The Hard Rock Caf茅: Nutrient And Energy Sources Supporting The Deep Terrestrial Biosphere In 欧美口爆视频
Swanner, Elizabeth D 1 ; Templeton, Alexis S 2
1 University of 欧美口爆视频
2 University of 欧美口爆视频
It is now established that microbial life inhabits pore spaces and fractures deep within the solid rock of our continents. However, the nutrient and energy sources that support the deep terrestrial biosphere remain largely unconstrained. The Henderson Molybdenum Mine near Empire, CO is a hard rock laboratory for the study of life in granite. We used a geochemical approach to quantify the inorganic energy sources available to microbes in Henderson subsurface fluids and to predict which reactions should support life. Culturing campaigns revealed that as predicted, metal-oxidizing metabolisms are common. Detailed study of an Fe-oxidizing isolate delineated biological and geochemical controls over the formation of Fe minerals that sequester nutrients and metals, and may serve as electron donors for Fe-reducing bacteria in situ.
Our geochemical dataset led us to question the origin of certain nutrients, particularly nitrogen. The presence of nitrogen in multiple oxidation states (NO3-, NO2-, NH4+) in subsurface fluids further suggested that nitrogen was not only a nutrient but an energy source. Due to the higher abundance of NH4+ in the most metal-rich fluids, we hypothesized NH4+ was sourced from water-rock interaction with NH4+-bearing biotite. However, FTIR analyses of biotites from drill cores did not detect NH4+. Concomitantly, we amplified N2-fixing genes (nifH) from a metal-rich fluid DNA sample. Further amplification of archaeal ammonium-oxidation genes (amoA) from the sample confirmed that biologically-fixed nitrogen likely drives the subsurface nitrogen cycle that was predicted from our geochemical calculations. These genes were only detected in the metal-rich fluid samples, suggesting the abundance of Mo, V and other metals required for nitrogen cycling enzymes may select the microbial community.
Our findings demonstrate the utility of paired geochemical, microbiological and molecular methods for unraveling the nutrient and energy sources supporting this biosphere. At Henderson, metal oxidation appears to be a major energy source, and the mineral products can in turn supply oxidants to metal-reducing organisms. Metals may also select for N2-fixing organisms that support the nutritional and energetic demands of the biosphere. This is the first demonstrated example of Fe-oxidation supporting deep subsurface life, and the first investigation of the origin of nitrogen to the subsurface biosphere.