Carbon and Hydrogen Stable Isotope Fractionation Associated with the Aerobic and Anaerobic Degradation of Saturated and Alkylated Aromatic Hydrocarbons

Abstract

Saturated hydrocarbons (alkanes) and alkylated aromatic hydrocarbons are abundant environmental compounds. Hydrocarbons are primarily removed from the environment by biodegradation, a process usually associated with moderate carbon and significant hydrogen isotope fractionation allowing monitoring of biodegradation processes in the environment. Here, we review the carbon and hydrogen stable isotope fractionation associated with the cleavage of C-H bonds at alkyl chains of hydrocarbons. Propane, n-butane and ethylbenzene were used as model components for alkyl moieties of aliphatic and aromatic hydrocarbons with emphasis on the cleavage of the C-H bond without the involvement of molecular oxygen. The carbon and hydrogen isotope fractionation factors were further used to explore the diagnostic potential for characterizing the mode of bond cleavage under oxic and anoxic conditions. Λ factors, calculated to correlate carbon and hydrogen fractionation, allowed to distinguish between aerobic and anaerobic biodegradation processes in the environment.

Elucidating the Role of O2 Uncoupling in the Oxidative Biodegradation of Organic Contaminants by Rieske Non-heme Iron Dioxygenases

“…This phenomenon likely precludes the quantitative interpretation of isotope fractionation associated with the dioxygenation processes. Our insights would therefore call for a re-evaluation of stable isotope based data from biodegradation reactions of various contaminants that are likely catalyzed through oxygenations by non-heme iron oxygenases − once the O 2 uncoupling behavior of the involved enzymes is known.…”

Anaerobic Microbial Degradation of Hydrocarbons: From Enzymatic Reactions to the Environment

“…Carbon and hydrogen stable isotope fractionation resulting from C-H bond cleavage during microbial degradation of hydrocarbons and its prospects for monitoring respective degradation processes in situ are summarized by Musat et al [2016]. An intrinsic property of enzymes is the faster turnover of the lighter isotopologue of the substrate, resulting in an enrichment of the heavier isotopologue in the residual substrate pool.…”

Carbon and hydrogen stable isotope fractionation due to monooxygenation of short-chain alkanes by butane monooxygenase of Thauera butanivorans Bu-B1211

“…Alkanes are the major fraction of non-degraded crude oils, accounting for over 50% by mass ( Tissot and Welte 1984 ). Short-chain, gaseous alkanes are mainly released in the biosphere from deep-seated oil or gas reservoirs by natural seepage or during the anthropogenic exploration and exploitation of fossil fuels; global annual emissions have been estimated at 42–64 Tg/year for methane, about 10 Tg/year for ethane, propane and n-butane, respectively, and about 4 Tg/year for isobutane ( Etiope and Ciccioli 2009 ; Pozzer et al, 2010 ; Musat et al, 2016 ).…”

“…Two major functionalization mechanisms and subsequent degradation pathways can be distinguished. Nitrate- and sulfate-reducing bacteria use glycyl radical enzymes which catalyze the hemolytic cleavage of a C-H-bond of the alkane, followed by carbon–carbon addition of the generated alkyl radical to fumarate ( Savage et al, 2010 ; Musat 2015 ; Musat et al, 2016 ; Wu et al, 2022 ); the reaction can take place simultaneously at the terminal and subterminal carbon atoms (propane) or only at the subterminal carbon atom (butane) ( Kniemeyer et al, 2007 ; Jaekel et al, 2014 ). The formed alkylsuccinates are subsequently channeled into the central metabolic pathways by ligation to coenzyme A, C-skeleton rearrangement, and beta-oxidation ( Musat 2015 ; Chen et al, 2022 ).…”