Distribution and characterization of mosquitocidal toxin genes in some strains of Bacillus sphaericus

Abstract

The binary toxin of Bacillus sphaericus strains forms a crystal in sporulating cells, while the mosquitocidal toxin is located in the cytoplasm of vegetative cells. The distribution of binary toxin (btx) and mosquitocidal toxin (mtx) genes in 53 strains of B. sphaericus was determined by hybridization of specific gene probes to chromosomal DNA in Southern blots. btx genes were found in all strains of serotype 5a5b examined and in some strains of serotypes 1a, 3, 6, 25, and 48, while mtx genes were detected in strains of serotypes 1a, 2a2b, 5a5b, 6, 9a9c, 25, and 48. Serotype 26a26b strains lacked both toxin genes, as did some strains of serotypes 2a2b, 3, 6, and 48. Partial DNA sequences of btx genes from five strains, together with published sequences, revealed four types of toxin among mosquitocidal B. sphaericus strains. Most of the 42-kDa toxin gene of btx was identical in strains from serotypes 1a, 3, 6, and 48, and the gene is here classified as a type 1 btx gene. A serotype 3 strain isolated in Singapore possessed a unique 42-kDa toxin gene, here designated type 4; while the btx genes from strains of serotypes 5a5b and 25 are referred to as types 2 and 3, respectively.

Identification and molecular structural prediction analysis of a toxicity determinant in the Bacillus sphaericus crystal larvicidal toxin

“…The total lack of toxicity of the native Bin4 binary toxin indicates that it cannot account for the larvicidal activity of strain LP1-G on both B. sphaericus-susceptible and B. sphaericus-resistant C. pipiens colonies (data not shown). Although lower than that of strain 1593, the toxicity of strain LP1-G is significant, as also reported by Priest et al [7], and cannot be attributed to Mtx1, as the gene encoding this toxin is not present [7]. Besides, Mtx toxins (1, 2 and 3) are only present during the vegetative growth stage [6].…”

“…The bin genes of several highly toxic strains have therefore been completely sequenced, and their amino-acid sequences have been found to be highly conserved [23]. The distribution of Bin and Mtx toxin genes among 53 B. sphaericus strains of various serotypes has been determined and the genes have been partially characterized, demonstrating an extremely high level of similarity [7]. However, strain LP1-G has a different amino-acid sequence [24] and slightly lower levels of larvicidal activity than the highly active B. sphaericus strains [IAB59 (type 1), 1593 (type 2) and 2297 (type 3)] [7].…”

“…The distribution of Bin and Mtx toxin genes among 53 B. sphaericus strains of various serotypes has been determined and the genes have been partially characterized, demonstrating an extremely high level of similarity [7]. However, strain LP1-G has a different amino-acid sequence [24] and slightly lower levels of larvicidal activity than the highly active B. sphaericus strains [IAB59 (type 1), 1593 (type 2) and 2297 (type 3)] [7]. The sequence of the BinA subunit of strain LP1-G (type 4) differs from those of the three other types of Bin toxin at six positions.…”

Interaction of Lysinibacillus sphaericus Cry48Aa/Cry49Aa toxin with midgut brush‐border membrane fractions from Culex quinquefasciatus larvae

“…High-toxicity strains exhibit toxicity against Culex and Anopheles species but are almost inactive against Aedes species (Baumann et al, 1991;Charles et al, 1996). The mosquitocidal activity predominantly relies on binary (Bin) toxins (BinA/BinB proteins), which form crystal inclusions during sporulation (Priest et al, 1997). Some strains, such as IAB59, 47-6B and NHA15b, have been shown to produce a unique twocomponent toxin during sporulation, consisting of Cry48Aa (135 kDa) and Cry49Aa (53 kDa) (Jones et al, 2007), representing a new insecticidal combination that acts in synergy and presents optimal toxicity at equimolar concentration.…”

Lack of cross‐resistance to Mtx1 from Bacillus sphaericus in B. sphaericus‐resistant Culex quinquefasciatus (Diptera: Culicidae)

“…1 The other is mosquitocidal toxin (Mtx) synthesised during the vegetative phase of growth both in low-activity strains and some highly toxic strains. 1,2 Although the purified Mtx toxins have high activity against a variety of mosquitoes, they only play a minor role in the overall toxicity of the highly toxic strains owing to their low expression level, as well as their liability to proteinases. 3 Mtx1, which was initially isolated from a lowtoxicity B. sphaericus strain SSII-1, is a 100 kDa mosquitocidal protein.…”