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

Abstract

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 methaneoxidizing 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.

Pharmaceutical Attenuation Differs within Woodchip-Based Lignocellulose Bioreactors across Nitrate- and Sulfate-Reducing Conditions

“…Removal in our experimental construct never exceeded 25%, indicating that other methods or substantial increases in residence time may be needed if sulfamethoxazole is a priority contaminant of concern. Recent evidence combining microcosm inhibition studies and field-based metatranscriptomics in an engineered wetland found that sulfamethoxazole biotransformation can be enhanced by methane-oxidizing activity . Given the limited removal of sulfamethoxazole (<25%) in our experimental construct, this highlights the potential for the collective treatment capability of the combination of nature-based systems that transition across redox domains for waters contaminated with a suite of pharmaceutical compounds.…”

Substrate promiscuity of xenobiotic-transforming hydrolases from stream biofilms impacted by treated wastewater

“…Most studies on biofilms have been conducted using amplicon sequencing to profile taxonomic community shifts that correlate with TrOC biotransformations in treated wastewater (Carles et al, 2022(Carles et al, , 2021Desiante et al, 2022;Mansfeldt et al, 2020;Tien et al, 2013). Metagenomics and metatranscriptomics analyses have recently deepened the resolution of community analysis to identify functional shifts in TrOCexposed engineered wetland biomats (Vega et al, 2023(Vega et al, , 2022. However, the number of studies conducted on the molecular mechanisms of TrOC biotransformations in freshwater biofilms or biomats is small relative to other systems such as enriched soil consortia (Vasileiadis et al, 2022) or activated sludge (Rich and Helbling, 2023).…”