Aerobic biotransformation of alkyl branched aromatic alkanoic naphthenic acids via two different pathways by a new isolate of Mycobacterium

Abstract

Naphthenic acids (NAs) are complex mixtures of carboxylic acids found in weathered crude oils and oil sands, and are toxic, corrosive and persistent. However, little is known about the microorganisms and mechanisms involved in NA degradation. We isolated a sediment bacterium (designated strain IS2.3), with 100% 16S rRNA gene sequence identity to Mycobacterium aurum, which degraded synthetic NAs (4'-n-butylphenyl)-4-butanoic acid (n-BPBA) and (4'-t-butylphenyl)-4-butanoic acid (t-BPBA). n-BPBA was readily oxidized with almost complete degradation (96.8% ± 0.3) compared with t-BPBA (77.8% ± 3.7 degraded) by day 49. Cell counts increased fourfold by day 14 but decreased after day 14 for both n- and t-BPBA. At day 14, (4'-butylphenyl)ethanoic acid (BPEA) metabolites were detected. Additional metabolites produced during t-BPBA degradation were identified by mass spectrometry of derivatives as (4'-carboxy-t-butylphenyl)-4-butanoic acid and (4'-carboxy-t-butylphenyl)ethanoic acid; suggesting that strain IS2.3 used omega oxidation of t-BPEA to oxidize the tert-butyl side-chain to produce (4'-carboxy-t-butylphenyl)ethanoic acid, as the primary route for biodegradation. However, strain IS2.3 also produced this metabolite through initial omega oxidation of the tert-butyl side-chain of t-BPBA, followed by beta-oxidation of the alkanoic acid side-chain. In conclusion, an isolate belonging to the genus Mycobacterium degraded highly branched aromatic NAs via two different pathways.

Occurrences and Behaviors of Naphthenic Acids in a Petroleum Refinery Wastewater Treatment Plant

“…This conclusion is consistent with the results of microbial biodegradation of individual aromatic alkanoic NAs. 30,33 Furthermore, estrogenic activities in wastewater from different treatment units were determined, since the aromatic NA fraction was reported to have an estrogenic effect. 31,32 Estrogenic activities were not observed in the sample extracts possibly due to the low concentrations of NA mixtures, but antiestrogenic activities were found in wastewater from physicochemical treatment units with ER antagonist potency ranging from 750 to 2100 ng Tamoxifen/L (Figure 4 and SI Figure S5).…”

“…29,30 For example, the aromatic NAs with chemical formulas similar to estrone-and estradiol-like compounds have been demonstrated to cause estrogenicity in fish larvae. 31,32 Several biodegradation studies reported the microorganisms and mechanisms involved in degradation of individual aromatic NA compounds; 30,33 however, there is very little understanding of aromatic NAs in water and solid fractions during physiochemical treatment and activated sludge treatment processes.…”

Identification of Estrogenic Compounds in Oil Sands Process Waters by Effect Directed Analysis

“…These are potentially metabolites or degradation products, with the O3 and O4 products representing possible hydroxylation 36 or carboxylation products 38. Major compounds that show greater abundance in the treated OSPW subfraction (F2.31T) compared to the untreated subfraction are primarily possible alicyclic NAs (such as C14 H 23 O 2 , C 14 H 21 O 2 , C 15 H 23 O 4 and C 15 H 21 O 2 )…”

Roles of Thermophiles and Fungi in Bitumen Degradation in Mostly Cold Oil Sands Outcrops

“…The action of specific enzymes also suffers if structurally similar compounds act as competitive inhibitors. Hence, although microorganisms which can grow by degrading specific NAs (15,16) or PAHs (17) have been isolated, these substrates degrade more slowly when present at ultralow concentrations in a bitumen mixture. For example, NA mixtures representing 10 3 to 10 4 compounds from oil sands bitumen end up in tailings ponds at concentrations of up to 100 mg/liter (18).…”