Browsing by Author "Martin, Jonathan W."
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- ItemDifferential protein expression during growth on model and commercial mixtures of naphthenic acids in Pseudomonas fluorescens Pf-5(2021) McKew, Boyd A.; Johnson, Richard; Clothier, Lindsay; Skeels, Karl; Ross, Matthew S.; Metodiev, Metodi; Frenzel, Max; Gieg, Lisa M.; Martin, Jonathan W.; Hough, Michael A.; Whitby, CorinneNaphthenic acids (NAs) are carboxylic acids with the formula (CnH2n+ZO2) and are among the most toxic, persistent constituents of oil sands process-affected waters (OSPW), produced during oil sands extraction. Currently, the proteins and mechanisms involved in NA biodegradation are unknown. Using LC-MS/ MS shotgun proteomics, we identified proteins overexpressed during the growth of Pseudomonas fluorescens Pf-5 on a model NA (4′-n-butylphenyl)- 4-butanoic acid (n-BPBA) and commercial NA mixture (Acros). By day 11, >95% of n-BPBA was degraded. With Acros, a 17% reduction in intensity occurred with 10–18 carbon compounds of the Z family −2 to −14 (major NA species in this mixture). A total of 554 proteins (n-BPBA) and 631 proteins (Acros) were overexpressed during growth on NAs, including several transporters (e.g., ABC transporters), suggesting a cellular protective response from NA toxicity. Several proteins associated with fatty acid, lipid, and amino acid metabolism were also overexpressed, including acyl-CoA dehydrogenase and acyl-CoA thioesterase II, which catalyze part of the fatty acid beta-oxidation pathway. Indeed, multiple enzymes involved in the fatty acid oxidation pathway were upregulated. Given the presumed structural similarity between alkyl-carboxylic acid side chains and fatty acids, we postulate that P. fluorescens Pf-5 was using existing fatty acid catabolic pathways (among others) during NA degradation.
- ItemNeurodevelopmental and metabolomic responses from prenatal coexposure to perfluorooctanesulfonate (PFOS) and methylmercury (MeHg) in Sprague-Dawley rats(2019) Reardon, Anthony J. F.; Karathra, Jacqueline; Ribbenstedt, Anton; Benskin, Jonathan P.; MacDonald, Amy M.; Kinniburgh, David W.; Hamilton, Trevor; Fouad, Karim; Martin, Jonathan W.Methylmercury (MeHg) and perfluorooctanesulfonate (PFOS) are major contaminants of human blood that are both common in dietary fish, thereby raising questions about their combined impact on human development. Here, pregnant Sprague–Dawley rats ingested a daily dose, from gestational day 1 through to weaning, of either 1 mg/kg bw PFOS (PFOS-only), 1 mg/kg MeHg (MeHg-only), a mixture of 0.1 mg/kg PFOS and 1 mg/kg MeHg (Low-Mix), or of 1 mg/kg of PFOS and 1 mg/kg MeHg (High-Mix). Newborns were monitored for physical milestones and reflexive developmental responses, and in juveniles the spontaneous activity, anxiety, memory, and cognition were assessed. Targeted metabolomics of 199 analytes was applied to sectioned brain regions of juvenile offspring. Newborns in the High-Mix group had decreased weight gain as well as delayed reflexes and innate behavioral responses compared to controls and individual chemical groups indicating a toxicological interaction on early development. In juveniles, cumulative mixture effects increased in a dose-dependent manner in tests of anxiety-like behavior. However, other developmental test results suggested antagonism, as PFOS-only and MeHg-only juveniles had increased hyperactivity and thigmotaxic behavior, respectively, but fewer effects in Low-Mix and High-Mix groups. Consistent with these behavioral observations, a pattern of antagonism was also observed in neurochemicals measured in rat cortex, as PFOS-only and MeHg-only juveniles had altered concentrations of metabolites (e.g., lipids, amino acids, and biogenic amines), while no changes were evident in the combined exposures. The cortical metabolites altered in PFOS-only and MeHg-only exposed groups are involved in inhibitory and excitatory neurotransmission. These proof-of-principle findings at relatively high doses indicate the potential for toxicological interaction between PFOS and MeHg, with developmental-stage specific effects. Future mixture studies at lower doses are warranted, and prospective human birth cohorts should consider possible confounding effects from PFOS and mercury exposure on neurodevelopment.
- ItemPhotodegradation of bitumen-derived organics in oil sands process-affected water(2020) Challis, Jonathan K.; Parajas, Angelique; Anderson, Julie C.; Asiedu, Evelyn; Martin, Jonathan W.; Wong, Charles S.; Ross, Matthew S.The chemical composition of water-soluble organics in oil sands process-affected water (OSPW) is primarily composed of natural constituents of bitumen that are solubilized and concentrated during aqueous extraction of oil sands. OSPW organics are persistent and acutely toxic, and a leading remediation strategy is long-term ageing in end-pit lakes, despite limited data available on its photochemical fate. Here, direct photolysis of whole OSPW, or of its constituent fractions, was examined at environmentally relevant wavelengths (>290 nm) in bench-top studies. Changes in the chemical profiles of whole OSPW, acid- (AEO), and base-extractable organics (BEO) were characterized by liquid chromatography with ultra-high resolution mass spectrometry in negative (−) and positive (+) ionization modes. Following 18 d of irradiation, photolysis reduced the total ion intensity in all samples in both modes. The most photo-labile species included the O2−, O3−, O4−, O2S−, and O4S− chemical classes, which were depleted in whole OSPW by 93–100% after only 5 d. In positive mode, detected species were more recalcitrant than those detected in negative mode, with an average reduction across all heteroatomic classes of 75 ± 11.0% after 18 d. Estimated environmental half-lives for heteroatomic classes ranged from 57 d (O4S−) to 545 d (O3N+), with a greater recalcitrance for classes detected in positive mode compared to negative mode. Under field conditions in end-pit lakes, natural photolysis may be an important mechanism for effective OSPW remediation, and we suggest that future end-pit lakes be shallow to maximize light penetration and natural photolysis in ageing OSPW.
- ItemSupplemental information: photodegradation of bitumen-derived organics in oil sands process-affected water(2020) Challis, Jonathan K.; Parajas, Angelique; Anderson, Julie C.; Asiedu, Evelyn; Martin, Jonathan W.; Wong, Charles S.; Ross, Matthew S.Supplementary material consists of figures and tables.