Bacterial Communities Associated with Subsurface Geochemical Processes in Continental Serpentinite Springs

Abstract

Reactions associated with the geochemical process of serpentinization can generate copious quantities of hydrogen and low-molecular-weight organic carbon compounds, which may provide energy and nutrients to sustain subsurface microbial communities independently of the photosynthetically supported surface biosphere. Previous microbial ecology studies have tested this hypothesis in deep sea hydrothermal vents, such as the Lost City hydrothermal field. This study applied similar methods, including molecular fingerprinting and tag sequencing of the 16S rRNA gene, to ultrabasic continental springs emanating from serpentinizing ultramafic rocks. These molecular surveys were linked with geochemical measurements of the fluids in an interdisciplinary approach designed to distinguish potential subsurface organisms from those derived from surface habitats. The betaproteobacterial genus Hydrogenophaga was identified as a likely inhabitant of transition zones where hydrogen-enriched subsurface fluids mix with oxygenated surface water. The Firmicutes genus Erysipelothrix was most strongly correlated with geochemical factors indicative of subsurface fluids and was identified as the most likely inhabitant of a serpentinization-powered subsurface biosphere. Both of these taxa have been identified in multiple hydrogen-enriched subsurface habitats worldwide, and the results of this study contribute to an emerging biogeographic pattern in which Betaproteobacteria occur in near-surface mixing zones and Firmicutes are present in deeper, anoxic subsurface habitats.

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…”

“…Recent mapping efforts of Mars' surface have reported the dominance of mafic to ultramafic rocks [Hoefen et al, 2003;Christensen et al, 2005]. Ongoing initiatives on mid-ocean ridges and in ophiolites have already provided insight into the importance of this process for the life on our planet [Schrenk et al, 2004;Brazelton et al, 2006Brazelton et al, , 2010Brazelton et al, , 2013Schwarzenbach et al, 2013a]. However, the factors (e.g., H 2 , CH 4 fluxes, water input, pH, temperature gradients, and nutrient availability) that control the occurrence of microbial communities in these systems are still unknown.…”

Bacterial Diversity in the Hyperalkaline Allas Springs (Cyprus), a Natural Analogue for Cementitious Radioactive Waste Repository

“…Hydrogenophaga related sequences also dominated the bacterial communities in two spring water samples from the Tablelands ophiolite (Brazelton et al 2013), and were detected among the metagenomic reads and contigs of one of these samples (Brazelton et al 2012).…”

“…Microbial studies in serpentinization-driven (terrestrial) ophiolitic environments have been carried out only recently, at the Cabeço de Vide aquifer in Portugal (Tiago et al 2004;Tiago and Veríssimo 2013), the Del Puerto ophiolite in California (Blank et al 2009), the Tablelands ophiolite in Canada (Brazelton et al 2012;Brazelton et al 2013), and the Leka ophiolite in Norway (Daae et al 2013). Nevertheless, no comprehensive microbiological studies have been carried out yet on the ophiolitic sites that have been studied as natural analogues to geological repositories for radioactive wastes, despite the potential significance of these sites in informing radioactive waste disposal options.…”

Expedition 357 methods

“…Fluids were subsequently filtered onto 0.22 μm mesh Sterivex filter cartridges (Millipore, Billerica, Massachusetts, USA) using an inline peristaltic pump; 1-4 L of fluid was filtered in duplicate per sample. Sterivex filter cartridges were stored frozen at -80°C until analysis in a shore-based laboratory following previously described methods (Brazelton et al, 2013). Sediment Rhizon sampling, split plan, and fixation…”