Hydrogen Isotope Fractionation As a Tool to Identify Aerobic and Anaerobic PAH Biodegradation

Abstract

Aerobic and anaerobic polycyclic aromatic hydrocarbon (PAH) biodegradation was characterized by compound specific stable isotope analysis (CSIA) of the carbon and hydrogen isotope effects Of the enzymatic reactions initiating specific degradation pathways, using naphthalene and 2-methylnaphtalene as model compounds. Aerobic activation of naphthalene and 2-methylnaphthalene by Pseudoinonas putida NCIB 9816 and Pseudoinonas fluorescens ATCC 17483 containing naphthalene dioxygenases was associated with moderate carbon isotope fractionation (epsilon(C) = -0.8 +/- 0.1 parts per thousand to -1.6 +/- 0.2 parts per thousand). In contrast, anaerobic activation of naphthalene by a carboxylation-like mechanism by strain NaphS6 was linked to negligible carbon isotope fractionation (epsilon(C) = -0.2 +/- 0.2 parts per thousand to -0.4 +/- 0.3 parts per thousand). Notably, anaerobic activation of naphthalene by strain NaphS6 exhibited a normal hydrogen isotope fractionation (epsilon(H) = -11 +/- 2 parts per thousand to -47 +/- 4 parts per thousand), whereas an inverse hydrogen isotope fractionation was observed for the aerobic strains (epsilon(H) = +15 +/- 2 parts per thousand to +71 +/- 6 parts per thousand). Additionally, isotope fractionation of NaphS6 was determined in an overlaying hydrophobic carrier phase, resulting in more reliable enrichment factors compared: to immobilizing the PAHs on the bottle walls without carrier phase. The observed differences especially in hydrogen fractionation might be used to differentiate between aerobic and anaerobic naphthalene and 2-methylnaphthalene biodegradation pathways at PAH-contaminated field sites