David Kaftan

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 xanthorhodops...

Phototrophic Gemmatimonadetes evolved the ability to use solar energy following horizontal transfer of photosynthesis-related genes from an ancient phototrophic proteobacterium. The electron cryo-microscopy structure of the Gemmatimonas phototrophica photosystem at 2.4 Å reveals a unique, double-ring complex. Two unique membrane-extrinsic polypepti...

Metal nanoparticles exhibit unique properties that are highly appreciated in many novel-material applications, e.g., sensors and antibacterial coatings. However, low adherence of nanoparticles to surfaces limits their practical application. Therefore, the nanoparticles are often incorporated into a matrix, i.e., thin-film, which improves their atta...

In almost all photosynthetic organisms the photosynthetic pigments chlorophyll and bacteriochlorophyll (BChl) are Mg2+ containing complexes, but Mg2+ may be exchanged against other metal ions when these are present in toxic concentrations, leading to inactivation of photosynthesis. In this report we studied mechanisms of copper toxicity to the phot...

Surfaces with defined nanoroughness and topography are appreciated in many applications. However, such surfaces, often built from deposited nanoparticles, suffer from low hardness and overall mechanical stability. This paper reports the research of ZrN surfaces with defined nanoroughness attained by seed-like growth evoked by Cu nanoparticles. The...

An aerobic, yellow-pigmented, bacteriochlorophyll a-producing strain, designated AAP5 (=DSM 111157=CCUG 74776), was isolated from the alpine lake Gossenköllesee located in the Tyro-lean Alps, Austria. Here, we report its description and polyphasic characterization. Phylogenetic analysis of the 16S rRNA gene showed that strain AAP5 belongs to the ba...

Gemmatimonas phototrophica is, so far, the only described phototrophic species of the bacterial phylum Gemmatimonadetes. Its cells contain a unique type of photosynthetic complex with the reaction center surrounded by a double ring antenna, however they can also grow in the dark using organic carbon substrates. Its photosynthesis genes were receive...

Gemmatimonas phototrophica is, so far, the only described phototrophic species of the bacterial phylum Gem-matimonadetes. Its cells contain a unique type of photosynthetic complex with the reaction center surrounded by a double ring antenna, however they can also grow in the dark using organic carbon substrates. Its photosyn-thesis genes were recei...

The diversity of cyanobacteria along the Alaskan North Slope was investigated. We isolated and cultivated 57 strains of cyanobacteria and sequenced a section of their rRNA operon containing a fragment of the 16S rRNA gene. Here, we describe 17 found species belonging mainly to families Coleofasciculaceae, Microcoleaceae, Oculatellaceae, Leptolyngby...

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 fluo...

Magnesium (Mg2+) is the ubiquitous metal ion present in chlorophyll and bacteriochlorophyll (BChl), involved in photosystems in photosynthetic organisms. In the present study we investigated targets of toxic copper binding to the photosynthetic apparatus of the anoxygenic purple bacterium Rhodospirillum rubrum. This was done by a combination of in...

Targeting mutations to specific genomic loci is invaluable for assessing in vivo the effect of these changes on the biological role of the gene in study. Here, we attempted to introduce a mutation that was previously implicated in an increased heat stability of the mesophilic cyanobacterium Synechocystis sp. PCC6803 via homologous recombination to...

We tested the potential of Raman microspectroscopy to determine carotenoid pigments — both primary (lutein, beta-carotene) and secondary (astaxanthin) carotenoids — in the different species and life-cycle stages of snow algae from the order Chlamydomonadales (Chlorophyta). We compared the performance of Raman spectrometry to a reference method of b...

Temperature is one of the most important physical factors affecting microbial and biochemical processes. We investigated the performance of photosynthetic apparatus of marine photoheterotrophic bacterium Dinoroseobacter shibae under various temperatures. The primary photochemistry and electron transport was measured using variable infra-red fluorom...

Genotypic and morphological diversity of cyanobacteria in the Rupite hot spring (Bulgaria) was investigated by means of optical microscopy, cultivation, single-cell PCR, and 16S rRNA gene amplicon sequencing. Altogether, 34 sites were investigated along the 71–39 °C temperature gradient. Analysis of samples from eight representative sites shown tha...

The majority of life on Earth depends directly or indirectly on the sun as a source of energy. The initial step of photosynthesis is facilitated by light-harvesting complexes, which capture and transfer light energy into the reaction centers (RCs). Here, we analyzed the organization of photosynthetic (PS) complexes in the bacterium G. phototrophica...

