An analysis of geothermal and carbonic springs in the western United States sustained by deep fluid inputs

Abstract

Hydrothermal springs harbor unique microbial communities that have provided insight into the early evolution of life, expanded known microbial diversity, and documented a deep Earth biosphere. Mesothermal (cool but above ambient temperature) continental springs, however, have largely been ignored although they may also harbor unique populations of micro-organisms influenced by deep subsurface fluid mixing with near surface fluids. We investigated the microbial communities of 28 mesothermal springs in diverse geologic provinces of the western United States that demonstrate differential mixing of deeply and shallowly circulated water. Culture-independent analysis of the communities yielded 1966 bacterial and 283 archaeal 16S rRNA gene sequences. The springs harbored diverse taxa and shared few operational taxonomic units (OTUs) across sites. The Proteobacteria phylum accounted for most of the dataset (81.2% of all 16S rRNA genes), with 31 other phyla/candidate divisions comprising the remainder. A small percentage (~6%) of bacterial 16S rRNA genes could not be classified at the phylum level, but were mostly distributed in those springs with greatest inputs of deeply sourced fluids. Archaeal diversity was limited to only four springs and was primarily composed of well-characterized Thaumarchaeota. Geochemistry across the dataset was varied, but statistical analyses suggested that greater input of deeply sourced fluids was correlated with community structure. Those with lesser input contained genera typical of surficial waters, while some of the springs with greater input may contain putatively chemolithotrophic communities. The results reported here expand our understanding of microbial diversity of continental geothermal systems and suggest that these communities are influenced by the geochemical and hydrologic characteristics arising from deeply sourced (mantle-derived) fluid mixing. The springs and communities we report here provide evidence for opportunities to understand new dimensions of continental geobiological processes where warm, highly reduced fluids are mixing with more oxidized surficial waters.

Marine Fe-oxidizingZetaproteobacteria: Historical, ecological, and genomic perspectives

“…Thus, it was surprising and novel to find abundant populations of Zetaproteobacteria in CO 2 -rich terrestrial springs. Surveys of the 16S genes from carbonic springs at Tierra Amarilla Spring, New Mexico (∼9 ppt salinity) revealed a microbial population up to one third Zetaproteobacteria (78). Similarly, 16S and genomic work in CO 2 -rich Crystal Geyser, Utah, (∼11-14 ppt salinity; Figure 4F) found the Zetaproteobacteria to be both abundant and consistently present over a year of observation (79–81).…”

“…ZOTU54 is a striking example of a dominant ZOTU clearly successful within the terrestrial subsurface fluid environment. ZOTU54 is a deep-branching ZOTU that is primarily limited to this environment (78–81). The distribution of ZOTU54 suggests that it is endemic or adapted to thrive within terrestrial carbonic Fe-rich springs.…”

Continental smokers couple mantle degassing and distinctive microbiology within continents

“…Moreover, microbial phylogenetic analysis of 28 of the carbonic springs described here (Table S1) suggested that some of the springs with highest deep-fluid input contain organisms closely related to chemolithoautotrophs present at marine vent sites and iron-oxidizing biofilms (Colman et al, 2014a). Thus, microbiological studies from a wider range of lower-temperature terrestrial springs of the type presented here have rich potential to expand our understanding of subsurface geobiological processes and a fuller spectrum of microbial biodiversity.…”

“…Bulk crustal averages of v P /v S were derived from joint inversion of crustal receiver functions and gravity data (Lowry and Gussinve, 2011 (Table S1). Planktonic communities were collected by filtering ~1 L of spring water with a 0.22 µm Sterivex filter (Millipore, Bedford, MA) and DNA was extracted as described by Colman et al (2014a). 454 pyrosequencing was performed at Research and Testing Laboratories (Lubbock, TX) using universal bacterial PCR primers, quality-filtering steps, and analytical steps described elsewhere (Van Horn et al 2014).…”

“…Fluid-rock reactions determine the composition and distribution of metabolic niches in hydrothermal ecosystems such that the potential for variation within continental rocks is likely greater than in basalt/serpentinite/peridotitedominated submarine systems. A microbial community survey was conducted on 28 cool and warm springs in the western U.S.A in diverse geologic provinces that demonstrated differential mixing of deeply sourced fluids with shallowly circulated water (Colman et al, 2014a). The springs harbored diverse taxa, although the metabolically diverse Proteobacteria phylum dominated the dataset (81.2% of all bacterial 16S rRNA gene sequences recovered).…”