title: Structure, genetics and function of an exopolysaccharide produced by a bacterium living within fungal hyphae.
abstract: The rice seedling blight fungus Rhizopus microsporus has an unusual symbiosis with a bacterium, Burkholderia rhizoxinica, which lives within the fungal cytosol and produces a potent phytotoxin that causes severe losses in agriculture. To gain insight into symbiosis factors we investigated the endosymbiont's exopolysaccharide (EPS), a secreted matrix that plays pivotal roles in mediating cell-environment interactions. By a combination of homo- and heteronuclear 2D NMR experiments, we elucidated a previously unknown EPS structure: a repeating tetrasaccharide unit bearing a nonstoichiometric acetyl group on a mannose residue. We also analyzed the EPS biosynthesis gene cluster and generated a targeted mutant to compare the phenotypes. Scanning electron microscope images revealed a reduced ability of the mutant to form extracellular polymers around cell aggregates. Phylogenetic analyses suggest that the symbiont's EPS genes are retained through evolutionary processes.
authors.affiliation: Leibniz Institute for Natural Product Research and Infection Biology (HKI), Department of Biomolecular Chemistry, Beutenbergstrasse 11a, 07745 Jena (Germany).
authors.forename: Zerrin
authors.initials: Z
authors.lastname: Uzum
authors.forename: Alba
authors.initials: A
authors.lastname: Silipo
authors.forename: Gerald
authors.initials: G
authors.lastname: Lackner
authors.forename: Antonia
authors.initials: A
authors.lastname: De Felice
authors.forename: Antonio
authors.initials: A
authors.lastname: Molinaro
authors.forename: Christian
authors.initials: C
authors.lastname: Hertweck
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D019117:Burkholderia / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D002240:Carbohydrate Sequence; D025301:Hyphae / Q000502:physiology; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D005810:Multigene Family; D009154:Mutation; D010802:Phylogeny; D011135:Polysaccharides, Bacterial / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism*; D012233:Rhizopus / Q000502:physiology*; D013559:Symbiosis
chemical_list: D001426:Bacterial Proteins; D011135:Polysaccharides, Bacterial
keywords: Burkholderia; NMR spectroscopy; Rhizopus; bacteria-fungi interactions; exopolysaccharides; oligosaccharides