Microbial degr ada tion of naphthenic acids using constructed wetland treatment systems: metabolic and genomic insights for improved bioremediation of process-affected water

Abstract

Naphthenic acids (NAs) are a complex mixture of organic compounds released during bitumen extraction from mined oil sands that are important contaminants of oil sands process-affected water (OSPW). NAs can be toxic to aquatic organisms and, ther efor e, ar e a main target compound for OSPW. The ability of microorganisms to de gr ade N As can be exploited for bioremediation of OSPW using constructed wetland treatment systems (CWTS), which r e pr esent a possible low energy and low-cost option for scala b le in situ NA r emov al. Recent adv ances in genomics and anal ytical chemistr y hav e pr ovided insights into a better understanding of the meta bolic pathways and genes inv olv ed in N A de gr adation. Here , w e discuss the ecology of microbial N A de gr adation with a focus on CWTS and summarize the current knowledge related to the metabolic pathways and genes used by microorganisms to de gr ade N As. Evidence to date suggests that NAs are mostly de gr aded aerobically through ring cleavage via the beta-oxidation pathway, which can be combined with other steps such as aromatization, alpha-oxidation, omega-oxidation, or acti v ation as coenzyme A (CoA) thioesters. Anaer obic N A de gr adation has also been r e ported via the production of benzoyl-CoA as an intermediate and/or through the inv olv ement of methanogens or nitr ate , sulfate , and iron reducers. Furthermore , w e discuss how genomic, statistical, and modeling tools can assist in the development of improved bioremediation practices.