Optimization of growth medium for the production of spores from Bacillus thuringiensis using response surface methodology

Abstract

The effects of cultivation medium compositions including tapioca, fishmeal, CaCO3 and (NH4)2SO4 for the growth of Bacillus thuringiensis YMB 96-1988 were accessed by using response surface methodology (RSM). The two-level (24–1) fractional factorial designs (FFD) which involve two concentrations of each nutrient, and the paths of steepest ascent were effective in searching for the major factors of the bacteria growth. This allows the fitting of a first order linear model to the data. In this study, supplementary CaCO3 showed a negative effect on the spore production based on the first order regression coefficients derived from SAS programme. Subsequently, a 23 central composite design (CCD) was used for allocation of treatment combinations. Preliminary studies showed that tapioca and fishmeal is believed to be the major factors for the growth of B. thuringiensis. Estimated optimum compositions for the production of spores by B. thuringiensis are as follows: tapioca, 5.01%; fishmeal 5.86%; (NH4)2SO4 0.06% and resulted in a maximum spore count of 8.56 × 108/ml was obtained. This value is close to the 8.35 × 108/ml spore density as counted from actual experimental observations.