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要旨:
Nitrogen (N-2) 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 N-2 and carbon (C) fixation by unicellular diazotrophic cyanobacteria. The nifH gene abundance (10(4)-10(6) nifH L-1) and nifH gene transcript abundance (10(2)-10(4) cDNA nifH L-1) for two unicellular groups, UCYN-A and UCYN-B, were detected. UCYN-A was also identified and quantified (10(4)-10(3) cells 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 C-13-bicarbonate and N-15(2). Free UCYN-A cells were enriched in both C-13 and N-15 and estimated C and N-2 fixation rates for UCYN-A were lower compared to co-occurring unicellular cyanobacteria cells similar in size (3.1-5.6 mu m) and pigmentation to diazotroph Crocosphaera watsonii. Here, we identify and quantify two common co-occurring unicellular groups and measure their cellular activities by nanoSIMS. (C) 2013 Elsevier GmbH. All rights reserved.
