title: Variability in benthic diazotrophy and cyanobacterial diversity in a tropical intertidal lagoon.
abstract: Benthic nitrogen fixation has been estimated to contribute 15 Tg N year(-1) to the marine nitrogen budget. With benthic marine nitrogen fixation being largely overlooked in more recent surveys, a refocus on benthic diazotrophy was considered important. Variations in nitrogenase activity (acetylene reduction-gas chromatography) in a tropical lagoon in the western Indian Ocean (Zanzibar, Tanzania) were monitored over a 3-year period (2003-2005) and related to cyanobacterial and diazotrophic microbial diversity using a polyphasic approach. Different nitrogenase activity patterns were discerned, with the predominant pattern being high daytime activities combined with low nighttime activities. Analyses of the morphological and 16S rRNA gene diversity among cyanobacteria revealed filamentous nonheterocystous (Oscillatoriales) and unicellular (Chroococcales) representatives to be predominant. Analyses of the nifH gene diversity showed that the major phylotypes belonged to noncyanobacterial prokaryotes. However, as shown by cyanobacterial selective nifH-denaturing gradient gel electrophoresis analysis, cyanobacterial nifH gene sequences were present at all sites. Several nifH and 16S rRNA gene phylotypes were related to uncultured cyanobacteria or bacteria of geographically distant habitats, stressing the widespread occurrence of still poorly characterized microorganisms in tropical benthic marine communities.
authors.affiliation: Department of Botany, Stockholm University, Stockholm, Sweden. bauer@botan.su.se
authors.forename: Karolina
authors.initials: K
authors.lastname: Bauer
authors.forename: Beatriz
authors.initials: B
authors.lastname: Díez
authors.forename: Charles
authors.initials: C
authors.lastname: Lugomela
authors.forename: Susanna
authors.initials: S
authors.lastname: Seppälä
authors.forename: Agneta Julia
authors.initials: AJ
authors.lastname: Borg
authors.forename: Birgitta
authors.initials: B
authors.lastname: Bergman
mesh_terms: D001483:Base Sequence; D044822:Biodiversity; D003001:Cloning, Molecular; D000458:Cyanobacteria / Q000145:classification / Q000235:genetics / Q000302:isolation & purification* / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D008969:Molecular Sequence Data; D009591:Nitrogenase / Q000378:metabolism*; D010088:Oxidoreductases / Q000235:genetics*; D010802:Phylogeny; D012150:Polymorphism, Restriction Fragment Length; D012329:RNA, Bacterial / Q000235:genetics; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012623:Seawater / Q000382:microbiology*; D017423:Sequence Analysis, RNA; D013636:Tanzania; D014329:Tropical Climate
chemical_list: D012329:RNA, Bacterial; D012336:RNA, Ribosomal, 16S; D010088:Oxidoreductases; D009591:Nitrogenase; C029130:nitrogenase reductase