Dual production of amylase and δ-endotoxin by Bacillus thuringiensis subsp. kurstaki during biphasic fermentation

Abstract

This study examined the efficacy of a Bacillus thuringiensis (Bt) strain in producing amylase (EC 3.2.1.1) as a by-product without affecting its unique ability for producing δ-endotoxin, thus to establish a cultivation strategy for the dual production and recovery of both δ-endotoxin and amylase from the fermented medium with an industrial perspective. LB medium was individually supplemented (5 to 100%, wt/vol) with flour from six naturally available starchy stored foods (banana, Bengal gram, jack seed, potato, taro or tapioca); after initial fermentation (12 h), the supernatant in the medium obtained by centrifugation (1000 g, 10 min) was used for harvesting amylase and the resultant pellet was further incubated aseptically for the production of endospores and δ-endotoxin by solid-state fermentation. Maximum crude amylase activity (867 U/gram dry substrate, 12 h) was observed in potato flour-supplemented medium (10% wt/vol, 12 h), while the activity in LB control was only 4.36 U/mL. SDS-PAGE profile of the crude (supernatant), as well as partially purified (40–60% (NH4)2SO4 fractionation) amylase showed that its apparent molecular mass was 51 kDa, which was further confirmed by native PAGE. The harvest of industrially significant extracellular amylase (probably α-amylase) produced as a byproduct during early growth phase would boost the economics of the Bt-based bio-industry engaged in δ-endotoxin production.