Assist.-Prof. Dr. Sarah Pati

Oxygenase enzymes often initiate the microbial transformation of persistent organic chemicals in natural environments. While we have a good understanding of the substrate spectrum and catalytic cycles of these enzymes (Pati et al.), the overall importance of oxygenase enzymes for contaminant transformation in complex microbial communities (e.g., wastewater, freshwater, soil) is less investigated. One obstacle in quantifying enzymatic oxygenation reactions is the formation of unspecific transformation products, which can originate from various compounds and different reaction types. In addition, oxygenase enzymes can be inefficient in activating and incorporating O₂ into their substrates, leading to the formation of reactive oxygen species (Pati et al.). Our research addresses these issues by applying a combination of stable isotope labeling, high-resolution mass spectrometry, and reactive oxygen species assays to biotransformation experiments with diverse microbial communities and various organic compounds including rubber additives.

Stable isotope analysis is a powerful tool to distinguish different contamination sources of anthropogenic chemicals in the environment, identify transformation mechanisms of organic contaminants (Hofstetter et al.), and quantify net O₂ consumption/production in aquatic systems. For small inorganic compounds (e.g., O₂), and legacy contaminants (e.g., nitroaromatic explosives), such methods are well established and applicable to both field-scale and laboratory studies. Current methodological developments in our group focus on expanding stable isotope analysis to emerging polar contaminants (e.g., sulfonates and ionic liquids) with the use of high-resolution mass spectrometers. In addition, we employ high-resolution mass spectrometry to quantify compound mixtures in surface waters and sediments (Pati & Arnold) as well as identify transformation products in laboratory experiments.