Understanding the limitations of substrate degradation in bioelectrochemical systems
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ABSTRACT:
PROVIDER: PRJEB80810 | ENA |
REPOSITORIES: ENA
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Project description:Electrochemically active bacteria (EAB) are capable of electrochemical interactions with electrodes via extracellular electron transfer (EET) pathways and serve as essential components in bioelectrochemical systems. Previous studies have suggested that EAB, such as Shewanella oneidensis MR-1, use cyclic AMP (cAMP) receptor proteins for coordinately regulating the expression of catabolic and EET-related genes, allowing us to hypothesize that the intracellular cAMP concentration is an important factor determining electrochemical activities of EAB. The present study constructed an MR-1 mutant, cyaC-OE that overexpressed cyaC, a gene encoding a membrane-bound class III adenylate cyclase, and examined its electrochemical and transcriptomic characteristics. We show that intracellular cAMP concentration in cyaC-OE is more than double that in wild-type MR-1, and cya-OE generates approximately two-fold higher current in BES than the wild type. In addition, the expression of genes involved in EET and anaerobic carbon catabolism is up-regulated in cya-OE as compared to that in the wild type. These results suggest that enhancement of the intracellular cAMP level is a promising approach for constructing an EAB with high catabolic and electrochemical activities.
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Project description:We investigated ion transport limitations on 3D graphite felt electrodes by growing Geobacter sulfurreducens biofilms with advection to eliminate external mass transfer limitations. We characterized ion transport limitations by: (i) showing that serially increasing NaCl concentration up to 200 mM increased current linearly up to a total of +273% vs. 0 mM NaCl under advective conditions; (ii) growing the biofilm with a starting concentration of 200 mM NaCl, which led to a maximum current increase of 400% vs. current generation without NaCl, and (iii) showing that un-colonized surface area remained even after steady-state current was reached. After accounting for iR effects, we confirmed that the excess surface area existed despite a non-zero overpotential. The fact that the biofilm was constrained from colonizing and producing further current under these conditions confirmed the biofilms under study here were ion transport-limited. Our work demonstrates that the use of high surface area electrodes may not increase current density when the system design allows ion transport limitations to become dominant.
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