Accelerating the menaquinone-7 production in Bacillus amyloliquefaciens by optimization of the biosynthetic pathway and medium components

Menaquinone-7 (MK-7) has an important role in preventing diseases such as cardiovascular disease and osteoporosis. In this study, a combination strategy of strain improvement and medium optimization is investigated to increase MK-7 production in Bacillus amyloliquefaciens. Conventional breeding method was first used to modify the biosynthetic pathway to construct a MK-7 high-producing strain by atmospheric and room temperature plasma mutagenesis and protoplast fusion. The resulted strain Ba-4 with resistance to sulfaguanidine, 1-hydroxy-2-naphthoic acid, menadione, 2-deoxy-d-glucose and rifampicin as well as sensitive to β-fluoropyruvate produced 73.57 ± 1.61 mg/L of MK-7, which was 1.36 times more than that of the parent strain H.β.D.R.-5 (i.e., 31.12 ± 1.40 mg/L). Subsequently, single-factor optimization and response surface methodology (RSM) were used to optimize the medium components for increasing MK-7 production by strain Ba-4. Strain Ba-4 produced 90.43 ± 1.32 mg/L of MK-7 under the single-factor optimized medium. Moreover, the results of response surface methodology indicated that glycerol, soy peptone and Tween-80 had significant effects on MK-7 production, and the highest MK-7 production (i.e., 95.03 ± 1.01 mg/L) was obtained under the optimized medium, which was 0.29 times higher than that of the initial medium. These results confirmed that the conventional breeding methods and fermenter control system are effective strategies in improving MK-7 production by B. amyloliquefaciens.