Vegetative proteins from Malaysian strains of Bacillus thuringiensis israelensis strains
(Bt 11, Bt 12, Bt 15, Bt 16, Bt 17, Bt 21 and Bt 22) and Bacillus sphaericus H-25 strains (Bs 1 and
Bs 2) were screened for haemolytic, cytotoxic and larvicidal activity. SDS-PAGE profiles of the
Bacillus thuringiensis strains studied consistently showed major bands of 33-37 kDa and 47
kDa. Bt 16 also showed two bands of 66 kDa and 45 kDa similar to the previously reported binary
vegetative protein, Vip1Ac (66 kDa) and Vip 2Ac (45 kDa). Both the Bacillus sphaericus strains
showed a 35 kDa band that was similiar to a previously reported vegetative protein, the Mtx2
protein. Bs 2 also contains a 37 kDa band, similar to another vegetative protein, the Mtx 3 protein.
With the exception of Bt 17 and Bt 21, vegetative proteins from all Bacillus thuringiensis and
Bacillus sphaericus strains were highly haemolytic to human erythrocytes, causing more than
75% haemolysis at the highest concentration of 200 µg/ml. High haemolytic activity was associated
with high cytotoxic activity with most of the haemolytic strains being indiscriminately cytotoxic
to both CEM-SS (human T lymphoblastoid) and HeLa (human uterus cervical cancer) cell lines.
Interestingly, the less haemolytic vegetative proteins from Bt 17 and Bt 21 demonstrated cytotoxic
activity comparable to that of the highly haemolytic vegetative proteins. Bt 21 displayed toxicity
towards both cell lines while Bt 17 was more toxic towards CEM-SS cells. Bioassay against Aedes
aegypti and Culex quinquefasciatus larvae revealed that vegetative proteins from the Bacillus
thuringiensis strains had activity against both species of larvae but vegetative proteins from
Bacillus sphaericus were weakly larvicidal towards Cx. quinquefasciatus only.