Photoheterotrophic bacteria harvest light energy using either proton-pumping rhodopsins or bacteriochlorophyll (BChl)-based photosystems. The bacterium Sphingomonas glacialis AAP5 isolated from the alpine lake Gossenköllesee contains genes for both systems. Here, we show that BChl is expressed between 4°C and 22°C in the dark, whereas xanthorhodopsin is expressed only at temperatures below 16°C and in the presence of light. Thus, cells grown at low temperatures under a natural light-dark cycle contain both BChl-based photosystems and xanthorhodopsins with a nostoxanthin antenna. Flash photolysis measurements proved that both systems are photochemically active. The captured light energy is used for ATP synthesis and stimulates growth. Thus, S. glacialis AAP5 represents a chlorophototrophic and a retinalophototrophic organism. Our analyses suggest that simple xanthorhodopsin may be preferred by the cells under higher light and low temperatures, whereas larger BChl-based photosystems may perform better at lower light intensities. This indicates that the use of two systems for light harvesting may represent an evolutionary adaptation to the specific environmental conditions found in alpine lakes and other analogous ecosystems, allowing bacteria to alternate their light-harvesting machinery in response to large seasonal changes of irradiance and temperature.

• Klíčová slova
• anoxygenic photosynthesis, bacteriochlorophyll a, dual phototrophy, light energy, xanthorhodopsin,
• MeSH
• Bacteria metabolismus   MeSH
• bakteriální proteiny metabolismus   MeSH
• bakteriochlorofyly * chemie   MeSH
• ekosystém MeSH
• fotosyntéza MeSH
• jezera * analýza   MeSH
• protonové pumpy MeSH
• protony MeSH
• světlosběrné proteinové komplexy metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• bakteriální proteiny MeSH
• bakteriochlorofyly * MeSH
• protonové pumpy MeSH
• protony MeSH
• světlosběrné proteinové komplexy MeSH

Photosystem II (PSII) is the multi-subunit light-driven oxidoreductase that drives photosynthetic electron transport using electrons extracted from water. To investigate the initial steps of PSII assembly, we used strains of the cyanobacterium Synechocystis sp. PCC 6803 arrested at early stages of PSII biogenesis and expressing affinity-tagged PSII subunits to isolate PSII reaction center assembly (RCII) complexes and their precursor D1 and D2 modules (D1mod and D2mod). RCII preparations isolated using either a His-tagged D2 or a FLAG-tagged PsbI subunit contained the previously described RCIIa and RCII* complexes that differ with respect to the presence of the Ycf39 assembly factor and high light-inducible proteins (Hlips) and a larger complex consisting of RCIIa bound to monomeric PSI. All RCII complexes contained the PSII subunits D1, D2, PsbI, PsbE, and PsbF and the assembly factors rubredoxin A and Ycf48, but we also detected PsbN, Slr1470, and the Slr0575 proteins, which all have plant homologs. The RCII preparations also contained prohibitins/stomatins (Phbs) of unknown function and FtsH protease subunits. RCII complexes were active in light-induced primary charge separation and bound chlorophylls (Chls), pheophytins, beta-carotenes, and heme. The isolated D1mod consisted of D1/PsbI/Ycf48 with some Ycf39 and Phb3, while D2mod contained D2/cytochrome b559 with co-purifying PsbY, Phb1, Phb3, FtsH2/FtsH3, CyanoP, and Slr1470. As stably bound, Chl was detected in D1mod but not D2mod, formation of RCII appears to be important for stable binding of most of the Chls and both pheophytins. We suggest that Chl can be delivered to RCII from either monomeric Photosystem I or Ycf39/Hlips complexes.

