Abstract
Human gut Bacteroides 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 Escherichia coli, transport loci for vitamin B12 (cobalamin) and other corrinoids in human gut Bacteroides 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 B. thetaiotaomicron. BtuG binds B12 with femtomolar affinity and can remove B12 from intrinsic factor, a critical B12 transport protein in humans. Our studies suggest that Bacteroides use surface-exposed lipoproteins not only for capturing polysaccharides, but also to acquire key vitamins in the gut.
Highlights
Our understanding of the factors that shape gut microbial community composition is largely based on the primary economy of this ecosystem: the flow of carbon from the diet to bacterial biomass and fermentation products
The complex organometallic cofactor vitamin B12 is representative of this challenge: de novo biosynthesis requires the coordinated activity of nearly 30 dedicated enzymes (Roth et al, 1993)
Wexler et al showed that a protein called BtuG on the surface of a type of gut bacteria called Bacteriodes grabs onto vitamin B12 with extraordinary strength
Summary
Our understanding of the factors that shape gut microbial community composition is largely based on the primary economy of this ecosystem: the flow of carbon from the diet to bacterial biomass and fermentation products. Microbiology and Infectious Disease eLife digest Eating is the first step in an hours-long process that extracts the nutrients we need to live It nourishes us, and a vast community of bacteria in our gut called the microbiota. Wexler et al showed that a protein called BtuG on the surface of a type of gut bacteria called Bacteriodes grabs onto vitamin B12 with extraordinary strength. These bacterial proteins bind to vitamin B12 so strongly that they can even pry it away from our own vitamin B12 collecting protein. More studies are needed to learn whether BtuG contributes to vitamin B12 deficiencies in humans with gut bacteria overgrowth and determine the best ways to combat such deficiencies. BtuG2 directly binds vitamin B12 with femtomolar affinity, thereby enabling it to acquire this vitamin from intrinsic factor, a critical B12 transport protein in humans
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