Visible light induced hydrogen production with Mg chlorophyll-a from spirulina and colloidal platinum

Photoinduced hydrogen production with Mg chlorophyll-a from spirulina as a visible light photosensitizer by use of three component system consisting of nicotineamide adenine dinucleotide phosphate, reduced form (NADPH) as an electron donor, methylviologen as electron relay reagent and colloidal platinum as hydrogen evolution catalyst was investigated. By the addition of NADPH, the photostability of Mg chlorophyll-a was increased. The effective visible-light induced hydrogen production system with colloidal platinum was established using Mg chlorophyll-a.     

H2 production from maltose derived from starch using the visible light, photosensitization of Mg chlorophyll-a from Spirulina

A photoinduced H₂ production system, coupling d-maltose degradation by glucoamylase and glucose dehydrogenase (GDH) and H₂ production with colloidal platinum as a catalyst using the visible light-induced photosensitization of Mg chlorophyll-a (Mg Chl-a), has been developed. H₂ production was continuous when the reaction mixture containing d-maltose, glucoamylase, GDH, NAD⁺, Mg Chl-a, Methyl Viologen (MV²⁺, an electron relay reagent) and colloidal platinum was irradiated by visible light. The amount of H₂ production was estimated to be 5 ± 0.5 mol after 4 h irradiation. The yield of the conversion of d-maltose to H₂ in this system was ca. 1.8 %.     

Photoinduced H2 production with Mg chlorophyll-a from Spirulina and colloidal platinum by visible light

Photoinduced H₂ production with Mg chlorophyll-a from Spirulina as a visible light photosensitizer by use of a three component system consisting of NADPH as an electron donor, Methyl Viologen as electron relay and colloidal platinum as catalyst was investigated. By using this system, the H₂ production rate was estimated to be 0.70 ± 0.03 × 10^–6 mol h^–1.     

Visible light-induced H2 production from cellulose using photosensitization of Mg chlorophyll a

A photoinduced-H₂ production system, coupling cellulose degradation by cellulase and glucose dehydrogenase (GDH) and H₂ production with colloidal Pt as a catalyst using the visible light-induced photosensitization of Mg chlorophyll a, has been developed. When the sample solution containing methylcellulose, cellulase, GDH, NAD⁺, Mg chlorophyll a, Methyl viologen and colloidal Pt was irradiated, continuous H₂ production was observed. The amount of H₂ production was about 12 mol after 4 h irradiation.     

Visible light induced biohydrogen production from sucrose using the photosensitization of Mg chlorophyll-a

A photoinduced hydrogen production system, coupling sucrose degradation with invertase and glucose dehydrogenase (GDH) and hydrogen production with colloidal platinum as a catalyst using the visible light-induced photosensitization of Mg chlorophyll-a (Mg Chl-a), has been developed. Continuous hydrogen gas production was observed when the reaction mixture containing sucrose, invertase, GDH, nicotinamide adenine dinucleotide (NAD(+)), Mg Chl-a, methyl viologen (MV(2+), an electron relay reagent), and colloidal platinum was irradiated by visible light.     

Biohydrogen production from sucrose using the visible light sensitization of artificial Zn chlorophyll-a

A photoinduced hydrogen production system that couples sucrose degradation with invertase and glucose dehydrogenase (GDH) and hydrogen production with colloidal platinum as a catalyst using visible light-induced photosensitization of artificial Zn chlorophyll-a (Zn Chl-a) has been developed. Continuous hydrogen gas production over more than 240 min was observed when the reaction mixture containing sucrose, invertase, GDH, nicotinamide adenine dinucreotide (NAD(+)), Zn Chl-a, methyl viologen (MV(2+), an electron relay reagent), and colloidal platinum was irradiated by visible light. Zn Chl-a was superior to that of Mg Chl-a in photostability and photosensitization activity.     

