Identification of a novel cyanobacterial group as active diazotrophs in a coastal microbial mat using NanoSIMS analysis |
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| Authors: | Dagmar Woebken Luke C Burow Leslie Prufert-Bebout Brad M Bebout Tori M Hoehler Jennifer Pett-Ridge Alfred M Spormann Peter K Weber Steven W Singer |
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| Affiliation: | 1.Departments of Chemical Engineering, and of Civil and Environmental Engineering, Stanford University, Stanford, CA, USA;2.Exobiology Branch, NASA Ames Research Center, Moffett Field, CA, USA;3.Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, CA, USA;4.Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA |
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| Abstract: | N2 fixation is a key process in photosynthetic microbial mats to support the nitrogen demands associated with primary production. Despite its importance, groups that actively fix N2 and contribute to the input of organic N in these ecosystems still remain largely unclear. To investigate the active diazotrophic community in microbial mats from the Elkhorn Slough estuary, Monterey Bay, CA, USA, we conducted an extensive combined approach, including biogeochemical, molecular and high-resolution secondary ion mass spectrometry (NanoSIMS) analyses. Detailed analysis of dinitrogenase reductase (nifH) transcript clone libraries from mat samples that fixed N2 at night indicated that cyanobacterial nifH transcripts were abundant and formed a novel monophyletic lineage. Independent NanoSIMS analysis of 15N2-incubated samples revealed significant incorporation of 15N into small, non-heterocystous cyanobacterial filaments. Mat-derived enrichment cultures yielded a unicyanobacterial culture with similar filaments (named Elkhorn Slough Filamentous Cyanobacterium-1 (ESFC-1)) that contained nifH gene sequences grouping with the novel cyanobacterial lineage identified in the transcript clone libraries, displaying up to 100% amino-acid sequence identity. The 16S rRNA gene sequence recovered from this enrichment allowed for the identification of related sequences from Elkhorn Slough mats and revealed great sequence diversity in this cluster. Furthermore, by combining 15N2 tracer experiments, fluorescence in situ hybridization and NanoSIMS, in situ N2 fixation activity by the novel ESFC-1 group was demonstrated, suggesting that this group may be the most active cyanobacterial diazotroph in the Elkhorn Slough mat. Pyrotag sequences affiliated with ESFC-1 were recovered from mat samples throughout 2009, demonstrating the prevalence of this group. This work illustrates that combining standard and single-cell analyses can link phylogeny and function to identify previously unknown key functional groups in complex ecosystems. |
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| Keywords: | cyanobacteria dinitrogenase reductase (nifH) microbial mats NanoSIMS N2 fixation |
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