Biodegradation kinetics of select polycyclic aromatic hydrocarbon (PAH) mixtures by <Emphasis Type="Italic">Sphingomonas paucimobilis</Emphasis> EPA505 |
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Authors: | Anuradha M Desai Robin L Autenrieth Petros Dimitriou-Christidis Thomas J McDonald |
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Institution: | (1) Department of Civil Engineering, Texas A&M University, College Station, TX 77843-3136, USA;(2) Present address: Department of Civil and Environmental Engineering, University of Houston, Houston, TX 77204-4003, USA;(3) Present address: Carollo Engineers, 376 E Warm Springs Road Suite 250, Las Vegas, NV 89119, USA;(4) Health Science Center, School of Rural Public Health, Texas A&M University, College Station, TX 77802-1266, USA |
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Abstract: | Many contaminated sites commonly have complex mixtures of polycyclic aromatic hydrocarbons (PAHs) whose individual microbial
biodegradation may be altered in mixtures. Biodegradation kinetics for fluorene, naphthalene, 1,5-dimethylnaphthalene and
1-methylfluorene were evaluated in sole substrate, binary and ternary systems using Sphingomonas paucimobilis EPA505. The first order rate constants for fluorene, naphthalene, 1,5-dimethylnaphthalene, and 1-methylfluorene were comparable;
yet Monod parameters were significantly different for the tested PAHs. S. paucimobilis completely degraded all the components in binary and ternary mixtures; however, the initial degradation rates of individual
components decreased in the presence of competitive PAHs. Results from the mixture experiments indicate competitive interactions,
demonstrated mathematically. The generated model appropriately predicted the biodegradation kinetics in mixtures using parameter
estimates from the sole substrate experiments, validating the hypothesis of a common rate-determining step. Biodegradation
kinetics in mixtures were affected by the affinity coefficients of the co-occurring PAHs and mixture composition. Experiments
with equal concentrations of substrates demonstrated the effect of concentration on competitive inhibition. Ternary experiments
with naphthalene, 1,5-dimethylnaphthalene and 1-methylfluorene revealed delayed degradation, where depletion of naphthalene
and 1,5-dimethylnapthalene occurred rapidly only after the complete removal of 1-methylfluorene. The substrate interactions
observed in mixtures require a multisubstrate model to account for simultaneous degradation of substrates. PAH contaminated
sites are far more complex than even ternary mixtures; however these studies clearly demonstrate the effect that interactions
can have on individual chemical kinetics. Consequently, predicting natural or enhanced degradation of PAHs cannot be based
on single compound kinetics as this assumption would likely overestimate the rate of disappearance. |
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Keywords: | PAHs Biodegradation kinetics Mixtures Substrate interactions Monod parameters Multisubstrate |
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