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The chromophorylated PBLcm domain of the ApcE linker protein in the cyanobacterial phycobilisome (PBS) serves as a bottleneck for Förster resonance energy transfer (FRET) from the PBS to the antennal chlorophyll of photosystem II (PS II) and as a redirection point for energy distribution to the orange protein ketocarotenoid (OCP), which is excitonically coupled to the PBLcm chromophore in the process of non-photochemical quenching (NPQ) under high light conditions. The involvement of PBLcm in the quenching process was first directly demonstrated by measuring steady-state fluorescence spectra of cyanobacterial cells at different stages of NPQ development. The time required to transfer energy from the PBLcm to the OCP is several times shorter than the time it takes to transfer energy from the PBLcm to the PS II, ensuring quenching efficiency. The data obtained provide an explanation for the different rates of PBS quenching in vivo and in vitro according to the half ratio of OCP/PBS in the cyanobacterial cell, which is tens of times lower than that realised for an effective NPQ process in solution.

Cyanidiales were named enigmatic microalgae due to their unique polyextreme properties, considered for a very long time unattainable for eukaryotes. Cyanidiales mainly inhabit hot sulfuric springs with high acidity (pH 0-4), temperatures up to 56°C, and ability to survive in the presence of dissolved heavy metals. Owing to the minimal for eukaryotes genome size, Cyanidiales have become one of the most important research objects in plant cell physiology, biochemistry, molecular biology, phylogenomics, and evolutionary biology. They play an important role in studying many aspects of oxygenic photosynthesis and chloroplasts origin. The ability to survive in stressful habitats and the corresponding metabolic pathways were acquired by Cyanidiales from archaea and bacteria via horizontal gene transfer (HGT). Thus, the possibility of gene transfer from prokaryotes to eukaryotes was discovered, which was a new step in understanding of the origin of eukaryotic cell.

The theory of endosymbiotic origin of chloroplasts has become basal in present-day biology. In this regard, the emergence of eukaryotic photosynthesis has been established as a result of phagocytal capture of cyanobacteria by some ancestral eukaryotic cell. The phenomenon of endosymbiosis is an indispensable element of cell evolution theory. The process of endosymbiogenesis belongs to the crucial factors of biological progress that gave rise to astonishing diversity and complexity of the eukaryotic organisms. The modern theory of evolution is built on the joint base of the phenomena of endosymbiosis, parallel gene transfer, the theory of natural selection, and the data of phylogenomics. Ultimately, eukaryogenesis has integrated different supramolecular complexes in the cells, created the diversity of organelles, and has led to biosphere oxygenation and modern diversity of living forms.

Imbalanced light absorption by photosystem I (PSI) and photosystem II (PSII) in oxygenic phototrophs leads to changes in interaction of photosystems altering the linear electron flow. In plants and green algae, this imbalance is mitigated by a partial migration of the chlorophyll a/b containing light-harvesting antenna between the two photosystem core complexes. This migration is registered as fluorescence changes of the pigment apparatus and is termed the reverse transitions between States 1 and 2. By contrast, the molecular mechanism of State 1/2 transitions in phycobilisome (PBS)-containing photosynthetics, cyanobacteria and red algae, is still insufficiently understood. The suggested hypotheses – PBS movement along the surface of thylakoid membrane between PSI and PSII complexes, reversible PBS detachment from the dimeric PSII complex, and spillover – have some limitations as they do not fully explain the accumulated data. Here, we have recorded changes in the stationary fluorescence emission spectra of red algae and cyanobacteria in States 1/2 at room temperature, which allowed us to offer an explanation of the existing contradictions. The change of room temperature fluorescence of chlorophyll belonged to PSII was revealed, while the fluorescence of PBS associated with the PSII complexes remained during States 1/2 transitions at the stable level. Only the reversible dissociation of PBS from the monomeric PSI was revealed earlier which implied different degree of surface contact of PBS with the two photosystems. The detachment of PBS from the PSI corresponds to ferredoxin oxidation as electron carrier and the increase of cyclic electron transport in the pigment apparatus in State I.

Deceased. Cryptophyte algae belong to a special group of oxygenic photosynthetic organisms containing pigment combination unique for plastids - phycobiliproteins and chlorophyll a/c-containing antenna. Despite the progress in investigation of morphological and ecological features, as well as genome-based systematics of cryptophytes, their photosynthetic apparatus remains poorly understood. The ratio of the photosystems (PS)s I and II is unknown and information on participation of the two antennal complexes in functions of the two photosystems is inconsistent. In the present work we demonstrated for the first time that the cryptophyte alga Rhodomonas salina had the PSI to PSII ratio in thylakoid membranes equal to 1 : 4, whereas this ratio in cyanobacteria and higher plants was known to be 3 : 1 and 1 : 1, respectively. Furthermore, it was established that contrary to the case of cyanobacteria the phycobiliprotein antenna represented by phycoerythrin-545 (PE-545) in R. salina was associated only with the PSII, which indicated specific spatial organization of these protein pigments within the thylakoids that did not facilitate interaction with the PSI.