Detailed discussion of the BChl a stoichiometry in PS complex. BChl, bacteriochlorophyll; PS, photosynthetic. (DOC)

Flash-induced absorbance spectra of purified photosynthetic complexes of G. phototrophica. As expected for the type 2 RC, the signal is dominated by signatures of the oxidized primary donor (P870+): bleaching around 865 nm, electrochomic shift of the accessory BChl a around 800 nm and bleaching of the Qx band of the primary donor at 600 nm. BChl, b...

Parameters used for computation of the steady-state optical spectra of G. phototrophica PS complex. PS, photosynthetic. (PDF)

Absorption spectra of PS membranes from G. phototrophica (red) and R. rubrum (grey). PS, photosynthetic. (TIF)

Upper panel: size exclusion chromatography of the partially purified PS complexes from G. phototrophica. The blue line recorded at 820 nm shows the fraction with the purified complex, and the red trace at 490 nm represent the carotenoids. Lower panel: the absorption spectrum of the obtained complex (blue) and the spectrum of the “free” carotenoids...

Example of a raw TEM image of G. phototrophica complexes. TEM, transmission electron microscopy. (TIF)

PS complex of G. phototrophica analyzed by native and SDS polyacrylamide gel electrophoresis. (A) Clear-native gel electrophoresis of G. phototrophica membrane complexes in comparison with membrane complexes of R. rubrum and Synechocystis sp. PCC 6803; the membranes were solubilized using 2% dodecyl-β-maltoside and loaded on 4%–14% clear-native gel...

BChl a fluorescence induction and relaxation recorded using the kinetic fluorometer FL-3000 (Photon Systems Instruments Ltd., Brno, Czech Republic). The BChl fluorescence induction transient was elicited by a 140 μs-long square-wave pulse of light with an intensity of approximately 0.1 mol photon m−2s−1 provided by an array of blue-green 505 nm Lux...

Estimated angular distance between neighboring subunits of the PS complex. The angle was measured as shown in the insert. The data were derived from 23 measurements from 4 individual complex images. PS, photosynthetic. (TIF)

The spectro-temporal datasets obtained from the measurements were analyzed globally by fitting package DAFit (Pascher Instruments). To visualize the excited state dynamics, we assumed that the excited states evolved according to a sequential, irreversible scheme A → B, B → C, C → D. The arrows represent increasingly slower processes and the time co...

Comparison of B816 and B868 absorption bands. Red line: absorption spectrum of G. phototrophica PS complex. Grey area: absorption spectrum of R. rubrum complex scaled and blue-shifted to match the B868 band. Blue area: the difference between the red and grey spectra, corresponds to the pure spectrum of the B816 absorption band. The ratio of B816 an...

Aerobic Anoxygenic Photosynthetic (AAP) bacteria are an important component of marine microbial communities. They produce energy in light using bacteriochlorophyll a containing photosystems. This extra energy provides an advantage over purely heterotrophic bacteria. One of the most intensively studied AAP bacteria is Dinoroseobacter shibae, a membe...

Interquinone QA− → QB electron-transfer (ET) in isolated photosystem II reaction centers (PSII-RC) is protein-gated. The temperature-dependent gating frequency “k” is described by the Eyring equation till levelling off at T ≥ 240 °K. Although central to photosynthesis, the gating mechanism has not been resolved and due to experimental limitations,...

Interquinone QA− → QB electron-transfer (ET) in isolated photosystem II reaction centers (PSII-RC) is protein-gated. The temperature-dependent gating frequency “k” is described by the Eyring equation till levelling off at T ≥ 240 °K. Although central to photosynthesis, the gating mechanism has not been resolved and due to experimental limitations,...

A red-pigmented, bacteriochlorophyll (BChl) a-producing strain, AP64T, was isolated previously from the freshwater Swan Lake located in the western Gobi Desert. Based on its 16S rRNA gene sequence identity (96.1 %) to the type strain Gemmatimonas aurantiaca T-27T, the new isolate was tentatively classified as a member of the bacterial phylum Gemmat...

A red pigmented bacteriochlorophyll a producing strain AP64T was isolated from the freshwater Swan lake located in the western Gobi Desert [Proc. Natl. Acad. Sci. USA 2014, 111(21):7795-7800]. Based on its 16S rRNA sequence identity (96.1%) with the type strain Gemmatimonas aurantiaca T-27T, the new isolate was tentatively classified as a member of...

