title: A Highly Active Endo-Levanase BT1760 of a Dominant Mammalian Gut Commensal Bacteroides thetaiotaomicron Cleaves Not Only Various Bacterial Levans, but Also Levan of Timothy Grass.
abstract: Bacteroides thetaiotaomicron, an abundant commensal of the human gut, degrades numerous complex carbohydrates. Recently, it was reported to grow on a β-2,6-linked polyfructan levan produced by Zymomonas mobilis degrading the polymer into fructooligosaccharides (FOS) with a cell surface bound endo-levanase BT1760. The FOS are consumed by B. thetaiotaomicron, but also by other gut bacteria, including health-promoting bifidobacteria and lactobacilli. Here we characterize biochemical properties of BT1760, including the activity of BT1760 on six bacterial levans synthesized by the levansucrase Lsc3 of Pseudomonas syringae pv. tomato, its mutant Asp300Asn, levansucrases of Zymomonas mobilis, Erwinia herbicola, Halomonas smyrnensis as well as on levan isolated from timothy grass. For the first time a plant levan is shown as a perfect substrate for an endo-fructanase of a human gut bacterium. BT1760 degraded levans to FOS with degree of polymerization from 2 to 13. At optimal reaction conditions up to 1 g of FOS were produced per 1 mg of BT1760 protein. Low molecular weight (<60 kDa) levans, including timothy grass levan and levan synthesized from sucrose by the Lsc3Asp300Asn, were degraded most rapidly whilst levan produced by Lsc3 from raffinose least rapidly. BT1760 catalyzed finely at human body temperature (37°C) and in moderately acidic environment (pH 5-6) that is typical for the gut lumen. According to differential scanning fluorimetry, the Tm of the endo-levanase was 51.5°C. All tested levans were sufficiently stable in acidic conditions (pH 2.0) simulating the gastric environment. Therefore, levans of both bacterial and plant origin may serve as a prebiotic fiber for B. thetaiotaomicron and contribute to short-chain fatty acids synthesis by gut microbiota. In the genome of Bacteroides xylanisolvens of human origin a putative levan degradation locus was disclosed.
authors.affiliation: Department of Genetics, Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia.
authors.forename: Karin
authors.initials: K
authors.lastname: Mardo
authors.affiliation: Department of Genetics, Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia.
authors.forename: Triinu
authors.initials: T
authors.lastname: Visnapuu
authors.affiliation: Laboratory of Environmental Toxicology, National Institute of Chemical Physics and Biophysics, Tallinn, Estonia.
authors.forename: Heiki
authors.initials: H
authors.lastname: Vija
authors.affiliation: Department of Genetics, Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia.
authors.forename: Anneli
authors.initials: A
authors.lastname: Aasamets
authors.affiliation: Department of Genetics, Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia.
authors.forename: Katrin
authors.initials: K
authors.lastname: Viigand
authors.affiliation: Department of Genetics, Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia.
authors.forename: Tiina
authors.identifier: http://orcid.org/0000-0001-6596-0844
authors.initials: T
authors.lastname: Alamäe
mesh_terms: D000070077:Bacteroides thetaiotaomicron / Q000201:enzymology*; D004885:Erwinia / Q000201:enzymology; D005630:Fructans / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D006026:Glycoside Hydrolases / Q000378:metabolism*; D020632:Halomonas / Q000201:enzymology; D006602:Hexosyltransferases / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D007422:Intestines / Q000382:microbiology; D008970:Molecular Weight; D009844:Oligosaccharides / Q000378:metabolism; D031784:Phleum / Q000378:metabolism*; D044224:Pseudomonas syringae / Q000201:enzymology; D017385:Sequence Homology; D013379:Substrate Specificity; D017355:Zymomonas / Q000201:enzymology
chemical_list: D005630:Fructans; D009844:Oligosaccharides; C116580:fructooligosaccharide; D006602:Hexosyltransferases; C021513:levansucrase; D006026:Glycoside Hydrolases; C021512:levanase