Phycobilisome (PBS) is a giant photosynthetic antenna associated with the thylakoid membranes of cyanobacteria and red algae. PBS consists of two domains: central core and peripheral rods assembled of disc-shaped phycobiliprotein aggregates and linker polypeptides. The study of the PBS architecture is hindered due to the lack of the data on the structure of the large ApcE-linker also called LCM. ApcE participates in the PBS core stabilization, PBS anchoring to the photosynthetic membrane, transfer of the light energy to chlorophyll, and, very probably, the interaction with the orange carotenoid protein (OCP) during the non-photochemical PBS quenching. We have constructed the cyanobacterium Synechocystis sp. PCC 6803 mutant lacking 235 N-terminal amino acids of the chromophorylated PBLCM domain of ApcE. The altered fluorescence characteristics of the mutant PBSs indicate that the energy transfer to the terminal emitters within the mutant PBS is largely disturbed. The PBSs of the mutant become unable to attach to the thylakoid membrane, which correlates with the identified absence of the energy transfer from the PBSs to the photosystem II. At the same time, the energy transfer from the PBS to the photosystem I was registered in the mutant cells and seems to occur due to the small cylindrical CpcG2-PBSs formation in addition to the conventional PBSs. In contrast to the wild type Synechocystis, the OCP-mediated non-photochemical PBS quenching was not registered in the mutant cells. Thus, the PBLCM domain takes part in formation of the OCP binding site in the PBS.

The functions of phycobiliproteins and phycobilisomes as photosynthetic antenna pigments in cells of cyanobacteria and a range of algae were considered. Achievements in the area of biological and natural sciences connected with study of phycobiliproteins are described. Sources and different possibilities of the practical application of these pigments in fluorescent spectroscopy, pharmacy, and biotechnology are analyzed.

The phycobilisome (PBS) is the cyanobacterial antenna complex which transfers absorbed light energy to the photosystem II (PSII), while the excess energy is nonphotochemically quenched by interaction of the PBS with the orange carotenoid protein (OCP). Here, the molecular model of the PBS-PSII-OCP supercomplex was utilized to assess the resonance energy transfer from PBS to PSII and, using the excitonic theory, the transfer from PBS to OCP. Our estimates show that the effective energy migration from PBS to PSII is realized due to the existence of several transfer pathways from phycobilin chromophores of the PBS to the neighboring antennal chlorophyll molecules of the PSII. At the same time, the single binding site of photoactivated OCP and the PBS is sufficient to realize the quenching.

In the large linker ArcE polypeptide of the phycobilisome (PBS) from the cyanobacterium Synechocystis sp. PCC 6803, the chromophore-containing 26-kDa domain was deleted with consequent disturbance of the main PBS functions. Phycobilisomes in mutant cells staying in contact with photosystem I cannot transfer energy to the photosystem II. Under the bright light conditions, the interaction of PBSs with the photoprotective orange carotenoid protein in the mutant was lost and the implementation of transition states 1 and 2 of the pigment apparatus was significantly reduced.

The phycobilisome (PBS) is a major light-harvesting complex in cyanobacteria and red algae. To obtain the detailed structure of the hemidiscoidal PBS core composed of allophycocyanin (APC) and minor polypeptide components, we analyzed all nine available 3D structures of APCs from different photosynthetic species and found several variants of crystal packing that potentially correspond to PBS core organization. Combination of face-to-face APC trimer crystal packing with back-to-back APC hexamer packing suggests two variants of the tricylindrical PBS core. To choose one of these structures, a computational model of the PBS core complex and photosystem II (PSII) dimer with minimized distance between the terminal PBS emitters and neighboring antenna chlorophylls was built. In the selected model, the distance between two types of pigments does not exceed 37 Å corresponding to the Förster mechanism of energy transfer. We also propose a model of PBS and photosystem I (PSI) monomer interaction showing a possibility of supercomplex formation and direct energy transfer from the PBS to PSI.

On p. 679 in the list of authors and affiliations instead of: 1 Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, 127726 Moscow, Russia 2 Bach Institute of Biochemistry, Research Center of Biotechnology, Russian Academy of Sciences, 119071 Moscow, Russia 3 Institute of Fundamental Problems of Biology of the Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia 4 Kovalevski Institute of Biology of the Southern Seas, Russian Academy of Sciences, 299011 Sevastopol, Russia 5 Lomonosov Moscow State University, Faculty of Biology, 119991 Moscow, Russia Should read: 1 Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, 127726 Moscow, Russia 2 Kovalevski Institute of Biology of the Southern Seas, Russian Academy of Sciences, 299011 Sevastopol, Russia 3 Institute of Fundamental Problems of Biology of the Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia 4 Bach Institute of Biochemistry, Research Center of Biotechnology, Russian Academy of Sciences, 119071 Moscow, Russia 5 Lomonosov Moscow State University, Faculty of Biology, 119991 Moscow, Russia

The phycobilisome (PBS) is a giant highly-structured pigment-protein antenna of cyanobacteria and red algae. PBS is composed of the phycobiliproteins and several linker polypeptides. The large core-membrane linker protein (LCM or ApcE) influences many features and functions of PBS and consists of several domains including the chromophorylated PB-domain. Being homologous to the phycobiliprotein α-subunits this domain includes a so-called PB-loop insertion whose functions are still unknown. We have created the photoautotrophic mutant strain of the cyanobacterium Synechocystis sp. PCC 6803 with lacking PB-loop. Using various spectral techniques we have demonstrated that this mutation does not destroy the PBS integrity and the internal PBS excitation energy transfer pathways. At the same time, the deletion of the PB-loop leads to the decrease of connectivity between the PBS and thylakoid membrane and to the compensatory increase of the relative photosystem II content. Mutation provokes the violation of the thylakoid membranes arrangement, the inability to perform state transitions, and diminishing of the OCP-dependent non-photochemical PBS quenching. In essence, even such a minute mutation of the PBS polypeptide component, like the PB-loop deletion, becomes important for the concerted function of the photosynthetic apparatus.