Light-harvesting properties of zinc complex of chlorophyll-<Emphasis Type="Italic">a</Emphasis> from <Emphasis Type="Italic">spirulina</Emphasis> in surfactant micellar media

Zn chlorophyll-a was prepareted from Mg chlorophyll-a from spirulina and the optical properties of the ground state and the photoexited state of Zn chlorophyll-a in aqueous surfactant micellar media were studied using UV-vis absorption, fluorescence emission spectra, electrochemical and fluorescence lifetime measurements. In comparison of the UV-vis absorption and fluorescence emission spectra of Zn chlorophyll-a and Mg chlorophyll-a, the blue-shift in the absorption bands and emission peak of Zn chlorophyll-a was observed. The energies of the first excited singlet state of Zn chlorophyll-a was 1.87eV. The first oxidation and reduction potentials of the photoexcited singlet state of Zn chlorophyll-a were −0.67 and 0.60V, respectively. Fluorescence lifetime of Zn chlorophyll-a was 9.0 ns in CTAB micellar solution. The fluorescence lifetime of Zn chlorophyll-a is shorter than that of Mg chlorophyll-a (9.8 ns). The photositability of Zn chlorophyll-a was superior to that of Mg chlorophyll-a in various pH conditions. Published online December 2004     

Bio-mimetic hydrogen production from polysaccharide using the visible light sensitization of zinc porphyrin

A biohydrogen production system coupling the polysaccharide such as sucrose and maltose degradation with invertase and glucose dehydrognase (GDH) and hydrogen production with colloidal platinum as hydrogen-evolved catalyst using the visible light-induced photosensitization of water-soluble zinc porphyrin, zinc tetraphenylporphyrin tetrasulfonate (ZnTPPS) has been investigated. Continuous hydrogen gas production was observed when the sample solution containing polysaccharide, invertase, GDH, nicotinamide adenine dinucreotide (NAD(+)), ZnTPPS, methylviologen (an electron relay reagent), and colloidal platinum was irradiated by visible light. After 240-min irradiation, the amount of hydrogen production in the system using sucrose and maltose was estimated to be 3.1 and 0.35 micromol, respectively.     

In situ nutrient assays of periphyton growth in a lowland Costa Rican stream

Nutrient limitation of primary production was experimentally assessed using an in situ bioassay technique in the Quebrada Salto, a third-order tropical stream draining the northern foothills of the Cordillera Central in Costa Rica. Bioassays employed artificial substrata enriched with nutrients that slowly diffuse through an agar-sand matrix (Pringle & Bowers, 1984). Multiple comparisons of regression coefficients, describing chlorophyll-a accrual through time for different nutrient treatments, revealed positive micronutrient effect(s). Micronutrient treatment combinations (Fe, B, Mn, Zn, Co, Mo, EDTA), supplemented with and without nitrate and phosphate, exhibited significantly greater chlorophyll-a accrual over all other treatments (P < 0.05), supporting over three times that of the control after 14-d of substratum colonization. Neither of the major nutrients (N or P) produced a significant stimulation, although the N treatment displayed 50% more chlorophyll-a than the control after 14-d. Similarly, Si, EDTA, and Si + N + P treatments did not exhibit chlorophyll-a response curves that were significantly different from the control. During the experiment, mean NH₄-N and (NO₂ + NO₃)-N concentrations in the Salto were 2.0 µM (28.6 µg · l^–1) and 7.2 µM (100.2 µg · l ^–1), respectively. High concentrations of PO₄-P ( = 2.0 µM; 60.9 µg · l^–1) and TP ( = 3.0 µM; 94.0 µg · l^–1) were also found, and consequently low molar N:P ratios = 4.7). Despite the potential for N limitation in the system, both N and P appear to be at growth saturating levels. This may be due to micronutrient limitation and/or light limitation of periphyton growth in densely shaded upstream portions of the stream.     

Dynamics and distribution of microphytobenthic chlorophyll-a in the Western Scheldt estuary (SW Netherlands)

The temporal dynamics and spatial distribution of microphytobenthic chlorophyll-a in the layer 0–1 cm were determined in the Western Scheldt estuary over the period 1991–1992. Connections between the annually averaged benthic chlorophyll-a and station elevation and sediment composition (as a measure of the hydrodynamic energy caused by currents and waves) were also examined.Microphytobenthic chlorophyll-a showed one main peak in early summer and a smaller peak in autumn. The mean chlorophyll-a concentration of 113 mg Chl-a m^–2 in the upper centimeter is of the same order of magnitude as in other estuarine areas. The average annual primary production of the microphytobenthos has been estimated at 136 g C m^–2 y^–1 The primary production of sediment inhabiting microalgae is at least 17% of the total primary production in the estuary.Considerable differences in annually averaged chlorophyll-a emerges between the stations. These differences are related mainly to the interaction between station elevation and clay content of the sediment.     

