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.
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.
Project description:To get insights in the electrogenic anaerobic lifestyle of P. putida KT2440 cultivated in a bioelectrochemical system (BES), we employed whole genome microarray expression profile.
Project description:We report an integrated experimental and simulation study of ammonia recovery using microbial electrolysis cells (MECs). The transport of various species during the batch-mode operation of an MEC was examined experimentally and the results were used to validate the mathematical model for such an operation. It was found that, while the generated electrical current through the system tends to acidify (or basify) the anolyte (or catholyte), their effects are buffered by a cascade of chemical groups such as the NH3/NH4(+) group, leading to relatively stable pH values in both anolyte and catholyte. The transport of NH4(+) ions accounts for ~90% of the total current, thus quantitatively confirming that the NH4(+) ions serve as effective proton shuttles during MEC operations. Analysis further indicated that, because of the Donnan equilibrium at cation exchange membrane-anolyte/catholyte interfaces, the Na(+) ion in the anolyte actually facilitates the transport of NH4(+) ions during the early stage of a batch cycle and they compete with the NH4(+) ions weakly at later time. These insights, along with a new and simple method for predicting the strength of ammonia diffusion from the catholyte toward the anolyte, will help effective design and operation of bioeletrochemical system-based ammonia recovery systems.
Project description:Microbial electrochemical technologies have been extensively employed for phenol removal. Yet, previous research has yielded inconsistent results, leaving uncertainties regarding the feasibility of phenol degradation under strictly anaerobic conditions using anodes as sole terminal electron acceptors. In this study, we employed high-performance liquid chromatography and gas chromatography-mass spectrometry to investigate the anaerobic phenol degradation pathway. Our findings provide robust evidence for the purely anaerobic degradation of phenol, as we identified benzoic acid, 4-hydroxybenzoic acid, glutaric acid, and other metabolites of this pathway. Notably, no typical intermediates of the aerobic phenol degradation pathway were detected. One-chamber reactors (+0.4 V vs. SHE) exhibited a phenol removal rate of 3.5 ± 0.2 mg L-1 d-1, while two-chamber reactors showed 3.6 ± 0.1 and 2.6 ± 0.9 mg L-1 d-1 at anode potentials of +0.4 and + 0.2 V, respectively. Our results also suggest that the reactor configuration certainly influenced the microbial community, presumably leading to different ratios of phenol consumers and microorganisms feeding on degradation products.
Project description:Overexpression of the adenylate cyclase gene cyaC facilitates current generation by Shewanella oneidensis in bioelectrochemical systems
Project description:To investigate the specificity of protein degradation and identify potential neo-substrates for the OsTIR1-AID2 and hCRBN-S4D systems, we conducted proteomics analyses of thymocytes 16 hours after intraperitoneal injection of 5-Ph-IAA or PBS in Rosa26OsTIR1/+;Satb1V-AID/V-AID and Rosa26OsTIR1/+;Satb1 +/+ mice, as well as POM or DMSO in Rosa26hCRBN/+;Satb1V-S4D/V-S4D and Rosa26hCRBN/+;Satb1+/+ mice, alongside with wildtype control mice. Furthermore, we conducted proteomics analysis in the cerebrum of DMSO- and POM-treated Rosa26hCRBN/+;Satb1+/+ mice to identify neo-substrates in the brain for the hCRBN-S4D system.