Chitinase produced by Bacillus thuringiensis var .israelensis (Bti) may play a role in the activity of Culex pipiens larvae as biopesticide. The toxicities of suspended culture pellet and supernatant of Bti(NRRL HD-522) were assayed toward laboratory reared second and third-instar larvae. The results showed 100% mortality after 30 min with 2.4x102 spores/mL, 50% and100% mortality after 6 and 12h respectively with 0.024x102 cfu/mL .Each portion of 1000, 500, 250 and 100 µL of culture supernatant persisted to eliminate all larvae during the daytime experimental period. No larvaecidal activity occurred in containers treated with portions of 50 µL (or less) of culture supernatant. The chitinase activity was the highest culture supernatant concentration at 3.5U/mL .Chitinase gene from (Bti) was cloned and expressed in Escherichia coli. The gene sequence alignment showed 99% similarity to Chi36 of Bti HD-789 (accession number: CP003763). The sequence result was submitted into GenBank under accession number JX474751. The expressed chitinase reached maximal activity after 2 h of incubation (about 133.4U/mL) in liquid medium. Also, did not exhibit any insecticidal activity at maximum concentration obtained in the bioassay experiment (about 57.5 U/mL) toward second and third-instar C.pipiens larvae. |
