| dc.description.abstract | Bacillus thuringiensis (Bt) are gram-positive, soil-dwelling, spore-forming, rod-shaped bacterial species possessing insecticidal properties. The objectives of this study were to screen for Aedes aegypti larva killing Bt strains from soil samples collected from different localities in Vietnam. The study also initially investigated the effects of different media on the Bt growths and their crystal protein and endospore production. From 23 soil samples, 44 different bacterial colonies were obtained, 10 (22.73%) of those were identified as Bt-like bacteria based on their morphological characteristics. The Bt isolates were grown on T3 and H.de Barjac media for the preparation of spore crystal proteins mixture. Microscopic observations showed that T3 medium was better medium for sporulation and crystal spore formation while H.de Barjac was more suitable for cell growth. These would be also the reason explaining for the fact that the isolates cultured on T3 medium showed higher toxicity against A. aegypti larvae. Generally, 50% lethal concentrations of the studied the isolates were quite high, the most potential isolate was NB3 collected from Ninh Binh province, of which the LC50 was 1577.67μg/ml. The identification of selected Bt isolates were then confirmed by the presence of Cry genes. Key words: Bacillus thuringiensis, Aedes aegypti, crystal protein, spore crystal mixture, 50% lethal concentration. | en_US |
