Biochar promotes the biophotoelectrochemical process driven by chlorophyll a and electroactive microorganisms

Photoelectrons produced by natural photocatalysts under illumination can serve as a potential energy source for electroactive microorganisms, driving a variety of reductive reactions that play a key role in Earth's biogeochemical cycles. The impact of biochar widely distributed in terrestrial and aquatic systems on anaerobic reduction reactions co-driven by natural photocatalysts and electroactive microorganisms remains unexplored. Thus, a pure culture system consisting of chlorophyll a and Geobacter sulfurreducens was established to investigate the influence and underlying mechanisms of biochar. Results demonstrated that biochar addition significantly enhanced the anaerobic reduction co-driven by the natural photocatalyst-electroactive microorganism (97.6% ± 0.4% vs. 83.9% ± 0.6% within 220 min). The non-soluble fraction of biochar exerted a more pronounced effect than the dissolved fraction, likely due to its superior electron exchange capacity. Investigations revealed that biochar primarily facilitates photoelectron transfer between chlorophyll a and electroactive microorganisms, as well as extracellular electron transfer from the microbes to terminal electron acceptors. Mutant-based assays demonstrated that the addition of conductive carbon materials can provide an alternative to the conductive pili and OmcB, forming a new photoelectron transport pathways. These findings provide a basis for accurately predicting the anaerobic photoelectrochemical reduction capacity of natural photocatalyst-electroactive microbe systems in biochar-rich environments, and offer insights into optimizing microbial reduction of some pollutants in engineered or natural systems through biochar application.