A variety of hydrogenotrophic enrichment cultures catalyze cathodic reactions

Biocathodes where living microorganisms catalyse reduction of CO2 can potentially be used to producevaluable chemicals. Microorganisms harbouring hydrogenases may play a key role for biocathodeperformance since H2 generated on the electrode surface can act as an electron donor for CO2 reduction.In this study, the possibility of catalysing cathodic reactions by hydrogenotrophic methanogens,acetogens, sulfate-reducers, denitrifiers, and acetotrophic methanogens was investigated. The cultureswere enriched from an activated sludge inoculum and performed the expected metabolic functions. Allenrichments formed distinct microbial communities depending on their electron donor and electronacceptor. When the cultures were added to an electrochemical cell, linear sweep voltammogramsshowed a shift in current generation close to the hydrogen evolution potential (−1 V versus SHE)with higher cathodic current produced at a more positive potential. All enrichment cultures exceptthe denitrifiers were also used to inoculate biocathodes of microbial electrolysis cells operated withH+ and bicarbonate as electron acceptors and this resulted in current densities between 0.1–1 A/m2.The microbial community composition of biocathodes inoculated with different enrichment cultureswere as different from each other as they were different from their suspended culture inoculum. It wasnoteworthy that Methanobacterium sp. appeared on all the biocathodes suggesting that it is a keymicroorganism catalysing biocathode reactions