Enclosed outdoor photobioreactors: light regime,photosynthetic efficiency,scale-up,and future prospects

Enclosed outdoor photobioreactors need to be developed and designed for large-scale production of phototrophic microorganisms. Both light regime and photosynthetic efficiency were analyzed in characteristic examples of state-of-the-art pilot-scale photobioreactors. In this study it is shown that productivity of photobioreactors is determined by the light regime inside the bioreactors. In addition to light regime, oxygen accumulation and shear stress limit productivity in certain designs. In short light-path systems, high efficiencies, 10% to 20% based on photosynthetic active radiation (PAR 400 to 700 nm), can be reached at high biomass concentrations (>5 kg [dry weight] m(-3)). It is demonstrated, however, that these and other photobioreactor designs are poorly scalable (maximal unit size 0.1 to 10 m(3)), and/or not applicable for cultivation of monocultures. This is why a new photobioreactor design is proposed in which light capture is physically separated from photoautotrophic cultivation. This system can possibly be scaled to larger unit sizes, 10 to >100 m(3), and the reactor liquid as a whole is mixed and aerated. It is deduced that high photosynthetic efficiencies, 15% on a PAR-basis, can be achieved. Future designs from optical engineers should be used to collect, concentrate, and transport sunlight, followed by redistribution in a large-scale photobioreactor.     

Control of the Light Saturation Point for Photosynthesis in Tomato

The light saturation curves for photosynthesis in Lycopersicon esculentum have been studied for a yellow-green mutation and for hormone treated plants. Comparisons have been made between saturation point and the size of the photosynthetic unit in these plants. These data suggest a function in the regulation of photosynthetic rates.     

Structure and Photosynthetic Characteristics of Awns of Wheat and Barley

The surface and the cross section of awns of wheat and barley were examined by scanning electron microscopy,ultrastructure of cells were observed under a transmisson electron microscope and the photosynthetic rates were measured with an oxygen, electrode and infra-red CO2 analyser. The main results were as follows :The cross section of wheat awn appeared to be acutely trianglular whereas that of barley awn was obtusely triangular. There were rows of stomota on either side of epidermis in both wheat and barley awns. Under the stomatic band there were green tissues. The green cells in the awn were differentiated from the parenchyma cells . The mature green cells possessed papillae which were rich in chloroplasts and mitochondria. The tamella system in chloroplasts was well developed and contained many starch grains. There were three vascular bundles in each awn. The sheath cells near the green tissues contained chloroplasts. The photosynthate in the green cells might pass through the sheath cells and companion cells to sieve elements. The highest photosynthetic rate of the awn was seen at the flowering stage ,reaching about 20 μmol CO2·m-2·s-1. The light compensation point was 70—80 μE·m-2· s-1. The light saturation point was about 1500 μE·m-2·s-1. The CO2 compensation point was 50—60 ppm and the CO2 saturation point was about 900ppm . The photosynthetic rate and stomatal conductance were easily effected by CO2 concentration, light intensity and the duration of illumination . There was a positive correlation between the photosynthetic rate and the chloro-phyll content in the awns. The CO2-releasing rate in photorespiration of awn was about 4–5 μmol CO2·m-2·s-1.     

Equilibrium gel permeation: a single-photon counting spectrophotometer for studies of protein interaction.

When a small column or flow cell packed with gel particles is completely saturated with a solution containing molecular species of interest, the average cross-sectional area occupied by the solute (partition cross section) is conveniently and precisely determined by direct optical scanning. For a mixture of interacting solutes this equilibrium gel permeation measurement yields the weight average of the species partition cross sections and the variation of this quantity with solute concentration permits determination of the solute interaction parameters (stoichiometry, equilibrium constants). We have developed a computer-controlled single-photon counting spectrophotometer for these measurements. The instrument exhibits high precision over a wide range of optical density. With counting times in the range of 10-1000 s the standard deviations on optical densities of protein solutions measured at 220 nm are typically 0.0006 at 1 OD, 0.002 at 2 OD, 0.005 at 4 OD. Beer's law tests show that deviations from linearity are less than these precision limits. Partition cross-section measurements for proteins can be made with an accuracy of better than 0.001 and information can be obtained with protein solutions at least as low as 1 mug/ml.     

Adsorption of globular proteins on locally planar surfaces: models for the effect of excluded surface area and aggregation of adsorbed protein on adsorption equilibria.

Equilibrium statistical-thermodynamic models are presented for the surface adsorption of proteins modeled as regular convex hard particles. The adsorbed phase is treated as a two-dimensional fluid, and the chemical potential of adsorbed protein is obtained from scaled particle theory. Adsorption isotherms are calculated for nonassociating and self-associating adsorbing proteins. Area exclusion broadens adsorption isotherms relative to the Langmuir isotherm (negative cooperativity), whereas self-association steepens them (positive cooperativity). The calculated isotherm for adsorption of hard spheres using scaled particle theory for hard discs agrees well with that calculated from the hard disc virial expansion. As the cross section of the adsorbing protein in the plane of the surface becomes less discoidal, the apparent negative cooperativity manifested in the isotherm becomes more pronounced. The model is extended to the case of simultaneous adsorption of a tracer protein at low saturation and a competitor protein with a different size and/or shape at arbitrary fractional saturation. Area exclusion by competitor for tracer (and vice versa) is shown to substantially enhance the displacement of tracer by competitor and to qualitatively invalidate the standard interpretation of ligand competition experiments, according to which the fractional displacement of tracer by competitor is equal to the fractional saturation by competitor.     

The measurement of histochemically-stained NADP-dependent isocitrate dehydrogenase in the sebaceous glands of hairless hamster.

The effect of substrate, co-factor and Nitroblue Tetrazolium concentration on the production of formazan by the action of NADP-dependent isocitrate dehydrogenase was studied in the sebaceous glands of the hairless hamster. The measurement (in average optical density units per unit area) of formazan in histochemically stained skin sections was carried out by television scanning microdensitometry (Quantimet 720D). Having established optimal conditions for this enzyme, a second study was carried out to determine the effect of different power objectives and wide-band wavelength light instead of white light on the average optical density per unit area, recorded by the instrument, of the formazan produced in a defined number of sebaceous glands in a single skin section. It was found that there was no difference in the average optical density per unit area recorded by the instrument at different power objectives and a peak value of average optical density per unit area could be obtained using a K4 or a K5 Balzer filter (550-650 nm).     

Scanning gel chromatography: determination of transport parameters from dynamic profiles measured at low solute concentration

Direct optical scanning of solute boundaries in large zone gel Chromatography experiments provides an accurate means of determining boundary profile shapes and rates of motion. A method has been developed for correcting such boundaries to a constant time frame, eliminating the distortion which arises from finite column scanning rate Centroids or the corrected profiles can be used to determine the partition cross section for the solute of interest The partition cross section and flow rate determine translational motion within the column. The axial dispersion coefficient, L, which characterizes rate of boundary spreading may also be calculated from the profiles. In order to explore these procedures a study of four noninteracting solutes was conducted. Partition cross sections determined from rates of motion of boundary centroids were found to be in good agreement with those determined by the equilibrium saturation method on the same column.In order to explore the lowest concentration limits of the technique and to illustrate the boundary characteristics for a selfassociating solute, a study of carboxyhemoglobin was conducted over a wide concentration range. From measurements at 220 nm the lowest concentration where useful data could be obtained was 2 micrograms per ml (0.12 πM heme) These results establish validity of the procedures used in analyzing the rates of boundary transport and in studying solute transport over a wide range of conditions.     

Analysis of the differential cross section for ionization of a hydrogen atom by fast electrons in a uniform electric field

The differential cross section for ionization of a hydrogen atom by fast electrons in an external uni-form electric field is calculated using the nonrelativistic Born approximation. It is shown that the cross section obtained can differ substantially from a similar ionization cross section of an isolated atom in the angular dis-tribution of secondary electrons in momentum space, oscillation terms, and magnitude.     

Functional and structural organization of chlorophyll in the developing photosynthetic membranes of Euglena gracilis Z. II. Formation of system II photosynthetic units during greening under optimal light intensity.

The relationships between light-harvesting chlorophyll and reaction centers in Photosystem II were analyzed during the chloroplast development of dark-grown, non-dividing Euglena gracilis Z. Comparative measurements included light saturation of photosynthesis, oxygen evolution under flashing-light and fluorescence induction. The results obtained can be summarized as follows: (1) Photosystem II photocenters are formed in parallel with chlorophyll synthesis, but after a long lag phase. (2) As a consequence, the chlorophyll reaction center ratio (Emerson's type photosynthetic unit) decreases during greening. (3) This decrease is accompanied by considerable changes in the energy transfer and trapping properties of Photosystem II. Most of the initially synthesized chlorophylls are inactive in the transfer of excitations to active photochemical centers and are shared among newly formed Photosystem II photocenters; as a consequence, the number of chlorophylls functionally connected to each Photosystem II photocenter decreases and cooperatively between these centers appears. Results are discussed in terms of chlorophyll organization in developing photosynthetic membranes with reference to the lake or puddle models of photosynthetic unit organization.     

Kinetics of excited states of pigment clusters in solubilized light-harvesting complex II: photon density-dependent fluorescence yield and transmittance.

Relative fluorescence yield, phi F, and transmittance, T, were measured in solubilized light-harvesting complex II (LHCII) as a function of photon density, Ip, of monochromatic 645-nm laser pulses (duration: approximately 2.5 ns). Special efforts were made in constructing an optical set-up that allows the accurate determination of the fluorescence from an area of constant Ip, phi F(Ip) starts to decline at approximately 10(14) and drops to values below 0.01% at maximum Ip (approximately 10(19) photons cm-2 pulse-1). T(Ip) decreases only slightly at photon densities of approximately 10(15) but increases steeply at values of > 10(17) photons cm-2 pulse-1. The interpretation of the phi F(Ip) data using the saturation limit of Mauzerall's multiple hit model leads to a unit size of about 10-15 chlorophyll molecules. One interpretation is to attribute this result to a very fast exciton-exciton annihilation of multiple excited states generated within this small domain. Alternatively, based on the assumption that delocalized cluster states within the monomeric/trimeric subunit of LHCII exist, the results can be consistently described by a kinetic model comprising ground, monoexcitonic, and biexcitonic states of clusters and a triplet state that is quenched by carotenoids in LHCII. Within the framework of this model the annihilation of multiple excitations is explained as ultrafast radiationless relaxation of higher excited cluster states. Comparative measurements in diluted acetonic Chl a solution are consistently described by the depletion of the ground state, taking the absorption cross section at the used wavelength.     

Functional and structural organization of chlorophyll in the developing photosynthetic membranes of Euglena gracilis Z. I. Formation of System II photosynthetic units during greening under optimal light intensity

The relationships between light-harvesting chlorophyll and reaction centers in Photosystem II were analyzed during the chloroplast development of dark-grown, non-dividing Euglena gracilis Z. Comparative measurements included light saturation of photosynthesis, oxygen evolution under flashing-light and fluorescence induction. The results obtained can be summarized as follows: (1) Photosystem II photocenters are formed in parallel with chlorophyll synthesis, but after a longer lag phase. (2) As a consequence, the chlorophyll: reaction center ratio (Emerson's type photosynthetic unit) decreases during greening. (3) This decrease is accompanied by considerable changes in the energy transfer and trapping properties of Photosystem II. Most of the initially synthesized chlorophylls are inactive in the transfer of excitations to active photochemical centers and are shared among newly formed Photosystem II photocenters; as a consequence, the number of chlorophylls functionally connected to each Photosystem II photocenter decreases and cooperativity between these centers appears. Results are discussed in terms of chlorophyll organization in developing photosynthetic membranes with reference to the lake or puddle models of photosynthetic unit organization.     

The energy distribution between the photosystems and light-induced changes in the stoichiometry of system I and II reaction centers in the chlorophyll b-containing alga Mantoniella squamata (Prasinophyceae)

The chlorophyll b-containing alga Mantoniella squamata was analyzed with respect to its capacity to balance the energy distribution from the light-harvesting antenna to photosystem I or photosystem II. It was shown, that this alga is unable to alter the absorption cross section of the two photosystems in terms of short-time regulations (state transitions). The energy absorbed by the LHC, which contains 60% of total photosynthetic pigments, is transferred to both photosystems without any preference. The stoichiometry of the two photosystems is found to be extremely unequal and variable during light adaptation. In high light, the molar ratio of P-680 per P-700 is found to be two, whereas under low light conditions this ratio accounts to nearly four. This very unbalanced stoichiometry of the reaction centers gives some new insights into the concept of the photosynthetic unit as well as in the importance of the regulation of the energy distribution. It is assumed that the high concentration of photosystem II can be understood as a mechanism to prevent the overexcitation of photosystem I. In addition, the changes im membrane protein pattern are not accompanied by variations in the ratio of appressed to nonappressed membranes as probed by ultrastructural analysis. It is suggested that the thylakoids are organized like a homogenous pigment bed. The lack of state transitions can be interpreted as a consequence of this unusual membrane morphology.Abbreviations Chl chlorophyll - CPa chlorophyll a-protein of PSII - CPl P-700 chlorophyll a-protein - CPD Chlorophyll packing density index - cyt f cytochrome f - FP free pigments - LHC light-harvesting complex - P_max light saturated photosynthetic rates per chlorophyll - n number of experiments - PQ plastoquinone - PS photosystem - PSU photosynthetic unit - Q_E non-photochemical quenching - Q_Q photochemical quenching     

Use of a light-induced respiratory transient to measure the optical cross section of photosystem I in chlorella

A method has been developed whereby the magnitude of a transient in O₂ uptake attributable to photosystem (PS) I activity, following single-turnover laser flashes of varying energy, can be used to measure the optical cross section of PSI. As measurements are made under the identical physiological conditions for which the cross section of PSII has previously been determined (AC Ley, DC Mauzerall 1982 Biochim Biophys Acta 680: 96-105), it is now possible to simultaneously measure the cross section of both photosystems in intact, photosynthetically competent cells, without the use of inhibitors or artificial mediators of electron transport. Plots of light-saturation behavior of the respiratory oscillation following pulses at 596 nanometers indicate a mean optical cross section similar to that of PSII at this wavelength, but suggest significant heterogeneity in the cross section of PSI. If this method measures only PSI activity, this result implies that there exist units with different numbers of identical chromophores, or units having populations of chromophores with different absorption spectra.     

COMPARATIVE PHYSIOLOGICAL STUDY OF MARINE DIATOMS AND DINOFLAGELLATES IN RELATION TO IRRADIANCE AND CELL SIZE. II. RELATIONSHIP BETWEEN PHOTOSYNTHESIS,GROWTH, AND CARBON/CHLOROPHYLL a RATIO1,2

Photosynthetic rates, growth rates, cell carbon, cell protein, and chlorophyll a content of two diatom and two dinoflagellate species were measured. The microalgae were chosen to have one small and one large species from each phylogenetic group; the two size categories differed from each other by 1.5 orders of magnitude in terms of cell carbon or cell protein. The cultures for the experiments were grown under continuous light at an irradiance high enough for the light-saturation of growth for all four species. The four species were found to have similar maximum photosynthetic rates per unit chlorophyll a. The diatom species showed lower carbon/chlorophyll a ratios and higher photosynthetic rates per unit carbon than the dinoflagellates. The higher growth rates of the diatoms were shown to be related to their higher photosynthetic rates per unit carbon. The ecological significance of the physiological difference between these two groups of microalgae is discussed.     

Photosynthetic characteristics of leaves developed at different irradiances and temperatures: an extension of the current hypothesis

Photosynthetic characteristics at high measurement irradiance were analyzed for single leaves of two C₃ and one C₄ species grown under twenty one combinations of irradiance level, irradiance duration, and air temperature in order to test the idea that photosynthetic characteristies developed by leaves in different environments are controlled by the daily amount of photosynthesis. Photosynthetic rates per unit area and mesophyll conductances at 25°C and air levels of CO₂ and O₂, and parameters for two photosynthesis models were used to characterize the photosynthetic properties of the leaves. Leaves with highest values of the photosynthetic parameters for each species were often developed in environments with irradiance levels below saturation for photosynthesis, and with only 12 hours of irradiance per day. Lower air temperature during growth increased the photosynthetic characteristics for a given irradiance regime. Photosynthetic characteristics had higher correlation coefficients with daily photosynthesis of mature leaves divided by 24-hour leaf elongation rates of young leaves, than with daily photosynthesis alone, indicating that photosynthetic characteristics may be related to a balance between photosynthesis and leaf expansion.     

SEASONAL ALTERATION OF PHOTOSYNTHETIC UNIT SIZES IN THREE HERB LAYER COMPONENTS OF A DECIDUOUS FOREST COMMUNITY

The pigment content and photosynthetic unit size of three herbs on the floor of a mature yellow oak (Quercus meuhlenbergii) forest were measured during most of the growing season. Two species, dutchman's breeches (Dicentra cucullaria) and Virginia bluebell (Mertensia virginica) are spring ephemerals, while Hepatica acutiloba has a semi-evergreen habit. Although pigment composition changed in Dicentra, photosynthetic unit size only varied slightly. Mertensia was nearly invariant in pigment composition, but unit size was modified as the growing season progressed. The semi-evergreen herb, Hepatica, underwent a remarkable alteration in pigment content, photosynthetic unit size, and number following overstory leaf expansion. The results indicate that an alteration of photosynthetic unit size is possible in fully expanded leaves of two forest floor herbs.     

Photosynthetic characteristics of leaves developed at different irradiances and temperatures: an extension of the current hypothesis.

Photosynthetic characteristics at high measurement irradiance were analyzed for single leaves of two C₃ and one C₄ species grown under twenty one combinations of irradiance level, irradiance duration, and air temperature in order to test the idea that photosynthetic characteristics developed by leaves in different environments are controlled by the daily amount of photosynthesis. Photosynthetic rates per unit area and mesophyll conductances at 25°C and air levels of CO₂ and O₂, and parameters for two photosynthesis models were used to characterize the photosynthetic properties of the leaves. Leaves with highest values of the photosynthetic parameters for each species were often developed in environments with irradiance levels below saturation for photosynthesis, and with only 12 hours of iradiance per day. Lower air temperature during growth increased the photosynthetic characteristics for a given irradiance regime. Photosynthetic characteristics had higher correlation coefficients with daily photosynthesis of mature leaves divided by 24-hour leaf elongation rates of young leaves, than with daily photosynthesis alone, indicating that photosynthetic characteristics may be related to a balance between photosynthesis and leaf expansion.     

Energetic aspects of photophosphorylation capacity and reaction center content of Rhodopseudomonas capsulata, grown in a turbidostat under different irradiances

Cells of Rhodopseudomonas capsulata were grown in a turbido-stat and adapted to high (1400 W/m²) or low (40 W/m²) light intensities. In high-light-grown cells the specific BChl content was about 10-times lower, the number of intracytoplasmatic membrane vesicles smaller by a factor of about 20, the photosynthetic unit smaller by a factor of 1.9 and the reaction center content about 5-times lower than in low-light-grown cells. However, the photophosphorylation rate per reaction center under saturating light was higher in high-light-grown cells by a factor of 7.7, apparently compensating the lower amount of reaction centers. Adaptation of the cells to different irradiances not only seems to comprise a variation of the size and composition of the antennae, but also a change in the affinity of the photosynthetic system to light, as concluded from saturation curves obtained from the two adaptation stages of cells.     

Electrophysiological basis for the spatial dependence of the inhibitory coupling in the Limulus retina

A technique for measuring, with total optical isolation, the inhibition between two individual receptor units in the Limulus lateral eye is described. The extracellular responses of pairs of units were recorded, using light piping microelectrodes. The inhibitory coupling between two units was found to be nonlinear and describable by a simple hyperbolic equation written in terms of saturation rate (S), half saturation (H), and threshold (ft). By plotting reciprocal frequencies, the data could be linearized and compared for different pairs of units. The magnitude of inhibition (in terms of S and H) was found to decrease monotonically as the anatomical distance between receptors increased. An electrical model of the inhibitory system was developed which accounts for many of the properties of the observed inhibitory interactions. Using the equations from the model and the experimental data, it is shown that the "electrical distances" (which are computed in terms of space constants lambda) of the inhibitory synapses from the impulse-generating region of the test unit are directly related to the anatomical distance between receptors. It is also shown that "synaptic strength" is relatively constant with separation. The electrical distances of the inhibitory synapses range from about 0.1lambda to 0.25lambda for adjacent units to greater than 0.5lambda for units seven to nine receptors away. It is concluded that the nonlinear character of the inhibitory coupling is attributable to synaptic effects, and that the decrease of inhibition with distance between receptors is caused primarily by an increase in the electrical distance of the inhibitory synapses from the test unit.     

Measurements of cross-sectional area of collagen structures (knee ligaments) by means of an optical method

Measurement methods of cross-sectional area of collagen tissues and structures, so far chosen, are critically reviewed. A new optical method, founded on section outline plotting, by which it is easy to compute the cross-sectional area, is suggested and shown in particular. Experimental results, achieved by applying the method to the measurement of bovine knee ligament sections, are reported; these results are compared with those taken from samples coming from the same ligaments.