Oxygen Evolution Measurements Research Articles

Polydopamine-coated photoautotrophic bacteria for improving extracellular electron transfer in living photovoltaics

Living photovoltaics are microbial electrochemical devices that use whole cell–electrode interactions to convert solar energy to electricity. The bottleneck in these technologies is the limited electron transfer between the microbe and the electrode surface. This study focuses on enhancing this transfer by engineering a polydopamine (PDA) coating on the outer membrane of the photosynthetic microbe Synechocystis sp. PCC6803. This coating provides a conductive nanoparticle shell to increase electrode adhesion and improve microbial charge extraction. A combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–Vis absorption, and Raman spectroscopy measurements were used to characterize the nanoparticle shell under various synthesis conditions. The cell viability and activity were further assessed through oxygen evolution, growth curve, and confocal fluorescence microscopy measurements. The results show sustained cell growth and detectable PDA surface coverage under slightly alkaline conditions (pH 7.5) and at low initial dopamine (DA) concentrations (1 mM). The exoelectrogenicity of the cells prepared under these conditions was also characterized through cyclic voltammetry (CV) and chronoamperometry (CA). The measurements show a three-fold enhancement in the photocurrent at an applied bias of 0.3 V (vs. Ag/AgCl [3 M KCl]) compared to non-coated cells. This study thus lays the framework for engineering the next generation of living photovoltaics with improved performances using biosynthetic electrodes.

Effects of light quality and intensity on growth and bromoform content of the red seaweed Asparagopsis taxiformis

AbstractSpecies of the genus Asparagopsis are rich in halogenated bioactive compounds, particularly bromoform. Its use as a feed additive in ruminant livestock drastically decreases the animal’s methane production, thereby reducing the industry’s environmental impact. Addressing the high demand for Asparagopsis biomass requires the understanding of the culture conditions that promote higher growth rates and bromoform content. Here we evaluated how different light quality combinations (High-Blue:Red, Medium Blue:Red, High-Blue:Green:Red, and White) and four light intensities (30, 60, 90 and 120 μmol photons m−2 s−1) affect the growth and bromoform content of the Asparagopsis taxiformis tetrasporophyte in indoor tumbling cultures at two biomass densities. We also assessed the effect of light intensity on the photosynthetic response by measuring oxygen evolution rates. Light spectra containing intermediate wavelengths promoted higher growth, regardless of biomass density. Of the different light qualities tested, white light promoted the highest bromoform content. Increasing light intensity led to a positive response in A. taxiformis growth. However, the photosynthetic parameters estimated showed that the two higher light intensity treatments were above the saturation irradiance, for both culture densities. This, along with the observed development of contamination, suggests that long-term cultures of A. taxiformis should be maintained at light intensities no higher than 60 μmol photons m−2 s−1. In addition, we found that exposing cultures to higher irradiances does not guarantee a bromoform-richer biomass. These results offer valuable insights for optimizing biomass and bioactive compound production in indoor cultures of the Asparagopsis genus.

Salinity-induced changes in plastoquinone pool redox state in halophytic Mesembryanthemum crystallinum L.

We have analyzed the effect of salinity on photosystem II (PSII) photochemistry and plastoquinone (PQ) pool in halophytic Mesembryanthemum crystallinum plants. Under prolonged salinity conditions (7 or 10 days of 0.4 M NaCl treatment) we noted an enlarged pool of open PSII reaction centers and increased energy conservation efficiency, as envisaged by parameters of the fast and slow kinetics of chlorophyll a fluorescence. Measurements of oxygen evolution, using 2,6-dichloro-1,4-benzoquinone as an electron acceptor, showed stimulation of the PSII activity due to salinity. In salt-acclimated plants (10 days of NaCl treatment), the improved PSII performance was associated with an increase in the size of the photochemically active PQ pool and the extent of its reduction. This was accompanied by a rise in the NADP+/NADPH ratio. The presented data suggest that a redistribution of PQ molecules between photochemically active and non-active fractions and a change of the redox state of the photochemically active PQ pool indicate and regulate the acclimation of the photosynthetic apparatus to salinity.

Photosynthesis Monitoring in Microalgae Cultures Grown on Municipal Wastewater as a Nutrient Source in Large-Scale Outdoor Bioreactors.

