Bacteria Genomes - BACILLUS THURINGIENSIS

B. thuringiensisare Gram-positive spore-forming, rod-shaped aerobic bacteria in the genus Bacillus.

B. thuringiensis is an insecticidal bacterium, marketed worldwide for control of many important plant pests - mainly caterpillars of the Lepidoptera (butterflies and moths) but also mosquito larvae, and simuliid blackflies that vector river blindness in Africa. B. thuringiensis products represent about 1% of the total 'agrochemical' market (fungicides, herbicides and insecticides) across the world. The commercial B. thuringiensis products are powders containing a mixture of dried spores and toxin crystals. They are applied to leaves or other environments where the insect larvae feed. The toxin genes have also been genetically engineered into several crop plants

B. thuringiensis products are produced commercially in large industrial fermentation tanks. The bacterial cells usually produce a spore and a crystalline protein toxin - called an endotoxin - as they develop. Most commercial B. thuringiensis products contain the protein toxin and spores, but some contain only the toxin component. When B. thuringiensis is ingested by a susceptible insect, the protein toxin is activated by alkaline conditions and enzyme activity in the insect's gut. If the activated toxin attaches to specific receptor sites, it paralyzes and destroys the cells of the gut wall, allowing the gut contents to enter the insect's body cavity. Poisoned insects may die quickly from the activity of the toxin or may stop feeding and die within 2 or 3 days from the effects of septicaemia (blood-poisoning).

B. thuringiensis does not reproduce and persist in the environment in sufficient quantities to provide continuing control of target pests. The bacteria may multiply in the infected host, but because few spores or crystalline toxins are produced, few infective units are released when a poisoned insect dies. Consequently, B. thuringiensis products are applied much like synthetic insecticides. B. thuringiensis treatments are inactivated within one to a few days in many outdoor situations, and repeated applications may be necessary for some crops and pests.

Until the early 1980s, commercial B. thuringiensis products were effective only against caterpillars. In recent years, however, additional isolates that kill other types of pests have been identified and developed. The nature of the endotoxin differs among B. thuringiensis subspecies and isolates, and the characteristics of these specific endotoxins determine what insects will be poisoned by each product.

Spraying or dusting plants with spores of this bacterium appear to be an environmentally safe ways to attack pests such as the gypsy moth, the tent caterpillar, and the tobacco hornworm (which also attacks tomatoes).

References:

http://helios.bto.ed.ac.uk/bto/microbes/bt.htm
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/B/B.thuringiensis.html
http://www.websters-online-dictionary.org/definition/english/Ba/Bacillus.html