The term gut microbiota refers to microorganisms such as, for example, bacteria, fungi, etc., that live in the gastrointestinal (GI) tract of humans. In the intestine, there are lactic acid bacteria that are known to synthesize vitamin K2 (also known as menaquinone). Moreover, there are GI bacteria that play roles in the metabolism of bile acids and sterols. Finally, intestinal bacteria from a group named Proteobacteria produce gas, this group is especially in the guts of colicky babies, where cause pain and lead to crying.
