A "high-efficiency, low-carbon, cofactor recycling" MK-7 synthetic strain was constructed according to research published in Microbial Cell Factories.

The study, which was conducted by a research team from Institute of Intelligent Machines, Hefei Institutes of Physical Science (HFIPS) of the Chinese Academy of Sciences (CAS), laid the foundation for the large-scale production of high-value MK-7 as well as terpenoids.

MK-7, a lipid-soluble vitamin K2, played a vital role in the clotting cascade, maintenance of bone metabolism, prevention of arteriosclerosis, regulation of inflammation and neuroprotection.
In this study, the research team tried a different strategy to improve the production of menaquinone-7 (MK-7). It's a bottom-up synthetic biology approach.

And after three rounds of Design-Build-Test-Learn cycle, they reconstructed the pathways of MK-7 synthesis in Bacillus subtilis, promoted the central carbon metabolism flow to the MK-7 synthesis module, and balanced intracellular reducing force metabolism.

The classical gene editing technology Cre/Loxp was mainly used to replace the native promoters of key enzymes and rate-limiting enzymes in the MK-7 synthesis pathway with constitutive strong promoters, and knock out the competitive bypass metabolism, realizing "open source and throttling".

Moreover, they calculated the transformation of matter and energy in the pathway of synthesizing MK-7 from glycerol in Bacillus subtilis, and found that there is a cofactor imbalance in the synthesis of MK-7. After rational design of cofactor regeneration pathway, they introduced a heterologous NADH kinase (Pos5P) to increase the availability of NADPH for MK-7 biosynthesis. By testing the fermentation performance of the constructed MK-7 recombinant bacteria, it was found that it had excellent MK-7 synthesis ability and reached 53.07 mg/L MK-7, which was 4.52 times that of B. subtilis 168.

Additionally, the balance of cofactors not only improved the synthesis efficiency of MK-7 in Bacillus subtilis, but also reduced the synthesis of by-products such as lactic acid, which decreases energy loss and improves carbon conversion.