Cycle du soufre | EPFL Graph Search

Le cycle du soufre est le cycle biogéochimique des différentes formes du soufre. Le soufre est un élément essentiel à la vie qui, comme le carbone, le phosphore, l'oxygène, l'azote ou encore l'eau, possède son propre cycle de vie. En effet, le soufre est présent partout sur Terre, atmosphère, océans, continents, mais aussi chez tous les êtres vivants sous forme de molécules organiques : les acides aminés soufrés constituants de protéines (méthionine et cystéine). Dans l'atmosphère, on rencontre le soufre sous forme de gaz : dioxyde de soufre (SO2), hydrogène sulfuré (H2S) ; de soufre réduit comme dans le diméthylsulfure (DMS) dont la formule est CH3SCH3 et le carbonyle de sulfure (COS) ; ainsi que dans les sulfates volatils (SO42−). Le SO2 et l'H2S proviennent de la minéralisation de la matière organique selon le pH du milieu ou du métabolisme de certaines bactéries (ex: Désulfovibrio spp.). Les volcans participent au cycle en produisant d'énormes quantités de sulfates (SO4) qui vien

Active sulfur cycling in the terrestrial deep subsurface

Emma Bell, Rizlan Bernier-Latmani, Manon Frutschi

The deep terrestrial subsurface remains an environment where there is limited understanding of the extant microbial metabolisms. At Olkiluoto, Finland, a deep geological repository is under construction for the final storage of spent nuclear fuel. It is therefore critical to evaluate the potential impact microbial metabolism, including sulfide generation, could have upon the safety of the repository. We investigated a deep groundwater where sulfate is present, but groundwater geochemistry suggests limited microbial sulfate-reducing activity. Examination of the microbial community at the genome-level revealed microorganisms with the metabolic capacity for both oxidative and reductive sulfur transformations. Deltaproteobacteria are shown to have the genetic capacity for sulfate reduction and possibly sulfur disproportionation, while Rhizobiaceae, Rhodocyclaceae, Sideroxydans, and Sulfurimonas oxidize reduced sulfur compounds. Further examination of the proteome confirmed an active sulfur cycle, serving for microbial energy generation and growth. Our results reveal that this sulfide-poor groundwater harbors an active microbial community of sulfate-reducing and sulfide-oxidizing bacteria, together mediating a sulfur cycle that remained undetected by geochemical monitoring alone. The ability of sulfide-oxidizing bacteria to limit the accumulation of sulfide was further demonstrated in groundwater incubations and highlights a potential sink for sulfide that could be beneficial for geological repository safety.

2020

Active anaerobic methane oxidation and sulfur disproportionation in the deep terrestrial subsurface

Emma Bell, Rizlan Bernier-Latmani, Manon Frutschi

Microbial life is widespread in the terrestrial subsurface and present down to several kilometers depth, but the energy sources that fuel metabolism in deep oligotrophic and anoxic environments remain unclear. In the deep crystalline bedrock of the Fennoscandian Shield at Olkiluoto, Finland, opposing gradients of abiotic methane and ancient seawater-derived sulfate create a terrestrial sulfate-methane transition zone (SMTZ). We used chemical and isotopic data coupled to genome-resolved metaproteogenomics to demonstrate active life and, for the first time, provide direct evidence of active anaerobic oxidation of methane (AOM) in a deep terrestrial bedrock. Proteins from Methanoperedens (formerly ANME-2d) are readily identifiable despite the low abundance (≤1%) of this genus and confirm the occurrence of AOM. This finding is supported by 13C-depleted dissolved inorganic carbon. Proteins from Desulfocapsaceae and Desulfurivibrionaceae, in addition to 34S-enriched sulfate, suggest that these organisms use inorganic sulfur compounds as both electron donor and acceptor. Zerovalent sulfur in the groundwater may derive from abiotic rock interactions, or from a non-obligate syntrophy with Methanoperedens, potentially linking methane and sulfur cycles in Olkiluoto groundwater. Finally, putative episymbionts from the candidate phyla radiation (CPR) and DPANN archaea represented a significant diversity in the groundwater (26/84 genomes) with roles in sulfur and carbon cycling. Our results highlight AOM and sulfur disproportionation as active metabolisms and show that methane and sulfur fuel microbial activity in the deep terrestrial subsurface.

2022

Trace gas and aerosol interactions in the fully coupled model of aerosol-chemistry-climate ECHAM5-HAMMOZ: 2. Impact of heterogeneous chemistry on the global aerosol distributions

Isabelle Bey, Luca Pozzoli

We use the ECHAM5-HAMMOZ aerosol-chemistry-climate model to quantify the influence of trace gas–aerosol interactions on the regional and global distributions and optical properties of aerosols for present-day conditions. The model includes fully interactive simulations of gas phase and aerosol chemistry including a comprehensive set of heterogeneous reactions. We find that as a whole, the heterogeneous reactions have only a small effect on the

{SO}_{2}

and sulfate burden because of competing effects. The uptake of

{SO}_{2}

on dust and sea salt decreases the

{SO}_{2}

concentrations while the decrease in OH (that results from the uptake of (

{HO}_{2}

{N}_{2}{O}_{5}

, and

{O}_{3}

) tends to increase

{SO}_{2}

(because of reduced oxidation). The sulfate formed in sea salt aerosols from

{SO}_{2}

uptake accounts for 3.7 Tg(S) a−1 (5%) of the total sulfate production. Uptake and subsequent reaction of SO2 on mineral dust contributes to a small formation of sulfate (0.55 Tg(S) a−1,

2008