| Bacillus thuringiensis (Bt) is a fascinating bacterium, producing a number of toxins which have spawned a whole industry and forms the basis of over 90% of all biopesticides currently sold around the world. Bt has been in commercial for over 60 years. For many years, it was regarded as a "safe" biopesticide, with toxicity limited to a few Lepidoptera and no indications of mammalian or non-target impacts. But knowledge of Bt had rapidly advanced; each year new strains and toxins have been identified and the whole picture of what constitutes Bt has become more confused. With the isolation of new Bt strains came the discovery of Bt activity against a greater range of organisms, which worked against one of the original safety tenets that Bt was specific to Lepidoptera. In a purified form, some of the proteins produced by Bt are acutely toxic to mammals. However, in their natural form, acute toxicity of commonly-used Bt varieties is limited to caterpillars, mosquito larvae, and beetle larvae. Bt is closely related to B. cereus, a bacterium that causes food poisoning and to B. anthracis, the agent of the disease anthrax. A few studies have been conducted on the chronic health effects, carcinogenicity, or mutagenicity of Bt. Public concern over Bt safety is increasing.The presence of hemolysin HblA (HblA), enterotoxin T(BceT) and enterotoxin (Ent) genes from 45 strains of B. thuringiensis (from BGSC) and 16 strains of B. thuringiensis (from our lab) have been detected respectively by polymerase chain reaction (PCR). The results showed that 60% Bt strains of BGSC contained hblA gene sequences, 66.7% and 44.7% of them contained bceT and ent genes sequences respectively. These strains from BGSC include 44 H-serotypes, 44 serovars. Therefore, the enterotoxin genes were proved present extensively in B. thuringiensis strains. Sequencing and analysis of the hblA, bceTand ent gene fragment of 8010 showed that the fragment of hblA and bceT gene is 96-99% identical to the similar gene of Be, the fragment of ent gene is 94-99% identical to the similar gene of Be or BaPlasmid DNA and chromosomal DNA of 8010 was extracted to determine the localization of ent gene. Both of them were blotted onto a sheet of nylon membrane (Hybond N+) respectively, and allowed to hybridize with a probe specific to ent gene. The result indicated that ent gene of 8010 is in the chromosome.The ORF of ent gene from Bt 8010,WB9, TS16, 1072 and Be 6A1 have been cloned and sequenced. Analysis by blast online showed that ent gene of 8010 is very high homologous with the known enterotoxin gene of B cereus and B. anthracis. The predicted amino acid sequence of these Bt strains was analyzed to understand the protein. The result showed that the N-terminal portion, which consists of 26 amino acid residues, appeared to be a signal peptide sequence; The protein has a repeating Gln-Thr sequence around residue 40. Sequence comparisons revealed that there is high homologous between 4 Bt strains and Be Cx5, the main difference between 8010 and Be Cx5 is that there are 4 amino acids (Gln-Thr-Gln-Thr) deleted around residue 40 in the protein of 8010 and several another amino acids added in the protein of Be Cx5.Four strains, HD2 and HD9, which are high enterotoxin activity tested with tow commercially available kit (BECT-RPLA and VIA SLISA), Bt WB9 and Be 6A1 were used for rat acute oral toxicity testing with high doses of ferment filter. The result showed that there was no discernible difference in the behavior or condition of any of the animals during the trial, nor ill-effects in pathology of their internal organs.It is not confirmed whether Bt enterotoxin is safe or not. There are still some...
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