Energy transfer pathways between phycobiliproteins chromophores in the phycobilisome (PBS) core of the cyanobacterium Synechocystis sp. PCC 6803 were investigated. The computer 3D model of the PBS core with determination of chromophore to chromophore distance was created. Our kinetic equations based on this model allowed us to describe the relative intensities of the fluorescence emission of the short(peaked at 665 nm) and long-wavelength (peaked at 680 nm) chromophores in the PBS core at low and room temperatures. The difference of emissions of the PBS core at 77 and 293 K are due to the back energy transfer, which is observed at room temperature and is negligible at 77 K.

We report on theoretical efficiency of non-photochemical fluorescense quenching of phycobilisomes by the orange carotenoid protein. The created 3D computer model of the three-cylindrical phycobilisomes core allowed us to determine the distances between centers of mass of all phycobilin chromophores of the core and calculate the time and an average number of energy migration steps for the resulting non-radiative excitation transfer from the phycobilisomes to photosystem II. The obtained kinetic scheme equations for a way of energy transfer confirm the incomplete interception of energy flow in the phycobilisomes core by the orange carotenoid protein. Theoretical estimation of the rate of phycobilisomes quenching is in good agreement with experimental data.

Using molecular modeling and known spatial structure of proteins, we have derived a universal 3D model of the orange carotenoid protein (OCP) and phycobilisome (PBS) interaction in the process of non-photochemical PBS quenching. The characteristic tip of the phycobilin domain of the core-membrane linker polypeptide (LCM) forms the attachment site on the PBS core surface for interaction with the central inter-domain cavity of the OCP molecule. This spatial arrangement has to be the most advantageous one because the LCM, as the major terminal PBS-fluorescence emitter, accumulates energy from the most other phycobiliproteins within the PBS before quenching by OCP. In agreement with the constructed model, in cyanobacteria, the small fluorescence recovery protein is wedged in the OCP's central cavity, weakening the PBS and OCP interaction. The presence of another one protein, the red carotenoid protein, in some cyanobacterial species, which also can interact with the PBS, also corresponds to this model.

Using computational modeling and known 3D structure of proteins, we arrived at a rational spatial model of the orange carotenoid protein (OCP) and phycobilisome (PBS) interaction in the non-photochemical fluorescence quenching. The site of interaction is formed by the central cavity of the OCP monomer in the capacity of a keyhole to the characteristic external tip of the phycobilin-containing domain (PB) and folded loop of the core-membrane linker LCM within the PBS core. The same central protein cavity was shown to be also the site of the OCP and fluorescence recovery protein (FRP) interaction. The revealed geometry of the OCP to the PBLCM attachment is believed to be the most advantageous one as the LCM, being the major terminal PBS fluorescence emitter, gathers, before quenching by OCP, the energy from most other phycobilin chromophores of the PBS. The distance between centers of mass of the OCP carotenoid 3'-hydroxyechinenone (hECN) and the adjacent phycobilin chromophore of the PBLCM was determined to be 24.7 Å. Under the dipole-dipole approximation, from the point of view of the determined mutual orientation and the values of the transition dipole moments and spectral characteristics of interacting chromophores, the time of the direct energy transfer from the phycobilin of PBLCM to the S1 excited state of hECN was semiempirically calculated to be 36 ps, which corresponds to the known experimental data and implies the OCP is a very efficient energy quencher. The complete scheme of OCP and PBS interaction that includes participation of the FRP is proposed.

In cyanobacteria, phycobilisomes (PBS) act as antennae of the photosynthetic pigment apparatus. They contain brightly colored phycobiliproteins (PBP) and form giant supramolecular complexes (up to 3000-7000 kDa) containing 200 to 500 phycobilin chromophores covalently bound to the proteins. Over ten various PBP are known, which fall into three groups: phycoerythrins, phycocyanins, and allophycocyanins. Hollow disks of PBP trimers and hexamers are arranged into cylinders by colorless linker proteins; the cylinders are then assembled into PBS. Typical semidiscoid PBS consist of a central nucleus formed by three allophycocyanin cylinders and of six lateral cylinders consisting of other PBP and attached as fans to the nucleus. The PBS number, size, and pigment composition in cyanobacteria depend on illumination and other ambient factors. While PBS have certain advantages compared to other antennae, these pigment-protein complexes require more energy than the chlorophyll a/b- and chlorophyll a/c-proteins of oxygenic photosynthetic organisms.

Endosymbiotic origin of chloroplasts from unicellular cyanobacteria is presently beyond doubt. Oxygenic photosynthesis is based on coordinated action of two photosystems (PS), PS I and PS II, cooperating with several variants of the pigment antenna. In cyanobacteria, red algae, and glaucophytes, phycobilisomes (PBS) act as antennae, while in terrestrial plants, as well as most macro- and microalgae antennae are formed by chlorophyll a/b- and chlorophyll a/c-containing proteins. Advantages and disadvantages of the PBS antenna compared to other light-gathering complexes form the basis for adaptive variations of the antenna in the course of development of eukaryotic photosynthesis. During the evolution of the "green" and "chromophyte" lineages of the chloroplasts, PBS, in spite of their optimal features of light absorption,were replaced by chlorophyll a/b- and chlorophyll a/c-containing light-gathering complexes. Development of the cell wall associated with limited motility and with tissue formation in photosynthetic eukaryotes were the factors responsible for the antenna shift. The subsequent redistribution of cell resources in favor of cellulose biosynthesis required increased for CO2 consumption, higher PS II levels, and greater number and density of the thylakoids in the chloroplasts, got incompatible with the energy-consuming and overly large PBS antenna.

