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PUL0308 |
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29020628, Cell Rep. 2017 Oct 10;21(2):417-430. doi: 10.1016/j.celrep.2017.09.049. |
| | Molecular Mechanism by which Prominent Human Gut Bacteroidetes Utilize Mixed-Linkage Beta-Glucans, Major Health-Promoting Cereal Polysaccharides. |
| | Tamura K, Hemsworth GR, Dejean G, Rogers TE, Pudlo NA, Urs K, Jain N, Davies GJ, Martens EC, Brumer H |
| | Microbial utilization of complex polysaccharides is a major driving force in shaping the composition of the human gut microbiota. There is a growing appreciation that finely tuned polysaccharide utilization loci enable ubiquitous gut Bacteroidetes to thrive on the plethora of complex polysaccharides that constitute "dietary fiber." Mixed-linkage beta(1,3)/beta(1,4)-glucans (MLGs) are a key family of plant cell wall polysaccharides with recognized health benefits but whose mechanism of utilization has remained unclear. Here, we provide molecular insight into the function of an archetypal MLG utilization locus (MLGUL) through a combination of biochemistry, enzymology, structural biology, and microbiology. Comparative genomics coupled with growth studies demonstrated further that syntenic MLGULs serve as genetic markers for MLG catabolism across commensal gut bacteria. In turn, we surveyed human gut metagenomes to reveal that MLGULs are ubiquitous in human populations globally, which underscores the importance of gut microbial metabolism of MLG as a common cereal polysaccharide. |
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22205877, PLoS Biol. 2011 Dec;9(12):e1001221. doi: 10.1371/journal.pbio.1001221. Epub 2011 Dec 20. |
| | Recognition and degradation of plant cell wall polysaccharides by two human gut symbionts. |
| | Martens EC, Lowe EC, Chiang H, Pudlo NA, Wu M, McNulty NP, Abbott DW, Henrissat B, Gilbert HJ, Bolam DN, Gordon JI |
| | Symbiotic bacteria inhabiting the human gut have evolved under intense pressure to utilize complex carbohydrates, primarily plant cell wall glycans in our diets. These polysaccharides are not digested by human enzymes, but are processed to absorbable short chain fatty acids by gut bacteria. The Bacteroidetes, one of two dominant bacterial phyla in the adult gut, possess broad glycan-degrading abilities. These species use a series of membrane protein complexes, termed Sus-like systems, for catabolism of many complex carbohydrates. However, the role of these systems in degrading the chemically diverse repertoire of plant cell wall glycans remains unknown. Here we show that two closely related human gut Bacteroides, B. thetaiotaomicron and B. ovatus, are capable of utilizing nearly all of the major plant and host glycans, including rhamnogalacturonan II, a highly complex polymer thought to be recalcitrant to microbial degradation. Transcriptional profiling and gene inactivation experiments revealed the identity and specificity of the polysaccharide utilization loci (PULs) that encode individual Sus-like systems that target various plant polysaccharides. Comparative genomic analysis indicated that B. ovatus possesses several unique PULs that enable degradation of hemicellulosic polysaccharides, a phenotype absent from B. thetaiotaomicron. In contrast, the B. thetaiotaomicron genome has been shaped by increased numbers of PULs involved in metabolism of host mucin O-glycans, a phenotype that is undetectable in B. ovatus. Binding studies of the purified sensor domains of PUL-associated hybrid two-component systems in conjunction with transcriptional analyses demonstrate that complex oligosaccharides provide the regulatory cues that induce PUL activation and that each PUL is highly specific for a defined cell wall polymer. These results provide a view of how these species have diverged into different carbohydrate niches by evolving genes that target unique suites of available polysaccharides, a theme that likely applies to disparate bacteria from the gut and other habitats. |
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32801182, Appl Environ Microbiol. 2020 Oct 1;86(20):e01651-20. doi: 10.1128/AEM.01651-20. Print 2020 Oct 1. |
| | Sharing a beta-Glucan Meal: Transcriptomic Eavesdropping on a Bacteroides ovatus-Subdoligranulum variabile-Hungatella hathewayi Consortium. |
| | Centanni M, Sims IM, Bell TJ, Biswas A, Tannock GW |
| | Whole-transcriptome analysis was used to investigate the molecular interplay between three bacterial species that are members of the human gut microbiota. Bacteroides ovatus, Subdoligranulum variabile, and Hungatella hathewayi formed associations in cocultures fed barley beta-glucan, a constituent of dietary fiber. B. ovatus depolymerized beta-glucan and released, but did not utilize, 3-O-beta-cellobiosyl-d-glucose (DP3) and 3-O-beta-cellotriosyl-d-glucose (DP4). These oligosaccharides provided growth substrates for S. variabile and H. hathewayi with a preference for DP4 in the case of the latter species. There was increased transcription of a B. ovatus mixed-linkage-beta-glucan utilization locus, as well as carbohydrate transporters in S. variabile and H. hathewayi when in batch coculture. Increased transcription of the beta-glucan utilization locus did not occur in continuous culture. Evidence for interactions relating to provision of cobalamin, alterations to signaling, and modulation of the "stringent response" (an adaptation to nutrient deprivation) were detected. Overall, we established a bacterial consortium based on barley beta-glucan in vitro, which can be used to investigate aspects of the functional blueprint of the human gut microbiota.IMPORTANCE The microbial community, mostly composed of bacterial species, residing in the human gut degrades and ferments polysaccharides derived from plants (dietary fiber) that would not otherwise be digested. In this way, the collective metabolic actions of community members extract additional energy from the human diet. While the variety of bacteria present in the microbial community is well known, the formation of bacterial consortia, and the consequent interactions that result in the digestion of dietary polysaccharides, has not been studied extensively. The importance of our work was the establishment, under laboratory conditions, of a consortium of gut bacteria that formed around a dietary constituent commonly present in cereals. This enabled the metabolic interplay between the bacterial species to be studied. This kind of knowledge is required to construct an interactive, metabolic blueprint of the microbial community that inhabits the human gut. |