Simple SummaryThe remediation of waste nutrients, mainly nitrogen, phosphorous, and carbon, results in low-cost biomass production. In this work, raceway ponds with an area of 1 and 0.5 ha were built in Mérida, Spain next to a municipal wastewater (WW) treatment plant. These DEMO bioreactors are operated continuously all year round. At the start of the trials, the bioreactors were filled with urban WW as a sole source of nutrients and left to be populated by the sewage-born phytoplankton. The fitness and growth of the phytoplankton population (dominated by the green microalga Micractinium) were monitored by photosynthesis measuring techniques. The cultures showed suitable photosynthetic activity. Productivity values ranged between 15 and 25 g DW m−2 day−1 and processed biomass revealed biostimulating activity. In these trials, photosynthesis measuring techniques, i.e., oxygen evolution and chlorophyll (Chl) fluorescence techniques, were validated to monitor large-scale bioreactors using municipal WW remediation for biomass production, which can be used for agricultural purposes as biofertilizer/biostimulant.Microalgae cultures were used for a WW treatment to remediate nutrients while producing biomass and recycling water. In these trials, raceway ponds (RWPs; 1 and 0.5 ha) were located next to a municipal (WW) treatment plant in Mérida, Spain. The ponds were used for continuous, all-year-round microalgae production using WW as a source of nutrients. Neither CO2 nor air was supplied to cultures. The objective was to validate photosynthesis monitoring techniques in large-scale bioreactors. Various in-situ/ex-situ methods based on chlorophyll fluorescence and oxygen evolution measurements were used to follow culture performance. Photosynthesis variables gathered with these techniques were compared to the physiological behavior and growth of cultures. Good photosynthetic activity was indicated by the build-up of dissolved oxygen concentration up to 380% saturation, high photochemical yield (Fv/Fm = 0.62–0.71), and relative electron transport rate rETR between 200 and 450 μmol e− m−2 s−1 at midday, which resulted in biomass productivity of about 15–25 g DW m−2 day−1. The variables represent reliable markers reflecting the physiological status of microalgae cultures. Using waste nutrients, the biomass production cost can be significantly decreased for abundant biomass production in large-scale bioreactors, which can be exploited for agricultural purposes.

Unexpected Boost in Activity of a Cu(I) Photosensitizer by Stabilizing a Transient Excited State.

In this study, we present a slight but surprisingly successful structural modification of the previously reported heteroleptic Cu(I) photosensitizer Cubiipo ([(xantphos)Cu(biipo)]PF6; biipo = 16H-benzo-[4',5']-isoquinolino-[2',1':1,2]-imidazo-[4,5-f]-[1,10]-phenanthrolin-16-one). As a key feature, biipo bears a naphthalimide unit at the back, which is directly fused to a phenanthroline moiety to extend the conjugated π-system. This ligand was now altered to include two additional methyl groups at the 2,9-positions at the phenanthroline scaffold. Comparing the novel Cudmbiipo complex to its predecessor, ultrafast transient absorption spectroscopy reveals the efficient suppression of a major deactivation pathway by stabilization of a transient triplet state. Furthermore, quantitative measurements of singlet oxygen evolution in solution confirmed that a larger fraction of the excited-state population is transferred to the photocatalytically active ligand-centered triplet 3LC state with a much longer lifetime of ∼30 μs compared to Cubiipo (2.6 μs). In addition, Cudmbiipo was compared with the well-established reference complex Cubcp ([(xantphos)Cu(bathocuproine)]PF6) in terms of its photophysical and photocatalytic properties by applying time-resolved femto- and nanosecond absorption, step-scan Fourier transform infrared (FTIR), and emission spectroscopies. Superior light-harvesting properties and a greatly enhanced excited-state lifetime with respect to Cubcp enable Cudmbiipo to be more active in exemplary photocatalytic applications, i.e., in the formation of singlet oxygen and the isomerization of (E)-stilbene.

