Microbial degradation of coumarin under methanogenic conditions

Coumarins are benzopyrones which occur naturally in plants and inhibit the growth of bacteria as they provide a defence against pathogens. Coumarin-rich plants like sweet clover are currently investigated as potential substrates for biogas production. However, the addition of coumarin to anaerobic digestion processes caused an inhibition of the methane production potentially due to its antimicrobial activity. In this study, the anaerobic degradation of coumarin by a methanogenic enrichment culture was investigated. The physiology of the enrichment culture was described in terms of gas production and gas composition. Details of the degradation pathway of coumarin were elucidated by gas chromatography coupled to mass spectrometry (GC-MS) using deuterium-labeled coumarin. The bacterial as well as archaeal communities of the enrichment culture were characterized by amplicon sequencing of 16S rRNA genes and functional mcrA genes. Furthermore, the activity of the present microorganisms was assessed by an untargeted metaproteomic approach.