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Humans harbor numerous species of colonic bacteria that digest fiber polysaccharides in commonly consumed terrestrial plants. More recently in history, regional populations have consumed edible macroalgae seaweeds containing unique polysaccharides. It remains unclear how extensively gut bacteria have adapted to digest these nutrients. Here, we show that the ability of gut bacteria to digest seaweed polysaccharides is more pervasive than previously appreciated. Enrichment-cultured Bacteroides harbor previously discovered genes for seaweed degradation, which have mobilized into several members of this genus. Additionally, other examples of marine bacteria-derived genes, and their mobile DNA elements, are involved in gut microbial degradation of seaweed polysaccharides, including genes in gut-resident Firmicutes. Collectively, these results uncover multiple separate events that have mobilized the genes encoding seaweed-degrading-enzymes into gut bacteria. This work further underscores the metabolic plasticity of the human gut microbiome and global exchange of genes in the context of dietary selective pressures.

Humans have co-evolved with a dense community of microbial symbionts that inhabit the lower intestine. In the colon, secreted mucus creates a barrier that separates these microorganisms from the intestinal epithelium.sup.1. Some gut bacteria are able to utilize mucin glycoproteins, the main mucus component, as a nutrient source. However, it remains unclear which bacterial enzymes initiate degradation of the complex O-glycans found in mucins. In the distal colon, these glycans are heavily sulfated, but specific sulfatases that are active on colonic mucins have not been identified. Here we show that sulfatases are essential to the utilization of distal colonic mucin O-glycans by the human gut symbiont Bacteroides thetaiotaomicron. We characterized the activity of 12 different sulfatases produced by this species, showing that they are collectively active on all known sulfate linkages in O-glycans. Crystal structures of three enzymes provide mechanistic insight into the molecular basis of substrate specificity. Unexpectedly, we found that a single sulfatase is essential for utilization of sulfated O-glycans in vitro and also has a major role in vivo. Our results provide insight into the mechanisms of mucin degradation by a prominent group of gut bacteria, an important process for both normal microbial gut colonization.sup.2 and diseases such as inflammatory bowel disease.sup.3. A single sulfatase produced by a bacterium found in the human colon is essential for degradation of sulfated O-glycans in secreted mucus., Author(s): Ana S. Luis [sup.1] [sup.2] , Chunsheng Jin [sup.2] , Gabriel Vasconcelos Pereira [sup.1] , Robert W. P. Glowacki [sup.1] , Sadie R. Gugel [sup.1] , Shaleni Singh [sup.1] [...]

The human gut microbiota is able to degrade otherwise undigestible polysaccharides, largely through the activity of Bacteroides. Uptake of polysaccharides into Bacteroides is controlled by TonB-dependent transporters (TBDTs), whose transport is energized by an inner membrane complex composed of the proteins TonB, ExbB, and ExbD. Bacteroides thetaiotaomicron (B. theta) encodes 11 TonB homologs that are predicted to be able to contact TBDTs to facilitate transport. However, it is not clear which TonBs are important for polysaccharide uptake. Using strains in which each of the 11 predicted tonB genes are deleted, we show that TonB4 (BT2059) is important but not essential for proper growth on starch. In the absence of TonB4, we observed an increase in the abundance of TonB6 (BT2762) in the membrane of B. theta, suggesting functional redundancy of these TonB proteins. The growth of the single deletion strains on pectic galactan, chondroitin sulfate, arabinan, and levan suggests a similar functional redundancy of the TonB proteins. A search for highly homologous proteins across other Bacteroides species and recent work in Bacteroides fragilis suggests that TonB4 is widely conserved and may play a common role in polysaccharide uptake. However, proteins similar to TonB6 are found only in B. theta and closely related species, suggesting that the functional redundancy of TonB4 and TonB6 may be limited across Bacteroides. This study extends our understanding of the protein network required for polysaccharide utilization in B. theta and highlights differences in TonB complexes across Bacteroides species. [ABSTRACT FROM AUTHOR]