A local isolate of Bacillus thuringiensis (B.t. 81) contained five dis
tinct plasmids Relative amounts of these plasmids varied at different
stages of growth.Two Cry- mutants of the strain maintained all plasmid
s. The mutants, however, exhibited some variations in the patterns of
large plasmids depending on the composition of culture medium even tho
ugh they failed to produce crystal protein. Restriction analysis of th
e plasmids was also carried out for future cloning studies.