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Production of delta‐endotoxin by Bacillus thuringiensis subsp kurstaki and overcoming of catabolite repression by using highly concentrated gruel and fish meal media in 2‐ and 20‐dm 3 fermenters

2002; Wiley; Volume: 77; Issue: 8 Linguagem: Inglês

10.1002/jctb.650

1097-4660

Nabil Zouari, Omar Achour, Samir Jaoua,

Insect and Pesticide Research

Abstract Delta‐endotoxin production by a strain of Bacillus thuringiensis subsp kurstaki exhibiting larvicidal toxicity towards lepidoptera was investigated in 2‐ and 20‐dm 3 fermenters, using gruel‐ and fish meal‐based media. The results show clearly that in such complex media, aeration plays an important role in bioinsecticide production. Optimal aeration led to improvement of delta‐endotoxin concentrations with decreases of final spore count and proteolytic activity. Moreover, in order to use high gruel concentrations, a fermenter configuration with an efficient aeration system should be used. In a 20‐dm 3 Biolafite fermenter, 59 g dm −3 or 75 g dm −3 gruel was used to produce bioinsecticides with a significant reduction of carbon catabolite repression of delta‐endotoxin synthesis. This result is very interesting in order to produce high final delta‐endotoxin concentrations in the culture broth. It was also concluded, by considering the key role of oxidative pathways in delta‐endotoxin synthesis, that oxygen supply must be adequate for bioinsecticide production at high substrate concentrations. Moreover, the role of sodium chloride in improving delta‐endotoxin production is dependent not only on protease synthesis and its effect on crystal stability, but also on the aeration level of the production medium. © 2002 Society of Chemical Industry