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The bacterial photosynthetic reaction centre (RC) is a membrane spanning protein that, upon illumination, promotes the reduction of a ubiquinone molecule withdrawing electrons from cytochrome c2. This photo-activated reaction has been often exploited, in suitably designed photoelectrochemical cells, to generate photocurrents sustained by the reduction at the working electrode of the photo-oxidized electron donor or by the oxidation of the electron acceptor. In this work we have explored in more detail the factors affecting the photocurrent generation in commercially available screen-printed electrochemical cells containing an electrolyte solution where RC proteins and suitable mediators are solubilized. In particular, the role of the applied potential and the influence of concentration and structure of acceptor and donor molecules have been assessed. We show that efficient generation of cathodic photocurrents in a three electrode configuration occurs at an applied potential of 0.0 V versus quasi-ref Ag (the open circuit potential of the system measured in the dark) in presence of ferrocenemethanol and decylubiquinone, which proved to guarantee high performances as electron donor and acceptor respectively. Moreover, we employed a set of differential equations, describing reaction and diffusion processes, for modelling with high accuracy the chronoamperometry profiles recorded at variable RC concentrations. This model allowed us to estimate the kinetic parameters relevant to the chemical and electrochemical reactions triggered by light and to get a snapshot of the electrolyte composition in the bulk and electrode surroundings at different times from the light exposure. The characteristic time course of the photocurrent, showing a fast rise to a peak value followed by a slower decay, has been therefore explained as the result of the strict interconnection between the dynamical processes involved.

The reconstitution of the integral membrane protein photosynthetic reaction center (RC) in polymersomes, i.e. artificial closed vesicles, was achieved by the micelle-to-vesicle transition technique, a very mild protocol based on size exclusion chromatography often used to drive the incorporation of proteins contemporarily to liposome formation. An optimized protocol was used to successfully reconstitute the protein in a fully active state in polymersomes formed by the tri-block copolymers PMOXA22-PDMS61-PMOXA22. The RC is very sensitive to its solubilizing environment and was used to probe the positioning of the protein in the vesicles. According to charge-recombination experiments and to the enzymatic activity assay, the RC is found to accommodate in the PMOXA22 region of the polymersome, facing the water bulk solution, rather than in the PDMS61 transmembrane-like region. Furthermore, polymersomes were found to preserve protein integrity efficiently as the biomimetic lipid bilayers but show a much longer temporal stability than lipid based vesicles.

Charge recombination kinetics of bacterial photosynthetic protein Reaction Center displays an exquisite sensitivity to the actual occupancy of ubiquinone-10 in its QB-binding site. Here, we have exploited such phenomenon for assessing the growth and the aggregation/fusion of phosphocholine vesicles embedding RC in their membrane, when treated with sodium oleate.

In this theoretical work, we analyse the kinetics of charge recombination reaction after a light excitation of the Reaction Centres extracted from the photosynthetic bacterium Rhodobacter sphaeroides and reconstituted in small unilamellar phospholipid vesicles. Due to the compartmentalized nature of liposomes, vesicles may exhibit a random distribution of both ubiquinone molecules and the Reaction Centre protein complexes that can produce significant differences on the local concentrations from the average expected values. Moreover, since the amount of reacting species is very low in compartmentalized lipid systems the stochastic approach is more suitable to unveil deviations of the average time behaviour of vesicles from the deterministic time evolution.

The functionalization of screen-printed electrodes (SPEs) with a thin film of reaction centre (RC) proteins from the phototrophic bacterium Rhodobacter (R.) sphaeroides, by means of laser induced forward transfer (LIFT) technique, allowed the fabrication of robust and sensitive bio-hybrid devices for terbutryn detection and analysis. The optimal wiring between RCs and the gold electrode surface, achieved by LIFT, led to the generation of cathodic photocurrents sustained by a direct electron transfer (DET) mechanism, which were attenuated by addition of the herbicide inhibitor. (C) 2016 The Authors. Published by Elsevier Ltd.

We present some preliminary results relevant to the ability of the purple non-sulphur bacterium Rhodobacter sphaeroides strain R26.1 to sequester heavy metals from contaminated growth media. The microorganism was chosen because of its significant tolerance to relatively high concentrations of the investigated ions Ni2+, Co2+, CrO4(2-), and MoO4(2-). In this paper the optimized conditions for the bacterial growth and the sample preparation used to infer the ability of the microorganism to cope with metal pollutants are presented. Elemental analysis has been performed by inductively coupled plasma atomic emission spectrometry previous mineralization of samples by a microwave system.

The thermodynamics and kinetics of light-induced electron transfer in bacterial photosynthetic RCs are sensitive to physiologically important lipids (phosphatidylcholine, cardiolipin and phosphatidylglycerol) in the environment. The analysis of the temperature-dependence of the rate of the P(+)Q(A)(-)Q(B)-> P(+)Q(A)Q(B)(-) interquinone electron transfer revealed high enthalpy change of activation in zwitterionic or neutral micelles and vesicles and low enthalpy change of activation in vesicles constituted of negatively charged phospholipids. The entropy change of activation was compensated by the changes of enthalpy, thus the free energy change of activation (approximate to 500 meV) did not show large variation in vesicles of different lipids. (c) 2006 Elsevier B.V. All rights reserved.

The potential of purple non-sulphur bacteria for bioremediation was assessed by investigating the ability of Rhodobacter sphaeroides strain R26.1 to grow photosynthetically in heavy metal contaminated environments. Bacterial cultures were carried out in artificially polluted media, enriched with the transition metal ions Hg2+, Cu2+, Fe2+, Ni2+, Co2+, MoO42-, and CrO42- in millimolar concentration range. For each investigated ion the effect on growth parameters was evaluated. The analysis of concentration-effect curves revealed a differentiated response, indicating that diverse mechanisms of tolerance and/or resistance are involved. Adaptation or selection procedures were not applied, leading to assess intrinsic abilities of coping with these contaminants. The microorganism proved to be highly tolerant to heavy metal exposure, especially towards Co2+, Fe2+ and MoO42-. In addition Ni2+ and Co2+ were found to decrease the cellular content of light harvesting complexes. A characteristic behavior was observed with mercuric ions, which produced a significant increase of the lag-phase. (c) 2005 Elsevier Ltd. All rights reserved.

Isolated and purified reaction centers (RC) from Rhodobacter sphaeroides R-26.1 were solubilised in detergent with excess quinone and external electron donors and illuminated in the presence of pyranine. The pH change accompanying the reaction center photocycle was monitored by recording the variation of the pyranine fluorescence intensity. Using Q(B)-depleted reaction centers or blocking the photocycle with terbutryne strongly reduced the pH change. The usefulness and limits of this technique in monitoring the pH changes during the RC photocycle are also discussed.