title: Isotope fractionation associated with the biodegradation of 2- and 4-nitrophenols via monooxygenation pathways.
abstract: 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 (13)C- and (15)N-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 (δ(15)N vs δ(13)C) 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 (15)N-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.
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology , CH-8600 Dübendorf, Switzerland.
authors.forename: Reto S
authors.initials: RS
authors.lastname: Wijker
authors.forename: Zohre
authors.initials: Z
authors.lastname: Kurt
authors.forename: Jim C
authors.initials: JC
authors.lastname: Spain
authors.forename: Jakov
authors.initials: J
authors.lastname: Bolotin
authors.forename: Josef
authors.initials: J
authors.lastname: Zeyer
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Hofstetter
mesh_terms: D001173:Arthrobacter / Q000378:metabolism; D001407:Bacillus / Q000378:metabolism; D016227:Benzoquinones / Q000737:chemistry / Q000378:metabolism; D055162:Biocatalysis; D001673:Biodegradation, Environmental; D002247:Carbon Isotopes; D005591:Chemical Fractionation; D004785:Environmental Pollutants / Q000032:analysis; D007700:Kinetics; D053858:Metabolic Networks and Pathways; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D009587:Nitrogen Isotopes; D009596:Nitrophenols / Q000737:chemistry / Q000378:metabolism*; D016958:Pseudomonas putida / Q000378:metabolism
chemical_list: D016227:Benzoquinones; D002247:Carbon Isotopes; D004785:Environmental Pollutants; D009587:Nitrogen Isotopes; D009596:Nitrophenols; C004532:quinone; C045573:2-nitrophenol; D006899:Mixed Function Oxygenases; C024836:4-nitrophenol