Metformin (Glucophage) Biodegradation: Insights from Microbiome and Biochemical Analyses

Abstract

Metformin is the most prescribed type 2 diabetes medication in the United States and in many countries worldwide. In diabetes patients, this drug has been shown to alter the gut microbiome resulting in improved glucose metabolism. More recently, metformin has been proposed to have anti-aging and antiviral properties making the drug a potential candidate to treat other health conditions. Metformin and its proposed “dead-end” product, guanylurea, are not fully metabolized by humans and enter municipal wastewater where they cannot be removed through conventional water treatment processes. These compounds have been detected in surface waters around the world and are currently considered emerging pollutants. This study examined a bacterial consortium enriched from activated sludge which demonstrated the ability to utilize metformin as a sole source of nitrogen, as well as to degrade metformin to its transformation product, guanylurea. Metagenomic sequencing yielded an 18 Mb assembly distributed over 7,440 contigs with an average GC content of 64%. 16S rRNA analysis suggested the presence of Sphingopyxis, Pseudomonas mendocina, Microbacterium, and Mesorhizhobium species within the consortia. Bioinformatic analysis led to the identification of three relevant enzymes involved in metformin metabolism: guanylurea hydrolase, carboxyguanidine deiminase, and allophanate hydrolase. Biochemical studies revealed that these proteins catalyze the degradation of guanylurea to ammonia and carbon dioxide. Protein sequence analyses and structural modeling studies are currently in progress to identify a candidate gene(s) encoding the enzyme initiating the metabolism of metformin. This research presents the first evidence for a biochemical pathway associated with the microbial degradation of guanylurea. Significantly, it also advances understanding of the microbial capacity for metformin biodegradation. These findings could lead to the development of practical biotechnological applications to improve water treatment processes and provide insight into the effects of metformin on human microbiome metabolism.