A improved pH-control fed-batch strategy for Bacillus thuringiensis subsp. darmstadiensis 032 producing thuringiensin was developed based on the analysis of the batch culture, constant rate fed-batch cultures and the original pH-control fed-batch. Having considered the pH variation and the glucose consumption status, the pH was adjusted from 6.5 to 7.0 by adding base in the late cultivation period of batch culture, and then the pH was kept at 7.0 by glucose feeding. The feeding was terminated when the pH could not be controlled by glucose feeding anymore. The proposed fed-batch strategy effectively avoided underfeeding or overfeeding, and it increased the thuringiensin yield and YP/X by 89.51% and 103.2% compared to that of the batch culture, respectively.

The solid state fermentation (SSF) was carried out for the production of poly g-glutamate (PGA) from a new strain Bacillus subtilis CCTCC202048. The fermentation factors, which included composition of substrates, initial moisture content, incubation temperature, fermentation period, and additional nutrients such as mineral salts, carbon sources and nitrogen sources, were investigated and optimized. The maximum PGA production (83.61g/kg of dry substrate) was obtained in the mixed substrates of soybean cake powder and wheat bran (11:9, w/w) supplemented with glutamate (40.14g/kg), citric acid (18.50g/kg), NH4NO3 (20.05g/kg) and mineral salts (MgSO4 7H2O, CaCl2 2H2O, FeCl3 6H2O and MnSO4 H2O), with initial moisture content as 65%, at 40 8C incubated for 42 h. This yield was four times more than that before optimization. This is the first report on optimization of PGA production in SSF.

A Bacillus subtilis strain B6-1, previously isolated from the rhizosphere of vegetable, selectively produced antibiotics or poly-gammaglutamic acid (c-PGA) in two kinds of liquid media and their co-productions were obtained when using soybean and sweet potato residues in solid-state fermentation. The antibiotics were purified and identified as fengycins. After these residue cultures were introduced, cucumber wilts were effectively suppressed. The introduction also significantly increased the dry weights of roots and shoots of cucumber seedlings, and the roots to shoots ratio, especially at lower nutrition, which indicated the fertilizer synergistic effects. So the product of soybean and sweet potato residues, cultivated with B6-1 co-producing lipopeptides and c-PGA, can be expected to be used as both biocontrol agents and fertilizer synergists.

The effects of inlet air temperature, liquid feed rate and atomising air pressure on the yield, moisture content, crystal protein content and lethality of Bacillus thuringiensis powder during the spray drying of B. thuringiensis fermentation liquor were studied by an orthogonal experiment. The results of variance analysis indicate that the extent of influence of factors on the yield of B. thuringiensis is in the order: atomising air pressure greater than inlet air temperature greater than liquid feed rate; and on the moisture content, crystal protein content and lethality of B. thuringiensis is in the order: inlet air temperature greater than liquid feed rate greater than atomising air pressure. The mathematical models describing the relationship between spray drying parameters and the yield, moisture content, crystal protein content and lethality of B. thuringiensis were established. The optimum spray drying conditions determined by these mathematical models are: inlet temperature 1808C, liquid feed rate 60ml min 1, atomising air pressure 0 1MPa.The results of the validation experiment show that these mathematical models established by the orthogonal experiment are reliable.