Rationale: Alveolar liquid clearance is regulated by Na 1 uptake through the apically expressed epithelial sodium channel (ENaC) and basolaterally localized Na 1-K 1-ATPase in type II alveolar epithelial cells. Dysfunction of these Na 1 transporters during pulmonary inflammation can contribute to pulmonary edema. Objectives: In this study, we sough...

Rationale: Alveolar liquid clearance is regulated by Na(+) uptake through the apically expressed epithelial sodium channel (ENaC) and basolaterally localized Na(+)-K(+)-ATPase in type II alveolar epithelial cells. Dysfunction of these Na(+) transporters during pulmonary inflammation can contribute to pulmonary edema. Objectives: In this study, w...

Here we report an effect of short acclimation to a wide span of temperatures on photosynthetic electron transfer, lipid and fatty acid composition in the snow alga Chlamydomonas cf. nivalis. The growth and oxygen evolution capacity was low at 2ºC yet progressively enhanced at 10ºC and were significantly higher at temperatures from 5 to 15ºC in comp...

An isolated polynucleotide is provided. The isolated poly-nucleotide comprising a nucleic acid sequence encoding a polypeptide of a Type II reaction center of a photosynthetic organism, the nucleic acid sequence being capable of impart-ing the type II reaction center with an activity under a tem-perature range different than that of the type II rea...

Light harvesting complexes ensure necessary flow of excitation energy into photosynthetic reaction centers. In the present work, transient absorption measurements were performed on LH1-RC complexes isolated from two aerobic anoxygenic phototrophs (AAPs), Roseobacter sp. COL2P containing the carotenoid spheroidenone, and Erythrobacter sp. NAP1 which...

Raman microscopy permits structural analysis of protein crystals in situ in hanging drops, allowing for comparison with Raman measurements in solution. Nevertheless, the two methods sometimes reveal subtle differences in structure that are often ascribed to the water layer surrounding the protein. The novel method of drop-coating deposition Raman s...

DCDR spectrum of the crystallizing buffer for PsbP protein used in Raman crystallography. Buffer A was mixed in a 1∶1 ratio with crystallization reservoir solution containing 16% PEG 550 MME, 0.1 M Tris-HCl pH 7.0, 10 mM ZnSO4. (TIF)

The lectin-like domain of Tumor Necrosis Factor (TNF), mimicked by the TIP peptide, activates amiloride-sensitive sodium uptake in type II alveolar epithelial cells and as such increases alveolar liquid clearance in dysfunctional lungs. This protective effect is blunted upon mutation of residues T105, E107 and E110 in human TNF into alanine or upon...

Amplitudes of the fast decay component of chlorophyll fluorescence. The amplitudes represent the relative contribution of PSIIRCs that perform normal QA−→QB electron transfer to the total PSIIRC content. Fluorescence was measured in ΔKS grown at 30°C (open circles), ΔKS grown at 43°C (filled circles), AC grown at 30°C (open squares), AC grown at 43...

Changes in the QA−→QB electron transfer rates upon incubation at 43°C. AC mutant cells growing at 30°C for 3 days were transferred to 43°C and their QA−→QB electron transfer rate was measured at the indicated times (See Materials and methods). The values represent the mean ± SD of three independent experiments. (EPS)

D1 and Rubisco proteins immunoblot signal response. A dilution series of ΔKS (circles) and AC (squares) thylakoid membrane samples was loaded in SDS-PAGE and subsequently immunoblotted using specific antibodies raised against D1 (A) and Rubisco (B) proteins. Immunoblot signal changes were quantified by integrating variable pixel intensity from scan...

Photoautotrophic growth of the ΔKS and AC mutant cells at elevated temperatures and various CO2 concentrations. ΔKS (circles) and AC mutant (squares) cells were grown at the indicated temperature and CO2 supply under 40 µmol photons m−2 s−1. The inserts show the same data using a different scale. Growth was monitored by measuring the optical densit...

Thylakoid membrane lipids composition in Synechocystis sp. PCC6803 and Thermosynechococcus elongatus grown at the indicated temperatures. Lipids were extracted from thylakoid membranes. Lipid classes were separated by thin-layer chromatography, sprayed with a primuline solution and quantified by integrating variable pixel intensities of the scanned...

Photosynthetic biomass production rapidly declines in mesophilic cyanobacteria grown above their physiological temperatures largely due to the imbalance between degradation and repair of the D1 protein subunit of the heat susceptible Photosystem II reaction centers (PSIIRC). Here we show that simultaneous replacement of two conserved residues in th...

