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

Abstract

Corn steep liquor is a kind of intractable organic waste liquidproduced 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 inthe fermentation industry. Many starch processing enterprises cannot directlyutilize corn steep liquor and choose to discharge it directly, thus causingenvironmental pollution. Studies have shown that high ammonia nitrogen in cornsteep liquor can promote the increase of microbial biomass. B. subtilisis the dominant strain of microbial flora in corn steep liquor, it is a classicstrain in the research and industrial production of biological bacterialfertilizer. In this study, the dominant B. subtilis 3301, which issuitable 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 andthree-level Response Surface (RSM) analysis experiment. The highest celldensity was obtained when the concentration of corn steep liquor is 145 g·L^-1, pH is 7 and the inoculationamount is 8. Then the dynamic changes of B. subtilis cultured in cornpulp and beef extract peptone medium (NB) were compared under response surfaceoptimization fermentation conditions. The results showed that B. subtiliscultured in corn pulp medium was significantlyhigher than in NB medium. Finally, the fermentation effect of fed-batch glucoseon the culture of B. subtilis in corn steep liquor was investigated andthe results showed that when feeding with glucose, the number of viablebacteria can reach 1.75 × 10¹⁰ CFUmL^-1, which issignificantly higher than the number of viable bacteria cultured without feedingglucose. All of the above results show that the optimized medium using cheapcorn-steep liquor shows a good production level. The research results provide atheoretical reference for further improving the biomass of biological bacterialfertilizer and at the same time provide a practical reference for theindustrial production of biological bacterial fertilizer to reduce the cost ofraw materials, alleviate the pollution of corn steep liquor to the environmentand promote the further development of the crop processing industry.