Potential of microbes to synthesize in situ vitamins can be exploited to naturally fortify foods and to synthesize vitamins to new matrices. In this project we study vitamin B12 synthesis focusing on bacteria which are allowed to be used in food production. The focus will be on Propionibacterium freudenreichii. We study vitamin B12 synthesis mechanisms and factors affecting efficiency of the synthesis. Integrating tools of molecular microbiology with those of food chemistry and technology will give excellent ground for scientific breakthroughs. On the other hand, understanding the molecular mechanisms governing in situ vitamin B12 production will enable new innovations in production of science-based functional foods and ingredients.