title: Molecular analysis of diazotroph diversity in the rhizosphere of the smooth cordgrass, Spartina alterniflora.
abstract: N(2) fixation by diazotrophic bacteria associated with the roots of the smooth cordgrass, Spartina alterniflora, is an important source of new nitrogen in many salt marsh ecosystems. However, the diversity and phylogenetic affiliations of these rhizosphere diazotrophs are unknown. Denaturing gradient gel electrophoresis (DGGE) of PCR-amplified nifH sequence segments was used in previous studies to examine the stability and dynamics of the Spartina rhizosphere diazotroph assemblages in the North Inlet salt marsh, near Georgetown, S.C. In this study, plugs were taken from gel bands from representative DGGE gels, the nifH amplimers were recovered and cloned, and their sequences were determined. A total of 59 sequences were recovered, and the amino acid sequences predicted from them were aligned with sequences from known and unknown diazotrophs in order to determine the types of organisms present in the Spartina rhizosphere. We recovered numerous sequences from diazotrophs in the gamma subdivision of the division Proteobacteria (gamma-Proteobacteria) and from various anaerobic diazotrophs. Diazotrophs in the alpha-Proteobacteria were poorly represented. None of the Spartina rhizosphere DGGE band sequences were identical to any known or previously recovered environmental nifH sequences. The Spartina rhizosphere diazotroph assemblage is very diverse and apparently consists mainly of unknown organisms.
authors.affiliation: Department of Biological Sciences, University of South Carolina, Columbia, South Carolina 29208, USA. lovell@biol.sc.edu
authors.forename: C R
authors.initials: CR
authors.lastname: Lovell
authors.forename: Y M
authors.initials: YM
authors.lastname: Piceno
authors.forename: J M
authors.initials: JM
authors.lastname: Quattro
authors.forename: C E
authors.initials: CE
authors.lastname: Bagwell
mesh_terms: D001421:Bacteria, Anaerobic / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification; D004269:DNA, Bacterial / Q000235:genetics; D004587:Electrophoresis, Agar Gel / Q000379:methods; D020563:Gammaproteobacteria / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification; D014644:Genetic Variation; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000235:genetics; D010802:Phylogeny; D018517:Plant Roots / Q000382:microbiology*; D006109:Poaceae / Q000382:microbiology*; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D012623:Seawater; D017422:Sequence Analysis, DNA
chemical_list: D004269:DNA, Bacterial; D010088:Oxidoreductases; C029130:nitrogenase reductase