title: Characterization of nitrogen-fixing cyanobacteria in the Brazilian Amazon floodplain.
abstract: The diversity of the free-living nitrogen-fixing cyanobacterial community in the floodplain sediments along the Solimões and Amazon Rivers and some of their tributaries (Japurá, Negro and Madeira) was investigated. Five cyanobacterial genera were morphologically identified, four of which (Nostoc, Calothrix, Cylindrospermum and Fischerella) have not previously been isolated from the Brazilian Amazon floodplain. Nostoc strains were the most commonly found heterocyst-forming cyanobacteria. Five strains (N. muscorum CENA18 and CENA61, N. piscinale CENA21, Cylindrospermum sp. CENA33 and Fischerella sp. CENA19) were selected for growth measurement, ability to fix N2 and phylogenetic analysis, based on their widespread distribution and morphological distinction. Molecular analyses employing 16S rRNA sequences indicated that some of the isolates may represent novel cyanobacterial species. Dinitrogen fixed by these strains was measured indirectly as acetylene reduction activity and ranged from 11.5 to 22.2 nmol C2H4 microg Chl a(-1) h(-1). These results provide evidence of widespread and importance of nitrogen-fixing cyanobacteria as a source of N inputs in the Amazonian ecosystem.
authors.affiliation: Centro de Energia Nuclear na Agricultura, Universidade de São Paulo, Av. Centenário 303, Caixa Postal 96, CEP 13400-970, Piracicaba-SP, Brazil. fiore@cena.usp.br
authors.forename: Marli de Fátima
authors.initials: Mde F
authors.lastname: Fiore
authors.forename: Brett A
authors.initials: BA
authors.lastname: Neilan
authors.forename: Janine N
authors.initials: JN
authors.lastname: Copp
authors.forename: Jorge L M
authors.initials: JL
authors.lastname: Rodrigues
authors.forename: Siu M
authors.initials: SM
authors.lastname: Tsai
authors.forename: Hung
authors.initials: H
authors.lastname: Lee
authors.forename: Jack T
authors.initials: JT
authors.lastname: Trevors
mesh_terms: D001938:Brazil; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D000458:Cyanobacteria / Q000145:classification / Q000302:isolation & purification / Q000502:physiology*; D004269:DNA, Bacterial / Q000235:genetics; D019015:Geologic Sediments / Q000382:microbiology; D009586:Nitrogen Fixation; D009591:Nitrogenase / Q000378:metabolism; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D045483:Rivers; D017422:Sequence Analysis, DNA
chemical_list: D004269:DNA, Bacterial; D012336:RNA, Ribosomal, 16S; D002734:Chlorophyll; D009591:Nitrogenase; D000077194:Chlorophyll A