Microbial fuel cells and microbial ecology: applications in ruminant health and production research

Abstract

Microbial fuel cell (MFC) systems employ the catalytic activity of microbes to produce electricity from the oxidation of organic, and in some cases inorganic, substrates. MFC systems have been primarily explored for their use in bioremediation and bioenergy applications; however, these systems also offer a unique strategy for the cultivation of synergistic microbial communities. It has been hypothesized that the mechanism(s) of microbial electron transfer that enable electricity production in MFCs may be a cooperative strategy within mixed microbial consortia that is associated with, or is an alternative to, interspecies hydrogen (H(2)) transfer. Microbial fermentation processes and methanogenesis in ruminant animals are highly dependent on the consumption and production of H(2)in the rumen. Given the crucial role that H(2) plays in ruminant digestion, it is desirable to understand the microbial relationships that control H(2) partial pressures within the rumen; MFCs may serve as unique tools for studying this complex ecological system. Further, MFC systems offer a novel approach to studying biofilms that form under different redox conditions and may be applied to achieve a greater understanding of how microbial biofilms impact animal health. Here, we present a brief summary of the efforts made towards understanding rumen microbial ecology, microbial biofilms related to animal health, and how MFCs may be further applied in ruminant research.

Figure 1

Microbial fuel cell schematic for wastewater management operating with microbes as catalysts for fuel oxidation at the anode electrode and oxidant reduction at the cathode electrode. If sludge is used as the fuel and oxygen as the oxidant, then the net reaction, without nitrification, is: C₁₈H₁₉O₉N + H⁺ → 8H₂O + 18CO₂ + NH₄⁺ [132]

Figure 2

Redox energy and MFC schematic [31]

Figure 3

Genus-level diversity based on clone libraries obtained from MFCs inoculated with rumen fluids a anode-associated biofilm; b suspended population in anode compartment. Charts are adapted from tables reported in Rizmani-Yazdi et al. [3]

Figure 4

Current vs. time (top) and corresponding temporal measurements of volatile fatty acids (VFA) and methane production (bottom) for a MFC operated at high-current flow conditions and b MFC held at open-circuit conditions. Figure adapted from Ishii et al. [12]

Figure 5

Genus-level diversity based on clone libraries obtained from a rice-paddy soil; b operational MFC; and c open-circuit MFC. Charts are adapted from tables reported in Ishii et al. [12]