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World J Microbiol Biotechnol (2008) 24:24652471 DOI 10.1007/s11274-008-9816-1
ORIGINAL PAPER
Optimization of a fermentation process for bioinsecticide production by Bacillus thuringiensis
G. Amin S. Alotaibi Narmen A. Youssef W. D. Saleh
Received: 20 February 2008 / Accepted: 24 April 2008 / Published online: 1 August 2008 Springer Science+Business Media B.V. 2008
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 rst 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 rst 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 1012 c.f.u./ml was obtained. The sporecrystal 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.
Keywords Bioinsecticides Bacillus thuringiensis
Exponentially fed-batch fermentation
Biomass production Two-stage process
Introduction
Optimization of a cost-effective process for production ofB. thuringiensis bioinsecticides, necessitates the development of a fermentation method that allows production of the mixture of spores and crystal protein toxin to a high concentration with high productivity and yield. SinceB. 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...