The crystallization of the higher plant 1 gigadalton homodimeric lipid-pigment−protein complex of photosystem II constitutes a challenging undertaking that has not been crowned with success to date. In the continuation of our previous efforts (Kuta-Smatanova et al. Photosyn. Res. 2006, 90, 255−259) that had provided needle and plate crystals of pla...

Higher harmonic contributions in the movement of an oscillating atomic force microscopy (AFM) cantilever are generated by nonlinear tip-sample interactions, yielding additional information on structure and physical properties such as sample stiffness. Higher harmonic amplitudes are strongly enhanced in liquid compared to the operation in air, and w...

Adjustment of catalytic activity in response to diverse ambient temperatures is fundamental to life on Earth. A crucial example of this is photosynthesis, where solar energy is converted into electrochemical potential that drives oxygen and biomass generation at temperatures ranging from those of frigid Antarctica to those of scalding hot springs....

Irradiance power and spectral composition as well as nutrient availability strongly influence differentiation of filamentous cyanobacteria. When monitoring the life cycle of Calothrix elenkinii Kossinsk., we found that low nitrogen concentration and growth under green light led to a transient appearance of high-fluorescence cells that rapidly bleac...

Progress in various fields of microscopy techniques brought up enormous possibilities to study the photosynthesis down to the level of individual pigment-protein complexes. The aim of this review is to present recent developments in the photosynthesis research obtained using such highly advanced techniques. Three areas of microscopy techniques cove...

The unicellular green alga Dunaliella was previously proposed as a model photosynthetic organism for adaptation to iron deficiency. The purpose of this study was to find out how iron limitation affects the structure and composition of the photosynthetic system of Dunaliella salina. Iron deprivation did not retard proliferation of D. salina cells, b...

Several million macromolecules are exchanged each minute between the nucleus and cytoplasm by receptor-mediated transport. Most of this traffic is controlled by the small GTPase Ran, which regulates assembly and disassembly of the receptor-cargo complexes in the appropriate cellular compartment. Here we applied dynamic force spectroscopy to study t...

Envelope-free chloroplasts were imaged in situ by contact and tapping mode scanning force microscopy at a lateral resolution of 3-5 nm and vertical resolution of approximately 0.3 nm. The images of the intact thylakoids revealed detailed structural features of their surface, including individual protein complexes over stroma, grana margin and grana...

Plants respond to excess light by a photoprotective reduction of the light harvesting efficiency. The notion that the non-photochemical quenching of chlorophyll fluorescence can be reliably used as an indicator of the photoprotection is put to a test here. The technique of the repetitive flash fluorescence induction is employed to measure in parall...

Fluorometers that measure the kinetics of chlorophyll fluorescence have become invaluable tools for determining the photosynthetic performance of plants. Many of these instruments use high frequency modulated light to measure the rate, efficiency and regulation of photosynthesis. The technique is non-invasive and is effective under diverse environm...

A modification of the double-modulation fluorometer is described that allows measuring very dilute phytoplankton samples. The high sensitivity is achieved by increasing the sample volume and by collecting the fluorescence from the large volume by an integrating sphere. The sensitivity of the instrument increased approximately proportionally to the...

The photosynthetic activity of the green alga Scenedesmus quadricauda was investigated during synchronous growth in light/dark cycles. The rate of O2 evolution increased 2-fold during the first 3 to 4 h of the light period, remained high for the next 3 to 4 h, and then declined during the last half of the light period. During cell division, which o...

The photosynthetic activity of the green alga Scenedesmus quadricauda was investigated during synchronous growth in light/dark cycles. The rate of O2 evolution increased 2-fold during the first 3 to 4 h of the light period, remained high for the next 3 to 4 h, and then declined during the last half of the light period. During cell division, which o...

We demonstrate that arrays of light-emitting diodes can be used to generate single-turnover flashes of light that saturate QA reduction in green algae. The fast version of a double-modulation fluorometer can measure induction during a single-turnover saturating flash (flash fluorescence induction). The method allows the effective antenna size, ante...

Synchronous cultures of algae have been repeatedly shown to exhibit a periodic modulation of the metabolic activity. In algal cells synchronized by light/dark periods, the photosynthetic activity exhibits a maximum during the early light period of the cell cycle and, then, declines to the lowest levels during cell division. Despite decades of resea...

Single-turnover saturating flashes of light are used to induce synchronous operation of Photosystem II reaction centers. The flash must be so short that the frequency of double-turnovers is negligible and must be powerful enough to turnover all reaction centers. The flashes produced by Xe flashlamps suffer from a flash-to-flash variability and from...