8-Endotoxins Bacillus thuringiensis

Preparations of the bacterium Bacillus thuringiensis (BT) are applied as sprays to control insect pests on agricultural crops. The bacterium produces endotoxins that are highly toxic to insects. 

The key insect-specific bacterium is Bacillus thuringiensis and this is through the production of delta-endotoxins. It has been shown that if the endotoxins are applied to crops together with living spores of the bacterium, insect control is improved. It is common for living formulations to be sold. 

Manasherob, R., Ben-Dov, E., Zaritsky, A. and Barak, Z. (1994) Protozoan-enhanced toxicity of Bacillus thuringiensis var. israelensis - Endotoxin against Aedes aegypti larvae, Journal of Invertebrate Pathology 63 (3), 244-248. 

Figure 1. SDS-PAGG analysis of alkaline-dissolved Bacillus thuringiensis subspecies kurstaki (BTK) and israelensis (BTI) -endotoxin at 25 yg per track (1) BTK -endotoxin from Biochem Products - US Division (Salsbury Labs., Inc.), (2) BTI 6-endotoxin from Sandoz Inc., (3) BTI (Sandoz) -endotoxin purified by DEAE-anion exchange chromatography, (4) percipitate formed after dialysis of BTI (Sandoz) -endotoxin into pH 4.5 sodium acetate buffer, (5) soluble fraction after dialysis of BTI (Sandoz) -endotoxin into pH 4.5 sodium acetate buffer, (6) BTI (Sandoz) -endotoxin purified by Sephadex G-75 gel filtration chromatography at Rf 1.35, (7) at Rf 1.58, and (8) BTI strain IFC-1 -endotoxin from Biochem Products - US Division (Salsbury Labs., Inc.). S, molecular weights as indicated X1000 for bovine serum albumin (BSA), ovalbumin (OA), trypsin, and myoglobin. Reproduced with permission from Ref. 29. Copyright 1984, Academic Press, Inc.

Figure 5. SDS-Page analysis of alkaline-dissolved Bacillus thuringiensis israelensis (BTI) 6-endotoxin from Sandoz Inc. at 25 yg per track (1) BTI 6-endotoxin as prepared in Figure 1 (Track 2), (2) soluble fraction after dialysis of BTI 6-endotoxin into pH 4.5 sodium acetate buffer, and (3) 25K component from BTI 6-endotoxin after pH 4.5 percipitation and DEAE-anion exchange chromatography. S, molecular weight markers from top to bottom bovine serum albumin (68K daltons), ovalbumin (43K), and myoglobin (16K).

Bacillus thuringiensis Berliner (commonly known as Bt) is an insecticidal bacterium discovered in the early 20th century. The commercial Bt products are powders containing a mixture of dried spores and crystalline 8-endotoxin, but some contain only the toxin component. Both spores and toxin crystals are produced within the bacterial vegetative cell by Bt (Figure 4.12). Currently, there are six strains that possess specific activity against different insect species as follows ... 

Figure 4.12 Diagram of Bacillus thuringiensis showing the position of the protein crystal (5-endotoxin) and reproductive spore in the bacterial vegetative cell (actual size of cell is about 5 pm).

The most important bacterium is Bacillus thuringiensis. This is ingested by caterpillars with their food, and an endotoxin that is active against insects is produced in the course of further development. 

Bacillus thuringiensis (Bt) Bacteria produce endotoxins that kill insects and larvae (insecticide)... 

Li JD, Carroll J, Ellar DJ (1991) Crystal structure of insecticidal delta-endotoxin from Bacillus thuringiensis at 2.5 A resolution. In Nature 353 815-821. 

English L and Slatin SL (1992) Mode of action of delta-endotoxins from Bacillus thuringiensis A comparison with other bacterial toxins. Insect Biochemistry and Molecular Biology 22 1-7. 

Structural and functional studies of a synthetic peptide that mimics a proposed membrane inserting segment of a Bacillus thuringiensis delta-endotoxin have been conducted. An NMR study of a methanol solution of a synthetic 31-mer peptide corresponding to the sequence of a putative pore-forming segment of the CrylA(c) toxin showed that the peptide exists as an a-helix. Hie peptide forms discrete, characterizable channels in planar lipid bilayers. It is possible that this helix is a component of the transmembrane pore formed by Bacillus thuringiensis delta-endotoxins in vivo. 

Gonzales JMJ, Brown BS, Carlton BC (1982) Transfer of Bacillus thuringiensis plasmids coding for 6-endotoxin among strains of Bacillus thuringiensis and Bacillus cereus. Proc Nat Acad SciUS A79 6951-6955... 

In the course of sporulation, protein crystals are formed by the side of the spores. The toxic effect of Bacillus thuringiensis can be traced back primarily to 5-endotoxin which constitutes these para-sporal formations. Endotoxin crystals consist of silicon-containing, nucleotide-free protein, which is a protomer of molecular weight 373 000, consisting of basic units of 25 000 molecular weight (Faust and Esters, 1966 Lecadet, 1965 Angus, 1956 Spencer, 1968 Akune et al 1971). 

Barton, K.A., Whiteiey, H.R. and Yang, N.-S. (1987). Bacillus thuringiensis 8-endotoxin expressed in transgenic Nicotiana tabaccum provides resistance to Lepidopteran insects. Plant Physiol. 85,1103-1109. 

Knowles, B.H. and Dow, J.A.T. (1993). The crystal delta-endotoxins of Bacillus thuringiensis - models for their mechanism of action in the insect gut. Bio Essays 15,469-476. 

Hofmann, C., Luthy, P., Hutter, R. and Pliska, V. (1988). Binding of the delta-endotoxin from Bacillus thuringiensis to brush-border membrane vesicles of the cabbage butterfly (Pieris brassicae). Eur. J. Biochem. 173, 85-91. 

Simpson, R.M., Burgess, E.P.J. and Markwick, N.P. (1997). Bacillus thuringiensis delta-endotoxin binding sites in two Lepidoptera, Wiseana spp. and Epiphyas postvittana. J. Invertebr. Pathol. 70,136-142. 

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