Impact of liquid formulation based on ultrafiltration-recovered bioactive components on toxicity of Bacillus thuringiensis subsp. kurstaki strain BLB1 against Ephestia kuehniella

• The 5 kDa MWCO membrane provided the highest recovery of Bt components.
• Obtained retentate was 49.00% more toxic toward E. kuehniella than the supernatant.
• The centrifugate–retentate was 42.70% more toxic than the centrifugate–supernatant.
• Proteases, chitinases and Vip3 proteins were involved in the synergetic action with delta-endotoxins.
• Toxicity of formulated centrifugate–retentate was maintained stable after 1 year of storage.

A study of the recovery process of Bacillus thuringiensis (Bt) strain BLB1-based bioinsecticides using ultrafiltration showed that the highest recovery of BLB1 bioactive components was achieved by using a 5 kDa MWCO ultrafiltration membrane to concentrate the supernatant. A bioassay against Ephestia kuehniella showed that the retentate was approximately 49% more toxic than the supernatant, with a lethal concentration (LC50) of 194.00 μg g−1 in the retentate compared to 380.00 μg g−1 in the supernatant. Furthermore, compared to the centrifugate (spore-crystal mixture) mixed with supernatant or saline water, the centrifugate retentate showed 42.7% and 56% higher toxicity against E. kuehniella, respectively. The involvement of proteases, chitinases and Vip3 proteins restored to the retentate suggests synergetic activity with delta-endotoxins and spores, and this activity was confirmed by enzymatic activity and western blot analysis. The formulated centrifugate retentate maintained stability and toxicity after 1 year of storage at 4 °C. These data suggest that the ultrafiltration process enabled significant virulence factors recovery from BLB1 supernatant grown in a complex medium and resulted in a highly toxic and stable formulation.

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