Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) of crude extracted insecticidal crystal proteins of Bacillus thuringiensis and Brevibacillus laterosporus

Abstract

Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) was conducted to determine the number and size of the insecticidal crystal proteins (ICPs) synthesized by four isolates of entomopathogenic spore-forming bacteria. Only three of the four bacteria produced ICPs with SDSPAGE profiles, of which two were strains of Bacillus thuringiensis and one was a strain of Brevibacillus laterosporus. Large sized proteins bands were present in the range of 73 kDa to 135 kDa for the B. thuringiensis strains. All the three isolates had smaller proteins in the range of 13 kDa to 44 kDa. One strain of B. thuringiensis, NDR11, produced an unusual large protein of 200 kDa. Small proteins in the range of 24 kDa to 40 kDa were produced by B. laterosporus. The Cry ICPs of isolate NDR3 did not produce any electrophoretic bands, indicating that its ICP did not dissolve under the conditions used.

Key words: Insecticidal crystal proteins, entomopathogenic bacteria.