Stable Carbon Isotope Fractionation by Methanogens

Introduction: Methanogenic archaea, which consume CO2 and H2, have been considered models for possible life forms on Mars for a long time, even before the discovery of methane in the Martian atmosphere (1-8). Several intensive experimental studies have been conducted to investigate survivability of methanogens under conditions that approach those found on Mars (2, 3, 9). Various potential sources of methane in the martian atmosphere have been suggested such as volcanic, meteoritic, cometary, hydrogeochemical, and biogenic sources (11). Isotopic fractionation is one of the methods to differentiate between biogenic and abiogenic organic compounds (10).