Acid denaturation of the B875 light-harvesting complex in membranes of Rhodobacter sphaeroides

The structural basis for the spectral red shift in the near-IR absorption band of the B875 light-harvesting complex was examined by treatment of membranes from Rhodobacter sphaeroides M21 with acid. This mutant strain lacks the overlapping spectral bands of the B800–850 light-harvesting antenna and gives rise to membrane fragments with both surfaces accessible to protons. At pH 2.2, about half the absorption at 876 nm was converted within 10 min to a free pigment band; the remaining absorption appeared at 880 nm and shifted to 845 nm over the next three hours. These spectral shifts could not be reversed by alkali. Approximately one-third of the characteristic near-IR CD signal of B875 was also lost initially and replaced by a broad trough centered near 854 nm. Thereafter, the CD spectrum was dominated by the strong conservative signal of the 845 nm absorbing component which was attributed to an oligomeric bacteriopheophytin a species, probably a dimer. A kinetic analysis of the acid-induced absorption changes suggested a multi-step model with rate constants of 0.37 min^-1 for the initial rapid change and 0.05 and 0.11 min^-1 for the respective subsequent steps. The non-conservative nature of the near-IR CD spectrum of the intact complex, together with the spectral changes observed after the initial loss of near-IR absorption and CD, suggest that pigment-pigment interactions are not solely responsible for the red shift in this complex.Abbreviations BChl bacteriochlorophyll a - BPheo bacteriopheophytin a     

Interaction of Saccharomyces cerevisiae with gold: toxicity and accumulation

This paper examines the effects of ionic gold on Saccharomyces cerevisiae, as determined by long-term (growth in gold-containing media) and short-term interactions (H⁺ efflux activity). An increasing gold concentration inhibited growth and at <0.2 mM Au, growth was not observed. Transmission electron microscopy revealed no differences in ultrastructure but fine electron dense particles were observed in unstained preparations from gold-containing medium. After glucose addition (to 10mM) to starved suspensions of S. cerevisiae, glucose-dependent reduction of external pH occurred as the cells extruded protons. In the presence of increasing gold concentrations, the lag time before proton extrusion did not change but the rate and duration decreased significantly with a marked influence on proton efflux rate being observed at 10 M. Extension of preincubation time of yeast cells in gold-containing medium resulted in a decreasing proton efflux rate and colloidal phase formation in the cell suspensions, the time between gold addition and the beginning of colloidal phase formation depending on the gold concentration used. Both Ca and Mg enhanced the inhibitory effect of gold on the yeast cells with Ca showing a stronger inhibitory effect than Mg.     

Photo-oxidative Degradation of Chlorophyll-a and Unsaturated Lipids in Liposomal Dispersions at Low-Temperature

Liposomal dispersions in water were used as a tool to study photo-oxidation of chlorophyll-a and photo-oxidation of unsaturated lipids at 1 or 4°C. The presence of monogalactosyl diglyceride stimulated chlorophyll-a degradation. In addition the level of linolenic acid was decreased in liposomal dispersions containing chlorophyll-a, dipalmitoyl phosphatidyl choline, and monogalactosyl diglyceride, indicating that monogalactosyl diglyceride and chlorophyll-a were coupled in the preparations. In liposomal dispersions containing equal (molar) quantities of a-tocopherol, monogalactosyl diglyceride, and chlorophyll-a, a-tocopherol fully protected linolenic acid against photo-oxidative degradation, while chlorophyll-a degradation was only slightly reduced. In liposomal preparations containing a-tocopherol, chlorophyll-a and phosphatidyl choline, a-tocopherol catalyzed degradation of chlorophyll-a. Absorption spectra of the liposomal dispersions showed that the presence of a-tocopherol caused increased absorption in red light, which was attributed to structural changes in the liposomal preparations and thus could explain the noted effects. Tocopherol itself was rapidly degraded in chlorophyll-a containing liposomal preparations. Complex formation between chlorophyll-a and monogalactosyl diglyceride in chloroplasts is suggested and protection by a-tocopherol against photo-oxidation in chilling-sensitive plants; a suggestion which is founded on the similarities that exist between chloroplast preparations and liposomal preparations containing chlorophyll-a and monogalactosyl diglyceride as regards photo-oxidative degradation of chlorophyll-a, a-tocopherol and linolenic acid.     

Phytoplankton biomass and chlorophyll-a in some shallow lakes in central Europe

Based on 388 parallel data of phytoplankton biomass and chlorophyll-a of two shallow lakes and two ponds, the following results were obtained:

1. Relative chlorophyll-a content of phytoplankton biomass varied between 0.08–1.88%; chlorophyll-a concentration showed great differences among lakes.
2. Significant correlations (r = 0.68–0.92) were established between phytoplankton biomass and chlorophyll-a concentration. The regression in the artificial ponds was non-linear.
3. In parallel with the increase of average cell volume, a decrease in relative chlorophyll-a content was observed. A significant correlation (r = + 0.83) between the two variables was found. Relative chlorophyll-a content of phytoplankton is a log-function of average cell volume.

