Evolution of bacteria in relation to BchF and reaction center proteins.

<p><b>A</b> shows a phylogenetic tree of BchF overlaid over a phylogenomic tree of prokaryotes. B and C show those of Type I and Type II reaction center proteins over the phylogenomic tree, respectively. The phylogenomic tree that depicts the evolutionary relationship of different phyla of bacteria was obtained from Segata et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0151250#pone.0151250.ref017" target="_blank">17</a>], which was published open access. It was constructed using hundreds of proteins and thousands of genomes and the phylogenetic method, sequence alignments, and the phylogenetic tree are freely available from the author’s website (<a href="http://huttenhower.sph.harvard.edu/phylophlan" target="_blank">http://huttenhower.sph.harvard.edu/phylophlan</a>). It is overall very similar to other phylogenomic trees, and the relationship of phyla containing phototrophic strains is virtually identical to those presented before, see for example Jun et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0151250#pone.0151250.ref020" target="_blank">20</a>], who implemented an alignment free approach. The phyla of bacteria highlighted in color represent those with photochemical reaction centers, with the exception of Actinobacteria that only recently was suggested to have been ancestrally phototrophic [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0151250#pone.0151250.ref002" target="_blank">2</a>]. The colored transparent lines that are overlaid on top of the phylogenomic tree represent the evolution of the selected proteins. The phylogenetic relations of Type I (<b>B</b>) and Type II (<b>C</b>) reaction centers are well-established and were recently reviewed in detail [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0151250#pone.0151250.ref001" target="_blank">1</a>].</p

Covalent Immobilization of Oriented Photosystem II on a Nanostructured Electrode for Solar Water Oxidation

Photosystem II (PSII) offers a biological and sustainable route of photochemical water oxidation to O₂ and can provide protons and electrons for the generation of solar fuels, such as H₂. We present a rational strategy to electrostatically improve the orientation of PSII from a thermophilic cyanobacterium, Thermosynechococcus elongatus, on a nanostructured indium tin oxide (ITO) electrode and to covalently immobilize PSII on the electrode. The ITO electrode was modified with a self-assembled monolayer (SAM) of phosphonic acid ITO linkers with a dangling carboxylate moiety. The negatively charged carboxylate attracts the positive dipole on the electron acceptor side of PSII via Coulomb interactions. Covalent attachment of PSII in its electrostatically improved orientation to the SAM-modified ITO electrode was accomplished via an amide bond to further enhance red-light-driven, direct electron transfer and stability of the PSII hybrid photoelectrode

Photoelectrochemical Water Oxidation with Photosystem II Integrated in a Mesoporous Indium–Tin Oxide Electrode

We report on a hybrid photoanode for water oxidation consisting of a cyanobacterial photosystem II (PSII) from <i>Thermosynechococcus elongatus</i> on a mesoporous indium–tin oxide (<i>meso</i>ITO) electrode. The three-dimensional metal oxide environment allows for high protein coverage (26 times an ideal monolayer coverage) and direct (mediator-free) electron transfer from PSII to <i>meso</i>ITO. The oxidation of water occurs with 1.6 ± 0.3 μA cm^–2 and a corresponding turnover frequency of approximately 0.18 ± 0.04 (mol O₂) (mol PSII)⁻¹ s^–1 during red light irradiation. Mechanistic studies are consistent with interfacial electron transfer occurring not only from the terminal quinone Q_B, but also from the quinone Q_A through an unnatural electron transfer pathway to the ITO surface