Anode-respiring

Lee, H.S., Torres, C.I., and Rittmann, B.E. (2009) Effects of substrate diffusion and anode potential on kinetic parameters for anode-respiring bacteria. Environ. Sci. Technol, 43 (19), 7571-7577. 

Torres Cl, Krajmalmk-Brown R, Parameswaran P, Marcus AK, Wanger G, Gorby YA, Rittmann BE. Selecting anode-respiring bacteria based on anode potential phylogenetic, electrochemical, and microscopic characterization. Environ Sci Technol 2009 43 9519-9524. 

Torres Cl, Marcus AK, Rittmann BE. Proton transport inside the biofilm limits electrical current generation by anode-respiring bacteria. Biotechnol Bioeng 2008 100 872-881. 

Torres Cl, Marcus AK, Parameswaran P, Rittmann BE. Kinetic experiments for evaluating the Nernst-Monod model for anode-respiring bacteria (ARB) in a biofilm anode. Environ Sci Technol 2008 42(17) 6593-6597. 

Torres Cl, Marcus AK, Lee HS, Parameswaran P, Krajmalnik-Brown R, Rittmaim BE. A kinetic perspective on extracellular electron transfer by anode-respiring bacteria. FEMS Rev 2010 34 3-17. 

Figure 8.1. Illustration of a typical two-chamber microbial fuel cell (MFC) specific bacteria species in the anode chamber, named exoelectrogenic or anode-respiring bacteria (ARB), break down organic substrates, i.e., acetate, to produce electrons, protons, and CO2. The electrons pass through an external resistor to be reduced at the cathode while protons pass through the proton exchange membrane (PEM) from the anode to the cathode chamber.

In a general sense, oxidation is a reaction in which a substance (molecule, atom or ion) loses electrons. These are transferred to another substance called - oxidant. The oxidation number of the substance being oxidized increases. Oxidation and reduction always occur simultaneously. In nature, oxidation reactions play an important role, e.g., in - respiration, metabolic processes, photooxidation, - corrosion and combustion, and, most importantly in electrochemistry, oxidation processes proceed at - anodes. 

The direct anodic oxidation of cytochrome c at a bipyridyl-modified electrode has already been incorporated in enzyme electrodes for lactate, carbon monoxide, and hydrogen peroxide. Here, cytochrome c is reduced by cytochrome b2, CO oxidoreductase, or horseradish peroxidase and anodically reoxidized. Cytochrome c has also been applied to couple mitochondria and chloroplasts to redox electrodes (Albery et al. 1987). Although no practically applicable sensor has been constructed as yet, this principle offers a new avenue to the determination of inhibitors of photosynthesis or respiration (Cardosi and Turner, 1987). 

Rhoads, A., Beyenal, H., and Lewandowski, Z. (2005) Microbial fuel cell using anaerobic respiration as an anodic reaction and biomineralized manganese as a cathodic reactant. Environ. Sci. Technol, 39 (12), 4666-4671. 

Under aerobic conditions, areas under respiring colonies can become anodic and surrounding areas cathodic. A thick biofilm can prevent diffusion of oxygen to cathodic sites and diffusion of aggressive anions, such as chlorides to anodic sites. Outward diffusion of metabolites and corrosion products also is impeded. If areas within the biofilm become anaerobic, the cathodic mechanism can change to reduction of water or microbiologically produced H2S. 

Figure 9.1. Schematic of a microbial fuel cell. Bacteria oxidize organic compounds, electrons travel through microbial respiratory enzymes generating ATP for the cell. Electrons are then transferred extra-cellularly to the anode where they travel through the circuit to the cathode. At the cathode, electrons combine with protons generated by microbial respiration and ambient oxygen at the platinum catalyst to generate water.

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