Formate-removing inoculum dominated by Methanobacterium congolense supports succinate production from crude glycerol...

We developed a formate-removing methanogenic inoculum (FRI) to facilitate succinate production from crude glycerol by Escherichia coli. FRI converted formate to methane, thereby enabling glycerol fermentation without additional electron acceptors under neutral pH. FRI was selectively enriched from sludge from the anaerobic digester of the Seonam sewage treatment plant (Seoul); this process was assessed via Illumina sequencing and scanning electron microscopy imaging. Methanobacterium congolense species occupied only 0.3% of the archaea community in the sludge and was enriched to 99.5% in complete FRI, wherein succinate-degrading bacteria were successfully eliminated. Co-culture with FRI improved glycerol fermentation and yielded 7.3 mM succinate from 28.7 mM crude glycerol, whereby FRI completely converted formate into methane. This study is the first to demonstrate methane production by M. congolense species, using formate. M. congolense-dominated FRI can serve as a renewable facilitator of waste feedstock fermentation and enable the production of commercially important compounds.