Exploring Fingerprints of the Extreme Thermoacidophile Metallosphaera sedula Grown on Synthetic Martian Regolith Materials as the Sole Energy Sources

Abstract

The biology of metal transforming microorganisms is of a fundamental and applied importance for our understanding of past and present biogeochemical processes on Earth and in the Universe. The extreme thermoacidophile Metallosphaera sedula is a metal mobilizing archaeon, which thrives in hot acid environments (optimal growth at 74°C and pH 2.0) and utilizes energy from the oxidation of reduced metal inorganic sources. These characteristics of M. sedula make it an ideal organism to further our knowledge of the biogeochemical processes of possible life on extraterrestrial planetary bodies. Exploring the viability and metal extraction capacity of M. sedula living on and interacting with synthetic extraterrestrial minerals, we show that M. sedula utilizes metals trapped in the Martian regolith simulants (JSC Mars 1A; P-MRS; S-MRS; MRS07/52) as the sole energy sources. The obtained set of microbiological and mineralogical data suggests that M. sedula actively colonizes synthetic Martian regolith materials and releases free soluble metals. The surface of bioprocessed Martian regolith simulants is analyzed for specific mineralogical fingerprints left upon M. sedula growth. The obtained results provide insights of biomining of extraterrestrial material as well as of the detection of biosignatures implementing in life search missions.

Keywords: EPR spectroscopy; Martian regolith simulants; Metallosphaera sedula; biosignatures; microbe–mineral interactions.

FIGURE 1

Multi-Labeled-Fluorescence in situ Hybridization (MiL-FISH) of Metallosphaera sedula cells grown on synthetic Martian regolith materials as the sole energy sources. (A,D,G,J) Overlaid epifluorescence images, showing overlap of the specific oligonucleotide probe targeting M. sedula with DAPI signals. (B,E,H,K) DAPI staining of the same field (blue). (C,F,I,L) MiL-FISH images of cells (green) after hybridization with the specific oligonucleotide probe targeting M. sedula. Cultures of M. sedula were examined with MiL-FISH conducted after Schimak et al. (2015) after 21 days of cultivation with JSC Mars 1A (A–C), P-MRS (D–F), S-MRS (G–I), and MRS07/52 (J–L).

FIGURE 2

Inductively coupled plasma-optical emission spectrometer (ICP-OES) analysis of released metal ions in supernatant of M. sedula cultures grown on the Martian regolith simulants [JSC Mars 1A (A); P-MRS (B); S-MRS (C); MRS07/52 (D)] as the sole energy sources. Samples were taken at “0” time point and after 21 days of cultivation of M. sedula on the Martian regolith simulants and from corresponding abiotic controls.

FIGURE 3

Scanning electron microscopy (SEM) images of the mineral surfaces of synthetic Martian regolith materials. (A) Scanning electron image showing a surface of mineral precipitate obtained after the cultivation of M. sedula on JSC 1A. (C) Scanning electron image showing a surface of mineral precipitate obtained after the cultivation of M. sedula on P-MRS. (E) Scanning electron image showing a surface of mineral precipitate obtained after the cultivation of M. sedula on S-MRS. (G) Scanning electron image showing a surface of mineral precipitate obtained after the cultivation of M. sedula on JSC 1A. Cultures of M. sedula were examined with SEM after 21 days of cultivation on the Martian regolith simulants. Aluminum/chlorine containing microspheroids occurred in mineral precipitates of JSC Mars 1A, P-MRS, and S-MRS after M. sedula growth, are depicted with arrows. Images (B,D,F,H) represent the corresponding abiotic controls.

FIGURE 4

Electron Paramagnetic Resonance (EPR) spectra of raw synthetic Martian regolith materials (green line), synthetic Martian regolith materials bioprocessed by M. sedula (red line), and synthetic Martian regolith materials after the treatment with cultivation medium, but without M. sedula (abiotic control, blue line). (A) EPR spectra of JSC Mars 1A; (B) EPR spectra of P-MRS; (C) EPR spectra of S-MRS; (D) EPR spectra of MRS07/52). Spectra recorded at 90 and 293 K are represented in left and right columns, respectively. g- values are depicted with the color code corresponding to the spectra; identical g-values are represented in black color. The EPR g-values recorded at 90 and 293 K are grouped in Supplementary Table 1. The corresponding EPR Linewidths (ΔH) values are provided in Supplementary Table 2.