ROLE OF PRESSURE IN THE FORMATION OF ORGANO-MINERAL INTERACTIONS: IMPLICATIONS FOR ORGANIC PRESERVATION IN THE ANOXIC SUBSURFACE

Abstract:

Microorganisms influence the formation of minerals and play a role in the formation of stable organo-mineral complexes that can help preserve organic carbon over geological timescales. However, biomineralization processes occurring in the anoxic subsurface have not been thoroughly investigated.

Iron sulfide minerals precipitate in anoxic sedimentary environments, including deep-sea marine sediments, as the result of the interaction between sulfide produced by microbial sulfate reduction (MSR) and various Fe phases. Sulfate-reducing bacteria influence the nucleation and growth of iron sulfide minerals, therefore modifying their physical properties (Picard et al. 2018 Geochimica et Cosmochimica Acta). Biogenic iron sulfide minerals associate tightly with microbially-derived organic carbon, potentially providing a preservation mechanism for labile organic carbon in anoxic environments (Picard et al. 2019 Chemical Geology).

MSR is ubiquitous in deep subsurface environments but the effects of pressure on MSR have rarely been investigated. In this work, we investigated the effects of pressure on the formation of organo-mineral aggregates by the deep-sea sulfate-reducing bacterium Desulfovibrio hydrothermalis AM13. We used scanning transmission X-ray microscopy (STXM) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy to characterize the chemistry and distribution of Fe and C in organo-mineral aggregates. We show that pressure influences microbial sulfide production, extracellular organic carbon production, and mineral transformations by AM13. Biogenic iron sulfide minerals could play an important role in the preservation of organic carbon in the deep biosphere living under pressure.