Microbial diversity in The Cedars, an ultrabasic, ultrareducing, and low salinity serpentinizing ecosystem

Abstract

The Cedars, in coastal northern California, is an active site of peridotite serpentinization. The spring waters that emerge from this system feature very high pH, low redox potential, and low ionic concentrations, making it an exceptionally challenging environment for life. We report a multiyear, culture-independent geomicrobiological study of three springs at The Cedars that differ with respect to the nature of the groundwater feeding them. Within each spring, both geochemical properties and microbial diversity in all three domains of life remained stable over a 3-y period, with multiple samples each year. Between the three springs, however, the microbial communities showed considerable differences that were strongly correlated with the source of the serpentinizing groundwater. In the spring fed solely by deep groundwater, phylum Chloroflexi, class Clostridia, and candidate division OD1 were the major taxa with one phylotype in Euryarchaeota. Less-abundant phylotypes include several minor members from other candidate divisions and one phylotype that was an outlier of candidate division OP3. In the springs fed by the mixture of deep and shallow groundwater, organisms close to the Hydrogenophaga within Betaproteobacteria dominated and coexisted with the deep groundwater community members. The shallow groundwater community thus appears to be similar to those described in other terrestrial serpentinizing sites, whereas the deep community is distinctly different from any other previously described terrestrial serpentinizing community. These unique communities have the potential to yield important insights into the development and survival of life in these early-earth analog environments.biodiversity | extremophile | alkaliphile | small subunit rRNA | hydrogen

Physiological and genomic features of highly alkaliphilic hydrogen-utilizing Betaproteobacteria from a continental serpentinizing site

“…While the shallow groundwater communities were similar to those described in other terrestrial serpentinizing sites, the deep groundwater microbial community was distinctly different from any other previously described terrestrial serpentinizing community16. The shallow groundwater-fed springs were numerically dominated by microbes related to the genus Hydrogenophaga within Betaproteobacteria 16. Furthermore, alkaline fluid from other terrestrial serpentine-hosted ecosystems also contained abundant Hydrogenophaga -related microbes17181920.…”

A metagenomic window into carbon metabolism at 3 km depth in Precambrian continental crust

“…Fluids with relatively recent recharge from the surface (on a scale of tens of thousands of years) lie along the GMWL, reflecting their meteoric origin (Craig, 1961). In contrast, saline waters and brines that have been sequestered in the deep crystalline rocks of the Precambrian Shields worldwide have been shown to have δ 18 O and δ 2 H signatures well elevated over those of the GMWL A similar pattern of community composition based on fluid origins has also been reported in the Fennoscandian Shield (Itävaara et al, 2011), a terrestrial serpentinite system in northern California (the Cedars) (Suzuki et al, 2013), the Tablelands Ophiolite and other serpentinizing sites . In the Fennoscandian Shield, the microbial communities inhabiting 100-m increments of the Outokumpu deep borehole (up to1500 m depth) were reported.…”

“…There, Proteobacteria dominated the oxygenated, shallow (0-900 m) samples, whereas Firmicutes dominated the deeper samples (900-1000 m, 1400-1500 m) of the borehole (Itävaara et al, 2011). In the case of terrestrial serpentinites Schrenk et al, 2013;Suzuki et al, 2013), it has been reported that Firmicutes (and Chloroflexi in the case of Suzuki et al (2013)) dominate serpentinite springs fed solely by deep groundwater, whereas the sites whose water was a mixture of deep and shallow groundwater contain communities dominated by Betaproteobacteria. In the shallow sites, it is expected that the Betaproteobacteria such as Hydrogenophaga make use of the abundant O 2 and H 2 associated with the paleometeoric waters, whereas the Firmicutes-dominated sites are characterized by organisms capable of dealing with the low abundance of oxidants and/or with the ability to switch between autotrophic and mixtrotrophic growth .…”

“…The recurring nature of the observation that distinct hydrogeological and geochemical niches select for Proteobacteria-versus Firmicutes-dominated communities in the South African subsurface, Fennoscandian Shield (Itävaara et al, 2011), and terrestrial serpentinites ,Suzuki et al, 2013 suggests this may be a genuine feature of the subsurface biome and not an artifact of methodology. The observation raises the question of whether the geochemical and hydrogeological history of fracture fluids influences the nature of the in situ microbial community and how it develops.…”

Geochemical evidence for active tropical serpentinization in the Santa Elena Ophiolite, Costa Rica: An analog of a humid early Earth?

“…The presence of H 2 and CH 4 , the latter formed through abiotic reduction of CO 2 [Proskurowski et al, 2008;Lang et al, 2012], are major energy sources for microbial activity and have been shown to support prolific microbial communities in peridotite-hosted hydrothermal systems [Kelley et al, 2005;Brazelton et al, 2006Brazelton et al, , 2012Suzuki et al, 2013;Brazelton et al, 2013]. Additionally, serpentinization of ultramafic rocks generally produces hyperalkaline fluids (pH > 10) with high Ca…”