Naproxen Is Transformed Via Acetogenesis and Syntrophic Acetate Oxidation by a Methanogenic Wastewater Consortium

Over-the-counter pharmaceutical compounds can serve as microbial substrates in wastewater treatment processes as well as in the environment. The metabolic pathways and intermediates produced during their degradation, however, are poorly understood. In this study, we investigate an anaerobic wastewater community that metabolizes naproxen via demethylation. Enriched cultures, established from anaerobic digester inocula receiving naproxen as the sole carbon source, transformed naproxen to 6-O-desmethylnaproxen (DMN) within 22 days. Continual enrichment and culture transfer resulted in consistent demethylation of naproxen with no loss of DMN observed. Methane was generated at 0.83 mmol per 1 mmol transformed naproxen. In addition to naproxen, the consortium readily demethylated syringic acid and vanillic acid. DNA analysis revealed a community of acetogenic bacteria and syntrophic acetate oxidizing archaea. Combined with the biotransformation data, this suggests the enriched consortium performs aromatic O-demethylation through a syntrophic relationship between specific acetogens, acetate oxidizers, and methanogens. The proposed model of carbon transfer through the anaerobic food web highlights the significance of linked community interactions in the anaerobic transformation of aromatic O-methyl compounds such as naproxen.