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

Abstract

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.

Keywords: Cu; Fermentative hydrogen production; Inhibition; Metagenomic analysis; Microbial community structure.