Optimization of Culture Condition for the Production of Menaquinone-7 by Bacillus Subtilis Natto

Background: Vitamin K2 refers to a series of naphthoquinone derivatives, which have a variety of physiological and pharmacological functions for the human body. The most important type of vitamin K2 is menaquinone-7 (MK-7), an expensive raw material with no local manufacturers in Iran. Objectives: Since there was no report on the yield of MK-7 produced by the currently available Bacillus subtilis natto species in Iran, this study aims to optimize the culture condition for the production of MK-7 using this Bacillus species. Materials and Methods: The base medium (BM) for MK-7 production contained glycerol (6.3%), soybean peptone (3%), and yeast extract (0.51%). The selected factors for optimizing the MK-7 production included the incubation temperature (30, 37, and 40°C) and incubation time (72, 96, and 120hr) with/without the addition of K2HPO4 to the fermentation medium. Three sets of experiments with six modes in each set were designed based on these parameters. MK-7 content was analyzed by the HPLC method. Results: Two experiments showed the highest MK-7 production yields of 0.319 and 0.3158 mg/L. The culture condition for both of these yields was as follows:120 hours incubation time in the presence of K2HPO4. However, the incubation temperature was different in these two experiments. The incubation temperature of 30°C resulted in 0.319 mg/L MK-7 concentration, and 37°C yielded 0.3158 mg/L. Conclusion: B. subtilis natto (IBRC-M 11153) is suitable to be used as a basic platform for the mutation and production of a high-producer species. Optimizing the culture conditions using the wild-type species is not beneficial in increasing the production ability of the bacterium. It is necessary to use different methods for enhancing the production yield of MK-7 to lower the cost of microbial production and make the industrial process economic