The fluorescence emission of the phycobilisome (PBS) core-membrane linker protein (L(CM)) can be directly quenched by photoactivated orange carotenoid protein (OCP) at room temperature both in vitro and in vivo, which suggests the crucial role of the OCP-L(CM) interaction in non-photochemical quenching (NPQ) of cyanobacteria. This implication was further supported (i) by low-temperature (77K) fluorescence emission and excitation measurements which showed a specific quenching of the corresponding long-wavelength fluorescence bands which belong to the PBS terminal emitters in the presence of photoactivated OCP, (ii) by systematic investigation of the fluorescence quenching and recovery in wild type and L(CM)-less cells of the model cyanobacterium Synechocystis sp. PCC 6803, and (iii) by the impact of dephosphorylation of isolated PBS on the quenching. The OCP binding site within the PBS and the most probable geometrical arrangement of the OCP-allophycocyanin (APC) complex was determined in silico using the crystal structures of OCP and APC. Geometrically modeled attachment of OCP to the PBS core is not at variance with the OCP-L(CM) interaction. It was concluded that besides being a very central element in the PBS to reaction center excitation energy transfer and PBS assembly, L(CM) also has an essential role in the photoprotective light adaptation processes of cyanobacteria.

Phycobilisome (PBS) is a giant water-soluble photosynthetic antenna transferring the energy of absorbed light mainly to the photosystem II (PSII) in cyanobacteria. Under the low light conditions, PBSs and PSII dimers form coupled rows where each PBS is attached to the cytoplasmic surface of PSII dimer, and PBSs come into contact with their face surfaces (state 1). The model structure of the PBS core that we have developed earlier by comparison and combination of different fine allophycocyanin crystals, as reported in Zlenko et al. (Photosynth Res 130(1):347–356, 2016b), provides a natural way of the PBS core face-to-face stacking. According to our model, the structure of the protein–protein contact between the neighboring PBS cores in the rows is the same as the contact between the APC hexamers inside the PBS core. As a result, the rates of energy transfer between the cores can occur, and the row of PBS cores acts as an integral PBS “supercore” providing energy transfer between the individual PBS cores. The PBS cores row pitch in our elaborated model (12.4 nm) is very close to the PSII dimers row pitch obtained by the electron microscopy (12.2 nm) that allowed to unite a model of the PBS cores row with a model of the PSII dimers row. Analyzing the resulting model, we have determined the most probable locations of ApcD and ApcE terminal emitter subunits inside the bottom PBS core cylinders and also revealed the chlorophyll molecules of PSII gathering energy from the PBS.

In cyanobacteria, the thermal dissipation of excess absorbed energy at the level of the phycobilisome (PBS)-antenna is triggered by absorption of strong blue-green light by the photoactive orange carotenoid protein (OCP). This process known as non-photochemical quenching, whose molecular mechanism remains in many respects unclear, is revealed in vivo as a decrease in phycobilisome fluorescence. In vitro reconstituted system on the interaction of the OCP and the PBS isolated from the cyanobacterium Synechocystis sp. PCC 6803 presents evidence that the OCP is not only a photosensor, but also an effecter that makes direct contacts with the PBS and causes dissipation of absorbed energy. To localize the site(s) of quenching, we have analyzed the role of chromophorylated polypeptides of the PBS using PBS-deficient mutants in conjunction with in vitro systems of assembled PBS and of isolated components of the PBS core. The results demonstrated that LCM, the core-membrane linker protein and terminal emitter of the PBS, could act as the docking site for OCP in vitro. The ApcD and ApcF terminal emitters of the PBS core are not directly subjected to quenching. The data suggests that there could be close contact between the phycocyanobilin chromophore of LCM and the 3′-hydroxyechinenone chromophore present in OCP and that LCM could be involved in OCP-induced quenching. According to the reduced average life-time of the PBS-fluorescence and linear dependence of fluorescence intensity of the PBS on OCP concentration, the quenching has mostly dynamic character. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.

The atypical unicellular cyanobacterium Gloeobacter violaceus PCC 7421, which diverged very early during the evolution of cyanobacteria, can be regarded as a key organism for understanding many structural, functional, regulatory and evolutionary aspects of oxygenic photosynthesis. In the present work, the performance of two basic photosynthetic adaptation/protection mechanisms, common to all other oxygenic photoautrophs, had been challenged in this ancient cyanobacterium which lacks thylakoid membranes: state transitions and non-photochemical fluorescence quenching. Both low temperature fluorescence spectra and room temperature fluorescence transients show that G. violaceus is capable of performing state transitions similar to evolutionarily more recent cyanobacteria, being in state 2 in darkness and in state 1 upon illumination by weak blue or far-red light. Compared with state 2, variable fluorescence yield in state 1 is strongly enhanced (almost 80%), while the functional absorption cross-section of PSII is only increased by 8%. In contrast to weak blue light, which enhances fluorescence yield via state 1 formation, strong blue light reversibly quenches Chl fluorescence in G. violaceus. This strongly suggests regulated heat dissipation which is triggered by the orange carotenoid protein whose presence was directly proven by immunoblotting and mass spectrometry in this primordial cyanobacterium. The results are discussed in the framework of cyanobacterial evolution.

It is shown that semiconductor nanocrystals (or quantum dots) can be used to increase the absorbability of a pigment protein. In the mixture of phycoerythrin with quantum dots, the fluorescence of the quantum dots is suppressed several times due to the transfer of absorbed energy to phycoerythrin. The Forster resonance energy transfer is discussed as a possible mechanism of energy transfer in quantum dot-phycoerythrin donor-acceptor pairs. Calculations based on experimental data show that the efficiency of energy migration from quantum dots to phycoerythrin is 88% and the corresponding rate constant is 1.17 × 109 s−1.

