title: A novel intracellular nitrogen-fixing symbiosis made by Ustilago maydis and Bacillus spp.
abstract: We observed that the maize pathogenic fungus Ustilago maydis grew in nitrogen (N)-free media at a rate similar to that observed in media containing ammonium nitrate, suggesting that it was able to fix atmospheric N2 . Because only prokaryotic organisms have the capacity to reduce N2 , we entertained the possibility that U. maydis was associated with an intracellular bacterium. The presence of nitrogenase in the fungus was analyzed by acetylene reduction, and capacity to fix N2 by use of (15) N2 . Presence of an intracellular N2 -fixing bacterium was analyzed by PCR amplification of bacterial 16S rRNA and nifH genes, and by microscopic observations. Nitrogenase activity and (15) N incorporation into the cells proved that U. maydis fixed N2 . Light and electron microscopy, and fluorescence in situ hybridization (FISH) experiments revealed the presence of intracellular bacteria related to Bacillus pumilus, as evidenced by sequencing of the PCR-amplified fragments. These observations reveal for the first time the existence of an endosymbiotic N2 -fixing association involving a fungus and a bacterium.
authors.affiliation: Departamento de Ingeniería Genética, Unidad Irapuato, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Irapuato, Guanajuato, México.
authors.forename: José
authors.initials: J
authors.lastname: Ruiz-Herrera
authors.affiliation: Departamento de Ingeniería Genética, Unidad Irapuato, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Irapuato, Guanajuato, México.
authors.forename: Claudia
authors.initials: C
authors.lastname: León-Ramírez
authors.affiliation: Departamento de Biotecnología y Bioquímica, Unidad Irapuato, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Irapuato, Guanajuato, México.
authors.forename: Antonio
authors.initials: A
authors.lastname: Vera-Nuñez
authors.affiliation: Departamento de Ingeniería Genética, Unidad Irapuato, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Irapuato, Guanajuato, México.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Sánchez-Arreguín
authors.affiliation: Departamento de Biotecnología y Bioingeniería, Unidad Zacatenco, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, México City, México.
authors.forename: Roberto
authors.initials: R
authors.lastname: Ruiz-Medrano
authors.affiliation: Departamento de Ingeniería Genética, Unidad Irapuato, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Irapuato, Guanajuato, México.
authors.forename: Holjes
authors.initials: H
authors.lastname: Salgado-Lugo
authors.affiliation: Departamento de Ingeniería Genética, Unidad Irapuato, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Irapuato, Guanajuato, México.
authors.forename: Lino
authors.initials: L
authors.lastname: Sánchez-Segura
authors.affiliation: Departamento de Biotecnología y Bioquímica, Unidad Irapuato, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Irapuato, Guanajuato, México.
authors.forename: Juan José
authors.initials: JJ
authors.lastname: Peña-Cabriales
mesh_terms: D000114:Acetylene / Q000378:metabolism; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001407:Bacillus / Q000187:drug effects / Q000502:physiology*; D004587:Electrophoresis, Agar Gel; D017404:In Situ Hybridization, Fluorescence; D042541:Intracellular Space / Q000382:microbiology*; D008969:Molecular Sequence Data; D009584:Nitrogen / Q000494:pharmacology; D009586:Nitrogen Fixation; D009587:Nitrogen Isotopes; D009591:Nitrogenase / Q000378:metabolism; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D013559:Symbiosis / Q000187:drug effects; D014588:Ustilago / Q000187:drug effects / Q000254:growth & development / Q000502:physiology* / Q000648:ultrastructure
chemical_list: D000900:Anti-Bacterial Agents; D009587:Nitrogen Isotopes; D012336:RNA, Ribosomal, 16S; D009591:Nitrogenase; D009584:Nitrogen; D000114:Acetylene
keywords: Bacillus pumilus; Ustilago maydis; endosymbiosis; nifH gene; nitrogen fixation; nitrogenase