Energy transfer pathways among phycobilin chromophores and fluorescence emission spectra of the phycobilisome core at 293 and 77 K

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.     

<Emphasis Type="Italic">Rhodobaca barguzinensis</Emphasis> sp. nov., a new alkaliphilic purple nonsulfur bacterium isolated from a soda lake of the Barguzin Valley (Buryat Republic,Eastern Siberia)

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°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.     

Dynamics of the biosynthesis of native chlorophyll forms from initial stages to the completion of the greening process in etiolated leaves]

The succession of the formation of the native chlorophill forms and the development of the energy migration between them was studied by means of the comparison of three spectrum types: absorption, fluorescence and fluorescence excitation, and of their second derivatives. Quantitatively the chlorophyll accumulation in 9 native forms was followed by means of mathematical disintegration of the spectra using computer.     

Phycobilisomes from the mutant cyanobacterium Synechocystis sp. PCC 6803 missing chromophore domain of ApcE

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 L_CM. 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 PBL_CM 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 PBL_CM domain takes part in formation of the OCP binding site in the PBS.     

Role of inter-domain cavity in the attachment of the orange carotenoid protein to the phycobilisome core and to the fluorescence recovery protein

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 (L_CM) 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 L_CM, 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.     

Coupled rows of PBS cores and PSII dimers in cyanobacteria: symmetry and structure

Photosynthesis Research - Phycobilisome&nbsp;(PBS) is a giant water-soluble photosynthetic antenna transferring the energy of absorbed light mainly to the...     

Fluorescence changes accompanying short-term light adaptations in photosystem I and photosystem II of the cyanobacterium <Emphasis Type="Italic">Synechocystis</Emphasis> sp. PCC 6803 and phycobiliprotein-impaired mutants: State 1/State 2 transitions and carotenoid-induced quenching of phycobilisomes

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.     

Nitric oxide-induced membrane tubulovesicular extensions (cytonemes) of human neutrophils catch and hold Salmonella enterica serovar Typhimurium at a distance from the cell surface

Nitric oxide (NO) plays an important role in host defense against bacterial infections such as salmonellosis. NO and 4-bromophenacyl bromide (BPB) induce the formation of long tubulovesicular extensions (TVE, cytonemes, membrane tethers) from human neutrophils. These TVE serve as cellular sensory and adhesive organelles. In the present study, we demonstrated that in the presence of the NO donor, diethylamine NONOate or BPB human neutrophils bound and aggregated Salmonella enterica serovar Typhimurium bacteria extracellularly by TVE. In contrast, inhibition of NO-synthase activity by N ^ω-nitro- l -arginine methyl ester stimulated neutrophil phagocytosis (ingestion) of bacteria. Neutrophil TVE consisted of membrane-covered cytoplasm as was shown by the fluorescent cytoplasmic dye 2',7'-bis(2carboxyethyl)-5,(6)-carboxyfluorescein, and the fluorescent lipid, BODIPY-labeled sulfatide. Disruption and shedding of TVE were accompanied by the appearance of specific invaginations (porosomes) on neutrophil cell bodies. These invaginations corresponded to the variations in diameter of TVE (160–240 nm). We hypothesized that TVE represented protrusions of neutrophil exocytotic trafficking through special structures on the neutrophil surface. In conclusion, we propose a novel mechanism by which NO-induced TVE formation enables neutrophils to bind and aggregate bacteria at a distance.     

Photosynthetic activity and components of the electron transport chain in the aerobic bacteriochlorophyll <Emphasis Type="Italic">a</Emphasis>-containing bacterium <Emphasis Type="Italic">Roseinatronobacter thiooxidans</Emphasis>

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 c ₅₅₁ 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 bc ₁ complex and two terminal oxidases: cbb ₃-cytochrome oxidase and the alternative cytochrome oxidase of the a ₃ 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.