An article published in the journal “Scientific Reports” describes a study on the ability of a species of archaea called Metallosphaera sedula to grow into typical meteorite materials using the metals they contain as an energy source. A team of researchers led by astrobiologist Tetyana Milojevic of the University of Vienna examined these archaea living and interacting with a real meteorite. The results can provide clues to the origin of life on Earth thanks to the possibility of identifying with greater certainty microfossils containing metals. This also means having better chances of evaluating possible traces of microscopic life found in other places in the solar system.
Archaea, or archaebacteria, are single-celled organisms lacking a nucleus. Knowledge about archaea is still limited, but in recent years advances in genetic analysis techniques expanded it enormously.
The identification of the species Metallosphaera sedula was announced in an article (link to a PDF file) published in the journal “Systematic and Applied Microbiology” in July 1989 after being discovered in Pisciarelli fumaroles, Italy. It’s a microorganism that grows best in environments that are hot, around 74° Celsius, and acid, with pH 2, and has a metabolism based on the oxidation of metals. For this ability to live in conditions that would kill most organisms, it’s classified among the so-called extremophiles.
Metallosphaera sedula has already been the center of studies for its characteristics, for example an article published in the journal “Frontiers in Microbiology” in October 2017 reported its growth using as sole energy source synthetic materials that replicate Martian regolith. Some of the researchers who studied that possibility examined more of them and, together with other colleagues, carried out the new study published in “Scientific Reports”.
In this meteorite-related study, the researchers used the meteorite cataloged as Northwest Africa 1172 (NWA 1172), a common chondrite classified with the H5 designation that contains various metals, particularly iron. Several spectroscopic techniques associated with electron microscopy were used to examine the interaction between Metallosphaera sedula and that meteorite. The result was the discovery of a series of biogeochemical traces generated by the growth of these archaea and the subsequent verification of a biotransformation of meteorite minerals.
Archaea are much more similar to the primordial life forms than the eukaryotic cells that form multi-cellular organisms, which are more complex. This means that the study of archaea can provide some clues about the development of life on Earth. Even today there are organisms with peculiar metabolisms and the fact that there are archaea capable of feeding on meteorite materials like those that probably fell in abundance in the first phase of the history of the Earth is interesting.
The traces left by Metallosphaera sedula on the meteorite NWA 1172 can provide useful information to evaluate possible traces of metal-containing microfossils. Sometimes there are controversies about the identification of primordial microfossils so any information on the type of traces they leave is useful.
The study of traces present in meteorites recently fallen on Earth is even more controversial. These are cases where it’s even more important to be able to distinguish traces of biological activity from traces generated by non-biological processes. Both the study published in “Frontiers in Microbiology” in 2017 and the one just published in “Scientific Reports” also offer new insights on the subject.
These studies may also offer new ideas regarding the mining of meteoritic materials or even asteroids. This is a new frontier also from the technological point of view that could also exploit these microorganisms as instruments.