Dynamic responses of Bacteroides thetaiotaomicron during growth on glycan mixtures

Abstract

Summary Bacteroides thetaiotaomicron (Bt) is a human colonic symbiont that degrades many different complex carbohydrates (glycans), the identities and amounts of which are likely to change frequently and abruptly from meal-to-meal. To understand how this organism reacts to dynamic growth conditions, we challenged it with a series of different glycan mixtures and measured responses involved in glycan catabolism. Our results demonstrate that individual Bt cells can simultaneously respond to multiple glycans and that responses to new glycans are extremely rapid. The presence of alternative carbohydrates does not alter response kinetics, but reduces expression of some glycan utilization genes as well as the cell’s sensitivity to glycans that are present in lower concentration. Growth in a mixture containing twelve different glycans revealed that Bt preferentially uses some before others. This metabolic hierarchy is not changed by prior exposure to lower priority glycans because re-introducing high priority substrates late in culture re-initiates repression of genes involved in degrading those with lower priority. At least some carbohydrate prioritization effects occur at the level of monosaccharide recognition. Our results provide insight into how a bacterial glycan generalist modifies its responses in dynamic glycan environments and provide essential knowledge to interpret related metabolic behavior in vivo.

Tracking heavy water (D 2 O) incorporation for identifying and sorting active microbial cells

“…B. acidifaciens and other Bacteroides spp. are capable of fermenting a wide range of simple and complex carbohydrates and using mixed substrates (70)(71)(72)(73)(74). Previous studies have shown that in pure culture, members of the Bacteroides prioritize mannose utilization over other sugars (74,75), and our results suggest that mannose may be a preferred substrate in vivo as well.…”

Efficient utilization of complex N-linked glycans is a selective advantage for Bacteroides fragilis in extraintestinal infections

“…To more easily compare in vivo expression of all PUL operons, the SusC homologs were used as a proxy for expression of PUL operons (11). This approach was validated by quantitative RT-PCR (qRT-PCR) which confirmed the in vivo induction of donC (Fig.…”

“…The carbon/energy sources available in the abdominal cavity are quite varied, so we were not surprised to see a robust, complex response in PUL expression. A recent study of Bacteroides thetaiotaomicron PUL regulation during growth on mixtures of dietary glycans provides some insight into this response (11). The work showed that there is a rapid response to the influx of new glycan sources, and that multiple PULs were simultaneously expressed to prioritize utilization of the most advantageous substrates.…”

Species-Specific Dynamic Responses of Gut Bacteria to a Mammalian Glycan

“…Given the natural heterogeneity in the structures of polysaccharides (i.e., sugar content, linkage, modification, and chain length) (17), it is possible that differences in the chemical specificities of orthologous gene products in PULs lead to the emergence of strain-specific glycan selection (13). This may be manifested in differences in the substrate repertoires among Bacteroides CS PULs (10) and/or the deployment of the same PULs, depending on the presence of additional nutrients (36,37).…”