A method for preparation of a feed additive containing surfactin, which uses a high-yield mutant strain, Bacillus subtilis T, and soybeans as the substrate in semi-solid state fermentation and after drying and grinding of the fermented soybeans into soybean powder to give a feed additive containing surfactin. Each kilogram of the fermented soybean powder contains about 6-7 g of surfactin. Feeding grouper with the feed additive containing surfactin can promote growth rate, increase expression of immune genes (e.g. AMP, Mx and IFN-induced protein), and lower mortality rate of virus-infected fish, indicating the feed containing surfactin has the effects of growth promotion, immunity enhancement and provides resistance to pathogen infection.
