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Metabolic effects of metformin on gut bacteria

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Metabolic effects of metformin on gut bacteria to increase their vitamin B12 uptake, leading to increasing competition for available dietary vitamin B12 and ultimately to human vitamin B12 deficiency. In E. coli metformin inhibits the respiratory chain complex I, and vitamin B12 transport through the bacterial inner wall is blocked so that vitamin B12 accumulates in the periplasm. By contrast, in Bacteroides ovatus metformin upregulates respiratory chain complex V so that vitamin B12 can be transported across the inner membrane to the bacterial cytoplasm. (Source: Chen M, Shu Y, Li Q, et al. Bacteroides ovatus accelerates metformin-induced vitamin B12 deficiency in type 2 diabetes patients by accumulating cobalamin. NPJ Biofilms Microbiomes 2023;9[1]:51. Creative Commons Attribution 4.0 International [CC BY 4.0] license, creativecommons.org/licenses/by/4.0.)