Anodic and cathodic microbial communities in single chamber microbial fuel cellsby Matteo Daghio, Isabella Gandolfi, Giuseppina Bestetti, Andrea Franzetti, Edoardo Guerrini, Pierangela Cristiani

New Biotechnology

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Year
2015
DOI
10.1016/j.nbt.2014.09.005
Subject
Molecular Biology / Biotechnology / Bioengineering

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New Biotechnology Volume 00, Number 00 October 2014 RESEARCH PAPER m e

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P ap erEdoardo Guerrini2 and Pierangela Cristiani3 1Dept. of Earth and Environmental Sciences – University of Milano-Bicocca, Piazza della Scienza 1, 20126 Milan, Italy 2Dept. of Chemistry, University of Milano, Via Golgi 19, 20133 Milan, Italy 3 RSE – Ricerca sul Sistema Elettrico S.p.A., Environment and Sustainable Development Department, Via Rubattino 54, 20134 Milan, Italy

Microbial fuel cells (MFCs) are a rapidly growing technology for energy production from wastewater and biomasses. In a MFC, a microbial biofilm oxidizes organic matter and transfers electrons from reduced compounds to an anode as the electron acceptor by extracellular electron transfer (EET). The aim of this work was to characterize the microbial communities operating in a Single Chamber Microbial Fuel Cell (SCMFC) fed with acetate and inoculated with a biogas digestate in order to gain more insight into anodic and cathodic EET. Taxonomic characterization of the communities was carried out by Illumina sequencing of a fragment of the 16S rRNA gene. Microorganisms belonging to Geovibrio genus and purple non-sulfur (PNS) bacteria were found to be dominant in the anodic biofilm. The alkaliphilic genus

Nitrincola and anaerobic microorganisms belonging to Porphyromonadaceae family were the most abundant bacteria in the cathodic biofilm.

Introduction

Microbial fuel cells (MFCs) are innovative systems for energy production from renewable biomass sources and from biomass derived wastes [1]. In an MFC bacteria can oxidize organic matter in anaerobic conditions and transfer the electrons to an anode that serves as solid electron acceptor. The electrons then pass through a circuit and combine with protons and a terminal electron acceptor at the cathode [2] where the process can be mediated by microorganisms [3]. The processes involved in the transfer of electrons to/from the electrodes are known as External

Electron Transfers (EET). The anodic communities can transfer the electrons by direct contact using membrane cytochromes or conductive pili, or by using shuttles that can be reduced on the cellular surface then diffuse to the anode where they are oxidized thus transferring the electrons to the electrode [4–7]. Although the EET involving the cathodic communities may be similar to those used to transfer the electrons to the anode [8], more insights are still needed to globally describe these mechanisms and the microorganisms involved.

The most typical tools used to characterize the microbial communities in MFCs use a molecular approach. The 16S rRNA gene is generally used as a molecular marker in performing the fingerprinting of the communities. In a previous study a Denaturing Gradient Gel Electrophoresis (DGGE) technique was used to describe both anodic and cathodic communities in Single

Chamber MFCs (SCMFCs) fed with acetate dissolved in an inoculum of raw municipal wastewater. The results suggested that the sulfur cycle could have a crucial role in cathodic EET [9–11].

Other studies used DGGE for molecular fingerprinting to assess the effect of the sediment matrix, the inoculum [12], the operational time [13], the electron donors [14] and to understand how the taxonomic composition can affect the power density [15].

Other molecular techniques adopted to describe microorganisms colonizing the electrodes are Fluorescence In Situ Hybridization (FISH), which uses specific probes that allow quantification of specific populations within the whole bacterial community [16],Corresponding author: Franzetti, A. (andrea.franzetti@unimib.it) http://dx.doi.org/10.1016/j.nbt.2014.09.005 www.elsevier.com/locate/nbt 1871-6784/ 2014 Published by Elsevier B.V. 1Anodic and cathodic communities in singl microbial fuel cells

Matteo Daghio1, Isabella Gandolfi1, GiusePlease cite this article in press as: Daghio, M. et al., Anodic and cathodic microbial communities j.nbt.2014.09.005icrobial chamber ina Bestetti1, Andrea Franzetti1, in single chamber microbial fuel cells, New Biotechnol. (2014), http://dx.doi.org/10.1016/ oR o g t c n c s [1 g s a

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P ap err Terminal Restriction Fragment Length Polymorphism (TFLP) [12]. Moving beyond these techniques, the recent develpment of Next Generation Sequencing (NGS) technologies has reatly improved the capability to describe microbial communiies. In recent years, sequencing costs have rapidly declined and onsequently the amount of available data has increased expoentially. Owing to their high throughput and the decreasing ost per sequence, NGS techniques have great potential to decribe the diversity and composition of microbial communities 7]. For example, Illumina and 454 pyrosequencing technoloies can generate up to millions of amplicon sequences in a ingle run, thus providing high coverage both to amplicon-based nd whole metagenomic studies of microbial communities. hus, this technology could be used to help fill the gaps in he current knowledge of microbial community structure inolved in EET mechanisms [18]. This approach has been applied recent studies reporting that the anode potential [19] and the ampling point position on the electrode surface [20] did not ffect the microbial composition of the anodic communities, hereas different chemical treatments of the anode surface can ad to the development of biofilms with different taxonomic ompositions [21]. However, there is still a considerable lack of nowledge in this field particularly regarding the microbial ommunities operating at the cathodes.

In this work we described the anodic and cathodic bacterial ommunities in a SCMFC operated with digestate from a biogas lant, using Illumina sequencing of the 16S rRNA gene in order to ain insight into the processes that select bacterial populations on