Consolidated bioprocessing of AFEX-pretreated corn stover to ethanol and hydrogen in a microbial electrolysis cell.

The consolidated bioprocessing (CBP) of corn stover pretreated via ammonia fiber expansion (AFEX-CS) into ethanol was investigated in a microbial electrolysis cell (MEC) driven by the exoelectrogen Geobacter sulfurreducens and the CBP bacterium Cellulomonas uda. C. uda was identified in a screening for its ethanologenic potential from AFEX-CS and for producing electron donors for G. sulfurreducens fermentatively. C. uda produced ethanol from AFEX-CS in MECs inoculated simultaneously or sequentially, with the concomitant conversion of the fermentation byproducts into electricity by G. sulfurreducens. The fermentation and electrical conversion efficiencies were high, but much of the AFEX-CS remained unhydrolyzed as nitrogen availability limited the growth of the CBP partner. Nitrogen supplementation stimulated the growth of C. uda, AFEX-CS hydrolysis and ethanologenesis. As a result, the synergistic activities of the CBP and exoelectrogen catalysts resulted in substantial energy recoveries from ethanologenesis alone (ca. 56%). The cogeneration of cathodic H(2) in the MEC further increased the energy recoveries to ca. 73%. This and the potential to optimize the activities of the microbial catalysts via culturing approaches and genetic engineering or adaptive evolution, make this platform attractive for the processing of agricultural wastes.