IDENTIFICATION OF A GENE FOR CYT1A-LIKE HEMOLYSIN FROM BACILLUS-THURINGIENSIS SUBSP MEDELLIN AND EXPRESSION IN A CRYSTAL-NEGATIVE BACILLUS-THURINGIENSIS STRAIN

A gene designated cyt1Ab1, encoding a 27,490-Da protein, was isolated from Bacillus thuringiensis subsp, medellin (H30 serotype) by using an oligonucleotide probe corresponding to the cyt1Aa1 gene, The sequence of the Cyt1Ab1 protein, as deduced from the sequence of the cyt1Ab1 g ene, was 86% identical to that of the Cyt1Aa1 protein and 32% identica l to that of the Cyt2Aa1 protein from B. thuringiensis subsp, kyushuen sis. The cyt1Ab1 gene was flanked upstream by a p21 gene, in the same orientation, encoding a 21,370-Da protein that showed 84% similarity t o the putative chaperone P20 protein from B. thuringiensis subsp, isra elensis and downstream, on the opposite strand, by a sequence showing 85% identity to the IS240A insertion sequence, The cyt1Ab1 gene was ex pressed at a high level in a nontoxic strain of B. thuringiensis subsp , israelensis in which large inclusions of the Cyt1Ab1 protein were pr oduced, Purified Cyt1Ab1 crystals were as hemolytic as those of the Cy t1Aa1 protein and were twice as hemolytic as those from the wild-type strain, Mosquitocidal activity toward Aedes aegypti, Anopheles stephen si, and Culex pipiens larvae was assayed, The toxicity of the Cyt1Ab1 protein was slightly lower than that of the Cyt1Aa1 protein for all th ree mosquito species, and Cyt1Ab1 was 150, 300, and 800 times less act ive toward Culex, Anopheles, and Aedes larvae, respectively, than were the native crystals from B. thuringiensis subsp. medellin.