Metagenomic insights into the inhibitory mechanisms of Cu on fermentative hydrogen production

[Display omitted] •The inhibitory mechanisms of Cu on fermentative H2 production were examined.•Cu exposure decreased the abundance of H2-producing genera Clostridium sensu stricto.•Cu exposure down-regulated the genes involved in glycolysis and H2 formation.•H2 yield decreased by 60.40% and 96.64% upon exposure to Cu2+ at 500 and 1000 mg/L.•Cu exposure inhibited the generation of liquid metabolites link to H2 production. Cu is widely present in the feedstocks of dark fermentation, which can inhibit H2 production efficiency of the process. However, current understanding on the inhibitory mechanisms of Cu, especially the microbiological mechanism, is still lacking. This study investigated the inhibitory mechanisms of Cu2+ on fermentative hydrogen production by metagenomics sequencing. Results showed that the exposure to Cu2+ reduced the abundances of high-yielding hydrogen-producing genera (e.g. Clostridium sensu stricto), and remarkably down-regulated the genes involved in substrate membrane transport (e.g., gtsA, gtsB and gtsC), glycolysis (e.g. PK, ppgK and pgi-pmi), and hydrogen formation (e.g. pflA, fdoG, por and E1.12.7.2), leading to significant inhibition on the process performances. The H2 yield was reduced from 1.49 mol H2/mol-glucose to 0.59 and 0.05 mol H2/mol-glucose upon exposure to 500 and 1000 mg/L of Cu2+, respectively. High concentrations of Cu2+ also reduced the rate of H2 production and prolonged the H2-producing lag phase.