Photoelectrochemical cells based on photosynthetic systems: a review

Photosynthesis is a process which converts light energy into energy contained in the chemical bonds of organic compounds by photosynthetic pigments such as chlorophyll (Chl a, b, c, d, f) or bacteriochlorophyll. It occurs in phototrophic organisms, which include higher plants and many types of photosynthetic bacteria, including cyanobacteria. In the case of the oxygenic photosynthesis, water is a donor of both electrons and protons, and solar radiation serves as inexhaustible source of energy. Efficiency of energy conversion in the primary processes of photosynthesis is close to 100%. Therefore, for many years photosynthesis has attracted the attention of researchers and designers looking for alternative energy systems as one of the most efficient and eco-friendly pathways of energy conversion. The latest advances in the design of optimal solar cells include the creation of converters based on thylakoid membranes, photosystems, and whole cells of cyanobacteria immobilized on nanostructured electrode (gold nanoparticles, carbon nanotubes, nanoparticles of ZnO and TiO2). The mode of solar energy conversion in photosynthesis has a great potential as a source of renewable energy while it is sustainable and environmentally safety as well. Application of pigments such as Chl f and Chl d (unlike Chl a and Chl b), by absorbing the far red and near infrared region of the spectrum (in the range 700-750 nm), will allow to increase the efficiency of such light transforming systems. This review article presents the last achievements in the field of energy photoconverters based on photosynthetic systems

Hydrogen peroxide participates in perception and transduction of cold stress signal in synechocystis

The double mutant ΔkatG/tpx of cyanobacterium Synechocystis sp. strain PCC 6803, defective in the anti-oxidative enzymes catalase (KatG) and thioredoxin peroxidase (Tpx), is unable to grow in the presence of exogenous H2O2. The ΔkatG/tpx mutant is shown to be extremely sensitive to very low concentrations of H2O2, especially when intensified with cold stress. Analysis of gene expression in both wild-type and ΔkatG/tpx mutant cells treated by combined cold/oxidative stress revealed that H2O2 participates in regulation of expression of cold-responsive genes, affecting either signal perception or transduction. The central role of a transmembrane stress-sensing histidine kinase Hik33 in the cold/oxidative signal transduction pathway is discussed

Cultivation of <i>Chlorella sorokiniana</i> IPPAS C-1 in Flat-Panel Photobioreactors: From a Laboratory to a Pilot Scale

Flat-panel photobioreactors are effective systems for microalgae cultivation. This paper presents the growth characteristics of the microalgae Chlorella sorokiniana IPPAS C-1 as a result of three-stage scale-up cultivation in a specially designed cultivation system. First, C. sorokiniana was grown aseptically in 250 mL glass vessels; then, it was diluted and inoculated into a 5-liter flat-panel horizontal photobioreactor; and, at the last stage, the culture was diluted and inoculated into a 70-liter flat-panel vertical photobioreactor. In the presented cycle, the cultured biomass increased by 326 times in 13 days (from 0.6 to 195.6 g dw), with a final biomass concentration of 2.8 g dw L−1. The modes of semi-continuous cultivation were considered. The biomass harvest and dilution of the suspension were carried out either every day or every 3–4 days. For C. sorokiniana IPPAS C-1, a conversion coefficient of optical density values to dry biomass (g L−1) was refined through a factor of 0.33. The key parameters of the photobioreactors tested in this work are discussed