Expression of mosquitocidal crystal protein genes in non‐insecticidal Bacillus thuringiensis subsp. israelensis

Bacillus thuringiensis NTB‐1 isolated from soil samples in Korea produces ovoidal parasporal inclusions with proteins of approximately 24–40 kDa in size. Although serological study indicated that the isolate has a flagella (H) antigen identical with subsp. israelensis, it seemed to be non‐insecticidal against Lepidoptera and Coleoptera as well as Diptera. To investigate the activity of non‐insecticidal B. thuringiensis transformed with insecticidal crystal protein genes, cryIVD and cytA genes of B. thuringiensis subsp. morrisoni PG‐14, highly toxic to mosquito larvae, were introduced into the isolate NTB‐1. The expression of mosquitocidal crystal protein genes in NTB‐1 was characterized by SDS–PAGE analysis and electron microscopy. The results showed that crystalline inclusions of host, CryIVD and CytA were stably expressed in the transformant. However, the mosquitocidal activity of transformant was similar to that of B. thuringiensis subsp. kurstaki Cry−B harbouring cryIVD and cytA genes, demonstrating that a synergistic effect by an interaction of both introduced insecticidal and resident non‐insecticidal crystal proteins was not observed.