Characteristic features of the hydrocarbon composition of Spiridonovskoe (Tatarstan) and Pitch Lake (Trinidad and Tobago) asphaltites

Microbial Degradation Rates of Natural Bitumen

“…Crude oil is one of the most important natural resources in our modern life but a major fraction of economically available oil exists as biodegraded heavy oil or bitumen. − During the degradation process, n -alkanes, monocyclic alkanes, and alkyl benzenes disappear first, which leads to a lower oil quality and finally to natural bitumen mostly consisting of saturated and aromatic hydrocarbons, resins, and asphaltene. − However, our knowledge about in situ biological processes and degradation rates in anoxic oil reservoirs is scarce due to the limited access to the deep subsurface. , The most common metabolisms found in oil reservoirs are sulfate reduction, fermentation, acetogenesis, and methanogenesis. ,,, A broad range of metabolic pathways like iron­(III)-, manganese­(IV)-, nitrate-, or nitrite reduction have been detected in oil reservoirs as well. , Nevertheless, their influence still remains unclear, since the microbial degradation of hydrocarbons in the environment is mostly limited by the availability of electron acceptors and the bioavailability of the hydrocarbons. , Since electron acceptors in oil reservoirs are quickly depleted by microorganisms and do not get replenished unless water flooding is implemented, fermentation and methanogenesis are believed to be mainly responsible for the oil degradation in most reservoirs. ,, Fermentative, syntrophic microorganisms degrade complex hydrocarbons like fatty acids, alcohols, sugars, amino acids, and aromatic compounds stepwise into smaller molecules such as hydrogen, acetate, and carbon dioxide. − In addition, acetate is alternatively oxidized by syntrophic acetate oxidation. − Many of these reactions are endergonic and are only energetically feasible if the products are kept at low concentrations. , Acetate is commonly converted by acetoclastic methanogens into methane and carbon dioxide, whereas hydrogen and carbon dioxide are used by hydrogenotrophic methanogens to produce methane. − However, sulfate-reducing bacteria (SRB) are present in practically every oil reservoir and are known for complete alkane (C 3 –C 20 ) oxidation to carbon dioxide in the presence of sulfate. , They are also capable of mineralizing aromatic hydrocarbon degradation such as benzene, toluene, naphthalene, 2-methylnaphthalene, phenanthrene, ethylbenzene, and xylene carbon dioxide. …”

Imprints of ecological processes in the taxonomic core community: an analysis of naturally replicated microbial communities enclosed in oil

“…S4 ). Linear extrapolation of these results yielded a maximum collision probability of 6.16 × 10 −3 per water droplet for the distance of 80 m between Pitch Lake bottom and surface (Kayukova et al 2016 ) and 7.6% for the distance of 1500 m between oil reservoir and lake surface (Fig. 1B ).…”

Assessing anaerobic microbial degradation rates of crude light oil with reverse stable isotope labelling and community analysis

“…Oil reservoirs are extreme habitats due to saturated hydrocarbon concentrations, low water activity and anoxic conditions (Pannekens et al, 2019). Nevertheless, microbial degradation is taking place in oil reservoirs where microorganisms favor the relatively easier-to-degrade light oil components such as alkanes over the more recalcitrant polycyclic aromatic hydrocarbons (PAHs) or asphaltenes (Larter et al, 2003;Mbadinga et al, 2011;Kayukova et al, 2016).…”