Susceptibility of Bacillus thuringiensis spores and toxin to UV-C (254nm) of
the solar spectrum reaching earth's surface may be responsible for its inactivation and
low persistence in nature. Spores of the Bt israeiensis (1977 &HD522) were more
resistant to UV-C radiation than spores of at tenebrionfs (tt4) and the isolated strain
(66). Maximum molluscicidal activities were obtained following successive rounds of
exposing the 2 strains; tt4 and 66 to UV-C. The mutants obtained designated as 6615c
& tt4/2a showed 100% mortality of Biomphalarla a/exandrina snails, while their
parental strains showed 60% & 80% of mortality, respectively. The highly toxic
mutants derived from at. (66 & tt4) appeared to produce number of crystals more than
that of their parental strains. The protein pattems at these mutants indicated that they
produced polypeptide of 65 KDa or its derivatives that caused high toxicity of these
mutants. ,.. ~ DNA profile of some mutants was established by using polymerase
chain reaction (PCR). 111e PCR screen can identify mutants with altered
electrophoretic panerns containing novel genes.