Living Photovoltaics Based on Recombinant Expression of Mtra Decaheme in Photosynthetic Bacteria

At the center of microbial bioelectricity applications lies the critical need to express foreign heme proteins that are capable of redirecting the electron flux of the cell’s metabolism. This study presents a genetic construct for the heterologous expression of the periplasmatic decaheme MtrA c-type cytochrome from S. oneidensis MR-1, a dissimilatory metal-reducing exoelectrogen, inside the light-harvesting bacterium, Synechocystis sp. PCC 6803. Protein expression was verified through western-blotting and immunostaining, and oxygen evolution, optical density, and absorption measurements confirm sustained cell activity and viability under the tested expression conditions. Furthermore, the bioengineered cells show enhanced mediated exoelectrogenicity, as confirmed through a colorimetric iron assay and electrochemical measurements. Compared to wildtype cells on graphite electrodes, the bioengineered cells show a 2-fold increased extracellular electron transfer. The increased capacitance obtained under illumination and suppressed photocurrents in the presence of the photosynthetic inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) suggest increased extraction of photosynthetically derived electrons from the recombinant cells. The improved bioelectricity transport across the outer membranes, as achieved through the heterologous heme expression inside cyanobacteria, presents new opportunities for re-wiring the metabolisms of light-harvesting microbes.

In Vivo Evaluation of Oxygenic Photogranules’ Photosynthetic Capacity by Pulse Amplitude Modulation and Phototrophic–Irradiance Curves

The commingled microbial moiety of oxygenic photogranules (OPGs) facilitates aeration-free wastewater treatment. Embedded in an extracellular polymeric substances (EPS) matrix, microbial producers and consumers of oxygen occupying granular niches exchange substrates among themselves and with the bulk fluid. An assessment of the OPG’s phototrophic potential or functional capacity may require combining different photoactivity signals. The photosynthetic capacity was evaluated using photosynthetic oxygen evolution (POE) and chlorophyll fluorescence (rapid light curves, RLC) measurements using OPGs grown at different light intensities.. A maximum oxygen generating capacity for optimal OPGs and reactor conditions was determined to be 284.4 mgO2 gVSS–1 h–1 The OPGs exhibited photoelasticity, with higher photosynthetic capacity in high light (HL) compared to that in low light (LL) adapted samples. Saturation irradiances before the onset of photoinhibition for LL and HL samples were 1000 and 1200 μmol m–2 s–1, respectively using POE signals, and 478 μmol m–2 s–1 and 611 μmol m–2 s–1 using RLC signals. Moreover, HL adapted samples had higher nonphotochemical quenching rates which allude to the OPG’s photoelastic potential. The correlation coefficients (κ) between POE and RLCs were lower than reported values for pure microbial cultures reflecting the enhanced contribution from different photosynthetic clades with a variety of light-harvesting pigments present in OPGs. In an OPG reactor, the photochemical activity can be influenced by the granular size, granular ecology, and reactor operation metrics related to irradiance interactions such as mixing, self-shading, light intensity, photoperiods, and reactor depth. This presents opportunities for design of intensive wastewater resource recovery using phototrophic granular biomass.

In-vivo quantification of electron flow through photosystem I – Cyclic electron transport makes up about 35% in a cyanobacterium

Photosynthetic electron flow, driven by photosystem I and II, provides chemical energy for carbon fixation. In addition to a linear mode a second cyclic route exists, which only involves photosystem I. The exact contributions of linear and cyclic transport are still a matter of debate. Here, we describe the development of a method that allows quantification of electron flow in absolute terms through photosystem I in a photosynthetic organism for the first time. Specific in-vivo protocols allowed to discern the redox states of plastocyanin, P700 and the FeS-clusters including ferredoxin at the acceptor site of PSI in the cyanobacterium Synechocystis sp. PCC 6803 with the near-infrared spectrometer Dual-KLAS/NIR. P700 absorbance changes determined with the Dual-KLAS/NIR correlated linearly with direct determinations of PSI concentrations using EPR. Dark-interval relaxation kinetics measurements (DIRKPSI) were applied to determine electron flow through PSI. Counting electrons from hydrogen oxidation as electron donor to photosystem I in parallel to DIRKPSI measurements confirmed the validity of the method. Electron flow determination by classical PSI yield measurements overestimates electron flow at low light intensities and saturates earlier compared to DIRKPSI. Combination of DIRKPSI with oxygen evolution measurements yielded a proportion of 35% of surplus electrons passing PSI compared to PSII. We attribute these electrons to cyclic electron transport, which is twice as high as assumed for plants. Counting electrons flowing through the photosystems allowed determination of the number of quanta required for photosynthesis to 11 per oxygen produced, which is close to published values.

