Engineering Artificial Three-Species Microbial Consortium to Produce High-Power Bioelectricity from Discarded Cellulosic Biomass of Liquor Industry

Converting cellulose and other widely distributed biomass resources into bioelectricity by exoelectrogen-based bioelectrochemical systems has been developed as a potential solution to the simultaneous environmental pollution treatment and power harvest. However, exoelectrogens are generally unable to utilize cellulose for cell growth and power generation due to a lack of relevant metabolic pathways and enzymes, which considerably limited practical applications. In this study, to use discarded cellulosic biomass from liquor industry as carbon source for power generation, we constructed an artificial three-species microbial consortium that included Trichoderma reesei, Lactobacillus pentosus, and Shewanella oneidensis. In this consortium, T. reesei digested cellulose into soluble sugars, which were then converted to lactate by L. pentosus, and S. oneidensis subsequently utilized lactate as the carbon source and electron donor to produce electricity. To enhance the energy conversion efficiency of this consortium, we first optimized the T. reesei–L. pentosus subconsortium, including the inoculum size and reaction temperature and pH, to increase degradation of cellulose and production of lactate, which led to an output power density of 40.39 mW/m2 by the artificial three-species microbial consortium. Second, to improve the extracellular electron transfer rate and biofilm formation of S. oneidensis, the flavin synthesis and extracellular polysaccharide accumulation were strengthened via overexpressing genes involved in the biosynthesis of flavin and extracellular polysaccharides, leading to an output power density of 453.52 mW/m2. Lastly, to enhance the thickness and conductivity of the electroactive biofilm, conductive materials (reduced graphene oxide and carbon nanotubes) were used to integrate with the engineered microbial consortium to form a 3D-assembled biohybrid, which dramatically enhanced the thickness and abundance of S. oneidensis in electroactive biofilm on the anode, thus achieving a maximum output power density of 816.93 mW/m2, 62.84-fold higher than that of the wild-type microbial consortium, which is, to the best our knowledge, the highest output power densities that have ever been reported in the genetically engineered microbial consortium using cellulosic biomass. This study lays a theoretical foundation for promoting circular carbon economy and realizing efficient utilization of biomass.