Spore production of entomopathogenic fungus Beauveria bassiana BNBCRC for biocontrol: Response surface optimization of medium using decanter cake from palm oil mill

Beauveria bassiana is an efficient entomopathogenic fungus for biological control. Optimization of medium composition for production of B. bassiana BNBCRC spores in decanter cake (DC)-based solid culture was performed using response surface methodology (RSM). Effects of inorganic and organic nitrogen sources, mineral salt, and incubation temperature in a DC-based composition were experimentally studied in two stages, first using a Taguchi design. Among the decision variables tested, urea, peptone, and MgSO4 significantly affected the spore concentration, and the maximal 1.89×108 spores g−1 was found at 30°C incubation temperature. In the second stage, these three selected decision variables were optimized by RSM, using a factorial central composite design. The maximum average spore concentration of B. bassiana BNBCRC increased to 4.80×108 spores g−1 in the optimal DC-based medium containing 0.80 g L−1 urea, 2.10 g L−1 peptone, and 0.75 g L−1 MgSO4. The coefficient of determination was R2=0.97 for the RSM model fit to data. Compared to the original DC-based medium, the performed optimization increased the spore production of B. bassiana BNBCRC by 2.5 fold. After optimization of moisture content, the DC -based medium containing 60% moisture gave the highest spore concentration of 4.71×108 spores g−1.