Amino acid signatures of salinity on an environmental scale with a focus on the Dead Sea

Authors

  • Matthew E. Rhodes,

    Corresponding author
    1. Penn State Astrobiology Research Center and
    2. Department of Geosciences, Pennsylvania State University, University Park, PA 16802, USA.
      E-mail mer251@psu.edu; Tel. (+1) 617 519 4778; Fax (+1) 814 863 7823.
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  • Sorel T. Fitz-Gibbon,

    1. Penn State Astrobiology Research Center and
    2. Center for Astrobiology, Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095, USA.
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  • Aharon Oren,

    1. The Institute of Life Sciences, and the Moshe Shilo Minerva Center for Marine Biogeochemistry, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel.
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  • Christopher H. House

    1. Penn State Astrobiology Research Center and
    2. Department of Geosciences, Pennsylvania State University, University Park, PA 16802, USA.
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E-mail mer251@psu.edu; Tel. (+1) 617 519 4778; Fax (+1) 814 863 7823.

Summary

The increase of the acidic nature of proteins as an adaptation to hypersalinity has been well documented within halophile isolates. Here we explore the effect of salinity on amino acid preference on an environmental scale. Via pyrosequencing, we have obtained two distinct metagenomic data sets from the Dead Sea, one from a 1992 archaeal bloom and one from the modern Dead Sea. Our data, along with metagenomes from environments representing a range of salinities, show a strong linear correlation (R2 = 0.97) between the salinity of an environment and the ratio of acidic to basic amino acids encoded by its inhabitants. Using the amino acid composition of putative protein-encoding reads and the results of 16S rRNA amplicon sequencing, we differentiate recovered sequences representing microorganisms indigenous to the Dead Sea from lateral gene transfer events and foreign DNA. Our methods demonstrate lateral gene transfer events between a halophilic archaeon and relatives of the thermophilic bacterial genus Thermotoga and suggest the presence of indigenous Dead Sea representatives from 10 traditionally non-hyperhalophilic bacterial lineages. The work suggests the possibility that amino acid bias of hypersaline environments might be preservable in fossil DNA or fossil amino acids, serving as a proxy for the salinity of an ancient environment. Finally, both the amino acid profile of the 2007 Dead Sea metagenome and the V9 amplicon library support the conclusion that the dominant microorganism inhabiting the Dead Sea is most closely related to a thus far uncultured relative of an alkaliphilic haloarchaeon.

Ancillary