Methane-Oxidizing Activity Enhances Sulfamethoxazole Biotransformation in a Benthic Constructed Wetland Biomat

Ammonia monooxygenase and analogous oxygenase enzymes
contribute
to pharmaceutical biotransformation in activated sludge. In this study,
we hypothesized that methane monooxygenase can enhance pharmaceutical
biotransformation within the benthic, diffuse periphytic sediments
(i.e., “biomat”) of a shallow, open-water constructed
wetland. To test this hypothesis, we combined field-scale metatranscriptomics,
porewater geochemistry, and methane gas fluxes to inform microcosms
targeting methane monooxygenase activity and its potential role in
pharmaceutical biotransformation. In the field, sulfamethoxazole concentrations
decreased within surficial biomat layers where genes encoding for
the particulate methane monooxygenase (pMMO) were transcribed by a
novel methanotroph classified as Methylotetracoccus. Inhibition microcosms provided independent confirmation that methane
oxidation was mediated by the pMMO. In these same incubations, sulfamethoxazole
biotransformation was stimulated proportional to aerobic methane-oxidizing
activity and exhibited negligible removal in the absence of methane,
in the presence of methane and pMMO inhibitors, and under anoxia.
Nitrate reduction was similarly enhanced under aerobic methane-oxidizing
conditions with rates several times faster than for canonical denitrification.
Collectively, our results provide convergent in situ and laboratory
evidence that methane-oxidizing activity can enhance sulfamethoxazole
biotransformation, with possible implications for the combined removal
of nitrogen and trace organic contaminants in wetland sediments.