title: Naphthenic acid biodegradation by the unicellular alga Dunaliella tertiolecta.
abstract: Naphthenic acids (NAs) are a major contributor to toxicity in tailings waste generated from bitumen production in the Athabasca Oil Sands region. While investigations have shown that bacteria can biodegrade NAs and reduce tailings toxicity, the potential of algae to biodegrade NAs and the biochemical mechanisms involved remain poorly understood. Here, we discovered that the marine alga Dunaliella tertiolecta is able to tolerate five model NAs (cyclohexanecarboxylic acid, cyclohexaneacetic acid, cyclohexanepropionic acid, cyclohexanebutyric acid and 1,2,3,4-tetrahydro-2-naphthoic acid) at 300mgL(-1), a level which exceeds that of any single or combination of NAs typically found in tailings ponds. Moreover, we show that D. tertiolecta can metabolize four of the model NAs. Analysis of NA-amended cultures of D. tertiolecta via low resolution gas chromatography-mass spectrometry allowed us to quantify decreasing NA levels, identify metabolites, and formulate putative mechanisms of biodegradation. Degradation of cyclohexanebutyric acid and cyclohexanepropionic acid proceeded via β-oxidation and resulted in the transient accumulation of cyclohexaneacetic acid and cyclohexanecarboxylic acid, respectively. Cyclohexanecarboxylic acid was metabolized via 1-cyclohexenecarboxylic acid suggesting that further degradation may occur by step-wise β-oxidation. When D. tertiolecta was inoculated in the presence of oil sands tailings water from the Athabasca region, biodegradation of single-ring NAs was observed relative to controls. This result corroborates the trend we observed with the single-ring model NAs.
authors: Institute for Biocomplexity and Informatics, University of Calgary, Alberta, Canada T2N 1N4.
authors: Dean M
authors: DM
authors: Quesnel
authors: Iyswarya M
authors: IM
authors: Bhaskar
authors: Lisa M
authors: LM
authors: Gieg
authors: Gordon
authors: G
authors: Chua
mesh_terms: D000085:Acetates / Q000378:metabolism; D001673:Biodegradation, Environmental; D002087:Butyrates / Q000378:metabolism; D002264:Carboxylic Acids / Q000378:metabolism* / Q000633:toxicity; D003509:Cyclohexanecarboxylic Acids / Q000378:metabolism; D003510:Cyclohexanes; D016823:Volvocida / Q000187:drug effects / Q000378:metabolism*; D014874:Water Pollutants, Chemical / Q000378:metabolism* / Q000633:toxicity
chemical_list: D000085:Acetates; D002087:Butyrates; D002264:Carboxylic Acids; D003509:Cyclohexanecarboxylic Acids; D003510:Cyclohexanes; D014874:Water Pollutants, Chemical; C034707:cyclohexanebutyric acid; C044895:cyclohexanecarboxylic acid; C018883:cyclohexaneacetic acid; C046170:naphthenic acid