Bacillus thuringiensis
Bacillus thuringiensis(Bt) is a gram-positive bacterium which
has been isolated from many habitats.
1
It produces different
insecticidal parasporal crystal proteins coded by cry genes
which may be present on plasmids or chromosomal DNA
during the stationary phase of its growth cycle.
2,3
Among
these Cry1 halotype protein toxins form the largest class of
insecticidal crystal proteins which are produced as protoxins
(ca. 130 kDa). The active toxins are approximately half the
sizes of the protoxins. The activation process involves
removal of 25e30 amino acids from the N-terminus and
approximately half of the remainder of the C-terminus
4