Vitamin K is essential for the regulation of blood coagulation, tissue mineralization, immune response and other physiological processes. Vitamin K1 (VK1) is the most common dietary form for humans and many animals. In this study, the feasibility of biotechnological production of VK1 was assessed. In a preliminary study, VK1, VK2 and a vitamin K analog (menadione nicotinamide bisulfite) were added to the diets of laying hens. Vitamin K1 supplementation achieved a blood concentration of over 20 ng mL-1, while vitamin K2 and the analog menadione achieved less than 5 ng mL-1. Vitamin K1 was the most bioavailable form for chickens.
Algae are known to be rich in VK1, so seven common strains of microalgae were screened for VK1 content. Among them, Anabaena cylindrica had the highest concentration (200 µg g-1 DW basis). The VK1 content of A. cylindrica was 6 times higher than rich sources such as parsley. One gram contained 3-fold and 4-fold daily intake of vitamin K for humans and chickens, respectively. An animal study demonstrated no acute toxicity of the freeze-dried biomass. Anabaena cylindrica was therefore selected for biotechnological production of VK1.
The effects of key nutrient levels were tested by growing A. cylindrica in a 5.0 L photo-bioreactor. Increasing the levels of light (from 160 to 330 µmol photons m-2 s-1) and sodium nitrate (from 170 to 1700 mg L-1) quadrupled vitamin K1 productivity to 22 µg L 1 d-1 and final titer to 129 µg L-1. Similar results were achieved when process was scaled up to a 50 L bubble column photo-bioreactor. At a light intensity of ~300 µmol photons m-2 s-1, VK1 productivity and final titer were doubled to ~40 µg L-1 d-1 and ~280 µg L-1 respectively by increasing the daily light duration from 12 to 24 hours. This study demonstrates the feasibility of using microalgae to sustainably produce VK1 for human and animal nutrition.