Vitamin K is a class of fat-soluble molecules that are required for blood clotting and calcium binding in the human body. Although acute vitamin K deficiency is rare, there is evidence that subclinical deficiency raises the risk of heart disease and osteoporosis. The menaquinones (vitamin K2) are an especially good dietary source of vitamin K because of their bioavailability and stability. Menaquinones can be found in fermented foods such as natto and dairy.
A team of researchers at the Norwegian University of Life Sciences wanted to enhance the menaquinone content of dairy to increase its functional value. To achieve this goal, they planned to genetically engineer a lactobacterium, Lactococcus lactis, that is involved in making yogurt. L. lactis contains a biosynthetic pathway to produce several menaquinones, especially menaquinone-9. The researchers tried overexpressing the genes in that pathway. Overexpression of some genes (menF, menA) caused L. lactis to produce extra menaquinone-3, instead of the more desirable menaquinone-9. The overexpression of other genes (mvk, llmg_0196) led to increased production of menaquinone-9.
When the engineered L. lactis was used to culture milk, the yogurt had enhanced levels of menaquinone-9. The researchers calculate that moderate intake of such yogurt would help many people get optimal vitamin K in their diet. This encouraging result suggests that engineered bacteria can be used more broadly to enhance nutrition.