Vitamin biosynthesis in the gut: interplay between mammalian host and its resident microbiota

In recent years, exhaustive efforts have been made to dissect the composition of gut-associated microbial communities and associated interactions with their human host, which are thought to play a crucial role in host development, physiology, and metabolic functions. Although such studies were initially focused on the description of the compositional shifts in the microbiota that occur between different health conditions, more recently, they have provided key insights into the functional and metabolic contributions of the gut microbiota to overall host physiology. In this context, an important metabolic activity of the human gut microbiota is believed to be represented by the synthesis of various vitamins that may elicit considerable benefits to human health. A growing body of scientific literature is now available relating to (predicted) bacterial vitamin biosynthetic abilities, with ever-growing information concerning the prevalence of these biosynthetic abilities among members of the human microbiota. This review is aimed at disentangling if and how cooperative trophic interactions of human microbiota members contribute to vitamin production, and if such, gut microbiota-mediated vitamin production varies according to different life stages. Moreover, it offers a brief exploration of how different diets may influence vitamin production by shaping the overall composition and metabolic activity of the human gut microbiota while also providing preliminary insights into potential correlations between human microbiota-associated vitamin production and the occurrence of human diseases and/or metabolic disorders.