Cryo-EM Structure of the Photosynthetic LH1-RC Complex from Rhodospirillum rubrum

We present a cryo-EM structure of the light-harvesting-reaction center (LH1-RC) core complex from purple phototrophic bacterium Rhodospirillum (Rsp.) rubrum at 2.76 Å resolution. The LH1 complex forms a closed, slightly elliptical ring structure with 16 αβ-polypeptides surrounding the RC. Our biochemical analysis detected rhodoquinone (RQ) molecules in the purified LH1-RC, and the cryo-EM density map specifically positions RQ at the QA site in the RC. The geranylgeraniol sidechains of bacteriochlorophyll (BChl) aG coordinated by LH1 β-polypeptides exhibit a highly homologous tail-up conformation that allows for interactions with the bacteriochlorin rings of nearby LH1 α-associated BChls aG. The structure also revealed key protein–protein interactions in both N- and C-terminal regions of the LH1 αβ-polypeptides, mainly within a face-to-face structural subunit. Our findings enable to evaluate past experimental and computational results obtained with this widely used organism and provide crucial information for more detailed exploration of light-energy conversion, quinone transport, and structure—function relationships in pigment-protein complexes.

Two-Component Model of Microalgae Growth in the Turbidostat

The paper focuses on the study of light influence mechanisms on microalgae culture growth in the turbidostat. The method of turbidostat culture provides the same light conditions for all cells, stabilization of their biochemical composition, as well as the constancy of all physicochemical factors of the environment. The main approaches and principles of modeling the microalgae culture growth are presented. Modern models are shown to be based on classical concepts of considering cell biomass as the sum of two or more compounds. The use of two-component models for microalgae is due to both photochemical and enzymatic processes of biosynthesis of cell structures from mineral substances due to the energy of high-potential forms of macroergs. The proposed mathematical model is represented by a system of two differential equations describing the synthesis of reserve biomass compounds at the expense of light and biosynthesis of structural components from reserve ones. The model takes into account that a part of the reserve compounds is spent on replenishing the pool of macroergs, and a part of the structural component can be converted into a reserve one. The rates of synthesis of structural and reserve forms of biomass are given by linear splines and expressed in terms of the reduced fluxes of the energy or plastic substrate. The model was verified on the experimental data of the chlorophyllostat culture Tetraselmis viridis. It is shown that the light curve of T. viridis is characterized by a double change in the limiting factor and can be divided into a region of metabolic, light limiting and a region of saturation. A decrease in the specific growth rate is related to a decrease in the efficiency of light energy conversion.

A Theoretical Perspective of the Photochemical Potential in the Spectral Performance of Photovoltaic Cells

We present a novel theoretical approach to the problem of light energy conversion in thermostated semiconductor junctions. Using the classical model of a two-level atom, we deduced formulas for the spectral response and the quantum efficiency in terms of the input photons’ non-zero chemical potential. We also calculated the spectral entropy production and the global efficiency parameter in the thermodynamic limit. The heat transferred to the thermostat results in a dissipative loss that appreciably controls the spectral quantities’ behavior and, therefore, the cell’s performance. The application of the obtained formulas to data extracted from photovoltaic cells enabled us to accurately interpolate experimental data for the spectral response and the quantum efficiency of cells based on Si-, GaAs, and CdTe, among others.

The natural design for harvesting far-red light: the antenna increases both absorption and quantum efficiency of Photosystem II

Cyanobacteria carry out photosynthetic light-energy conversion using phycobiliproteins for light harvesting and the chlorophyll-rich photosystems for photochemistry. While most cyanobacteria only absorb visible photons, some of them can acclimate to harvest far-red light (FRL, 700-800 nm) by integrating chlorophyll f and d in their photosystems and producing red-shifted allophycocyanin. Chlorophyll f insertion enables the photosystems to use FRL but slows down charge separation, reducing photosynthetic efficiency. Here we demonstrate with time-resolved fluorescence spectroscopy that charge separation in chlorophyll-f-containing Photosystem II becomes faster in the presence of red-shifted allophycocyanin antennas. This is different from all known photosynthetic systems, where additional light-harvesting complexes slow down charge separation. Based on the available structural information, we propose a model for the connectivity between the phycobiliproteins and Photosystem II that qualitatively accounts for our spectroscopic data. This unique design is probably important for these cyanobacteria to efficiently switch between visible and far-red light.

Effect of spectral composition of light on the production characteristics of Arthrospira (Spirulina) platensis

The study of the growth of the batch culture of Spirulina platensis with different spectral composition of LED and luminescent radiation in plane-parallel photobioreactors was carried out. In the experiments, we used LED lamps LCD Feron LB-213 10 W, as well as fluorescent lamps TDM Electric 18 W. It has been shown that the maximum productivity of A. platensis does not depend on the radiation spectrum and is 0,25 g·l-1·day-1 at an energy of 45 W·m-2. In the linear phase of growth, the efficiency of light energy conversion (efficiency of photobiosynthesis) was calculated, taking into account that the culture absorbs 90% of the incident light: the maximum value was obtained for LED and fluorescent lighting (23 W·m-2 and 17 W·m-2 respectively), which turned out to be the same and amounted to about 3,78 %. The minimum efficiency of 2,69% is obtained with fluorescent lighting at 34 W·m-2.

PRiME 2020 #F01-1561

Progress and a price reduction of the photovoltaic power generation technology are important research themes. Then, it is splendid if the poisonous plant and the activated carbon can be used. A poisonous plant and the used activated carbons are collected in large quantities and cheaply from the imminent place. With the I-V characteristics of dye-sensitized solar cell where four kinds of edible food colors for as an adsorption pigment each were used, the open circuit voltage, short circuit photocurrent density, and light energy conversion efficiency were showed the highest values for a gardenia blue pigment. With the CV curves of the glassy carbon electrode before and after the modification of the ingredient derived from charcoal burner, a cathodic peak potential around -755 mV was positively shifted to the approximately 125 mV after modification.

Anoxygenic phototrophic Chloroflexota member uses a Type I reaction center

Phototrophic bacteria within the Chloroflexota phylum are puzzling in their evolutionary origin. Previously known phototrophic Chloroflexota members use a Type II photosynthetic reaction center for light energy conversion but contain other photosynthesis machinery associated with Type I reaction center-utilizing phototrophs. We sampled an iron-rich boreal lake at the IISD-Experimental Lakes Area and enriched ‘Candidatus Chlorohelix allophototropha’, a phototrophic Chloroflexota member that uses a Type I reaction center. Phylogenomic evidence suggests that ancestors of ‘Ca. Chx. allophototropha’ served as a bridge for historic phototrophy gene exchange within the phylum. The Chloroflexota now represents the only bacterial phylum outside the Cyanobacteria where both major classes of photosynthetic reaction center occur and can serve as a model system to explore fundamental questions about the evolution of photosynthesis.