We are surrounded by many small organisms which are not illustrated to our naked eyes. These limited organisms are called as microorganisms. The base microorganisms which are present in our environment include bacteria, viruses, protozoans etc. Some of them are beneficial and some are the causative agents of harmful diseases. One such beneficial bacterium is the Bacillus thuringiensis which belongs to the kingdom Eubacteria and class Bacili. The name Bacillus thuringiensis was given by Berliner in 1915. Bacillus thuringiensis is de facto a Gram confident bacterium which dwells in soil and is generally used as a pesticide. It has also been reported in the gut of many caterpillars and moths and also in some plants.
Bacillus thuringiensis was first discovered by a Japanese biologist Shigetane Ishiwata in 1901. It was rediscovered in 1910 in Germany by Ernst Berliner as a causative agent of disease in the flour moth. Bacillus thuringiensis is closely associated to B. Cereus which is a soil bacterium and B. Anthracis which causes anthrax. These three differ in their plasmids. All these three are aerobes and share in endospore formation. During sporulation B. Thuringiensis produces proteinaceous crystals called δ-endotoxins which are encoded by cry genes and have insecticidal properties. These cry genes are found in the plasmid of the bacterium. The cry toxins are found to be toxic to the organisms like moths, butterflies, mosquitoes, flies, beetles, wasps, bees, ants and nematodes. So it is clear that B. Thuringiensis is helpful in the output of pest resistant crops. When the insects ingest the cry toxins the alkaline medium of their gut causes activation of these toxins which cause lysis of the cell membrane of the gut and ultimately resulting in death of the insect.
The crystalline proteins produced by B. Thuringiensis possess insecticidal properties so have been used against insect pest control since 1920s. They are specifically used with the trade names Dipel and Thuricide. The insecticides prepared with the crystalline proteins of B. Thuringiensis are environmental cordial and have no or limited side succeed on humans, animals and insect pollinators. Plants Genetic Systems a Belgian business in 1985 for the first time developed the genetically modified plants by incorporating the cry genes of B. Thuringiensis in them. B. Thuringiensis based insecticides are also used in the form of sprays which are later on ingested by the pests and it results in the lysis of the gut and ultimately death of the pest. A strain of B. Thuringiensis known as Bacillus thuringiensis serovar israelensis is succeed against the mosquito control.
B. Thuringiensis have been incorporated in crops specially the cotton and the corn and have resulted in yield growth when planted in the fields for the first time in 2006. It is believed that the Bt crops are a boon to the poor farmers. There are several advantages of using the Bt crops as the expression of toxin can be very high and so sufficient dosage can be delivered to the pest. The toxin level can be additional enhanced or lowered depending upon the severity of the pest. There are confident limitations of the B. Thuringiensis produced toxins also as quarterly use of these toxins can make the pest resistant to the toxins and thus reducing the crop yield. According to a narrative of 2009 the pink bollworm a serious pest of cotton has become resistant to the B. Thuringiensis produced toxins in Gujarat, Junagarh, Bhavnagar, Rajkot and Amreli in India and thus, ineffective in killing of this hazardous pest. Many farmers also committed suicide in dissimilar states of India because of this reason. This resistance of pest against the B. Thuringiensis produced toxins was first confirmed by Monsanto scientists. Chinese farmers have also reported the same question as after growing the Bt cotton for ten years continuously the pests of cotton became resistant against the B. Thuringiensis produced toxins. Similar problems with the mealy bugs have also been reported in India. The Bt crops have also been found to kill the Monarch Butterfly as the pollen also contains the toxins. The toxins in the pollens are present in very small quantity but are sufficient to kill the butterfly. Bt crops are also known to work on the honey bee colonies.
So it can be accomplished that B. Thuringiensis although has some beneficial effects shares negative properties also.
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