• MeSH
• chlorofyl metabolismus   MeSH
• feofytiny metabolismus   MeSH
• fotosystém I (proteinový komplex) metabolismus   MeSH
• fotosystém II (proteinový komplex) * metabolismus   MeSH
• Synechocystis * metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• chlorofyl MeSH
• feofytiny MeSH
• fotosystém I (proteinový komplex) MeSH
• fotosystém II (proteinový komplex) * MeSH

Photoheterotrophic bacteria represent an important part of aquatic microbial communities. There exist two fundamentally different light-harvesting systems: bacteriochlorophyll-containing reaction centers or rhodopsins. Here, we report a photoheterotrophic Sphingomonas strain isolated from an oligotrophic lake, which contains complete sets of genes for both rhodopsin-based and bacteriochlorophyll-based phototrophy. Interestingly, the identified genes were not expressed when cultured in liquid organic media. Using reverse transcription quantitative PCR (RT-qPCR), RNA sequencing, and bacteriochlorophyll a quantification, we document that bacteriochlorophyll synthesis was repressed by high concentrations of glucose or galactose in the medium. Coactivation of photosynthesis genes together with genes for TonB-dependent transporters suggests the utilization of light energy for nutrient import. The photosynthetic units were formed by ring-shaped light-harvesting complex 1 and reaction centers with bacteriochlorophyll a and spirilloxanthin as the main light-harvesting pigments. The identified rhodopsin gene belonged to the xanthorhodopsin family, but it lacks salinixanthin antenna. In contrast to bacteriochlorophyll, the expression of xanthorhodopsin remained minimal under all experimental conditions tested. Since the gene was found in the same operon as a histidine kinase, we propose that it might serve as a light sensor. Our results document that photoheterotrophic Sphingomonas bacteria use the energy of light under carbon-limited conditions, while under carbon-replete conditions, they cover all their metabolic needs through oxidative phosphorylation.IMPORTANCE Phototrophic organisms are key components of many natural environments. There exist two main phototrophic groups: species that collect light energy using various kinds of (bacterio)chlorophylls and species that utilize rhodopsins. Here, we present a freshwater bacterium Sphingomonas sp. strain AAP5 which contains genes for both light-harvesting systems. We show that bacteriochlorophyll-based reaction centers are repressed by light and/or glucose. On the other hand, the rhodopsin gene was not expressed significantly under any of the experimental conditions. This may indicate that rhodopsin in Sphingomonas may have other functions not linked to bioenergetics.

• Klíčová slova
• Sphingomonadaceae, aerobic anoxygenic phototrophic bacteria, bacteriochlorophyll a, gene expression, photosynthesis gene cluster, rhodopsin,
• Publikační typ
• časopisecké články MeSH

The influence of temperature on photosynthetic reactions was investigated by a combination of time-resolved bacteriochlorophyll fluorescence, steady-state and differential absorption spectroscopy, and polarographic respiration measurements in intact cells of purple non-sulphur bacterium Rhodospirillum rubrum. Using variable bacteriochlorophyll fluorescence, it was found that the electron-transport activity increased with the increasing temperature up to 41 °C. The fast and medium components of the fluorescence decay kinetics followed the ideal Arrhenius equation. The calculated activation energy for the fast component was Ea1 = 16 kJ mol-1, while that of the medium component was more than double, with Ea2 = 38 kJ mol-1. At temperatures between 41 and 59 °C, the electron transport was gradually, irreversibly inhibited. Interestingly, the primary charge separation remained fully competent from 20 to 59 °C as documented by both BChl fluorescence and differential absorption spectroscopy of the P870+ signal. At temperatures above 60 °C, the primary photochemistry became reversibly inhibited, which was manifested by an increase in minimal fluorescence, F0, whereas maximal fluorescence, FM, slowly declined. Finally, above 71 °C, the photosynthetic complexes began to disassemble as seen in the decline of all fluorometric parameters and the disappearance of the LH1 absorption band at 880 nm. The extended optimal temperature of photosynthetic reaction centre in a model species of Rhodospirillales adds on the evidence that the good thermostability of the photosynthetic reaction centres is present across all Alphaproteobacteria.

