British astrobiologists have discovered that meteoric organic carbon may have been the energy source of the first heterotrophic microorganisms. Researchers added anaerobic bacteria to the dust of the Aguas Zarcas meteorite and after analysis found that the microorganisms grew by feeding on the organic matter of this material.

It is assumed that early life on Earth was autotrophic because the first heterotrophic organisms lacked available organic molecules. At that time, the main source of organic carbon was carbon dioxide. But at the same time, the young Earth was bombarded with carbonaceous chondrites that could potentially be a source of organic carbon.

It has been experimentally proven that it is possible for microorganisms to grow in this meteorite material. However, previous experiments had been carried out under aerobic conditions and at a temperature virtually unavailable in the early stages of Earth’s formation. Other experiments have shown that microorganisms grow under anaerobic conditions on the same material, but biomass synthesis from the carbon of organic meteorites has not been demonstrated before.

British astrobiologists decided to fill this gap. They found that meteorite organic carbon was used by anaerobic microorganisms for nutrition and growth. The results show that this energy source could support the planet’s first biosphere. The study was published in the journal Scientific Reports.

For the experiment, scientists took a community of microorganisms from the bottom sediments of an Edinburgh pond. They chose “Aguas Zarcas” chondrite samples that fell in Costa Rica in 2019 as meteorite material. The meteorite was a perfect candidate because it contained minimal terrestrial organic pollution.

The researchers added cultures of the organisms to a control medium and meteor material and observed them for 14 and 33 days, respectively. Growth was slower in the Aguas Zarcas dust, but bacteria labeled with the stable carbon isotope 13C showed carbon transfer from the meteorite to microbial biomass.

In addition, the composition of the groups of microorganisms growing on “Aguas Zarcas” has also changed – with the exception of a large number of pseudomads (Pseudomonadaceae) After 14 days of observation, other bacterial families also emerged. Based on these results, astrobiologists concluded that meteoric organics may have been a source of carbon for the early Earth. Moreover, as the authors note, this confirms the possibility of heterotrophic metabolism of the first microorganisms.