UNIQUE REGULATION OF CRYSTAL PROTEIN PRODUCTION IN BACILLUS-THURINGIENSIS SUBSP YUNNANENSIS IS MEDIATED BY THE CRY PROTEIN-ENCODING 103-MEGADALTON PLASMID

In sporulating cultures of Bacillus thuringiensis subsp yunnanensis HD 977, two cell types are observed: cells forming only spores and cells forming only crystals. Curing analysis suggested that the crystal prot eins are plasmid encoded. Through plasmid transfer experiments, it was established that a 103-MDa plasmid is involved in the crystal product ion. Conjugal transfer of this plasmid to Cry(-) recipient cells of Ba cillus thuringiensis subsp kurstaki HD73-26 conferred the ability to p roduce crystals exclusively on asporogenous cells of the recipient, in dicating that the 103-MDa plasmid mediates the unique regulation of Cr y protein production. When the dipteran-specific cryIVB gene was intro duced into wild-type (Cry(+)) and Cry(-) backgrounds of B-thuringiensi s subsp yunnanensis by phage CP51ts45-mediated transduction, similar t o all other B-thuringiensis strains, irregular crystals of CryIVB prot ein were produced by spore-forming cells in both backgrounds. However, the synthesis of the bipyramidal inclusions of B-thuringiensis subsp yunnanensis was still limited only to asporogenous cells of the transd uctant. Thus, it appears that the unique property of exclusive crystal formation in asporogenous cells of B-thuringiensis subsp yunnanensis is associated with the crystal protein gene(s) per se or its cis actin g elements. As the crystals in B-thuringiensis subsp yunnanensis were formed only in asporogenous cells, attempts were made to find out whet her crystal formation had any inhibitory effect on sporulation. It was observed that both Cry(+) and Cry(-) strains of B-thuringiensis subsp yunnanensis (HD977 and HD977-1, respectively) exhibited comparable sp orulation efficiencies. In addition, the Cry(-) B-thuringiensis subsp kurstaki host (HD73-26) and its Cry(+) transconjugant (HD73-26-16), ex pressing the B-thuringiensis subsp yunnanensis crystal protein, were a lso comparable in their sporulation efficiencies, indicating that prod uction of the crystal proteins of B-thuringiensis subsp yunnanensis do es not affect the process of sporulation.