EFFICIENCY OF INSECTICIDAL CRYSTAL PROTEIN-PRODUCTION IN A BACILLUS-THURINGIENSIS MUTANT WITH DEREPRESSED EXPRESSION OF THE TERMINAL OXIDASE AA3 DURING SPORULATION

A Bacillus thuringiensis respiratory mutant (AB1 strain) that shows pr emature sporulation and insecticidal crystal protein (ICP) production was isolated. The mutant strain harbours the cryIC and cryID insectici dal genes and could be important for the production of ICP highly toxi c to Spodoptera sp. The mutant was selected by its increased capacity to oxidize. N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD). In this s train, cytochrome aa3 expression is not repressed during the sporulati on phase, in contrast with the wild-type strain. The growth, spore pro duction, dissolved O2, O2 consumption, CO2 evolution rate and ICP prod uction were recorded as a function of time. The AB1 mutant strain has a similar growth yield to the wild-type strain, but begins sporulation at least 4 h earlier. The AB1 strain consumes 74.5% more O2 than the wild-type strain, during the fermentation process. The mutation on str ain AB1 has an important positive effect on ICP production. This proce dure shows that ICP production could be increased during fermentation by increasing the respiration capacity of Bacillus thuringiensis.