Alternative hosts for Bacillus thuringiensis delta-endotoxin genes.
1990
Feitelson J.S. | Quick T.C. | Gaertner F.
Bacillus thuringiensis (BT) is widely used as a microbial insecticide for control of lepidopteran, coleopteran and dipteran pests. The active component has been identified as a parasporal, crystal protein that is released along with a spore upon lysis of the BT during stationary phase. In general, agricultural application has been limited to the use of formulated spore-crystal mixtures that typically degrade within one to three days following application. Degradation appears to be due to a number of factors including: cycles in temperature and humidity, proteolytic and microbial activity, photooxidation, and chemical interactions. We have developed a novel pesticide delivery system that overcomes these drawbacks by effectively microencapsulating the pesticidal protein within a stabilized Pseudomonas flourescens (PF) cell. Biotoxin genes isolated from BT were introduced into PF with the appropriate plasmid vectors. The biotoxin expressed in PF formed a crystalline array similar to that seen in BT, with expression levels up to 30%. Unlike BT, the cells of PF did not lyse, nor did they sporulate, during stationary growth. A chemical fixative was added to the complete fermentation broth to rapidly kill the biotoxin-containing PF and to simultaneously stabilize the cells. This stabilization process strengthened the cell wall by crosslinking, and inactivated biotoxin degrading proteolytic enzymes. The process resulted in an active stable biotoxin encapsulated within a nonviable cell. The bioencapsulated products (MCap) exhibited enhanced field persistence and are environmentally acceptable; the microorganism will not spread from the site of application. This delivery system is potentially applicable to a variety of pesticidal proteins.
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