Magnetite reducing bacteria from a high pH serpentinizing spring
What sorts of microbes would we expect to find on other planets and how would we find them?
Serpentinizing springs have garnered a lot of interest of late because of their importance to astrobiology (the study of life on early earth and other planets) and subsurface microbiology (which collectively makes up the largest weight of organisms on the planet, and little is understood about if and how these organisms survive in these low nutrient environments). Serpentinization is a low-temperature (~100°C) geological reaction between water and iron bearing minerals. The resulting fluids are high in H2 and very high in pH (very basic as opposed to acidic). Serpentinization is known to occur in the Earth’s subsurface and on other planets and exoplanets in our solar system. Though understanding how microbial life survives under such extreme conditions is of great interest to astrobiology and environmental microbiology, culturing from these environments has been challenging. Using electrodes to cultivate microbes from this system, we have been able to isolate microbes capable of extracellular electron transfer (the ability to breathe rocks/minerals/electrodes) and can do so at very high pH! While this is very much a modern microbe, it does give us some insights into how microbes might be conserving energy in these environments, and highlights potential roles for maghemetite and magnetite (iron minerals formed during serpentinization) as electron acceptors for metabolism. For more info see Rowe et al. Environmental Microbiology, 2017.
With any luck I will be tackling a similar question soon at a new terrestrial serpentinization site that looks more like a marine system because of the sulfur compounds present!