Production of delta‐endotoxin by Bacillus thuringiensis subsp kurstaki and overcoming of catabolite repression by using highly concentrated gruel and fish meal media in 2‐ and 20‐dm³ fermenters

Abstract

Delta-endotoxin production by a strain of Bacillus thuringiensis subsp kurstaki exhibiting larvicidal toxicity towards lepidoptera was investigated in 2-and 20-dm 3 fermenters, using gruel-and ®sh meal-based media. The results show clearly that in such complex media, aeration plays an important role in bioinsecticide production. Optimal aeration led to improvement of delta-endotoxin concentrations with decreases of ®nal spore count and proteolytic activity. Moreover, in order to use high gruel concentrations, a fermenter con®guration with an ef®cient aeration system should be used. In a 20-dm 3 Biola®te fermenter, 59 g dm À3 or 75 g dm À3 gruel was used to produce bioinsecticides with a signi®cant reduction of carbon catabolite repression of delta-endotoxin synthesis. This result is very interesting in order to produce high ®nal delta-endotoxin concentrations in the culture broth. It was also concluded, by considering the key role of oxidative pathways in delta-endotoxin synthesis, that oxygen supply must be adequate for bioinsecticide production at high substrate concentrations. Moreover, the role of sodium chloride in improving delta-endotoxin production is dependent not only on protease synthesis and its effect on crystal stability, but also on the aeration level of the production medium.

Scale-up of biopesticide production processes using wastewater sludge as a raw material

“…Therefore, it is preferable to eliminate the protease in the supernatant by centrifugation and use the residual solids containing Bt cells, spores and endotoxin for formulation. This will reduce the negative effects of proteases in Bt formulations, and the protease in the supernatant could be recovered for further use [36,37].…”

Selection and characterization of Bacillus thuringiensis isolates with a high insecticidal activity against Spodoptera frugiperda (Lepidoptera: Noctuidae)

“…The CFU and δ-endotoxin production of the Bt isolates were assessed in CCY medium (Stewart et al, 1981) after 72 h at 30°C in a rotary shaker set at 200 rpm (ZOUARI et al, 2002;AZZOUZ et al, 2014). The number of spores and the δ-endotoxin production were determined as described by Ghribi et al (2007).…”

Optimization of a fermentation process for bioinsecticide production by Bacillus thuringiensis

“…The proposed approach of two-stage exponentially fed-batch fermentation process is highly satisfactory. The catabolic repression that regulates bioinsecticide synthesis in B. thuringiensis at high glucose concentrations (Zouari et al 2002) must have been successfully avoided during the present study. Glucose and other nutrients were fed adequately to the growing cells at their specific growth rate maximizing cell growth, spore formation and toxin yield and productivity (Table 3).…”

“…Despite the relative improvement in toxin production by the fed-batch fermentation when compared to batch fermentation systems, both bioreactor productivities and toxin yields were markedly low due to incomplete consumption of added glucose. Excess substrate in the fermentation medium and substrate limitation have been found to have negative effects on cell growth and bioproduct formation (Amin 1994;Zouari et al 2002).…”

“…Since B. thuringiensis toxin is simultaneously produced with spore formation (Rivera 1998;Zouari et al 2002), it is assumed that a large number of cells produces a correspondingly large number of spores, and consequently a large amount of toxin. Thus, and in order to maximize toxin productivity, a complete fermentation of large amounts of glucose is essential.…”