• Klíčová slova
• Anoxygenic photosynthesis, Electron transfer, Reaction centre, Thermostability, Variable fluorescence,
• MeSH
• buněčné dýchání MeSH
• fluorescence MeSH
• fotosyntéza * MeSH
• kinetika MeSH
• Rhodospirillum rubrum fyziologie   MeSH
• světlosběrné proteinové komplexy metabolismus   MeSH
• teplota * MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• světlosběrné proteinové komplexy MeSH

Photosystem I (PSI) is a multi-subunit integral pigment-protein complex that performs light-driven electron transfer from plastocyanin to ferredoxin in the thylakoid membrane of oxygenic photoautotrophs. In order to achieve the optimal photosynthetic performance under ambient irradiance, the absorption cross section of PSI is extended by means of peripheral antenna complexes. In eukaryotes, this role is played mostly by the pigment-protein complexes of the LHC family. The structure of the PSI-antenna supercomplexes has been relatively well understood in organisms harboring the primary plastid: red algae, green algae and plants. The secondary endosymbiotic algae, despite their major ecological importance, have so far received less attention. Here we report a detailed structural analysis of the antenna-PSI association in the stramenopile alga Nannochloropsis oceanica (Eustigmatophyceae). Several types of PSI-antenna assemblies are identified allowing for identification of antenna docking sites on the PSI core. Instances of departure of the stramenopile system from the red algal model of PSI-Lhcr structure are recorded, and evolutionary implications of these observations are discussed.

• Klíčová slova
• Electron microscopy, Light-harvesting complex, Nannochloropsis, Photosystem I, Stramenopila,
• MeSH
• fotosystém I (proteinový komplex) metabolismus   MeSH
• plastidy metabolismus   MeSH
• Rhodophyta metabolismus   MeSH
• spektrofotometrie ultrafialová MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• fotosystém I (proteinový komplex) MeSH

Spatial segregation of photosystems in the thylakoid membrane (lateral heterogeneity) observed in plants and in the green algae is usually considered to be absent in photoautotrophs possessing secondary plastids, such as diatoms. Contrary to this assumption, here we show that thylakoid membranes in the chloroplast of a marine diatom, Phaeodactylum tricornutum, contain large areas occupied exclusively by a supercomplex of photosystem I (PSI) and its associated Lhcr antenna. These membrane areas, hundreds of nanometers in size, comprise hundreds of tightly packed PSI-antenna complexes while lacking other components of the photosynthetic electron transport chain. Analyses of the spatial distribution of the PSI-Lhcr complexes have indicated elliptical particles, each 14 × 17 nm in diameter. On larger scales, the red-enhanced illumination exerts a significant effect on the ultrastructure of chloroplasts, creating superstacks of tens of thylakoid membranes.

• MeSH
• chloroplasty metabolismus   účinky záření   ultrastruktura   MeSH
• fotosystém I (proteinový komplex) metabolismus   MeSH
• fotosystém II (proteinový komplex) metabolismus   MeSH
• multiproteinové komplexy metabolismus   ultrastruktura   MeSH
• rozsivky metabolismus   účinky záření   ultrastruktura   MeSH
• světlo MeSH
• světlosběrné proteinové komplexy metabolismus   MeSH
• transmisní elektronová mikroskopie MeSH
• tylakoidy metabolismus   účinky záření   ultrastruktura   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• fotosystém I (proteinový komplex) MeSH
• fotosystém II (proteinový komplex) MeSH
• multiproteinové komplexy MeSH
• světlosběrné proteinové komplexy MeSH

The arrangement of core antenna complexes (B808-866-RC) in the cytoplasmic membrane of filamentous phototrophic bacterium Chloroflexus aurantiacus was studied by electron microscopy in cultures from different light conditions. A typical nearest-neighbor center-to-center distance of ~18 nm was found, implying less protein crowding compared to membranes of purple bacteria. A mean RC:chlorosome ratio of 11 was estimated for the occupancy of the membrane directly underneath each chlorosome, based on analysis of chlorosome dimensions and core complex distribution. Also presented are results of single-particle analysis of core complexes embedded in the native membrane.

