PHAGE DISPLAY OF A BIOLOGICALLY-ACTIVE BACILLUS-THURINGIENSIS TOXIN

Activated forms of Bacillus thuringiensis insecticidal toxins have con sistently been found to form insoluble and inactive precipitates when they are expressed in Escherichia coli. Genetic engineering of these p roteins to improve their effectiveness as biological pesticides would be greatly facilitated by the ability to express them in E. coli, sinc e the molecular biology tools available for Bacillus are limited. To t his end, we show that activated B. thuringiensis toxin (Cry1Ac) can be expressed in E. coli as a translational fusion with the minor phage c oat protein of filamentous phage. Phage particles displaying this fusi on protein were viable, infectious, and as lethal as pure toxin on a m olar basis when the phage particles were fed to insects susceptible to native Cry1Ac. Enzyme-linked immunosorbent assay and Western blot ana lysis showed the fusion protein to be antigenically equivalent to nati ve toxin, and micropanning with anti-Cry1Ac antibody was positive for the toxin-expressing phage. Phage display of B. thuringiensis toxins h as many advantages over previous expression systems for these proteins and should make it possible to construct large libraries of toxin var iants for screening or biopanning.