Metaproteomic and Metagenomic-Coupled Approach to Investigate Microbial Response to Electrochemical Conditions in Microbial Fuel Cells.

MFCs represent a promising sustainable biotechnology that enables the direct conversion of organic matter from wastewater into electricity using bacterial biofilms as biocatalysts. A crucial aspect of MFCs is how electroactive bacteria (EAB) behave and their associated mechanisms during extracellular electron transfer to the anode. A critical phase in the MFC start-up process is the initial colonization of the anode by EAB. Two MFCs were operated with an external resistance of 1000 ohms, one with an applied electrical voltage of 500 mV during the initial four days of biofilm formation and the other without any additional applied voltage. After stabilization of electricity production, total DNA and protein were extracted and sequenced from both setups. The combined metaproteomic/metagenomic analysis revealed that the application of voltage during the colonization step predominantly increased direct electron transfer via cytochrome c, mediated primarily by Geobacter sp. Conversely, the absence of applied voltage during colonization resulted in a broader diversity of bacteria, including Pseudomonas and Aeromonas, which participated in electricity production via mediated electron transfer involving flavin family members.

Effect of Contact Area and Shape of Anode Current Collectors on Bacterial Community Structure in Microbial Fuel Cells.

Low electrical conductivity of carbon materials is a source of potential loss for large carbonaceous electrode surfaces of MFCs due to the long distance traveled by electrons to the collector. In this paper, different configurations of titanium current collectors were used to connect large surfaces of carbon cloth anodes. The current collectors had different distances and contact areas to the anode. For the same anode surface (490 cm2), increasing the contact area from 28 cm2 to 70 cm2 enhanced power output from 58 mW·m-2 to 107 mW·m-2. For the same contact area (28 cm2), decreasing the maximal distance of current collectors to anodes from 16.5 cm to 7.75 cm slightly increased power output from 50 mW·m-2 to 58 mW·m-2. Molecular biology characterization (qPCR and 16S rRNA gene sequencing) of anodic bacterial communities indicated that the Geobacter number was not correlated with power. Moreover, Geobacter and Desulfuromonas abundance increased with the drop in potential on the anode and with the presence of fermentative microorganisms. Electrochemical impedance spectroscopy (EIS) showed that biofilm resistance decreased with the abundance of electroactive bacteria. All these results showed that the electrical gradient arising from collectors shapes microbial communities. Consequently, current collectors influence the performance of carbon-based anodes for full-scale MFC applications.

Microbial fuel cell anodic microbial population dynamics during MFC start-up.

In order to optimize energy production in MFCs, a better understanding of anodic communities is essential. Our objective was to determine the taxonomic structure of the bacterial communities present at the surface of the anode during the formation and development of electro-active biofilms in MFCs inoculated with fresh primary clarifier overflow. Quantitative microbial community dynamics were evaluated as a function of time and electrical performance using 16S rRNA gene-based phylogenetic microarrays and flow cytometry. Results show that the bacterial community stabilized partially but not completely when voltage output was stable. Geobacter appeared to be the predominant genus, whose growth was associated with voltage, while some other genus still developed or declined after the voltage stabilization. Flow cytometry revealed that some genus showing a decreasing proportional fluorescence intensity over time were still actively respiring bacteria, and thus, active albeit minor members of the biofilm. Finally, this study shows that anodic biofilm selection and maturation is still occurring after more than 20 days of operation and over ten days after voltage is stabilized.