Meteorites: beneficial or toxic for life on Early Earth? Growth of an anaerobic microbial community on a carbonaceous chondrite

Meteoritic material accumulated on the surface of the anoxic Early Earth during the Late Heavy Bombardment around 4.0 Gya. These meteorites may have provided the Earth with extra-terrestrial nutrients and energy sources for early life. How could the presence of meteorites have affected the origin and evolution of early life on Earth? And what is the influence of geothermal activity on the Earth’s surface? This research investigates the growth of an anaerobic microbial community from pond sediment on non-pyrolyzed (pristine) or pyrolyzed (heat-treated) carbonaceous chondrite ‘Cold Bokkeveld’. A microbial community was grown anaerobically in batch cultures containing a liquid environment and powdered non-pyrolyzed or pyrolyzed Cold Bokkeveld. Cell concentrations were measured by Colony-Forming Units on agar plates. The community composition in the presence of non-pyrolyzed meteorite was determined by 16S rRNA amplicon sequencing. Non-pyrolyzed Cold Bokkeveld supported the growth of a stable, anaerobic community containing mainly the Deltaproteobacteria Geobacteraceae and Desulfuromonadaceae. Members of these families are known to use elemental sulfur and ferric iron as electron acceptors, and organic compounds as electron donors. Pyrolyzed Cold Bokkeveld however, was inhibitory to the growth of the microbial community. These results show that carbonaceous chondrites can host an anaerobic microbial community, but that pyrolysis, e.g. by geothermal activity, can inhibit microbial growth and potentially toxify the material. This indicates that extraterrestrial meteoritic material and the environment on Early Earth could have shaped the nature of early microbial ecosystems by enhancing growth of microorganisms with metabolic capabilities favored in the presence of this material.