     

The relation of biotic and abiotic interactions to eutrophication in Tjeukemeer,The Netherlands

During the summer months of 1974–1985 chlorophyll-a and total P concentration, biomass of Daphnia hyalina, smelt Osmerus eperlanus, bream Abramis brema and pikeperch Stizostedion lucioperca, water temperature and water intake from lake IJsselmeer were monitored in Tjeukemeer. During this period there were manipulations with the bream and pikeperch stocks as a consequence of the termination of a gill-net fishery in 1977, and larval smelt immigrated each year from the large lake IJsselmeer and contributed largely to the yearly smelt recruitment.The correlation matrix of the nine variables mentioned above showed a positive correlation between bream and chlorophyll-a, but surprisingly a negative one between smelt and chlorophyll-a. The latter can only be explained when smelt is the dependent variable. In a multi-linear regression there was a negative effect of temperature, chlorophyll a and pikeperch on smelt and a positive effect of water intake. Daphnia hyalina was negatively influenced by the biomass of smelt and the water intake of lake IJsselmeer. The positive relation of Daphnia hyalina and chlorophyll-a was probably related to better survival chances of D. hyalina in an Oscillatoria-rich environment when smelt is the most important predator. An increasing biomass of bream coincided with higher total-P levels and probably contributed to higher chlorophyll-a levels.     

The trophic state ‘chain of relationships’ in ponds: does size matter?

In contrast to shallow lakes, factors affecting trophic state in ponds are not well described, and may include unique effects related to pond size. We examined the interdependence of ambient N and P, phytoplankton biomass, light penetration and stratification in 13 ponds of varying area and mean depth in Chester County, PA (USA) during March, May and July of 2002. Seven of the ponds had primarily residential watersheds, and six were farm ponds. The ponds were all eutrophic or hypereutrophic based on Carlsons Trophic State Index, but varied widely in nutrient content (from 20 to 179 g total P/L and from 683 to 3895 g total N/L) and size (surface areas from 0.1 to 1.7 ha, mean depths from 0.6 to 1.8 m). Although total N (TN) typically declined while total P (TP) rose from March to July, the ratio TN/TP remained sufficiently high that algal growth was probably limited by P during the study period. Phytoplankton biomass (as chlorophyll-a) was positively correlated with TP and negatively correlated with Secchi depth on all three sampling dates. Despite their shallow nature, the ponds were frequently stratified with near-anoxic hypolimnia later in the study period; mixing depth was greater in ponds with greater light penetration. Residual variation in chlorophyll-a unexplained by TP, and in Secchi depth unexplained by chlorophyll-a, was related to either mean depth or surface area, suggesting that trophic state in ponds may be controlled differently than in much larger, shallow lakes.     

The significance of hydrogenase activity for the energy metabolism of green algae: anaerobiosis favours ATP synthesis in cells of Chlorella with active hydrogenase

In cells of the green alga Chlorella fusca, which contain active hydrogenase(s), the concentration of ATP, NADH and NADPH were measured during a 5 h period of anaerobiosis in the dark and upon subsequent illumination with high light intensities (770 W/m²), conditions which favour optimal hydrogen photoproduction.ATP concentrations were also determined in cells of Chlorella fusca, whose hydrogenase was inactivated prior to illumination, and in cells of Chlorella vulgaris which do not contain hydrogenase. In the dark, the ATP concentration increased slightly during anaerobiosis in cells with active hydrogenase. This increase in ATP concentration was accompanied by an increase of NADH and a decrease of NADPH content.Upon illumination, the ATP content increased in cells with an active hydrogenase, whereas the NADH content decreased. The rate of phosphorylation was twice that observed in cells without active hydrogenase.This ATP synthesis in the light was not inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) (10 mol/l) nor by carbonylcyanide-3-chlorophenyl-hydrazone (CCCP) (1 mol/l) but was diminished by 500 mol/l dibromothymoquinone (DBMIB) and 6 mol/l carbonylcyanide-3-chlorophenyl-hydrazone (CCCP).It was concluded that an active hydrogenase can support ATP production under anaerobic conditions in the dark as well as in the light. NADH might serve in vivo as electron donor for a fermentative production of hydrogen in the light.Possible mechanisms underlying ATP production under anaerobiosis and hydrogen productive conditions are discussed.Abbreviations CCCP Carbonylcyanide-3-chlorophenyl-hydrazone - DBMIB dibromothymoquinone - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - FCCP carbonylcyanide-p-trifluormethoxyphenyl-hydrazone - HEPES N-2-hydroxyethylpiperazin-N-2-ethan-sulfonic acid - PSI II, photosystem I, II respectively - PQ plastoquinone     

