Many bacterial strains produce several B- and K-complex vitamins to aid in a variety of metabolic processes including DNA synthesis and the catabolism of fats, carbohydrates, or proteins. Human intestinal bacteria, for example, are known to synthesize vitamin K1, biotin (B7), folic acid (B9), niacinamide (B3), cobalamin (B12), riboflavin (B2), pantothenic acid (B5), and thiamine (B1). Many of these bacterial-produced vitamins are used in humans as coenzymes or cofactors and are considerably essential for proper metabolism. In particular, vitamin K is necessary for the formation of several blood-clotting factors in the liver. In contrast, both pantothenic acid and biotin function as coenzymes in carbohydrate oxidation and carboxylation reactions, respectively.