Isolation and bioelectrochemical characterization of novel fungal sources with oxidasic activity applied in situ for the cathodic oxygen reduction in microbial fuel cells

• We isolated three novel filamentous fungi with high oxidasic activity from soils of the Brazilian Scrubland (Caatinga).
• We found interesting mono- and polyphenol oxidasic activities compared with other fungal sources.
• These fungal strains were applied during the in situ cathodic reduction of oxygen in microbial fuel cells air-cathodes.
• In bioelectrochemical terms, we observed high current densities and power out generations.
• Also high levels of substrate biotransformation into energy according to the coulombic efficiency were observed.

Brazilian filamentous fungi Rhizopus sp. (SIS-31), Aspergillus sp. (SIS-18) and Penicillium sp. (SIS-21), sources of oxidases were isolated from Caatinga's soils and applied during the in situ cathodic oxygen reduction in fuel cells. All strains were cultivated in submerged cultures using an optimized saline medium enriched with 10 g L−1 of glucose, 3.0 g L−1 of peptone and 0.0005 g L−1 of CuSO4 as enzyme inducer. Parameters of oxidase activity, glucose consumption and microbial growth were evaluated. In-cell experiments evaluated by chronoamperometry were performed and two different electrode compositions were also compared. Maximum current densities of 125.7, 98.7 and 11.5 μA cm−2 were observed before 24 h and coulombic efficiencies of 56.5, 46.5 and 23.8% were obtained for SIS-31, SIS-21 and SIS-18, respectively. Conversely, maximum power outputs of 328.73, 288.80 and 197.77 mW m−3 were observed for SIS-18, SIS-21 and SIS-31, respectively. This work provides the primary experimental evidences that fungi isolated from the Caatinga region in Brazil can serve as efficient biocatalysts during the oxygen reduction in air-cathodes to improve electricity generation in MFCs.

Diagram for the bicompartmented microbial fuel cell using an air-cathode and in situ fungal growth.Figure optionsDownload as PowerPoint slide