Compensating changes in the pigment apparatus of photosynthesis that resulted from a complete loss of phycobilisomes (PBS) were investigated in the cells of a PAL mutant of cyanobacterium Synechocystis sp. PCC 6803. The ratio PBS/chlorophyll calculated on the basis of the intensity of bands in the action spectra of photosynthetic activity of two photosystems in the wild strain was 1: 70 for PSII and 1: 300 for PSI. Taking into consideration the number of chlorophyll molecules per reaction center in each photosystem, these ratios could be interpreted as association of PBS with dimers of PSII and trimers of PSI as well as greater dependence of PSII as compared with PSI on light absorption by PBS. The ratio PSI/PSII determined by photochemical cross-section of the reactions of two photosystems was 3.5: 1.0 for wild strain of Synechocystis sp. PCC 6803 and 0.7: 1.0 for the PAL mutant. A fivefold increase in the relative content of PSII in pigment apparatus corresponds to a 5-fold increase in the intensity of bands at 685 and 695 nm as related to the band of PSI at 726 nm recorded in low-temperature fluorescence spectrum of the PAL mutant. Inhibition of PSII with diuron resulted in a pronounced stimulation of chlorophyll fluorescence in the PAL mutant as compared to the wild strain of Synechocystis sp. PCC 6803; these data suggested an activation of electron transfer between PSII and PSI in the mutant cells. Thus, the lack of PBS in the mutant strain of Synechocystis sp. PCC 6803 was compensated for by the higher relative content of PSII in the pigment apparatus of photosynthesis and by a rise in the rate of linear electron transport.

Bioenergetics of the aerobic bacteriochlorophyll a-containing (BCl a) bacterium (ABC bacterium) Roseinatronobacter thiooxidans is a combination of photosynthesis, oxygen respiration, and oxidation of sulfur compounds under alkaliphilic conditions. The photosynthetic activity of Rna. thiooxidans cells was established by the photoinhibition of cell respiration and reversible photobleaching discoloration of the BCl a of reaction centers (RC), connected by the chain of electron transfer with cytochrome c551 oxidation. The species under study, like many purple bacteria and some of the known ABC bacteria, possesses a light-harvesting pigment-protein (LHI) complex with the average number of 30 molecules of antenna BCl a per one photosynthetic RC. Under microaerobic growth conditions, the cells contained bc1 complex and two terminal oxidases: cbb3-cytochrome oxidase and the alternative cytochrome oxidase of the a3 type. Besides, Rna. thiooxidans was shown to have several different soluble low- and high-potential cytochromes c, probably associated with the ability of utilizing sulfur compounds as additional electron donors.

The features of the two types of short-term light-adaptations of photosynthetic apparatus, State 1/State 2 transitions, and non-photochemical fluorescence quenching of phycobilisomes (PBS) by orange carotene-protein (OCP) were compared in the cyanobacterium Synechocystis sp. PCC 6803 wild type, CK pigment mutant lacking phycocyanin, and PAL mutant totally devoid of phycobiliproteins. The permanent presence of PBS-specific peaks in the in situ action spectra of photosystem I (PSI) and photosystem II (PSII), as well as in the 77 K fluorescence excitation spectra for chlorophyll emission at 690 nm (PSII) and 725 nm (PSI) showed that PBS are constitutive antenna complexes of both photosystems. The mutant strains compensated the lack of phycobiliproteins by higher PSII content and by intensification of photosynthetic linear electron transfer. The detectable changes of energy migration from PBS to the PSI and PSII in the Synechocystis wild type and the CK mutant in State 1 and State 2 according to the fluorescence excitation spectra measurements were not registered. The constant level of fluorescence emission of PSI during State 1/State 2 transitions and simultaneous increase of chlorophyll fluorescence emission of PSII in State 1 in Synechocystis PAL mutant allowed to propose that spillover is an unlikely mechanism of state transitions. Blue-green light absorbed by OCP diminished the rout of energy from PBS to PSI while energy migration from PBS to PSII was less influenced. Therefore, the main role of OCP-induced quenching of PBS is the limitation of PSI activity and cyclic electron transport under relatively high light conditions.

A novel strain, alga-05, of alkaliphilic purple nonsulfur bacteria was isolated from sediments of a small saline (60 g/l) soda lake near Lake Algin (Barguzin Valley, Buryat Republic, Russia). These bacteria contain bacteriochlorophyll a and carotenoids of the alternative spirilloxanthin group with predominating demethylspheroidenone. They are facultative anaerobes; their photosynthetic structures are of the vesicular type and arranged along the cell periphery. Growth of this strain is possible in a salinity range of 5-80 g/l NaCl, with an optimum at 20 g/l NaCl. Best growth occurred at 20-35 degrees C. Analysis of the 16S rRNA gene sequences demonstrated that the studied isolate is closely related to the alkaliphilic purple nonsulfur bacterium Rhodobaca bogoriensis (99% similarity) isolated from soda lakes of the African Rift Zone. According to the results of DNA-DNA hybridization, strain alga-05 has a 52% similarity with the type species of the genus Rhodobaca. On the basis of the obtained genotypic data and some phenotypic properties (dwelling in a hypersaline soda lake of Siberia, moderate halophily, ability to grow at relatively low temperatures, etc.), the isolated strain of purple bacteria was described as a new species of the genus Rhodobaca, Rca. barguzinensis sp. nov.

