Postdiagenetic Bacterial Transformation of Nickel and Vanadyl Sedimentary Porphyrins of Organic-Rich Shale Rock (Fore-Sudetic Monocline, Poland)

Abstract

Nickel and vanadyl porphyrins belong to the so-called fossil geo- or sedimentary porphyrins. They occur in different types of organic matter-rich sediments but mostly occur in crude oils and their source rocks, oil shales, coals, and oil sands. In this study, we aimed to understand the process of bacterial transformation of geoporphyrins occurring in the subsurface shale rock (Fore-Sudetic Monocline, SW Poland). We studied these transformations in rock samples directly obtained from the field; in rock samples treated with bacterial strain isolated from shale rock (strain LM27) in the laboratory; and using synthetic nickel and vanadyl porphyrins treated with LM27. Our results demonstrate the following: (i) cleavage and/or degradation of aliphatic and aromatic substituents of porphyrins; (ii) degradation of porphyrin (tetrapyrrole) ring; (iii) formation of organic compounds containing 1, 2, or 3 pyrrole rings; (iv) formation of nickel- or vanadium-containing organic compounds; and (v) mobilization of nickel and vanadium. Our results also showed that the described bacterial processes change the composition and content of geoporphyrins, composition of extractable organic matter, as well as nickel and vanadium content in shale rock.

Biosynthesis of Tetrapyrrole Cofactors by Bacterial Community Inhabiting Porphyrine-Containing Shale Rock (Fore-Sudetic Monocline)

“…Vanadyl-cycloalkano-porphyrins [9] Etio and DPEP iron porphyrins [10] Etio,DPEP benzo-etio and benzo-DPEP vanadyl porphyrins Vanadyl porphyrins of series etio/DPEP [11] Octaethyl nickel porphyrin [12] Octaethyl vanadyl porphyrin Meso-tetraphenyl vanadyl porphyrin Meso-tetraphenyl nickel porphyrin…”

“…Previous studies have shown that bacteria degrades or cleaves aliphatic and aromatic substituents of nickel and vanadyl geoporphyrins, leading to the formation of modified geoporphyrins, and also degrades the tetrapyrrole ring. The end products observed due to the microbial activity on shale rock are mono-, di-, and tripyrrole compounds [12]. Table 1 shows the list of modified geoporphyrins and pyrrole compounds identified in the shale rock inhabited by bacteria.…”