Metagenomic exploration of the promotion of electricity production in mushroom substrate based microbial fuel cells by acid hydrolysis

Spent mushroom substrate (SMS) is an abundant renewable lignocellulosic biomass generated from the mushroom cultivation industry and represents a promising feedstock for bioenergy production. Due to its abundant carbohydrate content and significant biomass reserves, SMS may serve as an excellent substrate for microbial fuel cells (MFCs). This study demonstrated that untreated and acid-hydrolyzed SMS can be used as carbon sources in dual-chamber MFCs for bioelectricity generation, respectively. The peak voltage reached 0.56 ± 0.04 V in MFC-US fed with raw SMS, whereas 0.70 ± 0.02 V was observed in MFC-HS supplied with acid-hydrolyzed SMS. MFC-US produced a maximum power density of 305 mW/m2 at a current density of 713 mA/m2, but MFC-HS achieved a higher maximum power density of 365 mW/m2 at 822 mA/m2. Metagenomic analysis revealed significant differences in microbial communities between the anodic biofilms of MFC-US and MFC-HS. At the genus level, the electroactive bacteria Geobacter predominated in MFC-US (17.42%) and MFC-HS (53.41%). Other fermentative bacteria, including Mesorhizobium, Shinella and Rhizobium, were also enriched in the anodic biofilm. Carbohydrate-active enzyme annotation indicated that the abundance of glucosidases in MFC-US and MFC-HS increased by 4.39% and 3.10%, respectively, compared with the inoculated sludge. Glycosyltransferases were the dominant enzyme family, with relative abundance of 44.78%, 40.98%, and 48.41% in sludge, MFC-US, and MFC-HS, respectively. These results suggest that SMS could serve as a renewable feedstock for sustainable electricity production in MFCs, providing a promising strategy for energy recovery and cleaner production in the mushroom industry.