Acetogens living in the gap between Earth and Life

Serpentinization is a process when ocean water cuts into the earth’s crust with minerals that are rich in Fe2+. It’s called “Serpentinization” because the mineral deposits appear serpentine or snake-like. The Fe2+-rich minerals react with water by giving up electrons and forming Fe3+ minerals, while the water is converted to hydrogen gas that eventually bubbles up to the surface. Oxygen atoms from the water remain in the crust as iron oxides, and the surrounding water becomes alkaline. This process usually occurs around geothermal vents deep in the ocean, and as far as we know has been happening as long as water has been present on the surface of the Earth. Occasionally, through seismic and tectonic forces, pieces of this crust will be pushed to the surface. This oceanic crust on the surface is called ophiolite, and one of the more notable slabs of this ophiolite is called Samail ophiolite located in the Hajar mountains of Oman and the United Arab Emirates.

Its presence on the surface makes it easy to study, and a new paper has just been published that examines the bacteria that can live in such an environment. The authors state that they have discovered acetogens, a type on anaerobic bacteria, living in this rock. These organisms can live off of hydrogen and carbon dioxide as their carbon and energy source, while producing acetate as a byproduct. The researchers believe that they have characterized two types of acetogens living in this serpentinite rock: type I and type II, with the latter being more predominant. Their work sheds light on this ancient bacteria that was likely present many millions of years ago before even dinosaurs ruled the earth.

Serpentinite, the rock product of serpentinization (1–4). (Left) A sample of serpentinite from Lost City hydrothermal field. Field of view is 6 cm. Photo provided by D. S. Kelley and M. Elend (University of Washington, Seattle, WA), and NSF Grant OCEO137206 to D. S. Kelley. (Center) Serpentinite from an ophiolite. This outcrop is from the Tablelands Ophiolite in Gros Morne National Park, Newfoundland, Canada. Field of view is 80 cm. Photo provided by William J. Brazelton (University of Utah, Salt Lake City, UT). (Right) A piece of polished serpentinite as it is commonly used in buildings. Field of view is 30 cm. White lines show paths of water flow and rock–water interactions. Photo provided by John F. Allen (University College London, London, United Kingdom). From