• MeSH
• buněčná membrána metabolismus   ultrastruktura   MeSH
• Chloroflexus metabolismus   MeSH
• elektronová mikroskopie MeSH
• fotosyntetická reakční centra (proteinové komplexy) metabolismus   ultrastruktura   MeSH
• fotosyntéza MeSH
• organely metabolismus   ultrastruktura   MeSH
• Rhodopseudomonas metabolismus   MeSH
• světlo MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• fotosyntetická reakční centra (proteinové komplexy) MeSH

The authors present a study of the fluorescence and absorbance transients occurring in whole cells of purple nonsulfur bacterium Rhodobacter sphaeroides on the millisecond timescale under pulsed actinic illumination. The fluorescence induction curve is interpreted in terms of combination of effects of redox changes in the reaction center and the membrane potential. The results of this study support the view that the membrane potential act predominantly to increase the fluorescence yield. Advantages of the pulsed actinic illumination for study of the operation of the electron transport chain in vivo are discussed.

• MeSH
• absorpce účinky záření   MeSH
• fluorescenční spektrometrie MeSH
• karotenoidy metabolismus   MeSH
• kinetika MeSH
• membránové potenciály účinky záření   MeSH
• oxidace-redukce účinky záření   MeSH
• Rhodobacter sphaeroides cytologie   metabolismus   účinky záření   MeSH
• světlo MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• karotenoidy MeSH

The light-induced electron transport in purple bacterium Rhodobacter sphaeroides was studied in vivo by means of kinetic difference absorption spectroscopy and kinetics of bacteriochlorophyll fluorescence yield. Measurements of redox state of the oxidised primary donor and cytochrome c and the membrane potential revealed a complex pattern of changes of the electron flow. Effects of the membrane potential on the fluorescence yield were also analysed, and a model for the fluorescence induction curve is presented. The data indicate substantial positive effect of the membrane potential on the fluorescence emission in vivo. Moreover, light-induced changes in light scattering were observed, which suggests occurrence of structural changes on the level of the photosynthetic membrane.

• MeSH
• bakteriochlorofyly metabolismus   MeSH
• fluorescence MeSH
• fotosyntéza fyziologie   MeSH
• kinetika MeSH
• membránové potenciály fyziologie   MeSH
• Rhodobacter sphaeroides metabolismus   fyziologie   účinky záření   MeSH
• světlo MeSH
• transport elektronů MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• bakteriochlorofyly MeSH

Differential kinetic absorption spectra were measured during actinic illumination of photosystem II reaction centres and core complexes in the presence of electron acceptors silicomolybdate and ferricyanide. The spectra of samples with ferricyanide differ from those with both ferricyanide and silicomolybdate. Near-infrared spectra show temporary beta-carotene and peripheral chlorophyll oxidation during room temperature actinic illumination. Peripheral chlorophyll is photooxidized even after decay of beta-carotene oxidation activity and significant reduction of beta-carotene content in both reaction centres and photosystem II core complexes. Besides, new carotenoid cation is observed after about 1 s of actinic illumination in the reaction centres when silicomolybdate is present. Similar result was observed in PSII core complexes. HPLC analyses of illuminated reaction centres reveal several novel carotenoids, whereas no new carotenoid species were observed in HPLC of illuminated core complexes. Our data support the proposal that pigments of inner antenna are a sink of cations originating in the photosystem II reaction centre.

• MeSH
• beta-karoten metabolismus   MeSH
• chlorofyl metabolismus   MeSH
• ferrikyanidy metabolismus   MeSH
• fotosyntéza MeSH
• fotosystém II (proteinový komplex) metabolismus   MeSH
• hrách setý MeSH
• molybden metabolismus   MeSH
• oxidace-redukce MeSH
• sloučeniny křemíku metabolismus   MeSH
• světlo MeSH
• teplota MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• beta-karoten MeSH
• chlorofyl MeSH
• ferrikyanidy MeSH
• fotosystém II (proteinový komplex) MeSH
• hexacyanoferrate III MeSH Prohlížeč
• molybden MeSH
• silicomolybdate MeSH Prohlížeč
• sloučeniny křemíku MeSH