoculated apple fruits. The obtained efficacy after 14 days of incubation was 99.3% against Colletotrichum acutatum and 99.8% against Colletotrichum gloeosporioides. Application of supernatant of S. hygroscopicus cultivation medium, produced under defined conditions, in biological control of apple rot could offer safe and healthy apple fruits on the market, while simultaneously helping to solve the problem of waste glycerol disposal in the biodiesel industry.