AUTHOR=Thiel Vera , Wood Jason M. , Olsen Millie T. , Tank Marcus , Klatt Christian G. , Ward David M. , Bryant Donald A. 

TITLE=The Dark Side of the Mushroom Spring Microbial Mat: Life in the Shadow of Chlorophototrophs. I. Microbial Diversity Based on 16S rRNA Gene Amplicons and Metagenomic Sequencing

JOURNAL=Frontiers in Microbiology

VOLUME=7

YEAR=2016

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2016.00919

DOI=10.3389/fmicb.2016.00919

ISSN=1664-302X

ABSTRACT=<p>Microbial-mat communities in the effluent channels of Octopus and Mushroom Springs within the Lower Geyser Basin at Yellowstone National Park have been studied for nearly 50 years. The emphasis has mostly focused on the chlorophototrophic bacterial organisms of the phyla <italic>Cyanobacteria</italic> and <italic>Chloroflexi</italic>. In contrast, the diversity and metabolic functions of the heterotrophic community in the microoxic/anoxic region of the mat are not well understood. In this study we analyzed the orange-colored undermat of the microbial community of Mushroom Spring using metagenomic and rRNA-amplicon (iTag) analyses. Our analyses disclosed a highly diverse community exhibiting a high degree of unevenness, strongly dominated by a single taxon, the filamentous anoxygenic phototroph, <italic>Roseiflexus</italic> spp. The second most abundant organisms belonged to the <italic>Thermotogae</italic>, which have been hypothesized to be a major source of H<sub>2</sub> from fermentation that could enable photomixotrophic metabolism by <italic>Chloroflexus</italic> and <italic>Roseiflexus</italic> spp. Other abundant organisms include two members of the <italic>Armatimonadetes</italic> (OP10); <italic>Thermocrinis</italic> sp.; and phototrophic and heterotrophic members of the <italic>Chloroflexi</italic>. Further, an <italic>Atribacteria</italic> (OP9/JS1) member; a sulfate-reducing <italic>Thermodesulfovibrio</italic> sp.; a <italic>Planctomycetes</italic> member; a member of the EM3 group tentatively affiliated with the <italic>Thermotogae</italic>, as well as a putative member of the <italic>Arminicenantes</italic> (OP8) represented ≥1% of the reads. <italic>Archaea</italic> were not abundant in the iTag analysis, and no metagenomic bin representing an archaeon was identified. A high microdiversity of 16S rRNA gene sequences was identified for the dominant taxon, <italic>Roseiflexus</italic> spp. Previous studies demonstrated that highly similar <italic>Synechococcus</italic> variants in the upper layer of the mats represent ecological species populations with specific ecological adaptations. This study suggests that similar putative ecotypes specifically adapted to different niches occur within the undermat community, particularly for <italic>Roseiflexus</italic> spp.</p>