Vitamin K2 (menaquinone, MK) is an essential lipid-soluble vitamin with critical roles in blood coagulation and bone metabolism. Chemically, the term vitamin K2 encompasses a group of small molecules that contain a common naphthoquinone head group and a polyisoprenyl side chain of variable length. Among them, menaquinone-7 (MK-7) is the most potent form. Here, the biosynthetic pathways of vitamin K2 and different types of MK produced by microorganisms are briefly introduced. Further, we provide a new aspect of MK-7 production, which shares a common naphthoquinone ring and polyisoprene biosynthesis pathway, by analyzing strategies for expanding the product spectrum. We review the findings of metabolic engineering strategies targeting the shikimate pathway, polyisoprene pathway, and menaquinone pathway, as well as membrane engineering, which provide comprehensive insights for enhancing the yield of MK-7. Finally, the current limitations and perspectives of microbial menaquinone production are also discussed. This article provides in-depth information on metabolic engineering strategies for vitamin K2 production by expanding the product spectrum.

Phosphates are important components in the fermentation medium for biosurfactant production. In the present study, Ochrobactrum intermedium strain XY-1 was used as the experimental strain, the effects of various phosphates used in the biosurfactants fermentation media was preliminarily investigated on cell growth, and surface tension, and emulsifying activity of fermentation broth. Under the same total phosphorus concentration of 0.035 mol/L, KH2PO4 + Na2HPO4, KH2PO4, and Na2HPO4 was respectively used as the phosphorus source of biosurfactant fermentation at 30 °C and 160 rpm. The results showed that the bacteria grew slowly and the maximum emulsifying activity of fermentation broth reached 52.95% in the fermentation with KH2PO4 + Na2HPO4 as phosphorus source, and larger bacterial growth and 35.9% maximum emulsifying activity exhibited in the fermentation with KH2PO4, smaller bacterial growth and 24.54% maximum emulsifying activity exhibited in the fermentation with Na2HPO4. The phosphate mixture of KH2PO4 and Na2HPO4 benefits the biosurfactant fermentation by limiting the growth of Ochrobactrum intermedium strain XY-1, which might be the earliest report on the phosphorous source of biosurfactant fermentation by Ochrobactrum intermedium.