Optimization of Culture Conditions and Wheat Bran Class Selection in the Production of Bacillus thuringiensis-Based Biopesticides

Abstract

Bacillus thuringiensis is the leading microbial-based biopesticide, thanks to its parasporal crystal proteins or δ-endotoxins, which are toxic to insect larvae upon ingestion. Once in the insect larvae midgut, the crystal is solubilized by the alkaline pH and the δ-endotoxins activated by proteolytic cleavage. Thanks to its high efficiency as a biopesticide, several efforts have been made to enhance its growth and δ-endotoxins production, in various types of culture media. In this study, a culture medium based on wheat bran (WB), the by-product of cereal grain milling, was used to grow Bacillus thuringiensis and produce δ-endotoxins. Using the response surface methodology (RSM), the effects of three variables were evaluated: WB particles granulometry, their concentration, and their agitation in a 48-h shake-flask culture at 30 °C. Three response parameters were targeted: δ-endotoxins production, final culture pH, and dry-matter consumption. According to the RSM results, the optimum would be at 3.7 g WB/50 mL, with a granulometry above 680 μm and agitation between 170 and 270 rpm. This study is key to developing natural and cheap culture media that can be used at an industrial level for Bacillus thuringiensis-based biopesticides.

Complete genome sequences of two Bacillus thuringiensis serovar kurstaki strains isolated from Lebanon and Tunisia, highly toxic against lepidopteran larvae

“…Bacillus thuringiensis serovar kurstaki ( Btk ) strains Lip and BLB1 were isolated from Lebanese and Tunisia soil samples, respectively ( 1 - 3 ). Both strains showed an increased toxicity against the lepidopteran Ephestia kuehniella larvae in comparison to the reference strain HD-1.…”

“…Both strains showed an increased toxicity against the lepidopteran Ephestia kuehniella larvae in comparison to the reference strain HD-1. Their entomopathogenic potential was evaluated by in vivo toxicity assays and showed a lethal concentration of 50% of the larvae (LC50) of 33.27 and 70 ng of toxin per milligram of flour for Lip and BLB1, respectively ( 1 - 3 ). In the context of IPM-4-Citrus (MSCA RISE, No.…”

Physical limitations induced by a medium based on wheat bran for the production of biopesticides by Bacillus thuringiensis spp kurstaki

“…Considérant l'itinéraire technologique des matrices (sans traitement thermique et après traitement thermique), les tendances observées (Figure 2) sont : (i) un accroissement de la capacité de rétention en eau, (ii) une augmentation de la fraction volumique des pellets et (iii) une diminution des vitesses limite de chutes. En comparant les classes, pour une concentration de 73,6 gmh/L, concentration optimale de substrat lors de culture en fiole agitée (Fayad et al, 2022), la classe 2 (500-850µm) sans traitement thermique présente une vitesse limite de chute (moyenne) plus importante que celle des classes 3 et 4. Après traitement thermique, la vitesse limite de chute (moyenne) diminue pour chacune des classes mais reste la plus élevée pour la classe 2.…”

“…Ce substrat lignocellulosique est un co-produit de meunerie contenant tous les nutriments essentiels (substrat carboné fermentescible, protéines, minéraux) pour assurer la croissance et induire la sporulation de Btk (Onipe et al, 2015). Pour mieux comprendre les phases clés de la bioproduction et les bioperformances (titre, rendement, productivité), les compositions biochimiques du substrat (amidon, azote, composition élémentaire…) et du milieu de culture ont été étudiées (Fayad et al, 2022), (Barssoum, et al, 2023).…”