Abstract
Ultra-basic reducing springs at continental sites of serpentinization act as portals into the biogeochemistry of a subsurface environment with H2 and CH4 present. Very little, however, is known about the carbon substrate utilization, energy sources, and metabolic pathways of the microorganisms that live in this ultra-basic environment. The potential for microbial methanogenesis with bicarbonate, formate, acetate, and propionate precursors and carbon monoxide (CO) utilization pathways were tested in laboratory experiments by adding substrates to water and sediment from the Tablelands, NL, CAD, a site of present-day continental serpentinization. Microbial methanogenesis was not observed after bicarbonate, formate, acetate, or propionate addition. CO was consumed in the live experiments but not in the killed controls and the residual CO in the live experiments became enriched in 13C. The average isotopic enrichment factor resulting from this microbial utilization of CO was estimated to be 11.2 ± 0.2‰. Phospholipid fatty acid concentrations and δ13C values suggest limited incorporation of carbon from CO into microbial lipids. This indicates that in our experiments, CO was used primarily as an energy source, but not for biomass growth. Environmental DNA sequencing of spring fluids collected at the same time as the addition experiments yielded a large proportion of Hydrogenophaga-related sequences, which is consistent with previous metagenomic data indicating the potential for these taxa to utilize CO.
Highlights
The geochemical composition of spring fluids can provide insight into serpentinization driven subsurface processes, but these indicators are often overlaid by microbial biogeochemical transformations, which remain poorly understood in these extreme ecosystems
The concentrations of total inorganic carbon (TIC), nitrate, and sulfate, were lower in the recharge water compared to the pool water, while organic acid concentrations were higher in the recharge water compared to the pool water (Table 1)
BACTERIAL DIVERSITY OF WHC2 Betaproteobacteria belonging to the Comamonadaceae family dominated the WHC2 pool water samples collected in 2012 (Figure 2), which is consistent with previously published results from WHC2 pool samples collected in 2010 and 2011 (Brazelton et al, 2013)
Summary
The geochemical composition of spring fluids can provide insight into serpentinization driven subsurface processes, but these indicators are often overlaid by microbial biogeochemical transformations, which remain poorly understood in these extreme ecosystems. Distinct fluids associated with serpentinization result from subsurface water-rock reactions whereby groundwater or ocean water reacts with ultramafic rock (peridotite), producing serpentine minerals, H2 gas, and hydroxide ions (Barnes et al, 1967; Sleep et al, 2004, 2011). The continental sites share similar geochemical characteristics such as high pH, low Eh, scarce electron acceptors, and limited dissolved inorganic carbon for autotrophic growth, which is considered extreme for most microbial life as we know it. Suzuki et al (2014) have cultured organisms at high pH that correspond to highly abundant organisms in these serpentinizing environments, which are the same taxa (Serpentinomas/Hydrogenophaga) observed at the Tablelands (Suzuki et al, 2014)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
