Bacterial weathering of fossil organic matter and organic carbon mobilization from subterrestrial Kupferschiefer black shale: long-term laboratory studies

A large part of the organic carbon present in the lithosphere is trapped in fossil organic matter deposited in sedimentary rocks. Only specialized microorganisms are able to degrade it contributing to the return of the carbon to the global cycle. The role of bacteria in this process is not yet completely understood. In the present laboratory studies, subterrestrial organic-rich approximate to 256-million-year-old Kupferschiefer black shale was exposed to the activity of an indigenous consortium of lithobiontic bacteria for 365 days under aerobic conditions. An interdisciplinary research approach was applied, consisting of a detailed comparison of the chemical composition of extractable bitumens as well as resistant to extraction kerogen of the unweathered black shale to that of the bioweathered and chemically weathered, identification of mobilized organic compounds and spectrometry-based determination of proteomic composition of the bacterial biofilm. The oxidative bioweathering of bitumens and kerogen was confirmed. The mobilization of organic carbon in the form of oxidized organic compounds, such as monohydroxy and dihydroxy alcohols, aldehydes, monocarboxylic and dicarboxylic acids and esters due to the microbial activity, was documented. The enzymes crucial for the aerobic metabolism of aliphatic and aromatic hydrocarbons such as monooxygenases and dehydrogenases were identified in the epilithic biofilm inhabiting the black shale.