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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - AsLife (Life in Arsenic rich environments: a challenge or an opportunity?)

Teaser

Summary

Arsenic is a notorious toxin, and as such may have exerted a strong selective pressure on the distribution and evolution of life on Earth. Despite evidence supporting the high levels and prominent role of arsenic on the primitive Earth, the essentiality and toxicity of arsenic, and its impact on evolutionary processes remains unexplored.

AsLife aims at taking a novel approach to assessing microbial arsenic cycling in microbial mats from High-Altitude Andean Lakes, where it is known that arsenic concentrations are far above background levels. Specifically, living and diagenetically-modified microbial mats were investigated using scanning hard X-ray nanoprobe emerging at Nanoscopium beamline in SOLEIL Synchrotron. This non-invasive and non-destructive technique provides data on a sub-micrometer scale by which to tie physiological inference from trace metal(loid)s distribution and speciation patterns directly to the microfossil biomass. Thus, providing a means to understand the interplay between microbial metabolisms and bio-availability of trace metal(loid)s in living and fossil ecosystems.

Results highlighted metabolisms that may have been essential for establishing, maintaining or retarding life. Further analysis in this direction would lead to develop arsenic compounds as a tracer for life, evolution on the ancient Earth and, possibly, on other planets like Mars. In addition, the work has also taken into account the possibilities of microbial mats in biotechnological applications, particularly, in bioremediation by removal of arsenic via CaCO3 precipitation.

Work performed

We determined the relationship between living microbial mat activity, mineral occurrence, arsenic speciation, distribution of major and trace elements and their relationship with the mineralogy and the exopolymeric substances (EPS) in modern microbial mats from high-altitude Andean lakes, potential analogues of early Earth environments. Specifically, we documented a number of features that support the existence of the biological cycling of arsenic: the incorporation of arsenic into EPS, the heterogeneous distribution of As(III) and As(V), either together or separately, in confined areas, and the identification of organic-rich globules containing significant arsenic but no other trace metal(loid)s.

The presence of As(III) and As(V) represent the first geochemical evidence of arsenic microbial-mediated cycling in Diamante microbialites, supporting the metagenomic analysis done by Rascovan and co-workers (Rascovan et al., 2016). Moreover, we propose a mechanism for preserving the microbially-mediated cycle of arsenic in the carbonate structure of microbialites from a living, biological active area to an early diagenesis zone. This can be extended to the fossil record, where further studies can lead to develop arsenic as a fingerprint for life, evolution on the ancient Earth and, possibly, on other planets like Mars.

The obtained results within the AsLife project were presented at several international conferences and seminars:

Conferences:
- Goldschmidt Conference, Yokohama, Japan (July 2016): M. Sancho-TomÃ¡s, A. Somogyi, A. Bergamaschi, K. Medjoubi, M.E. Farias, P.T. Visscher and P. Philippot. Oxidation state distribution of arsenic in modern stromatolites: a trace of life evolution.
- Goldschmidt Conference, Yokohama, Japan (July 2016): Philippot, P., Medjoubi, K., Sancho-TomÃ¡s, M., Sugitani, K., Visscher, P.T., Konhauser, K., Wing, B. and Somogyi, A. (2016) Arsenic-based metabolisms in a 3.4 Ga old ecosystem.
- Goldschmidt Conference, Paris, France (July 2017): M. Sancho-TomÃ¡s, A. Somogyi, A. Bergamaschi, K. Medjoubi, A.E.S. van Driessche, P.T. Visscher, E. GÃ©rard, M.E. Farias, M. Contreras and P. Philippot. Arsenic in living microbial mats: distribution, redox state and (bio)geochemical implications.
- IMS, Toulouse, France (September 2017): M. Sancho-TomÃ¡s, A. Somogyi, A. Bergamaschi, K. Medjoubi, A.E.S. van Driessche, P.T. Visscher, E. GÃ©rard, M.E. Farias, M. Contreras and P. Philippot. Arsenic in microbial mats of La Brava: distribution, redox state and (bio)geochemical implications.

In addition to the above, I was the chair of the session Geochemistry on March 16th 2017 to the â€œCongrÃ¨s des doctorantsâ€ of the Doctoral School STEPâ€™UP.

Seminars:
- Petit-DÃ©jeuner, SOLEIL Synchrotron (October, 2017). Life in Arsenic rich environments:
A challenge or an opportunity?
- CONICET, Cordoba, Argentina (November, 2017). Life in Arsenic rich environments:
A challenge or an opportunity?

Publications: (at least, one more paper is planned)
- M. Sancho-TomÃ¡s, A. Somogyi, A. Bergamaschi, K. Medjoubi, A.E.S. van Driessche, P.T. Visscher, E. GÃ©rard, M.E. Farias, M. Contreras and P. Philippot. Distribution, redox state and (bio)geochemical implications of arsenic in present day microbialites of Laguna Brava, Salar de Atacama. Accepted in Chemical Geology. DOI: 10.1016/j.chemgeo.2018.04.029.
- M. Sancho-TomÃ¡s, A. Somogyi, A. Bergamaschi, K. Medjoubi, A.E.S. van Driessche, P.T. Visscher, E. GÃ©rard, M.E. Farias, M. Contreras and P. Philippot. Geochemical evidence for arsenic cycling in living microbialites of a High Altitude Andean lake. In prep.
- P. Philippot, K. Medjoubi, M. Sancho-TomÃ¡s, P. Visscher, K. Sugitani , A. Somogyi. Arsenic-based metabolisms and/or detoxication processes in a 3.45-billion-year-old ecosystem. In prep.

In addition, an interview was conducted and article published in Horizon, the EU Research & Innovation Magazine, entitled â€œArsenic and permafrost microbes help hunt for life on Mar

Final results

This fellowship was a unique opportunity to conduct an independent research that has never been attempted before and was termed as extremely ambitious work. I am now equipped with a valuable knowledge on different characterization techniques that I have been applied: X-ray fluorescence (XRF) spectrometry and spectro-microscopy, absorption, differential phase and dark field contrasts. In addition, I was able to strength my expertise in conventional geochemical techniques, including XRD, SEM-EDX, Raman and confocal scanning microscopy. By interaction with supervisors, colleagues and â€œlearning by doingâ€ approach, I have the full understanding of the methodology and can conduct similar projects in the future, using a different set of samples.

At least three articles, of high impact, are to be published as a result of the work conducted during AsLife and will significantly increase the attractiveness of my CV and enhance chances for getting another prestigious grant or/and a research position in Europe.

The approach of the project was novel and original, particularly because to our knowledge a defined and fast system for performing measurements with non-invasive and non-destructive techniques to investigate complex geobiological samples from the cm-scale down to the nm-scale did not exist elsewhere. As such, AsLife project has the potential for a deep impact on nano-paleontology and geobiology for measuring further unknown, complex natural samples. In addition, the relation between CaCO3 biomineralization and arsenic compounds has not been clarified yet; and lastly, further studies following the AsLife approach, can help to develop mineralogical bioremediation approaches for trapping arsenic.