Bacteria perform essential functions for human beings, including the production of vitamin K in the intestine.
Note: Vitamin K is required for production of the plasma proteins necessary for blood clotting. Newborn infants are not yet colonized by bacteria and cannot produce clotting factors, putting them at risk for hemorrhage. When babies are born, they are given an injection of vitamin K to aid in the production of clotting factors until they have been colonized with bacteria.