Insects endotoxin

B. thurigiensis is a common Gram-positive, spore-forming soil bacterium that produces inclusion bodies, microcrystalline clusters of many different proteins. These crystalline proteins, called 5-endotoxins, are the ion channel toxins that are sold commercially for pest control. Most such endotoxins are protoxins, which are inactive until cleaved to smaller, active proteins by proteases in the gut of a susceptible insect. One such crystalline protoxin. 

The crystal formed by any given strain of crystalliferous bacterium is a constant and a strain function. Constancy of insect susceptibility spectra for given bacillus strains tells us this, and differences between strains indicate uniqueness. Krywienczyk and Angus (22) demonstrated that dissolved endotoxins of strains of B. thurin-... 

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. 

Different subspecies have been shown to be active against different orders of insect. Although the method of insect death is the same, the different endotoxins either have different binding regimes or are activated by the gut enzymes of different insect species and this leads to the differences in activity spectrum. There is evidence, however, that different insect orders act upon the delta-endotoxins in different ways. Treatment of a pro-toxin with lepidopteran gut juice leads to a toxin that is active against Lepidoptera whereas treatment with dipteran gut juice produces... 

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. 

Fig. 9.5 Molecular cloning and expression of Factor C in the baculo viral system and expression in insect cells produced an rFC with remarkable sensitivity of 0.001 EU/mL endotoxin. (B BamHl, E EcoRI, X Xhol, H Hindlll, P PstI, N Ncol)...

Table IV. Symptoms elicited after the injection of alkaline-dissolved BTI 6-endotoxin (Track 2) into mice and insects...

A number of other lines of evidence also suggested that there may be another mode-of-action for BTI poisoning by injection other than its known, general cytolytic activity (3,22-24). Using the appearance of cytosolic lactate dehydrogenase (LDH) in insect hemolymph post-injection as a marker for cytotoxicity (36-37), we found that dissolved BTI 6-endotoxin was a potent cytotoxin. When T. ni, however, were injected with dissolved BTI 5-endotoxin and then incubated at 28, 15, and 9°, there was an increase in the LD50 with a decrease in temperature (Figure 2) but the LDH levels at 3.5 PPM BTI were unaffected by temperature. 

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 ... 

Reduced binding of toxin is a primary mechanism of insect resistance to Cry proteins (Ferre and Van Rie, 2002). Resistance of the Indian meal moth to Bt was due to a 50-fold reduction in affinity of the membrane receptor (from brush borer membrane vesicles of larval midguts) for 5-endotoxin. In pinkbollworms, Bt resistance is associated with reduced binding of CrylAb to the brush borer membrane vesicle. Similarly, CrylAc resistance in diamondback moths was demonstrated to be due to dramatically reduced target binding. 

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)... 

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. 

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