Cultivation of Bacillus thuringiensis subsp. kurstaki S93 in a fed-batch process: effect of the ratio glucose to yeast extract concentrations in the feeding culture media

The feeding media was studied in a fed-batch process for production of the complex spore-d-endotoxin by B. thuringiensis S93. The microorganism was first cultivated in a initial batch followed by an exponential feeding (m = 0,25 h super(-1)) with concentrated culture media (160 g glucose/L) containing different ratios of glucose and autolysed yeast: 8/7, 8/4 and 8/2 (g/g). The batch culture medium was composed of glucose (8 g/L), autolysed yeast (7 g//L) and mineral salts. Sporulation and d-endotoxin production were observed only after the end of feeding. To compare the experiments, batch cultivations were also performed with an initial concentration of 8 g/L of glucose and the same ratio of glucose and autolized yeast. Batch cultivations reached lower concentrations of total biomass and spores than the fed-batch ones and percentages of sporulation higher than 80%. The 8/7 ratio fed-batch cultivations reached the highest biomass concentration, producing however a very low level of sporulation (27%) and virtually no d-endotoxin. Cultivations with 8/4 and 8/2 ratios reached the highest concentrations of spores. In those assays, the maximum spores concentration and the maximum sporulation percentage were 8,3 times 10 super(9) spores/mL and 90% for the 8/4 ratio and 5,6 times 10 super(9) spores/mL and 89% for the 8/2 ratio.