Search for life in other planets: chemolithotroph metabolism detection based on electrochemical methods

EDUARDO CORTÓN; FEDERICO FIGUEREDO; ALBERT SAAVEDRA; XIMENA C. ABREVAYA

Lima

Congreso; Primer Congreso Latinoamericano de Astrobiología; 2016

Sociedad Científica de Astrobiología, Mars Society, Space Generation Advisory Council y Pontificia Universidad Católica

The search for life in other planets, is one of the most important goals in Astrobiology. There is a diverse group of microorganisms on Earth that can be models of potential extraterrestrial life in other planetary bodies. Chemolithoautotrophic microorganisms are an example in the case of Mars. In particular, Acidithiobacillus ferrooxidans is an acidophilic microorganism (pH 1.8), that can be considered as a potential life form on Mars. It use as carbon source, carbon dioxide and the energy source is obtained from the oxidation of iron and sulfur. In this work we will present an electrochemical method to detect this kind of metabolism, based on the bio-corrosion of pyrite (FeS2) in a three electrode system. Linear polarization measurements were performed, and the potential/corrosion current was obtained by the Stern-Geary equation. Additionally, Cyclic voltammetry measurements were performed (CV). Experiments were carried out with live bacteria, dead bacteria (106 cel.mL-1) and in its absence. Presence / absence of iron was also evaluated. In presence and absence of iron, the results showed significant differences in the corrosion current (Icorr) calculated, being 23, 5 and 5 μA.cm-2 (in the presence of 500 mg.L-1 iron) and 6, 1, 1 µA.cm-2 (in the absence of iron), for live bacteria, dead bacteria and in its absence, respectively. This difference in Icorr is due to the interaction between the bacteria and mineral, as it is a phenomenon related to the increase of the electroactive area, and the corrosion mediated by this microorganism. In the CV studies we detected electro-active zones at several potentials, which may suggest the presence of elemental sulfur and jarosite. In the presence of dead bacteria, was possible to detect an interaction between amino acids and pyrite, suggesting the detection of bacterial debris. We propose this method for the detection of life on Mars and in other planetary bodies, as well as for detecting microorganisms in extreme environments of Earth.