Fermentation Optimization For Novel Mosquitocidal Bacillus Thuringiensis BRC-LLP29

Bacillus thuringiensis BRC-LLP29 is a novel strain which has high mosquitocidal effect. Statistical methods were used to optimize the fermentation conditions for high toxicity against Culex pipiens quinquefasciatus. According to single factorial experiments,the most suitable carbon sources were glucose,maltose and soluble starch,the best nitrogen sources were typetone,casein and soy peptone,the best metal ions were Mg2+ and Al3+ . Plackett-Burman design revealed that in culture medium glucose,soy peptone and Al2(SO4)3 were the three prime factors from the eight factors affecting strain's toxicity. The path of steepest ascent experiment was adopted to approach the optimal region of the medium composition. Then the optimal combined concentration and mutual effect of the three factors were optimized by response surface methodology(RSM). The result showed that the best medium composition was glucose 19.8 g/L,casein 28.4 g/L,Al2(SO4)3 1.2 g/L,MgSO4·7H2O 2 g/L,K2HPO4 3 g/L,CaCO3 0.5 g/L,at which the corrected mortality of Culex pipiens quinquefasciatus reached to 61.11% which only 1.34% differed from the forecast by RSM. The tests of the fittest culture medium conditions indicated that fermentation temperature was 31℃, the initial pH was 7.0, the loading volume of medium was 40mL culture in 250mL shake flasks and inoculation volume was 3.5%. Under optimized fermentation conditions the mortality of Culex pipiens quinquefasciatus increased highest to 83.33% when the strain was cultivated to 72 hours.