Action spectra for photosystem II (PSII)-driven oxygen evolution and of photosystem I (PSI)-mediated H(2) photoproduction and photoinhibition of respiration were used to determine the participation of chlorophyll (Chl) a/b-binding Pcb proteins in the functions of pigment apparatus of Prochlorothrix hollandica. Comparison of the in situ action spectra with absorption spectra of PSII and PSI complexes isolated from the cyanobacterium Synechocystis 6803 revealed a shoulder at 650 nm that indicated presence of Chl b in the both photosystems of P. hollandica. Fitting of two action spectra to absorption spectrum of the cells showed a chlorophyll ratio of 4:1 in favor of PSI. Effective antenna sizes estimated from photochemical cross-sections of the relevant photoreactions were found to be 192+/-28 and 139+/-15 chlorophyll molecules for the competent PSI and PSII reaction centers, respectively. The value for PSI is in a quite good agreement with previous electron microscopy data for isolated Pcb-PSI supercomplexes from P. hollandica that show a trimeric PSI core surrounded by a ring of 18 Pcb subunits. The antenna size of PSII implies that the PSII core dimers are associated with approximately 14 Pcb light-harvesting proteins, and form the largest known Pcb-PSII supercomplexes.

The thermoacidophilic red alga Galdieria maxima is capable of heterotrophic growth. The content of carbohydrates in G. maxima grown heterotrophically increases by a factor of 4, reaching as much as 60% of cell dry weight. The increase in the level of carbohydrates in cells is due to accumulation of a storage α-glycan. According to a specific cleavage to glucose catalyzed by amyloglucosidase and the high positive specific optical rotation characteristic of polyglucans, this polysaccharide can be classified as a floridean starch. The data of 1H NMR spectroscopy and the results of methylation showed that the average length of the unbranched regions of the polysaccharide molecule is six to seven glucose residues. The degree of branching of the starch molecule of G. maxima is greater than that of storage polysaccharides of other red algae, glycogens of yeast, and phytoglycogens of cyanobacteria.

Two strains of pink-colored aerobic bacteriochlorophyll a-containing bacteria were isolated from aerobic (strain ROS 10) and anaerobic (strain ROS 35) zones of the water column of Mono Lake (California, United States). Cells of the bacteria were nonmotile oval gram-negative rods multiplying by binary fission by means of a constriction. No intracellular membranes were detected. Polyphosphates and poly-β-hydroxybutyric acid were the storage compounds. Pigments were represented by bacteriochlorophyll a and carotenoids of the spheroidene series. The strains were obligately aerobic, mesophilic (temperature optimum of 25–30°C), alkaliphilic (pH optimum of 8.5–9.5), and moderately halophilic (optimal NaCl concentration of 40 g/l). They were obligately heterotrophic and grew aerobically in the dark and in the light. Respiration was inhibited by light at wavelengths corresponding to the absorption of the cellular pigments. The substrate utilization spectra were strain-specific. In the course of organotrophic growth, the bacteria could oxidize thiosulfate to sulfate; sulfide and polysulfide could also be oxidized. The DNA G+C content was 59.4 mol % in strain ROS 10 and 59 mol % in strain ROS 35. In their phenotypic properties, the new strains were close but not identical to the alkaliphilic bacterium Roseinatronobacter thiooxidans. The distinctions in the nucleotide sequences of the 16S rRNA genes (2%) and low DNA-DNA hybridization level with Rna. thiooxidans (22–25%) allow the new strains to be assigned to a new species of the genus Roseinatronobacter, Roseinatronobacter monicus sp. nov. with the type strain ROS 35T (=UNIQEM U-251T = VKM B-2404T).

Using methods of molecular modeling, we have derived a universal spatial model of the orange carotenoid protein (OCP) and phycobilisome (PBS) core interaction in process of energy excess dissipation. The protrusion of the phy-cobilin domain (PB) of the core-membrane linker polypeptide (Lcm) forms the interaction site for the OCP central cavity on the PBS core surface. This spatial arrangement has to be the most advantageous one because the LCM, as the major terminal PBS-fluorescence emitter, gathers energy from the other phycobiliproteins within the PBS before quenching by OCP. In agreement with the constructed model, the small fluorescence recovery protein (FRP) also interacts with the OCPs central cavity weakening the PBS and OCP binding.

Distribution of phycobilisomes between photosystem I (PSI) and photosystem II (PSII) complexes in the cyanobacterium Spirulina platensis has been studied by analysis of the action spectra of H2 and O2 photoevolution and by analysis of the 77 K fluorescence excitation and emission spectra of the photosystems. PSI monomers and trimers were spectrally discriminated in the cell by the unique 760 nm low-temperature fluorescence, emitted by the trimers under reductive conditions. The phycobilisome-specific 625 nm peak was observed in the action spectra of both PSI and PSII, as well as in the 77 K fluorescence excitation spectra for chlorophyll emission at 695 nm (PSII), 730 nm (PSI monomers), and 760 nm (PSI trimers). The contributions of phycobilisomes to the absorption, action, and excitation spectra were derived from the in vivo absorption coefficients of phycobiliproteins and of chlorophyll. Analyzing the sum of PSI and PSII action spectra against the absorption spectrum and estimating the P700:P680 reaction center ratio of 5.7 in Spirulina, we calculated that PSII contained only 5% of the total chlorophyll, while PSI carried the greatest part, about 95%. Quantitative analysis of the obtained data showed that about 20% of phycobilisomes in Spirulina cells are bound to PSII, while 60% of phycobilisomes transfer the energy to PSI trimers, and the remaining 20% are associated with PSI monomers. A relevant model of organization of phycobilisomes and chlorophyll pigment-protein complexes in Spirulina is proposed. It is suggested that phycobilisomes are connected with PSII dimers, PSI trimers, and coupled PSI monomers.

