INVESTIGATING MICROBIAL COLONIZATION OF VOLCANIC TEPHRA DEPOSITED ON GLACIAL SURFACES USING ATP AS A UNIVERSAL BIOMARKER: IMPLICATIONS FOR MARS SAMPLE RETURN

Adenosine triphosphate (ATP) is a nucleotide used by living cells to store and transport energy. Despite ATP’s recognition as a “universal biomarker” for extant life, few studies have examined this biomarker in geologic systems. Subglacial environments, including basal regions of temperate glaciers, Lake Vostok, Antarctica and Grímsvötn Crater Lake, Iceland, have been shown to host diverse chemosynthetic communities. However, few studies have examined microbial colonization of glacial surfaces. Understanding microbial colonization of glaciovolcanic surface environments is critical, because volcanic eruptions associated with glaciers in Mars’ history would provide H₂O_(l), geochemical gradients, and thermal conditions hospitable to life. Here we present ATP biomarker evidence for rapid colonization of volcanic tephra deposited on the surface of Sólheimjökull glacier, Iceland.

Volcanic tephra preferentially collected in Sólheimjökull glacier crevasses where it had an insulating effect, resulting in topographic inversion of tephra covered areas. Subsequent tephra remobilization formed deep tephra deposits (>20 cm) on the glacier surface, which was sampled at 2.5 cm intervals utilizing aseptic technique. Sediment temperatures and pH ranged from 4-15°C and 6-7 respectively. Subsamples (0.33g) were crushed to increase surface area, incubated in 1 mL Tris-EDTA buffer (pH 7.5) for 1 h, and then placed into a 100°C water bath for 5 min to induce cell lysis. ATP bioluminescence assays indicate ATP concentrations increased from 3.3x10^-10 M at 0-2.5 cm depth to 5.3x10^-10-6.3x10^-10 M between 2.5-15 cm depth, despite decreasing T and changing sediment moisture and compaction. Microbial cell density extracted from ATP concentrations, range from 1.7x10⁸ cells ml^-1 at the surface to 2.5-3.5x10⁸ cells ml^-1 at depths of 2.5-15 cm, which is similar to estimates of subglacial microbial communities.

SEM analyses confirm endolithic microbial communities colonize volcanic tephra on glacial surfaces. Surface tephra deposits may shield microorganisms from rapid environmental changes (T, and UV) and provide a nutrient source for chemosynthetic organisms. These data extend ATP’s biomarker utility to glacial environments, which has important ramifications for future Mars sample return missions.