Oxygen-evolution reaction by nickel/nickel oxide interface in the presence of ferrate(VI)

In this study, we investigate the effect of K2FeO4, as a new and soluble Fe salt at alkaline conditions, on oxygen-evolution reaction (OER) of Ni oxide. Both oxidation and reduction peaks for Ni in the presence and absence of Fe are linearly changed by (scan rate)1/2. Immediately after the interaction of [FeO4]2- with the surface of the electrode, a significant increase in OER is observed. This could be indicative of the fact that either the [FeO4]2- on the surface of Ni oxide is directly involved in OER, or, it is important to activate Ni oxide toward OER. Due to the change in the Ni(II)/(III) peak, it is hypothesized that Fe impurity in KOH or electrochemical cell has different effects at the potential range. At low potential, [FeO4]2− is reduced on the surface of the electrode, and thus, is significantly adsorbed on the electrode. Finally, oxygen-evolution measurements of K2FeO4 and Ni2O3 are investigated under chemical conditions. K2FeO4 is not stable in the presence of Ni(II) oxide, and OER is observed in a KOH solution (pH ≈ 13).

Efficient In Vivo Screening Method for the Identification of C4 Photosynthesis Inhibitors Based on Cell Suspensions of the Single-Cell C4 Plant Bienertia sinuspersici.

The identification of novel herbicides is of crucial importance to modern agriculture. We developed an efficient in vivo assay based on oxygen evolution measurements using suspensions of chlorenchyma cells isolated from the single-cell C4 plant Bienertia sinuspersici to identify and characterize inhibitors of C4 photosynthesis. This novel approach fills the gap between conventional in vitro assays for inhibitors targeting C4 key enzymes and in vivo experiments on whole plants. The assay addresses inhibition of the target enzymes in a plant context thereby taking care of any reduced target inhibition due to metabolization or inadequate uptake of small molecule inhibitors across plant cell walls and membranes. Known small molecule inhibitors targeting C4 photosynthesis were used to validate the approach. To this end, we tested pyruvate phosphate dikinase inhibitor bisindolylmaleimide IV and phosphoenolpyruvate carboxylase inhibitor okanin. Both inhibitors show inhibition of plant photosynthesis at half-maximal inhibitory concentrations in the sub-mM range and confirm their potential to act as a new class of C4 selective inhibitors.

3D MnCo2O4@CoS nanoarrays with different morphologies as an electrocatalyst for oxygen evolution reaction

The efficiency and stability of electrocatalysts are the key factors for measuring oxygen evolution reaction. In this work, the MnCo2O4 structure assembled from well-arranged nanowires or nanosheet arrays has been grown vertically on nickel foam by in-situ hydrothermal method. Interestingly, different morphology of MnCo2O4 can be easily regulated by adding NH4F to a mixed solvent to achieve conversion from nanowires to nanosheets. In addition, further synthesis of unique three-dimensional hierarchical core/shell MnCo2O4@CoS nanowires or nanosheets arrays was performed primarily by electrochemical deposition. Both MnCo2O4@CoS-7 cycles nanowires and MnCo2O4@CoS-7 cycles nanosheets exhibit high efficiency and long-lasting stability for the oxygen oxidation reaction. The lower overpotential of only 280 mV and 270 mV at 20 mA cm−2 for the MnCo2O4@CoS-7 cycles nanowires and MnCo2O4@CoS-7 cycles nanosheets were obtained with lower Tafel slopes of 139. 19 mV dec−1 and 131.81 mV dec−1 in 1.0 M potassium hydroxide respectively comparing with our other MnCo2O4@CoS catalysts. The results demonstrate that the crystal morphology of MnCo2O4@CoS does not significantly influence their electrocatalytic activity in water oxidation reactions by comparing nanostructured MnCo2O4@CoS nanowires and MnCo2O4@CoS nanosheets. The high catalytic activity of the MnCo2O4@CoS nanoarrays is attributed to the possession of more active sites, larger specific surface area, abundant oxygen vacancy, and fast electron transport rate. Not only that, the durability of the MnCo2O4@CoS nanoarrays is also excellent after continuous oxygen evolution test of 1000 cycles. The results of XRD, SEM and XPS show that MnCo2O4@CoS-7 cycles nanowires and MnCo2O4@CoS-7 cycles nanosheets materials can be used as a highly efficient and stable catalyst for oxygen evolution reaction.

Initial testing and adaptation of a new method for measuring oxygen evolution from mixed metal oxides.

