THE DIVERSITY AND FUNCTIONAL POTENTIAL OF MICROBIAL COMMUNITIES ASSOCIATED WITH THE COLONIAL, N2-FIXING CYANOBACTERIUM TRICHODESMIUM (E)
The diazotrophic cyanobacteria Trichodesmium provide an important source of new nitrogen (N) to tropical and subtropical oceans, and are often found in colonial form. These colonies are composed of several clades of Trichodesmium in association with a diverse community of bacterial and eukaryotic epibionts. Here, we used high-throughput 16S rRNA and nifH sequencing, carbon and N2 fixation assays, and metagenomics to explore the diversity and functional potential within Trichodesmium colonies collected from Stn. ALOHA. The bacterial epibionts contained a large fraction of Bacteroidetes and several particle-associated taxa, and were relatively depleted in the cyanobacteria and small photoheterotrophs that dominate Stn. ALOHA surface waters. Sequencing the nifH gene (required for N2 fixation) revealed non-Trichodesmium diazotrophs associated with the colonies, predominantly nifH Cluster III (anaerobic delta-proteobacteria). Trichodesmium colonies may represent an important habitat for these heterotrophic Cluster III diazotrophs, which were rare in the surrounding seawater. The nifH RNA dataset contained few heterotrophic transcripts, but did contain transcripts of other cyanobacteria. Both the 16S rRNA and nifH datasets indicated strong differences between Trichodesmium epibionts and picoplankton in the surrounding seawater, and also between the epibionts from puff and tuft colony morphologies. Furthermore, comparative analyses of Trichodesmium colony and surface seawater metagenomes reveal a distinct functional potential of colony epibionts. We propose that this unique microbial consortium has a significant impact on the biochemical functioning of Trichodesmium colonies.
Gradoville, M. R., Oregon State University, USA, firstname.lastname@example.org
Crump, B. C., Oregon State University, USA, email@example.com
Letelier, R. M., Oregon State University, USA, firstname.lastname@example.org
Church, M. J., University of Montana, USA, email@example.com
White, A. E., Oregon State University, USA, firstname.lastname@example.org
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