Unveiling microbial preservation under hyperacidic and oxidizing conditions in the Oligocene Rio Tinto deposit

David C Fernández-Remolar,Daniel Carrizo,Laura Sánchez-García,Mourad Harir,Ting Huang,Ricardo Amils,Per Malmberg,David Gomez-Ortiz,Philippe Schmitt-Kopplin

doi:10.1038/s41598-021-00730-8

Abstract

The preservation of biosignatures on Mars is largely associated with extensive deposits of clays formed under mild early Noachian conditions (> 3.9 Ga). They were followed by widespread precipitation of acidic sulfates considered adverse for biomolecule preservation. In this paper, an exhaustive mass spectrometry investigation of ferric subsurface materials in the Rio Tinto gossan deposit (~ 25 Ma) provides evidence of well-preserved molecular biosignatures under oxidative and acidic conditions. Time of flight secondary ion mass spectrometry (ToF–SIMS) analysis shows a direct association between physical-templating biological structures and molecular biosignatures. This relation implies that the quality of molecular preservation is exceptional and provides information on microbial life formerly operating in the shallow regions of the Rio Tinto subsurface. Consequently, low-pH oxidative environments on Mars could also record molecular information about ancient life in the same way as the Noachian clay-rich deposits.

Highlights

The surface of Mars is widely acknowledged to be inhospitable for life because of the direct and indirect damaging effects of solar r adiation[1]
To determine the preservation potential of ferruginous deposits that formed under acidic and oxidizing conditions, sample 010,109–1 (Fig. 1b–d) collected from the top of the Upper Gossan unit in Peña de Hierro (~ 25 Ma)[11,20,31] was analyzed using different spectral techniques. Such analysis consisted of molecular mapping and characterization by means of three spectral techniques: FTICR-MS, gas chromatography coupled with mass spectrometry (GC–MS) and ToF–SIMS
Enabling highly accurate mass measurement and mass resolution, FTICR MS of terrestrial dissolved organic matter (TDOM) provides several thousand mass peaks for individual samples, of which several were assigned to C, H, N, O, and S compositional space[32,33,34]

Summary

Introduction

The surface of Mars is widely acknowledged to be inhospitable for life because of the direct and indirect damaging effects of solar r adiation[1]. The identification of large molecular species suggesting that the acidic ferruginous materials have a high preservation potential agrees with the finding of peptide c hains[24] in the oldest Rio Tinto terrace, which requires exceptional preservation conditions for its persistence In this regard, preservation is favored in the Rio Tinto acidic deposits despite high water availability for mineral transformation. As this was not the case for sediments formed under low-pH conditions on Mars with limited water[21], high preservation should be expected in those Hesperian materials In this context, the extensive ferruginous deposits formed in acidic and oxidizing Hesperian environments should be considered first-class targets to look for ancient traces of life if any biosphere emerged at some time on the red planet

Methods

Results

Discussion

Conclusion