[Screening of acrystalliferous mutants from Bacillus thuringiensis and their transformation properties]

After elevating growth temperature of YBT-1463 and other 8 Bacillus thuringiensis parental strains to 42 degrees C, 9 acrystalliferous(Cry-) mutants were obtained, and then a series of partial plasmid-cured mutants were further obtained from 3 Cry- mutants BMB151, BMB154 and BMB160 by elevating temperature to 44 degrees C. One of which, BMB170, was further treated by elevating temperature to 46 degrees C and adding 0.05% SDS as the plasmid-curing agent. The resulting mutant, which was designated BMB171 and had no resident plasmid, was finally obtained. The studies on the transformation efficiency and stability of Cry- mutants showed that the transformation frequencies, as well as stability of several exogenous plasmids(pHT3101, pBMB1736, etc.) introduced into Cry- mutants by electroporation, were correlated with the numbers of resident plasmids bearing by the relevant recipients, the patterns of plasmid replicons and the sizes of those exogenous plasmids. Meanwhile, a much higher electro-transformation frequencies of Cry- mutants than the parental strain YBT-1463 was found, and the highest of the transformation frequency, in BMB 171, could reach up to 10(7) transformants/microgram DNA, and the stability of those exogenous plasmids in BMB171 were also higher than in other Cry- mutants and YBT-1463 strain.