Biodegradation of refractory hydrocarbon biomarkers from petroleum under laboratory conditions

Biomarkers are of great value in petroleum exploration because they provide essential information about the geological history of oils and source rocks. Steranes are of particular importance as they can be related to naturally occurring precursors. These compounds generally experience intense biodegradation, however, which alters their original distribution and obscures the information that they carry regarding oil maturity and source material. In an attempt to identify the microorganisms responsible for this degradation, we have investigated the capacity of 73 aerobic bacteria to degrade steranes present in Rozel Point (Utah) oil. Seven Gram-positive strains, belonging to a limited number of genera, were found to be active. Using Nocardia sp. SEBR 16, which caused the most extensive alteration, we have determined biodegradation rates for several isomers of steranes and methylsteranes. The preference for alteration of different isomers reflects that observed in natural environments, suggesting that the degradation intermediates could be used as indicators of the extent of the biodegradation in an oil. In addition, the microorganisms used here might be effective in biodegrading oil spills.