Microbial phylogenetic diversity preserved in facies-specific modern, recent, Holocene and Pleistocene hot-spring travertine deposits of Yellowstone and Turkey
A systematic evaluation has been undertaken of the mechanisms and products of microbial community preservation within modern-to-ancient terrestrial hot-spring calcium carbonate (CaCO3) limestone deposits called travertine. Microbial 16S rRNA gene sequences preserved within Modern travertine deposited within the Proximal Slope Facies (PSF) at Mammoth Hot Springs (MHS), Yellowstone National Park, has been directly compared with analogous Holocene-Late Pleistocene PSF travertine at Gardiner, Montana, and Middle Pleistocene PSF travertine in Denizli, Turkey. Analyses have included: (1) Modern microbial communities inhabiting the PSF of an actively depositing travertine hot-spring system (water, microbial mats, travertine) at MHS (0 YBP Modern travertine, Angel Terrace, Spring AT-1); (2) 9 YBP Modern PSF travertine (Angel Terrace, Spring AT-2; MHS); (2) ~100 YBP Recent travertine (New Highland Terrace, MHS); (3) ~4,000 YBP Holocene travertine (USGS Y-10 Core); (3) ~30,000 YBP Late Pleistocene travertine (Gardiner Quarry); and (4) ~1.1 Ma YBP Middle Pleistocene travertine (all of the Mammoth Hot Springs (YNP) and (Cakmak Quarry, Turkey). Genomic DNA entombed during rapid (up to 5 mm/day) travertine deposition and preserved within CaCO3 fluid inclusions and between crystals, was extracted via bulk rock drilling under sterile clean room conditions. Pooled 16S rRNA gene sequence libraries were constructed via polymerase chain reactions (PCRs), terminal-restriction fragment length polymorphisms (T-RFLP), and MiSeq amplicon sequencing. Blast searches using multiple web-based bioinformatics tools identified over 400 operational taxonomic units (OTUs) affiliated with a total of 19 phyla (16 phyla and 3 candidate phyla) within the Domain Bacteria. Previous analyses of the living microbial communities inhabiting modern active PSF depositional environments at MHS have provided a baseline with which to compare the ancient travertine analyses. Combined results from both MHS and Denizli indicate that only 3 of 19 phyla were detected in PSF travertine samples of all ages. Increasing depositional age of the travertine deposits was associated with increasing extents of post-depositional water-rock geochemical alteration (diagenesis). Microbial community structure shifted across this spatial and temporal transect from being dominated by Cyanobacteria and Proteobacteria in the Modern and Recent, to dominance by Firmicutes in the Holocene and Pleistocene. This is not unexpected, as endospores of Firmicutes are known to be resistant and also persist under harsh environmental conditions and therefore show higher relative abundance in ancient samples in comparison to modern samples. Preliminary blast search results imply that libraries from all PSF travertine samples of all ages contain photoautotrophic, chemoautotrophic and heterotrophic metabolic activities, which is likely the result of both original hot-spring depositional processes and secondary diagenetic alteration.
Travertine, Hot springs, Ancient DNA, Phylogeny, Physiotypes
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign