Flash kinetics and light intensity dependence of oxygen evolution in the blue-green alga Anacystis nidulans

Patterns of oxygen evolution in flashing light for the blue-green alga Anacystis nidulans are compared with those for broken spinach chloroplasts and whole cells of the green alga Chlorella pyrenoidosa. The oscillations of oxygen yield with flash number that occur in both Anacystis and Chlorella, display a greater degree of damping than do those of isolated spinach chloroplasts. The increase in damping results from a two- to threefold increase in the fraction (α) of reaction centers “missed” by a flash. The increase in α cannot be explained by non-saturating flash intensities or by the dark reduction of the oxidized intermediates formed by the flash. Anaerobic conditions markedly increase α in Anacystis and Chlorella but have no effect on α in broken spinach chloroplasts. The results signify that the mechanism of charge separation and water oxidation involved in all three organisms is the same, but that the pool of secondary electron acceptors between Photosystem II and Photosystem I is more reduced in the dark, in the algal cells, than in the isolated spinach chloroplasts.Oxygen evolution in flashing light for Anacystis and Chlorella show light saturation curves for the oxygen yield of the third flash (Y₃) that differ markedly from those of the steady-state flashes (Y_s). In experiments in which all flashes are uniformly attenuated, Y₃ requires nearly twice as much light as Y_s to reach half-saturation. Under these conditions Y₃ has a sigmoidal dependence on intensity, while that of Y_s is hyperbolic. These differences depend on the number of flashes attenuated. When any one of the first three flashes is attenuated, the variation of Y₃ with intensity resembles that of Y_s. When two of the first three flashes are attenuated, Y₃ is intermediate in shape between the two extremes. A quantitative interpretation of these results based on the model of Kok et al. (Kok, B., Forbush, B. and McGloin, M. (1970) Photochem. Photobiol. 11, 457–475, and Forbush, B., Kok, B. and McGloin, M. P. (1971) Photochem. Photobiol. 14, 307–321) fits the experimental data.     

Characterization of energy conversion of Synechococcus sp. PCC7942 under photoautotrophic conditions based on metabolic flux and chlorophyll fluorescence analysis

Energy conversion efficiency of photoautotrophic microalgae plays an important role in the utilization of light energy for cell growth and production of metabolites. To understand the utilization of light energy, Synechococcus sp. PCC7942 was cultivated at different incident light intensities of 15.8, 47.3, and 94.6 μmol/m²/sec in continuous culture. The influence of light on the carbon and energy metabolism of microalgae was investigated by combining metabolic flux analysis (MFA) and chlorophyll fluorescence analysis (CFA). Results showed that the yields of biomass based on ATP (Y _ATP) and total light energy (Y _E) both declined with increasing light, and the maximal values of Y _ATP and Y _E were estimated to be 4.73 g/mol-ATP, and 17.10 × 10^?3 g/kJ respectively, at the examined conditions. The overall efficiency of energy conversion against total absorbed energy changed with the varying irradiances. However, the actual conversion efficiency of total energy based on CFA was almost constant, regardless of the different irradiances used in the present study.     

The regulation of cytochrome c oxidase of Rhodobacter capsulatus by light and oxygen

In order to distinguish between the regulatory effects of oxygen tension and light intensity on cytochrome c oxidase protein and enzymatic activity cells of Rhodobacter capsulatus were shifted from phototrophic (anaerobic, light) growth to aerobic-light, aerobic-dark and to anaerobic-dark conditions, respectively. During shift-experiments the formation of oxidase protein and regulation of oxidase activity was followed by immunological and enzymatic means. The results support the idea, that the formation of oxidase protein is regulated by oxygen tension and light intensity changes, whereas the regulation of oxidase activity seems only to be correlated to the oxygen tension. A DNA sequence involved in the oxygen-dependent regulation of cytochrome oxidase could be identified in the regulation-deficient oxidase mutant H41 of R. capsulatus. Immunological investigations of cytochrome c ₂ from mutant H41 demonstrated at the same time the participation of the c ₂-polypeptide in the regulation of cytochrome c oxidase.Abbreviations Bchl bacteriochlorophyll - CIE crossed immuno-electrophoresis - DMSO dimethyl sulfoxide     

Interaction between saline stress and photoinhibition of photosynthesis in the freshwater green algae Chlamydomonas reinhardtii. Implications for glycerol photoproduction

Light intensity is the main limiting factor for the photosynthetic bioconversion of CO₂ into glycerol which takes place when Chlamydomonas reinhardtii cells are exposed to saline stress conditions. Although productivity increases with light intensity for low irradiances, a strong inhibition is observed for high light intensity values. Saline stress enhances the damage caused by excess of light on the photosynthetic apparatus. The aim of this work is to evaluate the effect of high light intensity and saline stress on photosynthetic activity, cell growth and glycerol photoproduction by C. reinhardtii. The effect of light intensity on C. reinhardtii cells was studied immediately after transfer to a saline medium and after 24 h of adaptation to saline stress conditions. The influence of light intensity on the glycerol production rate was also evaluated for C. reinhardtii cultured in bioreactors of different radius. The factors that significantly affected photoinhibition were light intensity, cell density, radius of the bioreactor and time of exposure to the high light intensity. Our results suggest that bioreactors with a high surface/volume ratio will enable the achievement of high productivities with relatively low light intensities on the surface and will miminise the photoinhibition effect.     

Light-induced Enzyme Formation in a Chlorophyll-less Mutant of Euglena gracilis

A mutant strain, Y₉, of Euglena gracilis strain Z that is unable to produce protochlorophyll or chlorophyll has been isolated following treatment of wild type cells with nalidixic acid. Dark-grown cells of the mutant contain proplastids that show only limited ultrastructural development when placed in the light. Treatment of Y₉ cells with ultraviolet light brings about permanent cell bleaching with a target number similar to wild type Euglena, and with a slightly greater sensitivity to ultraviolet. Three enzymes of the reductive pentose phosphate cycle, fructose-1,6-diphosphate aldolase (class I), NADP-dependent glyceraldehyde-3-phosphate dehydrogenase, and 3-phosphoglycerate kinase, are detectable in dark-grown Y₉ cells at the low concentrations characteristic of dark-grown wild type cells, and increase substantially when these cells are exposed to light. The activity of ribulose-1,5-diphosphate carboxylase increases in the light to a lesser extent. Cytochrome 552, a carrier in the photosynthetic electron transport chain, is not present in light-grown cells of Y₉. The significance of this mutant for an understanding of the role of light in Euglena chloroplast development is discussed.     

Cell mass production of Acinetobacter calcoaceticus in palm oil-limited chemostat culture

Chemostat culture of Acinetobacter calcoaceticus KB-2 was done under palm oil-limiting conditions for cell production, and variation of cell compositions and yield coefficients were investigated in connection with the specific growth rates. At the concentration of 0.6% palm oil, the productivity of cells and yield coefficient were 4.76 g cells/l/h and 1.18 g cells/g palm oil, respectively, at a practical dilution rate of 0.85 h⁻¹. About 80% of the palm oil was assimilated by the strain, and the maintenance coefficient was 0.035 g palm oil/g cells/h. Although the carbohydrate content remained essentially constant when the growth rate was varied, the lipid, protein, and nucleic acid contents were increased slightly at higher growth rates. Although the protein content increased only 3%, the protein yield coefficient (Y_p) increased about 1.5 times over the range of specific growth rates between 0.1 and 0.7 h⁻¹. The increase in Y_p was due to the higher protein content of the biomass and to higher values of the cell yield coefficient.     

Performance of Chlorella sorokiniana under simulated extreme winter conditions

High annual microalgae productivities can only be achieved if solar light is efficiently used through the different seasons. During winter the productivity is low because of the light and temperature conditions. The productivity and photosynthetic efficiency of Chlorella sorokiniana were assessed under the worst-case scenario found during winter time in Huelva, south of Spain. The maximum light intensity (800?μmol photons m^-2 s^-1) and temperature (20°C) during winter were simulated in a lab-scale photobioreactor with a short light-path of 14?mm. Chemostat conditions were applied and the results were compared with a temperature-controlled situation at 38°C (optimal growth temperature for C. sorokiniana). When temperature was optimal the highest productivity was found at a dilution rate of 0.18 h^-1 (P _v?=?0.28?g Kg^-1 h^-1), and the biomass yield on light energy was high (Y _x,E?=?1.2?g?mol^-1 photons supplied). However, at suboptimal temperature, the specific growth rate of C. sorokiniana was surprisingly low, not being able to support continuous operation at a dilution rate higher than 0.02 h^-1. The slow metabolism under suboptimal temperature resulted in a decline of the light energy requirements of the cells. Consequently, the maximum winter irradiance was experienced as excessive, leading to a low photosynthetic efficiency and productivity (Y _x,E?=?0.5?g mol^-1 photons supplied, P _v?=?0.1?g Kg^-1 h^-1). At suboptimal temperature a higher carotenoid-to-chlorophyll ratio was observed indicating the activation of light-dissipating processes. We conclude that temperature control and/or light dilution during winter time will enhance the productivity.     

Kinetics of Growth and Amylase Production of Saccharomycopsis fibuligera on Potato Processing Wastewater

The kinetics of growth and amylase production of Saccharomycopsis fibuligera were studied in a chemostat on a synthetic potato processing blancher water. Dilution rates (D) from 0.101 to 0.480 h⁻¹ were examined. A mathematical model based on the Monod equation was developed. The yield of cell mass from carbohydrates was constant and equal to 0.84. The maximum specific growth rate and the Monod constant were determined to be 0.596 h⁻¹ and 0.226 mg/ml, respectively. An equation for the steady-state starch concentrations was empirically derived. The steady-state noncarbohydrate carbon levels rose linearly with D. Reducing sugars were the growth-limiting substrate, and their steady-state levels conformed to Monod kinetics. The yield of amylase from the cell mass (Y_z) declined as D rose and was described by the equation Y_z = (−8.005D + 4.076). The model predicted that the maximum production of cell mass should occur at D = 0.35 h⁻¹ and the maximum production of amylase should occur at D = 0.22 h⁻¹. The mathematical model presented agreed with the experimental results in its prediction of the steady-state level of reducing sugar, starch, cell mass, and amylase concentrations as well as the productivity of amylase.     

Effects of light and nitrogen starvation on the content and composition of carotenoids of the green microalga <Emphasis Type="Italic">Parietochloris incisa</Emphasis>

The changes in pigment content and composition of the unicellular alga Parietochloris incisa comb. nov (Trebouxiophyceae, Chlorophyta) were studied. This alga is unique in its ability to accumulate high amounts of arachidonic acid in the cell during cultivation under different irradiances and nitrogen availability in the medium. Under low irradiance of 35 μE/(m₂ s) photosynthetically active radiation the P. incisa cultures possessed slow growth and a relatively low carotenoid-to-chlorophyll ratio. At higher irradiances (200 and 400 μE/(m₂ s)) on complete medium, the alga displayed higher growth rate and an increase in the carotenoid content, especially that of β-carotene and lutein. Both on nitrogen-free (regardless of illumination intensity) and nitrogen-replete medium (under high light), a considerable increase in the ratio of carotenoid and chlorophyll contents was recorded. Predominant accumulation of xanthophylls took place in thylakoid membranes, whereas β-carotene deposition occurred mainly in the cytoplasmic lipid globules (oil bodies); lower amounts of carotenoids were accumulated in the absence of nitrogen. Under high light and nitrogen-deficiency conditions, an increase in violaxanthin de-epoxidation and nonphotochemical quenching was recorded together with a decline in variable chlorophyll fluorescence (F _v/F _m) level. A possible photoprotective role of carotenoids in adaptation of P. incisa to high light under nitrogen starvation conditions is discussed.     

Light availability determines susceptibility of reef building corals to ocean acidification

Elevated seawater pCO₂, and in turn ocean acidification (OA), is now widely acknowledged to reduce calcification and growth of reef building corals. As with other environmental factors (e.g., temperature and nutrients), light availability fundamentally regulates calcification and is predicted to change for future reef environments alongside elevated pCO₂ via altered physical processes (e.g., sea level rise and turbidity); however, any potential role of light in regulating the OA-induced reduction of calcification is still unknown. We employed a multifactorial growth experiment to determine how light intensity and pCO₂ together modify calcification for model coral species from two key genera, Acropora horrida and Porites cylindrica, occupying similar ecological niches but with different physiologies. We show that elevated pCO₂ (OA)-induced losses of calcification in the light (G _L) but not darkness (G _D) were greatest under low-light growth conditions, in particular for A. horrida. High-light growth conditions therefore dampened the impact of OA upon G _L but not G _D. Gross photosynthesis (P _G) responded in a reciprocal manner to G _L suggesting OA-relieved pCO₂ limitation of P _G under high-light growth conditions to effectively enhance G _L. A multivariate analysis of past OA experiments was used to evaluate whether our test species responses were more widely applicable across their respective genera. Indeed, the light intensity for growth was identified as a significant factor influencing the OA-induced decline of calcification for species of Acropora but not Porites. Whereas low-light conditions can provide a refuge for hard corals from thermal and light stress, our study suggests that lower light availability will potentially increase the susceptibility of key coral species to OA.     

Chloroplast translocations in Lemna trisulca L. induced by continuous irradiation and by light pulses

The analytical model describing the steady state position of chloroplasts in dependence of fluence rate as well as the chloroplast response to single strong light pulses has been proposed. The model is based on the following assumptions: 1. Irradiation of the cell generates the state X in the cell membrane region, proportional to the local fluence rate. After switching on the light, the value of X increases exponentially with the time constant of about 3 min. The dark decay of X is also exponential with the same time constant. The level of X controls all kinds of chloroplast arrangements. 2. The state X generates two further states: Y ₁ and Y ₂, the first of them representing attraction forces for chloroplasts and the second representing repulsion forces. Empirical equations have been found for both Y states. The fluence rate response curve can be described with the use of functions Y ₁ and Y ₂. 3. The kinetic analysis requires the introduction of two additional functions Z in order to account for delays and time dispersion of the chloroplast movement in response to driving and resistance factors. The computer program for the proposed model was developed and the results of calculations were compared with experimental data (fluence rate response curve and pulse effects) with satisfactory agreement. Initially no attempt was made to ascribe any physical meaning to the postulated states. Some suggestions in this respect are mentioned in the discussion.     

Growth yields of Desulfotomaculum orientis with hydrogen in chemostat culture

Desulfotomaculum orientis (strain Singapore 1) was grown autotrophically with H₂+CO₂ and sulfate, thiosulfate or sulfite as electron acceptor in sulfide- and pH-controlled continuous culture. Under sulfate-limiting conditions real growth yields of up to 9.7 g cell dry mass per mol sulfate were obtained. Electron acceptor limitation resulted in the excretion of up to 14.5 mmol acetate per liter, formed by reduction of CO₂ with H₂. Acetate production was not coupled to an increase of growth yields: under hydrogen-limiting conditions only 1.6 mmol acetate per liter was produced, and even higher growth yields of up to 12,4 g cell dry mass per mol sulfate were obtained. With thiosulfate or sulfite as electron acceptor growth yields increased up to 17.9 g cell dry mass per mol electron acceptor. Growth yields were not simply correlated with the growth rate, and did not allow the determination of maintenance coefficients and the extrapolation to maximal yields at infinite growth rate (Y ^max). The maximal growth rates (_max) with sulfate and thiosulfate were 0.090 and 0.109 h^-1, respectively, if cells were grown continuously in sulfidostat culture under nonlimiting conditions.The net energy yield of sulfate reduction and the energy requirement for the activation of sulfate by Desulfotomaculum orientis are discussed.     

Formation of N-Carboxymethyl Amino Acid from the Reaction of α-Amino Acid with Glyoxal

Enrichment cultures in a medium containing 0.1% methanol and 0.1% bicarbonate at pH 7.0 under anaerobic conditions in the light became mainly green in color. Forty-four enrichment cultures, which showed abundant growth, were obtained from 46 different sources and found to contain cells of methanol-utilizing bacteria and green algae as predominant members. From these enrichment cultures, two strains of bacteria and two strains of algae were isolated. The microorganisms isolated were designated as bacterium No. 7, bacterium No. 8, Chlorella sp. A-1 and Chlorella sp. B-1, respectively. Stable mixed cultures were easily formed by mixing the isolated cultures of bacteria and algae. Both methanol and bicarbonate were necessary for the growth of the mixed cultures under anaerobic-light conditions. Growth behavior of the mixed cultures was examined on a medium containing 0.1% methanol and 0.1 % bicarbonate at 30°C in the light (about 6000 lx). The maximum specific growth rate for the cultures, µ_max, was 0.092 hr^?1 (doubling time, 7.5 hr). The maximum cell yield was 0.87 g dry-cell weight per g of methanol used. The protein content of the biomass was 65%.     

Effects of light intensity and oxygen on photosynthesis and translocation in sugar beet

The mass transfer rate of ¹⁴C-sucrose translocation from sugar beet (Beta vulgaris, L.) leaves was measured over a range of net photosynthesis rates from 0 to 60 milligrams of CO₂ decimeters⁻² hour⁻¹ under varying conditions of light intensity, CO₂ concentration, and O₂ concentration. The resulting rate of translocation of labeled photosynthate into total sink tissue was a linear function (slope = 0.18) of the net photosynthesis rate of the source leaf regardless of light intensity (2000, 3700, or 7200 foot-candles), O₂ concentration (21% or 1% O₂), or CO₂ concentration (900 microliters/liter of CO₂ to compensation concentration). These data support the theory that the mass transfer rate of translocation under conditions of sufficient sink demand is limited by the net photosynthesis rate or more specifically by sucrose synthesis and this limitation is independent of light intensity per se. The rate of translocation was not saturated even at net photosynthesis rates four times greater than the rate occurring at 300 microliters/liter of CO₂, 21% O₂, and saturating light intensity.     

Adaptation of the Cyanobacterium Microcystis aeruginosa to Light Intensity

Light intensity adaptation (20 to 565 microeinsteins per square meter per second) of Microcystis aeruginosa (UV-027) was examined in turbidostat culture. Chlorophyll a and phycocyanin concentrations decreased with increasing light intensity while carotenoid, cellular carbon, and nitrogen contents did not vary. Variation in the number but not the size of photosynthetic units per cell, based on chlorophyll a/P₇₀₀ ratios, occurred on light intensity adaptation. Changes in the numbers of photosynthetic units partially dampened the effects of changes in light intensity on growth rates.     

A study on the growth of Salvinia molesta Mitchell in relation to light and temperature

The effects of light intensity and temperature on the growth of Salvinia molesta Mitchell were studied under shade and full sunlight conditions. Growth, in terms of increase in fresh weight and number of offshoots produced was significantly different (P<0.001) under the two light conditions; it was highest under shade during May–July, and in August–September under full sunlight. Mean relative growth rate (RGR) varied from 0.01 to 0.07 g g^?1 day^?1. Increase in the fresh weight had a significant positive nonlinear relationship with light intensity and atmospheric temperature. However, since there was a significant positive relationship between temperature and light intensity, it was not possible to separate their effects through regression analysis.     

Blue LED and succinic acid enhance the growth of Rhodobacter sphaeroides

Rhodobacter sphaeroides is a purple non-sulfur photosynthetic bacteria that participates in the anoxic cycling of carbon both as the primary producer and as the light-stimulated consumers of the reduced organic compounds. In this study, six different organic acids, i.e. acetate, lactate, oxaloacetate, malate, succinate, and citrate, were selected and used to analyze the relationships between the organic acid source and the cell growth. The C₄ compound exhibited an enhanced cell growth compared to the other organic acids, and the growth rate of R. sphaeroides that was grown with 0.03 M succinic acid was significantly 3.2-fold faster than the C₆ compound of 0.03 M citrate. Additionally, the cell growth of R. sphaeroides was enhanced with increasing light intensity, and the growth rate and the dry cell weight of R. sphaeroides that were grown under the light conditions of 15 W/m² were 2.0- and 1.2-fold higher than R. sphaeroides at 3 W/m². Therefore, the high light intensity probably affected the growth of R. sphaeroides. Moreover, the blue-colored light emitting diode (LED) exhibited a highest growth rate and cell concentration of R. sphaeroides among the various types of LEDs, and the enhanced cell growth phenomenon under the blue LED conditions was dramatically stimulated at low concentrations of succinic acid, which was compensatory for succinic acid. Therefore, a high light intensity and a blue LED as the light source were necessary for the enhanced cell growth for the C₄ organic acid, i.e. succinic acid.     

Productivity and heat generation of fermentation under oxygen limitation

The elemental balance equation of microbial growth on carbon substrate of generalized composition is given. Yield of dried bio-mass per oxygenY _o is calculated. Yield per oxygenY _o is found to be determined by two factors—carbon yieldy and the reducing power of substrate γ _s . The mode of dependence ofY _o on these two quantities is studied. The energetic interpretation ofy and γ _s is given. The dependence ofY _o ony and γ _s is shown to be equivalent to the dependence on a single factor, the energetie yield of growth η. Fermentor productivity increases with growth of η, the increase being directly proportional if η is not large (up to 25%) and becoming steeper if η is larger. The restrictions on a range of workable carbon yields during growth on various substrates are found. Metabolic heat generation of fermentor is shown to be proportional to oxygen consumption and to average 3.38 kcal per gram of O₂ irrespective of substrate and microorganism used.     

Electron transfer from Cyt b 559 and tyrosine-D to the S2 and S3 states of the water oxidizing complex in photosystem II at cryogenic temperatures

The Mn₄CaO₅ cluster of photosystem II (PSII) catalyzes the oxidation of water to molecular oxygen through the light-driven redox S-cycle. The water oxidizing complex (WOC) forms a triad with Tyrosine_Z and P₆₈₀, which mediates electrons from water towards the acceptor side of PSII. Under certain conditions two other redox-active components, Tyrosine_D (Y_D) and Cytochrome b ₅₅₉ (Cyt b ₅₅₉) can also interact with the S-states. In the present work we investigate the electron transfer from Cyt b ₅₅₉ and Y_D to the S₂ and S₃ states at 195 K. First, Y_D ^? and Cyt b ₅₅₉ were chemically reduced. The S₂ and S₃ states were then achieved by application of one or two laser flashes, respectively, on samples stabilized in the S₁ state. EPR signals of the WOC (the S₂-state multiline signal, ML-S₂), Y_D ^? and oxidized Cyt b ₅₅₉ were simultaneously detected during a prolonged dark incubation at 195 K. During 163 days of incubation a large fraction of the S₂ population decayed to S₁ in the S₂ samples by following a single exponential decay. Differently, S₃ samples showed an initial increase in the ML-S₂ intensity (due to S₃ to S₂ conversion) and a subsequent slow decay due to S₂ to S₁ conversion. In both cases, only a minor oxidation of Y_D was observed. In contrast, the signal intensity of the oxidized Cyt b ₅₅₉ showed a two-fold increase in both the S₂ and S₃ samples. The electron donation from Cyt b ₅₅₉ was much more efficient to the S₂ state than to the S₃ state.