Production of Bacillus Subtilis as Biological Fertilizer by Biotransformation of Corn Steep Liquor

: Corn steep liquor is a kind of intractable organic waste liquid produced during the processing of corn starch. But it is rich in nutrients, soluble protein, and amino acids and it could be used as a nitrogen source in the fermentation industry. Many starch processing enterprises cannot directly utilize corn steep liquor and choose to discharge it directly, thus causing environmental pollution. Studies have shown that high ammonia nitrogen in corn steep liquor can promote the increase of microbial biomass. B. subtilis is the dominant strain of microbial flora in corn steep liquor, it is a classic strain in the research and industrial production of biological bacterial fertilizer. In this study, the dominant B. subtilis 3301, which is suitable for high-density cultivation in corn steep liquor, was screened first. Then the optimal fermentation parameters, like corn steep liquor concentration, pH, and inoculation amount of the bacteria were analyzed by a three-factor and three-level Response Surface (RSM) analysis experiment. The highest cell density was obtained when the concentration of corn steep liquor is 145 g·L -1 , pH is 7 and the inoculation amount is 8. Then the dynamic changes of B. subtilis cultured in corn pulp and beef extract peptone medium (NB) were compared under response surface optimization fermentation conditions. The results showed that B. subtilis cultured in corn pulp medium was significantly higher than in NB medium. Finally, the fermentation effect of fed-batch glucose on the culture of B. subtilis in corn steep liquor was investigated and the results showed that when feeding with glucose, the number of viable bacteria can reach 1.75 × 10 10 CFUmL -1 , which is significantly higher than the number of viable bacteria cultured without feeding glucose. All of the above results show that the optimized medium using cheap corn-steep liquor shows a good production level. The research results provide a theoretical reference for further improving the biomass of biological bacterial fertilizer and at the same time provide a practical reference for the industrial production of biological bacterial fertilizer to reduce the cost of raw materials, alleviate the pollution of corn steep liquor to the environment and promote the further development of the crop processing industry.