Dartmouth Events

Microorganisms thrive across orders of magnitude differences in temperature, pressure, nutrient concentrations, and energy sources in nearly every environment on Earth. In addition to their resilience and ubiquity, microbes have had a profound effect on our planet’s evolution and continue to drive cycles of elements essential to life. This is especially true in the vast, rock-hosted, subsurface environment where sunlight is not an available energy source. By interrogating subsurface environments, we can improve our understanding of life under extreme conditions and its evolution and survival on geologic timescales. To characterize the potential activity of microorganisms from subseafloor basaltic aquifer fluids (4.5 km water depth, Mid-Atlantic Ridge), a series of stable isotope probing experiments coupled to single-cell NanoSIMS measurements were conducted. Through a combination of geochemical and genomic techniques, we have found that subsurface cells can maintain a range of cellular (re)generation times and metabolisms in this nutrient-limited environment. We also observed that the relative abundance and rates of heterotrophy (via acetate utilization) and autotrophy (via bicarbonate utilization) differed with depth within the basaltic aquifer. Together these results improve our understanding of the microbial role in water-rock reactions on Earth, with astrobiological implications for similar systems elsewhere.

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