communications / earth & environment

How might life on Mars look like?

Multiple lines of evidence indicate an active hydrogeological history of Mars and chemolithoautotrophy-suited environments within its Noachian terrains. As a result, one of the primary aims of upcoming missions to Mars is to search for signs of ancient life. Here we report on laboratory-scaled microbially assisted chemolithoautotrophic biotransformation of the Noachian Martian breccia Northwest Africa (NWA) 7034 composed of ancient (~4.5 Gyr old) crustal materials from Mars. Nanoanalytical hyperspectral analysis provides clues for the trafficking and distribution of meteorite inorganic constituents in the microbial cell. We decipher biomineralization patterns associated with the biotransformation and reveal microbial nanometer-sized lithologies located inside the cell and on its outer surface layer. These investigations provide an opportunity to trace the putative bioalteration processes of the Martian crust and to assess the potential biogenicity of Martian materials.

Fig. 1 Images of various lithologic components in the NWA 7034 fragment used in this study. a The high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) image of the focused ion beam (FIB) section extracted for STEM analysis from the NWA 7034 fragment used in this study. b False-color energy-dispersive X-ray spectroscopy (EDS) composite image of NWA 7034 (Si-magenta, P-red, Syellow, Ca-white, Ti-cyan, Fe-blue).

Fig. 4 Nanoanalytical spectroscopy investigations of M. sedula grown on NWA 7034. a The HAADF-STEM image of a cell of M. sedula used for highresolution investigations and electron energy loss spectroscopy (EELS) analysis. b, c Representative HR-STEM of biogenic crystalline mineral deposits inside the cell of M. sedula. Insets in panels represent the fast fourier transforms (FFTs) consistent with the phases of tetragonal Mn3O4-type nanoassemblages embedded into Fe3O4. d EDS false colors composed mineral map of a cell of M. sedula (Mn-red, P-green, Fe-blue).