The effect of complex carbon and nitrogen, salt, Tween-80 and acetate on delta-endotoxin production by a Bacillus thuringiensis subsp kurstaki

Delta-endotoxin production by a strain of Bacillus thuringiensis subsp kurs taki on complex media based on crude gruel and fish meal was investigated. High proteolytic activities were concomitantly produced with the bioinsecti cide. In such complex media, the repressive regulation due to readily consu med carbon sources was partially overcome. In order to improve substrate as similation, 0.5 g L-1 sodium chloride and 0.1% Tween-80 were supplemented t o the production medium, increasing delta-endotoxin yields when using gruel concentrations below 59 g L-1. At and beyond 75 g L-1 gruel, delta-endotox in yields were not affected in the presence of 0.5 g L-1 NaCl and 0.1% Twee n-80, but proteolytic activity yields were remarkably reduced. Thus, the us e of sodium chloride and Tween-80 allowed reduction of the initial gruel co ncentration to 42 g L-1 for the production of 3350 mg L-1 delta-endotoxin, while it was only 3800 mg L-1 with 92 g L-1 gruel. Moreover, similar to 0.5 g L-1 NaCl and 0.1% Tween-80, the use of 10 g L-1 sodium acetate significa ntly improved delta-endotoxin production and also reduced the proteolytic a ctivity to 250 U ml(-1).