Bacterial DGGE fingerprints of biofilms on electrodes of membraneless microbial fuel cells

Abstract Bacteria communities on electrodes of membraneless single chamber microbial fuel cells were sampled and analysed after one and three months of operation, using the fingerprinting molecular technique DGGE (Denaturing Gradient Gel Electrophoresis). The materials of the anodes were carbon brush, carbon cloth and stainless steel mesh (AISI 304). The cathodes were made of graphite, with or without Platinum as catalyst. The microbial fuel cells were inoculated with raw wastewater coming from a municipal plant of the city of Milan and fed with sodium acetate 3 g L −1 . DGGE profiles enabled to calculate the Jaccard similarity indexes for the bacterial communities. The excision and sequencing of selected bands permitted the characterization of the different communities and bacteria groups. The cluster analysis (based on band presence/absence and similarity data) showed that after one month the microbial populations of anodic biofilms diverged in relation to the material and the geometry of the anode. However, at the end of the three months of experimentation, the anodic communities did not significantly differed from those found at the cathodes. The results suggest a central role of Sulphate-reducing Bacteria (SRB) alone or in synergy with the other microorganisms found (Spirochetes and photosynthetic purple non-sulphur bacteria – PNS), at the cathode as well as at the anode. The mechanism of cathodic reaction activation by bacteria metabolism is put forward.