title: Nitrogen fixation in a non-heterocystous cyanobacterial mat from a mountain river.
abstract: In situ nitrogen fixation was investigated in a cyanobacterial mat growing on the bed of rocks of the Muga River, Spain. The filamentous non-heterocystous cyanobacterium Schizothrix dominated the mat, showing nitrogenase activity in the light at similar rates to those found in nearby heterocystous Rivularia colonies. N2 fixation in the light was significantly increased by an inhibitor of PSII and oxygen evolution, DCMU (3-[3,4-dichlorophenyl]-1,1-dimethylurea), and anaerobic conditions. However, no nitrogenase activity was found in the dark. Addition of fructose as a respiratory substrate induced nitrogenase activity in samples incubated under aerobic conditions in the dark but not in anaerobic conditions. Microelectrode oxygen profiles showed internal microaerobic microzones where nitrogen fixation might concentrate. Analyses of the 16S rRNA gene revealed only the presence of sequences belonging to filamentous non-heterocystous cyanobacteria. nifH gene diversity showed that the major phylotypes also belonged to this group. One of the three strains isolated from the Schizothrix mat was capable of fixing N2 and growing in the absence of combined N. This was consistent with the nifH gene analysis. These results suggest a relevant contribution of non-heterocystous cyanobacteria to nitrogen fixation in these mats.
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid, Darwin 2, 28049 Madrid, Spain.|Department of Botany, Faculty of Science, University of South Bohemia, 31 Branišovská, 370 05 České Budějovice, Czech Republic.
authors.forename: Esther
authors.initials: E
authors.lastname: Berrendero
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid, Darwin 2, 28049 Madrid, Spain.
authors.forename: Eduardo Fernández
authors.initials: EF
authors.lastname: Valiente
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid, Darwin 2, 28049 Madrid, Spain.
authors.forename: Elvira
authors.initials: E
authors.lastname: Perona
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid, Darwin 2, 28049 Madrid, Spain.
authors.forename: Claudia L
authors.initials: CL
authors.lastname: Gómez
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid, Darwin 2, 28049 Madrid, Spain.
authors.forename: Virginia
authors.initials: V
authors.lastname: Loza
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid, Darwin 2, 28049 Madrid, Spain.
authors.forename: M Ángeles
authors.initials: MÁ
authors.lastname: Muñoz-Martín
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid, Darwin 2, 28049 Madrid, Spain.
authors.forename: Pilar
authors.initials: P
authors.lastname: Mateo
mesh_terms: D000458:Cyanobacteria / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D004269:DNA, Bacterial / Q000235:genetics; D009586:Nitrogen Fixation / Q000502:physiology*; D009591:Nitrogenase / Q000378:metabolism*; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D045483:Rivers
chemical_list: D004269:DNA, Bacterial; D012336:RNA, Ribosomal, 16S; D009591:Nitrogenase