Generation of nanoparticles from technical powder of the insecticidal bacterium Bacillus thuringiensis var. kurstaki for improving efficacy

The technical powder of a local isolate of Bacillus thuringiensis (Bt) var. kurstaki namely DOR Bt-1 was subjected to high pressure homogenisation (HPH) to obtain nanoparticles (NPs) ranging 32–1,106 nm as determined through dynamic light scattering. NPs of Bt were also characterised for shape and size through scanning electron microscopy, field emission scanning electron microscopy and transmission electron microscopy that helped in visualising the smallest nanoparticles, i.e., less than even 50 nm. The larger particles comprised mainly Bt spores with a length and width of 1,139 and 813 nm respectively. HPH showed little effect on the spore viability. NPs had a zeta potential above +30 and were stable, resulted in higher mortality of Helicoverpa armigera larvae at a lower dose. Alkali solubilisation of the NPs resulted in higher values of protein and endotoxin quantified through Lowry’s method and ELISA respectively. This is indicative of an increased solubility of the toxin in the midgut alkaline fluid of the insect leading to higher mortality coupled with quicker kill. Thus Bt as NPs has brighter prospects for insect pest management with increased speed of kill at lower doses.