title: A novel bleb-dependent polysaccharide export system in nitrogen-fixing Azotobacter vinelandii subjected to low nitrogen gas levels.
abstract: The alginate biofilm-producing bacterium Azotobacter vinelandii aerobically fixes nitrogen by oxygen-sensitive nitrogenases. Here we investigated the bacterial response to nitrogen/oxygen gas mixtures. A. vinelandii cells were cultured in nitrogen-free minimal media containing gas mixtures differing in their ratios of nitrogen and oxygen. The bacteria did not grow at oxygen concentrations >75% but grew well in the presence of 5% nitrogen/25% oxygen. Growth of wild-type and alginate-deficient strains when cultured with 50% oxygen did not differ substantially, indicating that alginate is not required for the protection of nitrogenases from oxygen damage. In response to decreasing nitrogen levels, A. vinelandii produced greater amounts of alginate, accompanied by the formation of blebs on the cell surface. The encystment of vegetative cells occurred in tandem with the release of blebs and the development of a multilayered exine. Immunoelectron microscopy using anti alginate-antibody revealed that the blebs contained alginate molecules. By contrast, alginate-deficient mutants could not form blebs. Taken together, our data provide evidence for a novel bleb-dependent polysaccharide export system in A. vinelandii that is activated in response to low nitrogen gas levels.
authors.affiliation: Laboratory of Basic and Applied Molecular Biotechnology, Graduate School of Agriculture, Kyoto University, Kyoto, Japan.
authors.forename: Wataru
authors.initials: W
authors.lastname: Hashimoto
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Miyamoto
authors.forename: Mayumi
authors.initials: M
authors.lastname: Yamamoto
authors.forename: Fuminori
authors.initials: F
authors.lastname: Yoneyama
authors.forename: Kousaku
authors.initials: K
authors.lastname: Murata
mesh_terms: D000464:Alginates; D016948:Azotobacter vinelandii / Q000187:drug effects / Q000254:growth & development / Q000502:physiology* / Q000648:ultrastructure; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D020723:Glucuronic Acid / Q000378:metabolism; D006603:Hexuronic Acids; D009154:Mutation; D009584:Nitrogen / Q000494:pharmacology*; D010100:Oxygen / Q000494:pharmacology*; D011135:Polysaccharides, Bacterial / Q000378:metabolism*
chemical_list: D000464:Alginates; D001426:Bacterial Proteins; D006603:Hexuronic Acids; D011135:Polysaccharides, Bacterial; D020723:Glucuronic Acid; D009584:Nitrogen; D010100:Oxygen