Optimization of a fermentation process for bioinsecticide production by <Emphasis Type="Italic">Bacillus thuringiensis</Emphasis> |
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Authors: | G Amin S Alotaibi Narmen A Youssef W D Saleh |
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Institution: | (1) Department of Biotechnology, Faculty of Sciences, Taif University, 888 Taif, KSA;(2) Department of Biology, Faculty of Sciences, Taif University, Taif, KSA;(3) Department of Microbiology, Faculty of Agriculture, Cairo University, Giza, Egypt |
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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 × 1012 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 LC50 of the bioinsecticides against its larval instar and the highest virulence against adults emerged later on from the surviving
larvae. |
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Keywords: | Bioinsecticides Bacillus thuringiensis Exponentially fed-batch fermentation Biomass production Two-stage process |
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