Abstract
Black shales are one of the largest reservoirs of fossil organic carbon and inorganic reduced sulfur on Earth. It is assumed that microorganisms play an important role in the transformations of these sedimentary rocks and contribute to the return of organic carbon and inorganic sulfur to the global geochemical cycles. An outcrop of deep subterrestrial ~256-million-year-old Kupferschiefer black shale was studied to define the metabolic processes of the deep biosphere important in transformations of organic carbon and inorganic reduced sulfur compounds. This outcrop was created during mining activity 12 years ago and since then it has been exposed to the activity of oxygen and microorganisms. The microbial processes were described based on metagenome and metaproteome studies as well as on the geochemistry of the rock. The microorganisms inhabiting the subterrestrial black shale were dominated by bacterial genera such as Pseudomonas, Limnobacter, Yonghaparkia, Thiobacillus, Bradyrhizobium, and Sulfuricaulis. This study on black shale was the first to detect archaea and fungi, represented by Nitrososphaera and Aspergillus genera, respectively. The enzymatic oxidation of fossil aliphatic and aromatic hydrocarbons was mediated mostly by chemoorganotrophic bacteria, but also by archaea and fungi. The dissimilative enzymatic oxidation of primary reduced sulfur compounds was performed by chemolithotrophic bacteria. The geochemical consequences of microbial activity were the oxidation and dehydrogenation of kerogen, as well as oxidation of sulfide minerals.
Highlights
Sedimentary rocks are one of the largest reservoirs of fossil organic carbon and inorganic reduced sulfur compounds on Earth
Microbial processes of sulfide mineral dissolution based on chemolithotrophic oxidation have been known since the 1950s (Bryner et al, 1954), and the heterotrophic processes of assimilation of the fossil organic carbon trapped in black shales were discovered at the beginning of the Twenty first century (Petsch et al, 2001)
The taxonomic composition of lithobiontic microbial community (LMC) inhabiting the studied black shale based on the Ion TorrentTM next-generation sequencing of the metagenome is presented in Figure 2, and in Supplementary Presentation 1
Summary
The richest reservoir of Corganic and Ssulfidic are shales, the most abundant ancient sedimentary rocks on Earth, Hydrocarbon and Sulfide Microbial Metabolism in which they may constitute up to 20 and 0.4 wt%, respectively (Tourtelot, 1979; Rickard, 2012). The oxidation of these sedimentary rocks is of great significance, because it contributes to the return of organic carbon and inorganic sulfur trapped in the form of refractory fossil organic matter and insoluble sulfides to the global biogeochemical cycles on the Earth’s near surface and subsurface. The diversity of sedimentary rocks, in terms of their origin and age, location, geochemical composition and their physicochemical properties, justifies further research toward a better understanding of these unique geomicrobial processes
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