Isotope Fractionation Associated with the Biodegradation of 2-and 4-Nitrophenols via Monooxygenation Pathways

Date

2013-12-17

Author

Wijker, Reto S.
Kurt, Zöhre
Spain, Jim C.
Bolotin, Jakov
Zeyer, Josef
Hofstetter, Thomas B.

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Monooxygenation is an important route of nitroaromatic compound (NAC) biodegradation and it is widely found for cometabolic transformations of NACs and other aromatic pollutants. We investigated the C and N isotope fractionation of nitrophenol monooxygenation to complement the characterization of NAC (bio)degradation pathways by compound-specific isotope analysis (CSIA). Because of the large diversity of enzymes catalyzing monooxygenations, we studied the combined C and N isotope fractionation and the corresponding C-13- and N-15-apparent kinetic isotope effects (AKIEs) of four nitrophenol-biodegrading microorganisms (Bacillus spharericus JS905, Pseudomonas sp. 1A, Arthrobacter sp. JS443, Pseudomonas putida B2) in the pH range 6.1-8.6 with resting cells and crude cell extracts. While the extent of C and N isotope fractionation and the AKIE-values varied considerably for the different organisms, the correlated C and N isotope signatures (delta N-15 vs delta C-13) revealed trends, indicative of two distinct monooxygenation pathways involving hydroxy-1,4-benzoquinone or 1,2- and 1,4-benzoquinone intermediates, respectively. The distinction was possible based on larger secondary N-15-AKIEs associated with the benzoquinone pathway. Isotope fractionation was neither masked substantially by nitrophenol speciation nor transport across cell membranes. Only when 4-nitrophenol was biodegraded by Pseudomonas sp. 1A did isotope fractionation become negligible, presumably due to rate-limiting substrate binding steps pertinent to the catalytic cycle of flavin-dependent monooxygenases.

Subject Keywords

General Chemistry, Environmental Chemistry

URI

https://hdl.handle.net/11511/35300

Collections

Department of Environmental Engineering, Article