Segregation of the Anodic Microbial Communities in a Microbial Fuel Cell Cascade.

Douglas M Hodgson,Ann Smith,Jia V Li,Sonal Dahale,Julian R Marchesi,C Avignone Rossa,Michael E Bushell,James P Stratford,André Grüning

doi:10.3389/fmicb.2016.00699

Abstract

Metabolic interactions within microbial communities are essential for the efficient degradation of complex organic compounds, and underpin natural phenomena driven by microorganisms, such as the recycling of carbon-, nitrogen-, and sulfur-containing molecules. These metabolic interactions ultimately determine the function, activity and stability of the community, and therefore their understanding would be essential to steer processes where microbial communities are involved. This is exploited in the design of microbial fuel cells (MFCs), bioelectrochemical devices that convert the chemical energy present in substrates into electrical energy through the metabolic activity of microorganisms, either single species or communities. In this work, we analyzed the evolution of the microbial community structure in a cascade of MFCs inoculated with an anaerobic microbial community and continuously fed with a complex medium. The analysis of the composition of the anodic communities revealed the establishment of different communities in the anodes of the hydraulically connected MFCs, with a decrease in the abundance of fermentative taxa and a concurrent increase in respiratory taxa along the cascade. The analysis of the metabolites in the anodic suspension showed a metabolic shift between the first and last MFC, confirming the segregation of the anodic communities. Those results suggest a metabolic interaction mechanism between the predominant fermentative bacteria at the first stages of the cascade and the anaerobic respiratory electrogenic population in the latter stages, which is reflected in the observed increase in power output. We show that our experimental system represents an ideal platform for optimization of processes where the degradation of complex substrates is involved, as well as a potential tool for the study of metabolic interactions in complex microbial communities.

Highlights

The diverse microbial species present in natural environments interact with each other through metabolic and functional relationships that ensure the activity and stability of the community
We studied the anodic microbial communities and their associated metabolism in a cascade of microbial fuel cells (MFCs) fed with dried distiller’s grain with solubles (DDGS), a downstream product of the bioethanol industry (Eskicioglu et al, 2011) which has not been previously reported as a feed substrate in MFCs
In our experimental system (Schematically represented in Figure 1), four individual MFCs were connected hydraulically and the voltage and power output were monitored during the experiment

Summary

Introduction

The diverse microbial species present in natural environments interact with each other through metabolic and functional relationships that ensure the activity and stability of the community. Self-Segregation of Microbial Communities polysaccharides, proteins, nucleic acids, and lipids (Sieber et al, 2012; Morris et al, 2013) Those synergistic interactions are the basis of natural processes such as the degradation of plant or animal residues, or the biogeochemical cycling of carbon, nitrogen or sulfur, but can be essential in managed or artificial processes for agriculture, the food industry, wastewater treatment, or industrial bioprocesses (Brenner et al, 2008; Fuhrman, 2009; Chiu et al, 2014; Jacobsen and Hjelmsø, 2014). The interactions among the species in a microbial consortium affect the function, activity, and stability of the community, providing improved metabolic capabilities. This is exploited in microbial fuel cells (MFCs), bioelectrochemical devices that convert organic or inorganic substrate chemical energy into electrical energy, by the metabolic activity of microorganisms. Efficient degradation of complex feedstocks requires the complete breakdown of different macromolecules, achievable only through the combination of diverse microbial metabolic activities and long residence times in the anode chamber

Methods

Results

Conclusion