Identification of a novel cyanobacterial group as active diazotrophs in a coastal microbial mat using NanoSIMS analysis

• Published in: The ISME Journal 2012-07, Vol.6 (7), p.1427-1439
• Main Authors: Woebken, Dagmar, Burow, Luke C, Prufert-Bebout, Leslie, Bebout, Brad M, Hoehler, Tori M, Pett-Ridge, Jennifer, Spormann, Alfred M, Weber, Peter K, Singer, Steven W
• Format: Article
• Language: English
• Subjects: 631/326/2565/855; 631/326/325; 631/326/41/1969; Biogeochemistry; Biomedical and Life Sciences; Cyanobacteria - classification; Cyanobacteria - genetics; Cyanobacteria - isolation & purification; Cyanobacteria - metabolism; Dinitrogenase Reductase - genetics; DNA, Bacterial - genetics; Ecology; Ecosystems; ENVIRONMENTAL SCIENCES; Estuaries; Evolutionary Biology; Filaments; Fluorescence; Fluorescence in situ hybridization; Fluorescent indicators; GEOSCIENCES; Hybridization; In Situ Hybridization, Fluorescence; Life Sciences; Mass Spectrometry; Mass spectroscopy; Microbial Ecology; Microbial Genetics and Genomics; Microbial mats; Microbiology; Molecular Sequence Data; NifH gene; Nitrogen; Nitrogen fixation; Original; original-article; Phylogeny; Primary production; Pyruvic acid; reductase; rRNA 16S; Single-Cell Analysis; Transcription
• ISSN: 1751-7362; 1751-7370
• DOI: 10.1038/ismej.2011.200

N 2 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 N 2 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 N 2 at night indicated that cyanobacterial nifH transcripts were abundant and formed a novel monophyletic lineage. Independent NanoSIMS analysis of 15 N 2 -incubated samples revealed significant incorporation of 15 N 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 15 N 2 tracer experiments, fluorescence in situ hybridization and NanoSIMS, in situ N 2 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.