The repression effect of d -glucose on the pigment apparatus of photosynthesis in the unicellular acidophilic red alga Galdieria partita capable of heterotrophic growth was studied. The rate of cell growth under heterotrophic conditions was higher by more than one order of magnitude than that in the autotrophic ones, and the size of those cells was larger. The addition of 1% d -glucose to the growth medium caused an increase in the number of mitochondrion profiles in the cell and a decline of thylakoid number in the chloroplast of G. partita . The loss of thylakoid membranes is accompanied by a reduction of the contents of chlorophyll a . C-phycocyanin and allophycocyanin in the heterotrophic cells. Simultaneously, switching G. partita from autotrophic growth to heterotrophic nutrition led to the excretion of coproporphyrin(ogen) III into the growth medium. Thus, the presence of d -glucose caused a reduction of pigment contents in the cell, due to the inhibition of chlorophyll a and phycocyanobilin biosynthesis at the stage of the transformation of their universal precursor, coproporphyrinogen III, to protoporphyrinogen IX. In the mixotrophic culture of G. partita light induces both the biosynthesis of photosynthetic pigments and the excretion of coproporphyrin(ogen) III. It is supposed that light affects an earlier stage in the biosynthetic pathway of chlorophyll a and phycocyanobilin than does d -glucose.

B-Phycoerythrin, the major phycobiliprotein of Bangiophyceae red algae, is composed of chromophorylated α-, β- and γ-polypeptide chains. Two γ-subunits with distinct molecular masses were chromatographically separated from B-phycoerythrin of the red alga Porphyridium cruentum . Both γ-polypeptides were spectrophotometrically identified as having the same composition of five chromophoric prosthetic groups: three phycourobilins and two phycoerythrobilins.

The atypical unicellular cyanobacterium Gloeobacter violaceus PCC 7421, diverged very early during the evolution of cyanobacteria, can be regarded as a key organism for understanding many structural, functional, regulatory, and evolutionary aspects of oxygenic photosynthesis. In our current study we investigated whether this ancient cyanobacterium lacking thylakoid membranes is capable of two basic phenomena common to all other photoautrophs: state transitions and non-photochemical fluorescence quenching. Our results clearly indicate dynamic changes in light energy distribution between the two photosystems. Similar to “modern” cyanobacteria G. violaceus is in state II in darkness and in state I upon illumination with weak blue-or far red light. Compared to state II, state I is characterized by an increased functional absorption cross-section of PS2. Furthermore, in contrast to weak blue light, strong blue light reversibly quenches chlorophyll fluorescence in G. violaceus, which suggests the existence of regulated heat dissipation triggered by the orange carotenoid protein in this primordial cyanobacterium.

Three different chlorophyll (chl) c-type pigments were isolated from two cryptophyte species by silica thin-layer chromatography or polyethylene high-performance liquid chromatography. Chroomonas sp. Hansgirg contained chl c1 and magnesium-2,4-divinylpheoporphyrin a, mono-methylester; chl c2 and magnesium-2,4-divinylpheoporphyrin a5 monomethylester were found in Cryptomonas maculata (syn. Rhodomonas maculata Butcher). These identifications were based on spectral characteristics and on comparison with reference pigments isolated from the synurophycean Synura petersenii Korshikov and the prasinophyte Mantoniella squamata Manton & Park. Neither of the cryptophyte species contained chl c1 and chl c2. The significance of chl c1 as a major pigment and the occurrence of magnesium-2,4-divinylpheoporphyrin a5 monomethylester in cryptophytes are discussed.

The phosphorescence of R-phycoerythrin from the red alga Callithamnion corymbosum was detected. The phosphorescence spectrum of R-phycoerythrin has two main components with maxima at 720 nm and 820 nm and lifetimes of 2.5 ms and 6.0 ms respectively. The phosphorescence excitation spectrum exhibited three bands at 498, 541 and 566 nm, characteristic of the absorption spectrum of R-phycoerythrin, but their relative intensifies differed from those recorded in fluorescence excitation spectrum. The fluorescence quantum yield of the pigment was 0.8 at 77 K; the phosphorescence quantum yield was 1.6 × 10 −6 and it increased to 1.5 × 10 −4 for the R-phycoerythrin denatured with 8 M urea at pH 3.0. This might be explained partly by alteration of the chromophore conformation accompanying the perturbation of protein structure.

R-Phycoerythrin was purified from two species of red algae: Callithamnion corymbosum from the Black Sea and Antithamnion sparsum from the Sea of Japan. Three polypeptide γ-subunits differing slightly in molecular weight (31.6, 30.8 and 29.0 kDa) in a 1:5:2 stoichiometry were found in R-phycoerythrin from C. corymbosum by reverse-phase chromatography on a fast performance liquid chromatography (FPLC) system. The ratio of the total number of γ1-, γ2- and γ3-subunits to the total number of α- and β-subunits of R-phycoerythrin was 1:12 and suggested the well-known (αβ)6γ molecular structure. The chromophore contents of the γ-subunits were identical: three phycourobilins and two phycoerythrobilins. R-Phycoerythrin from A. sparsum also contained three γ-subunits but with different chromophore compositions: one carried three phycourobilins and two phycoerythrobilins while the other carried four phycourobilins and one phycoerythrobilin. The chromophore composition of the third γ-subunit remained unclarified.

