Modified semisynthetic medium MMBT for production of preparations based on Bacillus thuringiensis

One of the trends in the biological control of pests is the use of bacteria belonging to the genus Bacillus and, first of all, entomopathogenic strains of Bacillus thuringiensis . Of great interest to industrial biotechnology are studies related to the search for optimal cultivation conditions that can improve the manufacturability of the production of microbiological preparations and their effectiveness. Previously, the nutrient media for the production of microbiological preparations based on B. thuringiensis which include natural organic components have been developed. Nevertheless, during the production of biopreparations based on this bacterium, the foaming of the culture frequently occurs and expensive filters of bioreactors have to be replaced. Also, during the treatment of plants, working solutions containing organic components of the liquid medium can clog the nozzles. This effect complicates the treatment process. In addition, organic cultural media components are not standard and depend on the quality and source origin. In this regard, it is important to carry out the screening of optimal synthetic media that could eliminate these shortcomings. Our study was aimed at selecting the optimal synthetic media and evaluating the effectiveness of the obtained preparation samples in laboratory and field conditions. The objects of study were the cultures of B. thuringiensis var. thuringiensis 800/15 (BtH1 800/15) and B. thuringiensis var. darmstadiensis 25 (BtH10 25). The composition of the culture media was as follows: CCY medium - 0.5 mM MgCl2Ł6H2O, 0.01 mM MnCl2Ł4H2O, 0.05 mM FeCl3Ł6H2O, 0.05 mM ZnCl2, 0.2 mM CaCl2Ł6H2O, 13 mM KH2PO4, 26 mM K2HPO4, 20 mg /l glutamine, 1 g/l casein hydrolysate, 0.4 g/l yeast extract, 0.6 g/l glycerol; MBt medium: 7 g/l casein hydrolyzate, 6.8 g/l KH2PO4, 0.12 g/l MgSO4Ł7H2O, 0.0022 g/l MnSO4Ł4H2O, 0.014 g/l ZnSO4Ł7H2O, 0.02 g/l Fe2(SO4)3, 0.18 g/l CaCl2Ł4H2O; LB medium: 10 g/l trypton, 5 g/l yeast extract, 10 g/l NaCl; modified semi-synthetic medium MMBt (modified MBt): 7 g/l casein hydrolyzate, 6.8 g/l KH2PO4, 0.12 g/l MgSO4Ł7H2O, 0.0022 g/l MnSO4Ł4H2O, 0.014 g/l ZnSO4Ł7H2O, 0.02 g/l Fe2(SO4)3, 0.18 g/l CaCl2Ł4H2O (25), glucose (1.0 %), Na citrate (2 g/l). Yeast polysaccharide media (YPM) for BtH1 and BtH10 served as a reference. Bt strains were cultivated in 750 ml Erlenmeyer flasks filled with 40-50 ml of medium on a shaker at 220 rpm and 29 °C for 48-72 h until the maturation of culture, accompanied by the formation of spores and crystalline endotoxin. On the basis of BtH1 800/15 and BtH10 25 strains, batches of liquid preparations were obtained, the effectiveness of which was evaluated in 2020 and 2021 on potatoes ( Solanum tuberosum L.) of the Yantar variety in the Far East (Ussuri district of Primorsky Krai) against Henoseplachna vigintioctomaculata Motsch and on potatoes of the Emelya variety in the Tambov region against Leptinotarsa decemleniata Say. In the experiments, liquid preparations obtained on YPM and MMBt were used, which were used at consumption rates of 15 and 20 l/ha. The biological effectiveness of the preparations was calculated according to the formula W.S. Abbot. The antifungal activity of the preparation BtH10 25, obtained on MMBt and YPM, was determined by the method of agar blocks in vitro in Petri dishes. The control medium was used without the addition of drugs. Fungi Botrytis cinerea Pers (strain C-5) and Bipolaris sorokiniana (Sacc.) Shoemaker (strain C-20) serv