Human gut Bacteroides capture vitamin B12 via cell surface-exposed lipoproteins

Abstract

Human gut <i>Bacteroides</i> use surface-exposed lipoproteins to bind and metabolize complex polysaccharides. Although vitamins and other nutrients are also essential for commensal fitness, much less is known about how commensal bacteria compete with each other or the host for these critical resources. Unlike in <i>Escherichia coli</i>, transport loci for vitamin B₁₂ (cobalamin) and other corrinoids in human gut <i>Bacteroides</i> are replete with conserved genes encoding proteins whose functions are unknown. Here we report that one of these proteins, BtuG, is a surface-exposed lipoprotein that is essential for efficient B₁₂ transport in <i>B. thetaiotaomicron.</i> BtuG binds B₁₂ with femtomolar affinity and can remove B₁₂ from intrinsic factor, a critical B₁₂ transport protein in humans. Our studies suggest that <i>Bacteroides</i> use surface-exposed lipoproteins not only for capturing polysaccharides, but also to acquire key vitamins in the gut.