title: In situ identification and N₂ and C fixation rates of uncultivated cyanobacteria populations.
abstract: Nitrogen (N₂) fixation is a globally important process often mediated by diazotrophic cyanobacteria in the open ocean. In 2010, seawater was collected near Cape Verde to identify and measure N₂ and carbon (C) fixation by unicellular diazotrophic cyanobacteria. The nifH gene abundance (10⁴-10⁶ nifH L⁻¹) and nifH gene transcript abundance (10²-10⁴ cDNA nifHL⁻¹) for two unicellular groups, UCYN-A and UCYN-B, were detected. UCYN-A was also identified and quantified (10⁴-10⁵cells L⁻¹) by new probes (UCYN-A732 and UCYN-A159) using Catalyzed Reporter Deposition-Fluorescence In Situ Hybridization (CARD-FISH) assays. The UCYN-A were observed as free cells or attached to a larger unidentified eukaryotic cell. A Halogen In Situ Hybridization-Secondary Ion Mass Spectrometry (HISH-SIMS) assay using the UCYN-A732 probe was applied on samples previously incubated with ¹³C-bicarbonate and ¹⁵N₂. Free UCYN-A cells were enriched in both ¹³C and ¹⁵N and estimated C and N₂ fixation rates for UCYN-A were lower compared to co-occurring unicellular cyanobacteria cells similar in size (3.1-5.6 μm) and pigmentation to diazotroph Crocosphaera watsonii. Here, we identify and quantify two common co-occurring unicellular groups and measure their cellular activities by nanoSIMS.
authors.affiliation: Max Planck Institute for Marine Microbiology, Bremen D-28359, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Krupke
authors.forename: Niculina
authors.initials: N
authors.lastname: Musat
authors.forename: Julie
authors.initials: J
authors.lastname: Laroche
authors.forename: Wiebke
authors.initials: W
authors.lastname: Mohr
authors.forename: Bernhard M
authors.initials: BM
authors.lastname: Fuchs
authors.forename: Rudolf I
authors.initials: RI
authors.lastname: Amann
authors.forename: Marcel M M
authors.initials: MM
authors.lastname: Kuypers
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Foster
mesh_terms: D057486:Carbon Cycle; D002247:Carbon Isotopes / Q000032:analysis; D000458:Cyanobacteria / Q000145:classification / Q000235:genetics / Q000302:isolation & purification* / Q000502:physiology*; D020869:Gene Expression Profiling; D017404:In Situ Hybridization, Fluorescence; D013058:Mass Spectrometry; D009586:Nitrogen Fixation; D009587:Nitrogen Isotopes / Q000032:analysis; D015345:Oligonucleotide Probes / Q000235:genetics; D010088:Oxidoreductases / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D014158:Transcription, Genetic
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D015345:Oligonucleotide Probes; D012333:RNA, Messenger; D010088:Oxidoreductases; C029130:nitrogenase reductase