Of Microbes and Mummies: Tales of Microbial Activity and Inactivity at 6000 m a.s.l.

In this chapter, we address two broad dilemmas related to the potential for microbial life to function in extreme high-elevation, volcanic soils. The first dilemma was posed by the existence of almost perfectly preserved mummies found buried at over 6700 m a.s.l. on Volcan Llullaillaco. The lack of any microbial decay of these mummies after 500 years can best be explained by observations that the micro-environmental conditions (temperature and humidity) at deep soils depths at extreme elevations would remain at constant levels of extreme cold and dryness. The second dilemma that we address is if and how microbial life can function in surface tephra (soil) on these same volcanoes. Unlike deeper soil depths, the soil surface at high elevations is subjected to wildly fluctuating levels of temperature, moisture, and radiation, and among the lowest levels of nutrients and carbon yet observed for a terrestrial system on Earth. We review evidence that some bacteria in the Actinobacteria and Chloroflexi may subsist in these extreme soils by living just below the soil surface and utilizing trace gases (e.g., CO and H2) from the atmosphere. In addition, a fungus (Naganishia friedmannii) that dominates the simple eukaryotic community of these soils is able to withstand high levels of UV radiation and can actually grow during extreme daily freeze–thaw cycles, conditions that would kill almost all other life forms on Earth. Finally, we describe the abundant and diverse microbial ecosystems that develop near fumaroles at elevations of up to 6050 m a.s.l. on Volcan Socompa, and the first indications that unique ice formations (nieves penitentes) of these high mountains may support previously unreported communities of microbes, including snow algae.