Synergisitic effect of chitinases andBacillus thuringiensis israelensisspore-toxin complex againstAedes aegyptilarvae

Abstract

AbstractSix subspecies ofBacillus thuringiensisBerliner (Bt) were grown in minimal medium with chitin as the sole carbon source for 6 days to obtainBtcell-free fermented broths, which were then evaluated for chitinolytic activity and tested against third-instarAedes aegypti(L.) (Diptera: Culicidae) larvae.Bt pakistanishowed the highest chitinolytic activity (approximately >2700 mU/mL),Bt kurstakishowed the lowest activity (approximately <2000 mU/mL), andBt thompsoni,Bt aizawai,Bt israelensis, andBt alestishowed intermediate activities (approximately 2100–2400 mU/mL).Bt aizawaiandBt thompsonibroths showed the highest toxicity (LC50) against third-instarA. aegyptilarvae (approximately <290 mU/mL).Bt kurstakibroth showed the lowest toxicity (approximately 420 mU/mL), whileBt pakistani,Bt israelensis, andBt alestibroths showed intermediate toxicities (approximately 360–460 mU/mL). A purified and biochemically characterizedBt aizawaichitinase and commercial chitinases (fromSerratia marcescensBizio andStreptomyces griseusWaksman and Henrici) were evaluated and compared for synergistic effects onBt israelensisspore-toxin complex against third-instarA. aegyptilarvae. The synergism factor value ofStreptomyces griseusandBt aizawaichitinases were >2 and approximately 1.4; synergism was not evident for theSerratia marcescenschitinase (synergism factor value approximately 0.9).