Optimization of a fermentation process for bioinsecticide production by Bacillus thuringiensis

Abstract

In an attempt to develop a cost-effective process for bioinsecticide production by B. thuringiensis, the feeding regime during aerobic cultivation of the bacterium was investigated and optimized. The process was designed as a two-stage process; a first stage of active growth, where glucose and other nutrients were adequately supplied to the growing cells over 12 h, followed by a second stage of 2 h for spore formation and toxin release. In order to maximize spore and toxin yield and productivity, different quantities of glucose and nutrients were fed separately to the growing cells in four different fermentation runs. In all runs, glucose was converted to bacterial biomass during the first stage and subsequently to spores and crystal protein during the second phase. The best results were obtained with a fermentation run supplied with 190 g glucose in 1500 ml. Up to 20.1 g of bacterial insecticides/l were recovered from fermentation broth with a glucose to toxin conversion yield of 0.159 g/g. Also, a markedly high spore concentration of 2.31 9 10 12 c.f.u./ml was obtained. The spore-crystal protein mixture obtained was tested for its insecticidal activity against three of the most agronomically important pests. Among the bioinsecticide-treated insect pests, Egyptian cotton leafworm, Spodoptera littoralis was the most susceptible pest with the lowest LC 50 of the bioinsecticides against its larval instar and the highest virulence against adults emerged later on from the surviving larvae.

A novel strategy and kinetics analysis of half‐fractional high cell density fed‐batch cultivation of Zygosaccharomyces rouxii

“…The following formulas were employed for the calculation of substrate consumption (Amin, Alotaibi, Youssef, & Saleh, ):…”

“…The following formulas were employed for the calculation of substrate consumption (Amin, Alotaibi, Youssef, & Saleh, 2008):…”

Assessment of insecticidal activity of red pigment produced by the fungus Beauveria bassiana

“…The biomass obtained was dried in an oven at 80°C until constant weight. Residual glucose in supernatants was analysed using the enzymatic method employing glucose oxidase (Amin et al 2008b). The red pigment was determined using absorbance measurements at 530 nm which were converted into concentration (ppm) using a calibration curve.…”