Genetic determinants of host ranges of Bacillus sphaericus mosquito larvicidal toxins

Abstract

The 51.4-kDa-41.9-kDa binary toxin produced by different strains of Bacillus sphaericus shows differential activity toward Culex quinquefasciatus, Aedes atropalpus, and Aedes aegypti mosquito larvae. The patterns of larvicidal activity toward all three mosquito species and growth retardation in A. aegypti have been shown to be due to the 41.9-kDa protein. By using mutant toxins expressed in Escherichia coli, insecticidal activity and growth retardation correlated with amino acids centered around position 100 of the 41.9-kDa protein. In its response to these toxins, A. atropalpus resembled C. quinquefasciatus rather than its congener, A. aegypti.

Cyt1A from Bacillus thuringiensis Synergizes Activity of Bacillus sphaericus against Aedes aegypti (Diptera: Culicidae)

“…Because the highest proportion of Cyt1A-to-spore-crystal was associated with the lowest synergism level, the higher proportion of Cyt1A in tests using crystal may also have contributed to the decreased synergism. However, the role of spores in the observed synergism cannot be ruled out because B. sphaericus 2362 spores have been shown to be toxic to Aedes (4).…”

Introduction of Culex Toxicity into Bacillus thuringiensis Cry4Ba by Protein Engineering

“…There are various approaches to broadening the insecticidal spectrum of B. thuringiensis, including introduction of toxin genes that code for separate insecticidal activities into a recipient bacterium (4,7,26), creating a bacterium that expresses a combination of toxins instead of a single toxin (46), and engineering mutant toxins with new or broadened insecticidal spectra (6,8). In these approaches, multiple gene constructs with separate mechanisms of action are useful to forestall resistance development.…”

Role of cysteine at positions 67, 161 and 241 of a Bacillus sphaericus binary toxin BinB

“…Significance of this interaction is emphasized in the work showing that amino acid at position 93 of BinA is important for biological activity of the toxin by playing a major role in the formation of BinA-BinB complex (15). Also, amino acids centered around position 100 in BinA which has been proved to be important for host ranges of binary toxin may play a part in BinA-BinB interaction (14). In order to explore the possible role of C67 and C161 of BinB in function of binary toxin, binding between BinA and BinB mutants were tested employing dot blot analysis.…”

“…In the same report, it was suggested that both Nand C-terminal regions of BinA are important for BinA-BinB interaction (8). Site-directed mutagenesis of amino acid positions 93, 99, and 104 of BinA revealed that these residues are crucial for toxicity and it was proposed that residues in this region might play a role in the formation of BinA-BinB complex (14,15). Interestingly, mutagenesis of charged residues (R97, E98, R101, and E114) in the same region showed that these charged residues are also essential for biological activity of binary toxin, but not involved in BinA-BinB interaction (16).…”