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Vertical stratification of subsurface microbial community composition across geological formations at the Hanford Site

Authors

  • Xueju Lin,

    1. Pacific Northwest National Laboratory, Biological Sciences Division, Richland, WA 99352, USA.
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    • Present address: School of Biology, Georgia Institute of Technology, Atlanta, GA 30332, USA.

  • David Kennedy,

    1. Pacific Northwest National Laboratory, Biological Sciences Division, Richland, WA 99352, USA.
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  • Jim Fredrickson,

    1. Pacific Northwest National Laboratory, Biological Sciences Division, Richland, WA 99352, USA.
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  • Bruce Bjornstad,

    1. Pacific Northwest National Laboratory, Applied Geology and Geochemistry Group, Richland, WA 99352, USA.
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  • Allan Konopka

    Corresponding author
    1. Pacific Northwest National Laboratory, Biological Sciences Division, Richland, WA 99352, USA.
      E-mail allan.konopka@pnl.gov; Tel. (+1) 509 371 6950; Fax (+1) 509 371 6955.
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E-mail allan.konopka@pnl.gov; Tel. (+1) 509 371 6950; Fax (+1) 509 371 6955.

Summary

Microbial diversity in subsurface sediments at the Hanford Site 300 Area near Richland, Washington state (USA) was investigated by analysing 21 samples recovered from depths of 9–52 m. Approximately 8000 near full-length 16S rRNA gene sequences were analysed across geological strata that include a natural redox transition zone. These strata included the oxic coarse-grained Hanford formation, fine-grained oxic and anoxic Ringold Formation sediments, and the weathered basalt group. We detected 1233 and 120 unique bacterial and archaeal OTUs (operational taxonomic units at the 97% identity level) respectively. Microbial community structure and richness varied substantially across the different geological strata. Bacterial OTU richness (Chao1 estimator) was highest (> 700) in the upper Hanford formation, and declined to about 120 at the bottom of the Hanford formation. Just above the Ringold oxic–anoxic interface, richness was about 325 and declined to less than 50 in the deeper reduced zones. The deeper Ringold strata were characterized by a preponderance (c. 90%) of Proteobacteria. The bacterial community in the oxic sediments contained not only members of nine well-recognized phyla but also an unusually high proportion of three candidate divisions (GAL15, NC10 and SPAM). Additionally, 13 novel phylogenetic orders were identified within the Deltaproteobacteria, a clade rich in microbes that carry out redox transformations of metals that are important contaminants on the Hanford Site.

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