OPTIMIZATION OF COMPLEX CULTURE MEDIUM FOR INCREASE OF BACILLUS SUBTILIS TS01 ANTIMICROBIAL ACTIVITY AGAINST PHYTOPATHOGENSSEVDALINA TODOROVA, VESELIN STANCHEV AND LYUBKA KOZHUHAROVAAbstract A complex culture medium was optimized using response surface methodology in order to achieve maximum antimicrobial activity of Bacillus subtilis TS 01 against phytopathogens. Glucose concentration (X1), corn extract (in relation to nitrogen) (X2) and KH2PO4 (X3) were selected as the independent variables. Results showed that the regression models adequately explained the data variation and represented the actual relationships between the parameters and responses. The composition of two new optimized nutrient media more convenient for the production of antimicrobial activity by B. subtilis TS 01 was established, namely: 1st medium (in %): glucose 1.40, corn extract (in relation to nitrogen) 0.60, KH2PO4 0.10, MgSO4 0.01, pH 7.0 in order to reach maximum antifungal activity of the strain; 2nd medium (in %): glucose 2.50, corn extract (in relation to nitrogen) 0.56, KH2PO4 0.20, MgSO4 0.01, pH 7.0 in order to reach maximum antibacterial activity of B. subtilis TS 01. Relative to the initial medium, significantly higher both antifungal and antibacterial activity of the strain was chieved in the optimized media. In the 1st medium the activity of B. subtilis TS 01 against Botrytis cinerea was 42.00 mm (sterile zone) and in the 2nd medium.
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