In Vivo Participation of Artificial Porphyrins in Electron-Transport Chains: Electrochemical and Spectroscopic Analyses of Microbial Metabolism

Enhanced removal of veterinary antibiotic from wastewater by photoelectroactive biofilm of purple anoxygenic phototroph through photosynthetic electron uptake

Purple anoxygenic phototrophs have been recently attracted substantial attention for their growing potential in wastewater treatment and their diverse metabolic patterns can be regulated for process control and optimization. In this study, the photoheterotrophic metabolism of Rhodopseudomonas palustris (R. palustris) was modified by photosynthetic electron uptake using a poised electrode which was explored to enhance removal of veterinary antibiotic from aqueous medium. The results showed that R. palustris grown as biofilm on electrode surface had excellent photoelectroactive activity and the photosynthetic electron uptake from the photoelectroactive biofilm significantly enhanced antibiotic florfenicol (FLO) degradation. The specific degradation rate of FLO at the set electrode potential of 0 V was 2.59-fold higher than that without applied potential. Enhanced co-metabolic reductive dehalogenation by use of the photosynthetic electrons extracted from co-substrate was mainly responsible for FLO degradation which eliminated the antibacterial activity of FLO. The electrode potential controlled the processes of photosynthetic electron uptake and its resultant FLO degradation. The fastest degradation of FLO was achieved at 0 V because the electrode poised at this potential stroke a proper balance between the enhancing photosynthetic electron uptake by serving as electron acceptor and minimizing competition with FLO for the photosynthetic electron from co-substrate. The activity of photoelectroactive biofilm was not negatively affected by FLO at environmental relevant concentration, suggesting its great potential for removal of antibiotic contaminants in wastewater. R. palustris could serve as a reservoir for floR resistance gene but its abundance can be diminished by choosing appropriate electrode potential.

Direct electron transfer of Cellulomonas fimi and microbial fuel cells fueled by cellulose

The strain of Cellulomonas fimi NBRC 15513 can generate electricity with cellulose as fuel without mediator using a single chamber type microbial fuel cell (MFC) which had 100 mL of chamber and 50 cm² of the air cathode. The MFCs were operated over five days and showed the maximum current density of 10.0 ± 1.8 mA/m², the maximum power density of 0.74 ± 0.07 mW/m² and the ohmic resistance of 6.9 kΩ. According to the results of cyclic voltammetry, the appearance of the oxidation or reduction peak was not observed from the cell removed solution. The fact is that C. fimi does not secrete mediator-like compounds, while the oxidation peak was observed at +0.68 V from the phosphate buffer containing the washed cell. The peak appearance was caused by the electron transfer activity of which corresponds to cytochrome c, and disappeared after adding antimycin A which inhibits the electron transfer activity. The cell was alive throughout the experiment as the result of a colony forming unit on Luria-Bertani agar plates. This was thought that cytochrome c was on the membrane surface of the living cell and played a role in the direct electron transfer between the cells and anode.

Improving mediated electron transport in anodic bioelectrocatalysis

A microbial fuel cell loaded with bio-cocatalyst beads immobilized with recombinant riboflavin-secreting Escherichia coli shows significantly enhanced performance.

Electronic absorption, MCD, and luminescence properties of porphyrin J-aggregates

In this paper, we have investigated electronic absorption, magnetic circular dichroism, fluorescence, and phosphorescence spectra for a protonated form of H 2 TPPS 4( H 4 TPPS 4) and the J-aggregates of H 4 TPPS 4. The J-aggregation induces a large red-shift in the B (Soret) and Q absorption bands, while the phosphorescence peaks of H 4 TPPS 4 and its J-aggregates are almost entirely similar. The large red-shift of the B-band is quantitatively explained by the exciton interactions. Thus, the exciton interactions in the J-aggregates are proposed as a useful approach to decrease the energy splitting between the fluorescent and phosphorescent states.

Nanometrological porphyrins

A new cationic silver N-alkylpyridylporphyrin complex is able to 'sense' nanometric conductive particles with a diameter below 10 nm. The luminescence of the molecule changes its maximum from red to blue when it embraces a conductive (metallic or semiconducting) nanoparticle. The change is explained on the basis of a charge transfer between the molecule and the conductive nanoparticle along with a geometrical distortion of the porphyric ring and pyridinium substituents. This new molecule could be used to sense nanoparticle contamination in the environment, in the industry of heterogeneous catalysis and many other branches of nanometrological applications.