Solid-State Fermentation for the Concomitant Production of δ-Endotoxin and Endospore from <i>Bacillus thuringiensis</i> subsp. <i>kurstaki</i>

Abstract

Water stress and limited aeration imparted by solid-state fermentation (SSF) were reported as crucial factors for the enhancement of endospore production by Bacillus thuringiensis ( Bt ); and thus, more δ -endotoxin could be produced concomitantly with reduced time. Therefore, Bt subsp . kurstaki ( Btk ) was employed in the present study to evaluate its efficiency for the concomitant production of endospores and δ -endotoxin in LB medium supplemented with various naturally available agricultural products, i.e ., flours of soybean, Bengal gram or jack seed at various concentrations (10%, 20%, 30%, 40%, 50%, 60%, 80% or 100%, all w/v). After 12 h fermentation, the supernatant in it was centrifuged off aseptically to obtain solid substrate for subsequent SSF. Of them, soybean (30 %) supplemented medium was the best for the enhanced production of endospore and δ -crystals. The maximum yield of endospores during solid-state fermentation was observed 48 h, i.e ., compared to submerged fermentation in LB, it was 24 h less gestation period. In control sample, the endospores achieved the maximum length (1.10 ± 0.13 μm) and diameter (0.63 ± 0.07 μm) at 72 h; while in soybean supplemented medium, the maximum length (2.10 ± 0.16 μm) and diameter (1.63 ± 0.16 μm) were at 48 h and 72 h, respectively. Upon staining, acridine orange specifically stained the endospores; malachite green-saffranin stained both δ -crystals and endospores; and coomassie brilliant blue specifically stained δ -endotoxin. Briefly, normal gestation period or harvest time for Btk is 72 h, which could be reduced to 48 h, if SSF is employed as demonstrated in this study.