SARAH STARCOVIC, ISAAC BOYCE, KAYLEE ANDERSEN, LINDSEY LANEVE, ASHLEY RUZA, ALLISON MOORE, and ERICA HARVEY, Dept. of Natural Sciences, Fairmont State University, Fairmont, WV, 26554. Initial testing and adaptation of a new method for measuring oxygen evolution from mixed metal oxides. The oxygen generating capacity of mixed metal oxides deposited on a conductive glass sample plate is currently tested in our lab with a fluorescence-based device called HARPOON (Heterogeneous Anodes Rapidly Perused for Oxygen Evolution), developed and disseminated as part of the nationwide Solar Army research initiative. The research goal of the Solar Army is to find metal oxide combinations that speed up the splitting of water, with the ultimate goal of creating a device for solar hydrogen fuel generation. If a new metal oxide combination is more effective at oxygen generation than the internal standards included on every sample, this may indicate a promising catalyst. A recent literature paper outlined a new method to test for oxygen evolution that could potentially make our research and outreach significantly easier. A sample plate to be tested for oxygen evolution is placed in a suspension of TiO2nanoparticles in an electrolyte. As a voltage is applied and oxygen is produced at the surface of the metal oxides, oxygen gas bubbles are nucleated by the TiO2and visualized by light scattering. This work reports on the initial testing and adaptation of the literature method to our undergraduate laboratory setting. A preliminary comparison of results obtained from HARPOON and HARPOON 2.0 will be presented, along with an analysis of the pros and cons of the two methods. This research has been supported by the Fairmont State University College of Science and Technology as well as the NASA WV Space Grant Consortium.

Photosynthetic activity assessment in mixotrophically cultured Chlorella vulgaris biofilms at various developmental stages

Biofilm reactors have been used to grow the microalga Chlorella vulgaris, which under mixotrophic conditions can effectively grow as biofilm with reduced liquid volumes and low energy consumption requirements. Under mixotrophic conditions, CO2 is internally generated and can be reduced to carbohydrates or lipids, with changes in gene expression. However, our knowledge of the photosynthetic activity and gene expression profiles of C. vulgaris cultured in a biofilm reactor using glycerol and urea in the absence of external CO2 is limited. Our goal was to assess the 1) chlorophyll-a fluorescence, 2) oxygen evolution, and 3) gene expression levels of C. vulgaris biofilms in the exponential growth (0–96 h) and stationary phases at the onset of lipid biosynthesis (168 h). The maximum quantum efficiency of PSII (Fv/Fm) varied between 0.64 and 0.69, indicating no stress during growth for the mixotrophic C. vulgaris biofilms. In photosynthetic oxygen evolution measurements C. vulgaris mixotrophic cells exhibited dark respiration (higher than 25 mg O2 mg Chl-a−1 s−1); at the same time, they were photosynthetically active with electron transport rate (ETR) values up to 50 μmol electrons m−2 s−1. The change in gene expression of light-regulated enzymes linked to carbon fixation, such as rbcl, was slightly higher in the stationary phase, while the gene expression of other enzymes, such as G3PD and PRK, was reduced in 168-hour-old biofilms. On the other hand, the gene expression of MDH for carbon metabolism and of enzymes ACC and DGAT for lipid biosynthesis was upregulated in 168-hour-old biofilms. These results show that in algal biofilms under mixotrophic growth conditions, autotrophy is not limited by glycerol and is fully complemented by the heterotrophic metabolism through a cycle in which photosynthesis utilizes the CO2 released by the respiration of C. vulgaris in the presence of glycerol and urea.

High-light selection produces a fast-growing Picochlorum celeri

A new species of marine algae Picochlorum celeri was obtained by enriching for fast reproductive rates under constant high irradiance in semi-continuous culture. Several rapidly-growing cell lines were isolated from the enrichment culture by bringing up cultures from single cells in very high light. Therefore, individual cells are very resilient to inhibition by light. This is a prominent characteristic of this P. celeri in all cell lines. Measured oxygen evolution rates were unusually high. One of these lines is able to double in as short as 2.0 h. Doubling times of other cell lines were between 2.4 and 3.5 h. This species is characterized by high pigment content, high absorption cross section, and an antenna size that is very responsive to irradiance becoming very small at high irradiance.

