Production of a chloramphenicol-resistant mutant of Lysinibacillus sphaericus by solid state fermentation

Abstract

A highly active mosquitocidal mutant of Lysinibacillus sphaericus Ahmed 2362, namely, UCR-146, was efficiently produced on cottonseed meal (CSM) medium, using sand as a carrier under solid state fermentation (SSF). The optimum CSM concentration for the highest sporulation and toxin formation was 12%. The maximum toxicity of the tested organism against second instar larvae of Culex pipiens was obtained at 25% moisture content, initial pH 6–7, 1% sodium acetate, 18.9×106 CFU/g inoculum and 6 days incubation period at 30°C. Pilot scale production of UCR-146 under the optimum SSF conditions was assessed in aluminium trays. Spore count, mortality of larvae and LC50 of the final product were 5.5×1010 CFU/g, 72% at 1 part per million (PPM) and 0.54 PPM, respectively. These results were comparable with those obtained from bench-scale production (in flasks). The cost of 1 kg of this bio-larvicide was estimated at US $0.34.