title: Non-Frankia actinomycetes isolated from surface-sterilized roots of Casuarina equisetifolia fix nitrogen.
abstract: Based on partial 16S sequences, we previously described a novel group of nonsymbiotic, acetylene reduction activity-positive actinomycetes which were isolated from surface-sterilized roots of Casuarina equisetifolia growing in Mexico. An amplified rRNA restriction analysis confirmed that these actinomycetes are distinct from Frankia, a finding substantiated by a 16S rRNA gene phylogenetic analysis of two of the Mexican isolates. Further support for these actinomycetes being separate from Frankia comes from the very low DNA-DNA homology that was found. Nevertheless, the Mexican isolates may be diazotrophs based not only on their ability to grow in N-free medium and reduce acetylene to ethylene but also on the results from (15)N isotope dilution analysis and the finding that a nifH gene was PCR amplified. A comparison of the nifH sequences from the various isolates showed that they are closely related to nifH from Frankia; the similarity was 84 to 98% depending on the host specificity group. An analysis of complete 16S rRNA gene sequences demonstrated that the two strains analyzed in detail are most closely related to actinobacteria in the Thermomonosporaceae and the Micromonosporaceae.
authors.affiliation: Departamento de Microbiología, Escuela Nacional de Ciencias Biológicas, I. P. N., Plan De Ayala y Carpio, México.
authors.forename: María
authors.initials: M
authors.lastname: Valdés
authors.forename: Néstor-Octavio
authors.initials: NO
authors.lastname: Pérez
authors.forename: Paulina
authors.initials: P
authors.lastname: Estrada-de Los Santos
authors.forename: Jesús
authors.initials: J
authors.lastname: Caballero-Mellado
authors.forename: Juan José
authors.initials: JJ
authors.lastname: Peña-Cabriales
authors.forename: Philippe
authors.initials: P
authors.lastname: Normand
authors.forename: Ann M
authors.initials: AM
authors.lastname: Hirsch
mesh_terms: D039903:Actinobacteria / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D040161:Frankia / Q000145:classification; D020459:Genes, rRNA; D008800:Mexico; D008848:Micromonosporaceae / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation; D009693:Nucleic Acid Hybridization; D010088:Oxidoreductases / Q000235:genetics; D010802:Phylogeny; D018517:Plant Roots / Q000382:microbiology*; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D014197:Trees / Q000382:microbiology*
chemical_list: D012336:RNA, Ribosomal, 16S; D010088:Oxidoreductases; C029130:nitrogenase reductase