MICROPRONY

MICRObial ecosystem functioning in the serpentinizing-hydrothermal system of PRONY, New Caledonia - ANR MICROPRONY (2020-2025)

PI: Gael Erauso

The MICROPRONY project aims to study a unique shallow serpentinized alkaline hydrothermal system located in Prony Bay in the southern lagoon of New Caledonia.

The hydrothermal circulation at Prony is created by in-depth serpentinization reactions while the meteoric water percolates through the peridotite, generating very alkaline fluids, rich in H2, CH4, and abiotically formed organic compounds. This system has characteristics similar to those of terrestrial serpentinized sources (ex California, Oman) but also underwater (ex. Lost City).

The study of these systems brings important elements for the understanding of the processes at the origin of life on Earth. The main objective of the project - which builds on the results of our previous researches on this site - is to understand the functioning of this ecosystem, focusing on metabolisms using H2, CH4, and abiotically formed organic compounds.

Our working assumptions are as follows:

1. Prony microorganisms are specific to serpentinized environments and have developed specific metabolic strategies to cope with very difficult living conditions (few or no electron acceptors, extremely high pH);
2. Contrary to the widely shared assumption that microbial life in the deep subsurface is mainly due to chemiolithoautrophy (the "SLIME" hypothesis), we propose that the organic compounds produced by the serpentine reactions allow the growth of chemoorganotrophic bacteria, in particular, uncultivated relatives of Clostridiales as well as Phyla candidates such as Parcubacteria, Acetothermia, and Omnitrophica, and possibly of methanogenic archaea (Methanosarcinales). These bacteria, along with the methanogens, could thus constitute major primary producers in this type of ecosystem.

To respond exhaustively to these two hypotheses, we propose a multidisciplinary approach led by a scientific team that will gather among the best specialists in their field. This approach will incorporate advanced analytical techniques to cover a wide range of spatial resolution.

It is subdivided into 5 main tasks :

1. Identify the main microbial actors of the Prony ecosystem and elucidate their functions using cultural and molecular (metagenomic) approaches;
2. Characterize the age, nature and structure of microbial habitats, their associated microflora, and micro-mineral interactions, using a range of isotopic dating techniques, molecular imaging (coupled confocal microscope - Raman/FTIR spectrometry, FISH, SEM);
3. Describe in detail the fluid geochemistry for a robust interpretation of the biogeochemical processes operating at Prony and compare them with those of other terrestrial or marine serpentinized systems using a panel of geochemical analysis techniques;
4. Determine the relative importance of biotic vs abiotic productions, particularly CH4 and other organic compounds (HC, organic acids, etc.) present in fluids, by clumped isotopes thermometry methods (13C and D);
5. Model the key metabolisms of the Prony microbial ecosystem by integrating on the one hand bioenergetic calculations based on the thermodynamics of metabolic reactions and geochemical data, and on the other hand the functional annotation of metagenomes/metatranscriptomes.

The realization of the scientific program proposed here will allow us to exhaustively define the interactions between geochemical and microbiological processes in an environment that may have been abundant on Earth at the beginning of abiogenesis and that can now be compared to that of other planets of the solar system, candidates to host alien life forms (e.g. Europa, Enceladus).

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