title: Synthesis and assembly of a novel glycan layer in Myxococcus xanthus spores.
abstract: Myxococcus xanthus is a Gram-negative deltaproteobacterium that has evolved the ability to differentiate into metabolically quiescent spores that are resistant to heat and desiccation. An essential feature of the differentiation processes is the assembly of a rigid, cell wall-like spore coat on the surface of the outer membrane. In this study, we characterize the spore coat composition and describe the machinery necessary for secretion of spore coat material and its subsequent assembly into a stress-bearing matrix. Chemical analyses of isolated spore coat material indicate that the spore coat consists primarily of short 1-4- and 1-3-linked GalNAc polymers that lack significant glycosidic branching and may be connected by glycine peptides. We show that 1-4-linked glucose (Glc) is likely a minor component of the spore coat with the majority of the Glc arising from contamination with extracellular polysaccharides, O-antigen, or storage compounds. Neither of these structures is required for the formation of resistant spores. Our analyses indicate the GalNAc/Glc polymer and glycine are exported by the ExoA-I system, a Wzy-like polysaccharide synthesis and export machinery. Arrangement of the capsular-like polysaccharides into a rigid spore coat requires the NfsA-H proteins, members of which reside in either the cytoplasmic membrane (NfsD, -E, and -G) or outer membrane (NfsA, -B, and -C). The Nfs proteins function together to modulate the chain length of the surface polysaccharides, which is apparently necessary for their assembly into a stress-bearing matrix.
authors.affiliation: Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, 35043 Marburg, Germany.
authors.forename: Carina
authors.initials: C
authors.lastname: Holkenbrink
authors.affiliation: W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland 21205, and.
authors.forename: Egbert
authors.initials: E
authors.lastname: Hoiczyk
authors.affiliation: Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, 35043 Marburg, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Kahnt
authors.affiliation: Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, 35043 Marburg, Germany,; Department of Biological Sciences, Wayne State University, Detroit, Michigan 48202. Electronic address: pihiggs@wayne.edu.
authors.forename: Penelope I
authors.initials: PI
authors.lastname: Higgs
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry; D002499:Centrifugation, Density Gradient; D008854:Microscopy, Electron; D009154:Mutation; D016941:Myxococcus xanthus / Q000737:chemistry*; D019081:O Antigens / Q000737:chemistry*; D009844:Oligosaccharides / Q000737:chemistry; D010641:Phenotype; D011134:Polysaccharides / Q000737:chemistry*; D013171:Spores, Bacterial / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D019081:O Antigens; D009844:Oligosaccharides; D011134:Polysaccharides
keywords: Gram-negative Bacteria; Membrane Protein; Peptidoglycan; Polysaccharide; Sporulation