Improvement of the rice photosynthetic apparatus defence under cadmium stress modulated by salicylic acid supply to roots

The present study was conducted to investigate the effect of exogenous salicylic acid (SA) added to the nutrient solution on the growth parameters and the functions of the photosynthetic apparatus of rice plants under cadmium (Cd) stress. Our investigations have shown that 10 µM SA has an optimal effect in rice plants grown hydroponically. Pulse amplitude modulated chlorophyll fluorescence, low-temperature chlorophyll fluorescence, oxygen evolution (measured with Clark-type and Joliot-type electrodes) and P700 photo-oxidation measurements were carried out to assess the effect of SA on the activity of the photosynthetic apparatus. The levels of three important parameters associated with oxidative stress (hydrogen peroxide, lipid peroxidation and proline content) were measured. The application of low concentration of SA significantly decreased the levels of hydrogen peroxide, lipid peroxidation and proline under Cd stress. The results revealed that low concentration of SA, applied in plants exposed to 150 µM CdCl2, significantly improves plant growth, photochemical activities of both photosystems, the electron flow from QA to plastoquinone, energetic distribution between pigment-protein complexes and the kinetic parameters of oxygen-evolving reactions. This study suggests that exogenous application of 10 µM SA through the rooting medium has a protective effect against Cd toxicity in rice plants. The possible molecular mechanisms involved in the defence effect of SA on the function of photosynthetic apparatus are discussed.

An optimized protocol for the preparation of oxygen-evolving thylakoid membranes from Cyclotella meneghiniana provides a tool for the investigation of diatom plastidic electron transport

BackgroundThe preparation of functional thylakoid membranes from diatoms with a silica cell wall is still a largely unsolved challenge. Therefore, an optimized protocol for the isolation of oxygen evolving thylakoid membranes of the centric diatom Cyclotella meneghiniana has been developed. The buffer used for the disruption of the cells was supplemented with polyethylene glycol based on its stabilizing effect on plastidic membranes. Disruption of the silica cell walls was performed in a French Pressure cell and subsequent linear sorbitol density gradient centrifugation was used to isolate the thylakoid membrane fraction.ResultsSpectroscopic characterization of the thylakoids by absorption and 77 K fluorescence spectroscopy showed that the photosynthetic pigment protein complexes in the isolated thylakoid membranes were intact. This was supported by oxygen evolution measurements which demonstrated high electron transport rates in the presence of the artificial electron acceptor DCQB. High photosynthetic activity of photosystem II was corroborated by the results of fast fluorescence induction measurements. In addition to PSII and linear electron transport, indications for a chlororespiratory electron transport were observed in the isolated thylakoid membranes. Photosynthetic electron transport also resulted in the establishment of a proton gradient as evidenced by the quenching of 9-amino-acridine fluorescence. Because of their ability to build-up a light-driven proton gradient, de-epoxidation of diadinoxanthin to diatoxanthin and diatoxanthin-dependent non-photochemical quenching of chlorophyll fluorescence could be observed for the first time in isolated thylakoid membranes of diatoms. However, the ∆pH, diadinoxanthin de-epoxidation and diatoxanthin-dependent NPQ were weak compared to intact diatom cells or isolated thylakoids of higher plants.ConclusionsThe present protocol resulted in thylakoids with a high electron transport capacity. These thylakoids can thus be used for experiments addressing various aspects of the photosynthetic electron transport by, e.g., employing artificial electron donors and acceptors which do not penetrate the diatom cell wall. In addition, the present isolation protocol yields diatom thylakoids with the potential for xanthophyll cycle and non-photochemical quenching measurements. However, the preparation has to be further refined before these important topics can be addressed systematically.

A Rapid and Efficient Method to Obtain Photosynthetic Cell Suspension Cultures of Arabidopsis thaliana.

Photosynthetic cell suspension cultures are a useful experimental system to analyze a variety of physiological processes, bypassing the structural complexity of the plant organism in toto. Nevertheless, cell cultures containing functional chloroplasts are quite difficult to obtain, and this process is usually laborious and time-consuming. In this work a novel and rapid method to set up photosynthetic cell suspension cultures from the model plant Arabidopsis thaliana was developed. The direct germination of Arabidopsis seeds on a sucrose-containing agarized culture medium supplemented with 0.25 μg/ml 6-benzylaminopurine and 0.5 μg/ml 2,4-dichlorophenoxyacetic acid caused the straightforward formation of green calli at the level of seedling hypocotyls. The subsequent transfer of these calli in liquid culture medium containing the same concentrations of phytohormones and gradually decreasing sucrose levels allowed for the establishment of chloroplast-containing cell suspension cultures, containing functional chloroplasts, in a much faster way than previously described procedures. Pulse amplitude modulation analyses, measurements of oxygen evolution and electron transport rate, together with confocal and electron microscopy observations, confirmed the photosynthetic efficiency of these cell suspension cultures. The described procedure lends itself as a simple and effective way to obtain a convenient tool for a wide array of structural and functional studies on chloroplasts.

