Screening For Cry Genes From Bacillus Thuringiensis In Various Textural Classes Of Southwest Missouri Soils


Meghan Carter

Date of Graduation

Fall 2002


Master of Science in Biology



Committee Chair

John Steiert


Bacillus thuringiensis is a gram-positive endospore-forming bacterium that produces an insecticidal δ-endotoxin during sporulation. The δ-endotoxin consists of an inactive protein toxin crystal (protoxin) that becomes activated by the alkaline conditions in the intestinal lumen of specific insect species. Genes that code for the crystal protoxins (cry genes) are carried on plasmids. Multiple cry genes may be found in a single B. thuringiensis strain on one or more plasmids. The bacteria are found in a variety of environments, primarily in soil. Environmental strains of B. thuringiensis were isolated from 21 soil samples and each soil sample was classified texturally based on percentage of sand, silt, and clay. Population densities were used to analyze the frequency of B. thuringiensis and Bacillus isolates in each soil sample. Results indicated textural soil classification did not influence the populations of Bacillus or B. thuringiensis. However, the textural composition of the soil may affect the expression of certain cry genes. PCR was employed to screen the B. thuringiensis isolates for the presence of cry genes. Universal (Un9(d), Un9(r)) and specific primers (CJIII20, CJII21) were used in the screening process. The PCR products of the environmental isolates were compared to PCR products from known strains of B. thuringiensis. PCR products were cloned into E. coli plasmids and sequenced to identify the cry gene class for environmental isolates and to identify possible novel cry genes.

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© Meghan Carter