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this is the summary of bacillus thuringinesis,
it provide basic information about bt toxin

Veröffentlicht in: Wissenschaft
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  1. 1. Biopesticide Bt toxin/bacillus thuringinesis
  2. 2. Introduction • Biopesticide are toxic substances produced by living organisms that can specifically kill a particular pest species. • Some characteristics of pesticide : 1. Narrow target range 2. Specific mode of action 3. Slow acting & short residue effect 4. Safer to human & environmental than chemical pesticide.
  3. 3. Continued……. • It is estimated that about 15% of world crop yield is lost due to pest or insect attack. • The majority of insect that damage crop belong to the following order. 1. Lipidoptera (ballworm) 2. Coleoptera (bettles) 3. Orthoptera (grasshoppers) 4. Homoptera (aphids)
  4. 4. Bacillus thuringinesis • It was first discovered by Ishiwaki in 1901,but its commercial importance was ignored until 1995. • B.thuriginesis is a gram negative soil bacteria. • This bacteria produces a parasporal crystalline proteinous toxin with insecticidal activity. • The protein produced by B.thuringinesis is reffered as insecticidal crystalline protein(ICP).
  5. 5. Insecticidal crystalline protein • ICP are endotoxin protein produced by sporolating bacteria & were originally classified as delta endotoxin. • The commercial mixture usually contain spores, crystal protein & inert carriers. • it may be mixed with chemical insecticides or fungicides. • The crystal protein activity usually disappears with in 24-48 hours after application.
  6. 6. Bt toxin genes • Several strain of B.thunginesis producing a wide range of crystal (cry) proteins have been identified. • Cry gene is responsible for crystal protein. • The cry genes are classified into a large no. of distinct families (about 40), based on their size & sequence similarities. • The molecular weight of cry proteins may be either large (130 kDa) or small (70kDa).
  7. 7. Mode of action of Cry protein • When this parasporal crystal is ingested by the target insect, the protoxin gets activated with in its gut by a combination of alkaline pH (7.5 to 8.5) & proteolytic enzymes. • This result in conversion of protoxin into a active toxin . • The active form of toxin protein gets itself inserted into the membrane of the gut epithelial cells of the insect.
  8. 8. Continued……… • This result in formation of ions channels through which there occurs an excessive loss of cellular ATP. • As a consequence , cellular metabolism ceases, insect stop feeding & becomes dehydrated & finally dies. • The Bt toxin is not toxic to human & animals since the conversion of protoxin to toxin require alkaline pH & specific proteases. • These are absent in human & animals.