Corrigendum: Commercially Available WO3 Nanopowders for Photoelectrochemical Water Splitting: Photocurrent versus Oxygen Evolution

During re-evaluation of some data presented in this article, we noticed an error in the units for the oxygen on the y-axes in Figure 1. We re-calculated the values and corrected the figure. We regret this mistake, however, the conclusions are unaffected by this Corrigendum, because the ratio between the observed and theoretical amounts of oxygen were used for the discussion. Oxygen evolution measurements of WO3 photoanodes prepared from the Aldrich nanopowder in different electrolytes: a) 1 m CH3SO3H, b) 1 m H2SO4, c) 0.1 m Na2SO4 at pH 3, and d) 0.1 m Na2SO4 at pH 5.5.

Hydrogen Production by a Chlamydomonas reinhardtii Strain with Inducible Expression of Photosystem II.

Chlamydomonas reinhardtii cy6Nac2.49 is a genetically modified algal strain that activates photosynthesis in a cyclical manner, so that photosynthesis is not active constitutively in the presence of oxygen, but is turned on only in response to a metabolic trigger (anaerobiosis). Here, we further investigated hydrogen production by this strain comparing it with the parental wild-type strain under photoheterotrophic conditions in regular tris-acetate-phosphate (TAP) medium with a 10-h:14-h light/dark regime. Unlike the wild-type, whose level of H2 production remained low during illumination, H2 production in the mutant strain increased gradually with each subsequent light period, and by the final light period was significantly higher than the wild-type. The relatively low Photosystem II (PSII) activity of the mutant culture was shown by low fluorescence yield both in the dark (Fv/Fm) and in the light (δF/Fm’) periods. Measurement of oxygen evolution confirmed the low photosynthetic activity of the mutant cells, which gradually accumulated O2 to a lesser extent than the wild-type, thus allowing the mutant strain to maintain hydrogenase activity over a longer time period and to gradually accumulate H2 during periods of illumination. Therefore, controllable expression of PSII can be used to increase hydrogen production under nutrient replete conditions, thus avoiding many of the limitations associated with nutrient deprivation approaches sometimes used to promote hydrogen production.

The freshwater red alga Batrachospermum turfosum (Florideophyceae) can acclimate to a wide range of light and temperature conditions

ABSTRACT Batrachospermum turfosum Bory is one of the generalists among the few red algae that have adapted to freshwater habitats, occurring in a variety of primarily shaded, nutrient-poor micro-habitats with lotic (running) or lentic (standing) waters. Seasonal variations in water level and canopy cover can expose this sessile alga to widely fluctuating temperatures, solar irradiation and nutrient availability. Here we report on the ecophysiology of B. turfosum collected from an ultra-oligotrophic bog pool in the Austrian Alps. Photosynthesis as a function of photon fluence density (PFD) and temperature was studied by measuring oxygen evolution in combination with chlorophyll fluorescence. In addition, the effects of ultraviolet radiation (UVR) on photosynthetic pigments were analysed using HPLC and spectrophotometric methods, and cellular ultrastructure was studied using transmission electron microscopy. We found that B. turfosum is adapted to low light, with a light compensation point (I c) and a light saturation point (I k) of 8.4 and 29.7 µmol photons m–2 s–1, respectively, but also tolerates higher PFDs of ~1000 µmol photons m–2 s–1, and is capable of net photosynthesis at temperatures between 5°C and 35°C. Exposure to either UV-A or UV-AB for 102 h led to a strong transient drop in effective quantum yield (ΔF/FM’), followed by an acclimation to about 70% of initial ΔF/FM’ values. Ultrastructural changes included the accumulation of plastoglobules and dilated membranes after UVR treatment. Although all photosynthetic pigments strongly decreased upon UVR exposure and no UV-photoprotectants (e.g. mycosporine-like amino acids) could be detected, the alga was capable of recovering ΔF/FM’ and phycobiliproteins after UVR treatment. In summary, B. turfosum tolerates a wide range of irradiation and temperature regimes, and these traits may be the basis for its successful adaptation to challenging environments.