Respiratory electrogen Geobacter boosts hydrogen production efficiency of fermentative electrotroph Clostridium pasteurianum

Abstract

Electrogens and electrotrophs are microorganisms that generate and consume electricity in a bioelectrochemical system, respectively. However, the influence of respiratory electrogen Geobacter on the hydrogen production efficiency of fermentative electrotroph Clostridium pasteurianum remains unclear. Herein, cocultures with Geobacter sulfurreducens and C. pasteurianum were successfully established during glucose fermentation. Compared with those in C. pasteurianum monoculture alone, the maximum rate and yield of hydrogen production in the coculture increased by 122.2% and 28.92%, respectively. Meanwhile, substrate conversation efficiency elevated by 50.6%. The acetic and butyric acid fermentation pathways in the cocultures were also promoted relative to those in the monoculture. Carbon and electron balance analysis also unraveled that acetate production in syntrophic coculture accounted for approximately-two times more carbon and electron contributions than that in the monoculture. A direct manner mediated by pili-like structures or cell contacts was built between the two electroactive bacteria during the electric syntropy. Extracellular electron inputting from G. sulfurreducens shifted the fermentative pattern of C. pasteurianum, which resulted in an enhanced acetic acid fermentation pathway accompanied by a higher hydrogen yield. These findings provide new insights into electric syntrophy between respiratory electrogenic G. sulfurreducens and fermentative electrotrophic C. pasteurianum. A new strategy for hydrogen enhancement by coculturing hydrogen-producing electrotrophic bacteria with electrogenic microorganisms is also explored.