Products from the Incomplete Metabolism of Pyrene by Polycyclic Aromatic Hydrocarbon-Degrading Bacteria

Abstract

Pyrene is a regulated pollutant at sites contaminated with polycyclic aromatic hydrocarbons (PAH). It is mineralized by some bacteria but is also transformed to nonmineral products by a variety of other PAHdegrading bacteria. We examined the formation of such products by four bacterial strains and identified and further characterized the most apparently significant of these metabolites. Pseudomonas stutzeri strain P16 and Bacillus cereus strain P21 transformed pyrene primarily to cis-4,5-dihydro-4,5-dihydroxypyrene (PYRdHD), the first intermediate in the known pathway for aerobic bacterial mineralization of pyrene. Sphingomonas yanoikuyae strain R1 transformed pyrene to PYRdHD and pyrene-4,5-dione (PYRQ). Both strain R1 and Pseudomonas saccharophila strain P15 transform PYRdHD to PYRQ nearly stoichiometrically, suggesting that PYRQ is formed by oxidation of PYRdHD to 4,5-dihydroxypyrene and subsequent autoxidation of this metabolite. A pyrene-mineralizing organism, Mycobacterium strain PYR-1, also transforms PYRdHD to PYRQ at high initial concentrations of PYRdHD. However, strain PYR-1 is able to use both PYRdHD and PYRQ as growth substrates. PYRdHD strongly inhibited phenanthrene degradation by strains P15 and R1 but had only a minor effect on strains P16 and P21. At their aqueous saturation concentrations, both PYRdHD and PYRQ severely inhibited benzo[a]pyrene mineralization by strains P15 and R1. Collectively, these findings suggest that products derived from pyrene transformation have the potential to accumulate in PAH-contaminated systems and that such products can significantly influence the removal of other PAH. However, these products may be susceptible to subsequent degradation by organisms able to metabolize pyrene more extensively if such organisms are present in the system. Polycyclic aromatic hydrocarbons (PAH) are known to be degradable by a variety of soil bacteria (40). Consequently, the bioremediation of PAH contamination with naturally occurring microorganisms has been attempted at a number of sites (43,45). Most of the interest in the biodegradation of PAH in the field has been in the removal of the parent compounds, while most research on pure cultures of PAH-degrading bacteria has focused on their ability to grow on or mineralize specific PAH substrates. Relatively little attention has been paid to the potential formation of products from the partial transformation of PAH.Most of the information that does exist on PAH metabolites has been obtained in the context of identifying transient metabolites formed by isolates during growth on the parent compound (13,33,35,40) or metabolites formed by mutants of wild-type degraders (4, 40). Some bacteria, however, are capable of transforming one or more PAH despite an inability to grow on or mineralize the PAH in question (1,20,31,47). It is important to evaluate the products of such incomplete PAH metabolism because of their potential effects on PAH-degrading microorganisms or on potentially exposed human populations (44). Identification of common pr...

Bacterial Community Dynamics and Polycyclic Aromatic Hydrocarbon Degradation during Bioremediation of Heavily Creosote-Contaminated Soil

“…In a parallel study, a decrease in bioavailability was demonstrated (31). The accumulation of metabolites resulting from oxidation of PAHs can reduce the viability of several PAH degraders in addition to inhibiting the degradation of PAH (11,20,21). Nevertheless, this probably was not the case in this study, because polar metabolites determined by gas chromatography-mass spectrometry of the derivatized polar fraction did not accumulate in the soil (31).…”

Biology of Pseudomonas stutzeri

“…Strain P16 is able to grow, via salicylate, using phenanthrene (three rings), fluorene (two rings), naphthalene, and methylnaphthalenes (two rings) as the only carbon and energy sources (348,349). It is also able to transform pyrene (four rings) to nonmineral products (177). Interestingly, the phenanthrene bacterial growth rate increased in the presence of Tergitol NP10, an anionic surfactant.…”

Effects of Polycyclic Aromatic Hydrocarbon Mixtures on Degradation, Gene Expression, and Metabolite Production in Four Mycobacterium Species

“…The shunting of substrate through a new pathway, in combination with poor growth and suppressed degradation, suggest mechanisms of antagonism involving either toxicity or enzymelevel inhibition, both with precedents in published work on aromatic catabolism (19,25,57,65). For example, in Mycobacterium species and other bacteria, it is known that dihydrodiols are converted to diols, which autooxidize into toxic o-quinones (25,35,58,66). Detoxification involves retroconversion to a diol by quinone reductase enzymes, which can have narrow substrate ranges (66).…”