Salt pollution in a Japanese stream and its effects on water chemistry and epilithic algal chlorophyll-a

Concentrations of major ions, total phosphorus, dissolved organic carbon, biological oxygen demand and chlorophyll-a of epilithic algae were determined weekly at nine sites in a Japanese stream receiving effluent from a groundwater treatment plant. The concentrations of four major cations (Na, K, Ca and Mg) and chloride ion increased significantly immediately at downstream sites of the effluent outfall. The ionic concentrations decreased with increasing dilution from merging tributaries but never reached the original concentrations and relative composition of stream water within a 10.7 km stream distance from the outfall. The changes in total ionic concentration and relative ionic proportion also changed the chlorophyll-a content of epilithic algae. The results also showed significantly higher chlorophyll-a content in epilithic algae under moderate salinity.     

Photon- and carbon-use efficiency in<Emphasis Type="Italic"> Ulva rigida</Emphasis> at different CO<Subscript>2</Subscript> and N levels

The seaweed Ulva rigida C. Agardh (Chlorophyta) was cultured under two CO₂ conditions supplied through the air bubbling system: non-manipulated air and 1% CO₂-enriched aeration. These were also combined with N sufficiency and N limitation, using nitrate as the only N source. High CO₂ in U. rigida led to higher growth rates without increasing the C fixed through photosynthesis under N sufficiency. Quantum yields for charge separation at photosystem II (PSII) reaction centres (_PSII) and for oxygen evolution (_O2) decreased at high CO₂ even in N-sufficient thalli. Cyclic electron flow around PSII as part of a photoprotection strategy accompanied by decreased antennae size was suspected. The new re-arrangement of the photosynthetic energy at high CO₂ included reduced investment in processes other than C fixation, as well as in carbon diverted to respiration. As a result, quantum yield for new biomass-C production (^growth) increased. The calculation of the individual quantum yields for the different processes involved allowed the completion of the energy flow scheme through the cell from incident light to biomass production for each of the CO₂ and N-supply conditions studied.Abbreviations A total thallus absorptance - A_pig absorptance due to pigments - A_str Absorptance due to non-pigmented structures - a* spectrally averaged in vivo absorption cross-section of chlorophyll a - CCM carbon-concentrating mechanism - Chl chlorophyll - DOC dissolved organic carbon - ETR electron transport rate - F_v/F_m optimum quantum yield for PSII charge separation - GP gross O₂ evolution rate - k_pig specific light absorption coefficient for pigments - k_str specific light absorption coefficient for non-pigmented structures - OP optimum O₂ evolution rate - PFR photon fluence rate - POC particulate organic carbon - PS photosystem - q_N non-photochemical quenching - q_P photochemical quenching - ^growth quantum yield for new biomass-C production - _O2 quantum yield for gross O₂ evolution - _PSII quantum yield for PSII charge separation     

Imaging of chlorophyll-a-fluorescence in leaves: Topography of photosynthetic oscillations in leaves of Glechoma hederacea

Images of chlorophyll-a-fluorescence oscillations were recorded using a camera-based fluorescence imaging system. Oscillations with frequencies around 1 per min were initiated by a transient decrease in light intensity during assimilation at an elevated CO₂-concentration. The oscillation was inhomogenously distributed over the leaf. In cells adjacent to minor veins, frequency and damping rate was high, if there was any oscillation. In contrast, the amplitude was highest in cells most distant from phloem elements (maximal distance about 300 m). The appearance of minor veins in oscillation images is explained by a gradient in the metabolic control in the mesophyll between minor veins and by transport of sugar from distant cells to phloem elements. The potential of fluorescence imaging to visualize microscopic source-sink interactions and metabolic domains in the mesophyll is discussed.Abbreviations P_i inorganic phosphate - Fru2,6BP fructose-2,6-bisphosphate - FBPase fructose-1,6-bisphosphatase - SPS sucrose-phosphate synthetase - HP hexosephosphate