Studies On The Fermentation Condition Of Bacillus Thuringiensis Isolate WB₇

In this article, we study the fermentative process of Bacillus thuringiensis isolate WB7 in order to find out the effections of the nutritions and the fermentative conditions to the metabolism of Bt.An orthogonal design and a uniform design were used to screen fermentative medium of Bacillus thuringiensis isolate WB7 with shaking flasks. WB7 was grown in fermentation media using different agricultural by-products as the main carbon and nitrogen sources. Among these tests, yeast powder and fish meal were the most efficient substrates for producing Bt spores while corn meal didn't has evident influence on WB7, the interaction of corn meal and yeast powder and the interaction of corn meal and soybean flour were in the middle, however, the appending of peanut flour would reduce the Bt spore numbers. As far as inorganic salts concerned, MgSO4 had much more evident influence on Bt than the others, KH2PO4 was the lesser while CaCO3 and ZnSO4 were the leastAccording these two tests, the best combination(corn meal 4.0%, soybean flour 2.0%, yeast powder 2.0%, fish meal 2.0%, peptone 0.5%, CaCO3 0.5%, MgSO4 0.07%, KH2PO4 0.1% and ZnSO4 0.001%) was obtained.The fermentative conditions tests showed that air content (medium content) was the most important factor for Bt fermentation. As far as pH value was concerned, it was best at 7.5 before the media were disinfected. No difference existed for the efficacy of Bt fermentation liquid with the test range of temperature and inoculation quantity. The most appropriate fermentative conditions included medium content 3%, inoculation quantity 1%, incubated in 30C and adjust the pH value to 7.5 before the media were disinfected.