Phycobilisomes (PBS) are the major photosynthetic antenna complexes in cyanobacteria and red algae. In the red microalga Galdieria sulphuraria, action spectra measured separately for photosynthetic activities of photosystem I (PSI) and photosystem II (PSII) demonstrate that PBS fraction attributed to PSI is more sensitive to stress conditions and upon nitrogen starvation disappears from the cell earlier than the fraction of PBS coupled to PSII. Preillumination of the cells by actinic far-red light primarily absorbed by PSI caused an increase in the amplitude of the PBS low-temperature fluorescence emission that was accompanied by the decrease in PBS region of the PSI 77 K fluorescence excitation spectrum. Under the same conditions, fluorescence excitation spectrum of PSII remained unchanged. The amplitude of P700 photooxidation in PBS-absorbed light at physiological temperature was found to match the fluorescence changes observed at 77 K. The far-red light adaptations were reversible within 2–5min. It is suggested that the short-term fluorescence alterations observed in far-red light are triggered by the redox state of P700 and correspond to the temporal detachment of the PBS antenna from the core complexes of PSI. Furthermore, the absence of any change in the 77 K fluorescence excitation cross-section of PSII suggests that light energy transfer from PBS to PSI in G. sulphuraria is direct and does not occur through PSII. Finally, a novel photoprotective role of PBS in red algae is discussed.

Dark-grown leaves of three different species, maize, wheat, pea and a pea mutant (lip1) have been used to study protochlorophyllide (Pchlide) spectral forms. As a comparison also pea epicotyls were used. Different native forms of Pchlide were identified using the variation in the spectral properties of the plant material and the second derivatives of the 77 K fluorescence excitation and emission spectra. The spectral forms were further characterised by Gaussian deconvolution. In addition to short-wavelength and long-wavelength forms the area between 660 and 730 nm was shown to contain, together with some vibrational bands, five far-red Pchlide forms. They had pairs of excitation and emission peaks at 658 and 666 nm, 668 and 680 nm, 677 and 690 nm, 686 and 698 as well as 696 and 728 nm, respectively. The presence of several far-red Pchlide forms in dark-grown leaves gave evidence for additional aggregated states of Pchlide under native conditions.

The regulation of photosynthesis by sugars is considered to be a key control mechanism mediating cell homeostasis in algae and higher plants [1]. In cells of facultative photosynthetic heterotrophs D-glucose functions as an indispensable energy source and at the same time plays the part of a metabolic inhibitor [2]. In particular, biosynthesis of chlorophyll a and accompanying photosynthetic pigments in heterotrophically grown algae usually drops and the number of thylakoids is reduced. The site(s) of inhibition of the biosynthesis of chlorophyll a after autotrophic cells are transferred to organic nutrition remains unknown. It seems likely to occur at some of the precursor porphyrin stages [3].

A filamentous cyanobacterium Oscillatoria sp. was isolated from a thermal spring of the Kamchatka peninsula. It contained a phycoerythrin unusual for cyanobacteria in that it had a phycourobilin prosthetic group. The absorption spectrum of the native purified phycoerythrin displayed maxima at 498 and 567 nm. The phycoerythrin comprised α- and β-subunits of molecular weights 18,700 and 19,800, respectively, in 1:1 stoichiometry. Polyacrylamide gel isoelectric focusing revealed one protein band at pI 4.6. The α- and β-subunits differed in their chromophore composition and content: α-subunit carried two phycoerythrobilins while the β-subunit had three phycoerythrobilins and one phycourobilin. The chromophore composition of all known phycoerythrins of cyanobacteria and red algae were compared, and on the basis of this comparative study designations C1- to C5-phycoerythrin were proposed for cyanobacterial red pigments.

Brief – 10-second long – irradiation of a photosystem II-deficient mutant of cyanobacterium Synechocystis sp. PCC 6803 with intense blue or UV-B light causes an about 40% decrease of phycobilisome (PBS) fluorescence, slowly reversible in the dark. The registered action spectrum of PBS fluorescence quenching only shows bands at 500, 470 and 430 nm, typical of carotenoids, and an additional UV-B band; no peaks in the region of chlorophyll or PBS absorption have been found. We propose that quenching induced by carotenoids, possibly protein-bound or glycoside, reveals a new regulatory mechanism protecting photosynthetic apparatus of cyanobacteria against photodamage.

The phenotypic characteristics of the species Sulfobacillus thermotolerans Kr1(T), as dependent on the cultivation conditions, are described in detail. High growth rates (0.22-0.30 h(-1)) and high oxidative activity were recorded under optimum mixotrophic conditions at 40 degrees C on medium with inorganic (Fe(II), S(0), or pyrite-arsenopyrite concentrate) and organic (glucose and/or yeast extract) substrates. In cells grown under optimum conditions on medium with iron, hemes a, b, and, most probably, c were present, indicating the presence of the corresponding cytochromes. Peculiar extended structures in the form of cylindrical cords, never observed previously, were revealed; a mucous matrix, likely of polysaccharide nature, occurred around the cells. In the cells of sulfobacilli grown litho-, organo-, and mixotrophically at 40 degrees C, the enzymes of the three main pathways of carbon utilization and some enzymes of the TCA cycle were revealed. The enzyme activity was maximum under mixotrophic growth conditions. The growth rate in the regions of limiting temperatures (55 degrees C and 12-14 degrees C) decreased two- and tenfold, respectively; no activity of 6-phosphogluconate dehydrogenase, one of the key enzymes of the oxidative pentose phosphate pathway, could be revealed; and a decrease in the activity of almost all enzymes of glucose metabolism and of the TCA cycle was observed. The rate of 14CO2 fixation by cells under auto-, mixo-, and heterotrophic conditions constituted 31.8, 23.3, and 10.3 nmol/(h mg protein), respectively. The activities of RuBP carboxylase (it peaked during lithotrophic growth) and of carboxylases of heterotrophic carbon dioxide fixation were recorded. The physiological and biochemical peculiarities of the thermotolerant sulfobacillus are compared versus moderately thermophilic sulfobacilli.