Intestinal bacteria are main source of which one of the following vitamins ?

Intestinal bacteria, particularly those in the human gut microbiome, are a significant source of several B-group vitamins and Vitamin K. Specifically, Vitamin B12 (cobalamin) is synthesized by various enteric bacterial species within the gastrointestinal tract [1]. While humans primarily obtain Vitamin B12 from animal-based foods, the gut microbiota possesses the biosynthetic pathways to produce it internally. Research indicates that while small amounts of Vitamin B12 are synthesized by intestinal flora, the majority of this production occurs in the large intestine, where absorption is limited compared to the small intestine [1]. In contrast, Vitamins A, C, and E are not synthesized by gut bacteria; Vitamin C is obtained through diet, and Vitamin A and E are fat-soluble vitamins typically sourced from food and stored in the body [2]. Therefore, Vitamin B12 is the correct answer as it is a primary product of microbial synthesis in the gut.

Sources

1. [1] https://pmc.ncbi.nlm.nih.gov/articles/PMC8970816/
2. [2] https://www.sciencedirect.com/science/article/pii/S0271531721000580