Light regulation of light‐harvesting antenna size substantially enhances photosynthetic efficiency and biomass yield in green algae†

One of the major factors limiting biomass productivity in algae is the low thermodynamic efficiency of photosynthesis. The greatest thermodynamic inefficiencies in photosynthesis occur during the conversion of light into chemical energy. At full sunlight the light‐harvesting antenna captures photons at a rate nearly 10 times faster than the rate‐limiting step in photosynthetic electron transport. Excess captured energy is dissipated by non‐productive pathways including the production of reactive oxygen species. Substantial improvements in photosynthetic efficiency have been achieved by reducing the optical cross‐section of the light‐harvesting antenna by selectively reducing chlorophyll b levels and peripheral light‐harvesting complex subunits. Smaller light‐harvesting antenna, however, may not exhibit optimal photosynthetic performance in low or fluctuating light environments. We describe a translational control system to dynamically adjust light‐harvesting antenna sizes for enhanced photosynthetic performance. By expressing a chlorophyllide a oxygenase (CAO) gene having a 5′ mRNA extension encoding a Nab1 translational repressor binding site in a CAO knockout line it was possible to continuously alter chlorophyll b levels and correspondingly light‐harvesting antenna sizes by light‐activated Nab1 repression of CAO expression as a function of growth light intensity. Significantly, algae having light‐regulated antenna sizes had substantially higher photosynthetic rates and two‐fold greater biomass productivity than the parental wild‐type strains as well as near wild‐type ability to carry out state transitions and non‐photochemical quenching. These results have broad implications for enhanced algae and plant biomass productivity.     

Photosynthetic antenna engineering to improve crop yields

Planta - Evidence shows that decreasing the light-harvesting antenna size of the photosystems in tobacco helps to increase the photosynthetic productivity and plant canopy biomass accumulation...     

Combined ICR heating antenna for ion separation systems

A combination of one- and two-wave antennas (one and two turns of conductors around a plasma cylinder, respectively) is proposed. This combined antenna localizes an RF field within itself. It is shown that spent nuclear fuel processing systems based on ICR heating of nuclear ash by such a combined antenna have high productivity. A theory of the RF field excitation in ICR ion separation systems is presented in a simple and compact form.     

Solar energy conversion efficiencies in photosynthesis: Minimizing the chlorophyll antennae to maximize efficiency

The theoretical maxima of solar energy conversion efficiencies and productivities in oxygenic photosynthesis are evaluated. These are contrasted with actual measurements in a variety of photosynthetic organisms, including green microalgae, cyanobacteria, C4 and C3 plants. Minimizing, or truncating, the chlorophyll antenna size of the photosystems can improve photosynthetic solar energy conversion efficiency and productivity up to 3-fold. Generation of truncated light-harvesting chlorophyll antenna size (tla) strains, in all classes of photosynthetic organisms would help to alleviate excess absorption of sunlight and the ensuing wasteful dissipation of excitation energy, and to maximize solar-to-product energy conversion efficiency and photosynthetic productivity in high-density mass cultivations. The tla concept may find application in the commercial exploitation of microalgae and plants for the generation of biomass, biofuels, chemical feedstocks, as well as nutraceuticals and pharmaceuticals.     

<Emphasis Type="Italic">tla1</Emphasis>, a DNA insertional transformant of the green alga<Emphasis Type="Italic"> Chlamydomonas reinhardtii</Emphasis> with a truncated light-harvesting chlorophyll antenna size

DNA insertional mutagenesis and screening of the green alga Chlamydomonas reinhardtii was employed to isolate tla1, a stable transformant having a truncated light-harvesting chlorophyll antenna size. Molecular analysis showed a single plasmid insertion into an open reading frame of the nuclear genome corresponding to a novel gene ( Tla1) that encodes a protein of 213 amino acids. Genetic analysis showed co-segregation of plasmid and tla1 phenotype. Biochemical analyses showed the tla1 mutant to be chlorophyll deficient, with a functional chlorophyll antenna size of photosystem I and photosystem II being about 50% and 65% of that of the wild type, respectively. It contained a correspondingly lower amount of light-harvesting proteins than the wild type and had lower steady-state levels of Lhcb mRNA. The tla1 strain required a higher light intensity for the saturation of photosynthesis and showed greater solar conversion efficiencies and a higher photosynthetic productivity than the wild type under mass culture conditions. Results are discussed in terms of the tla1 mutation, its phenotype, and the role played by the Tla1 gene in the regulation of the photosynthetic chlorophyll antenna size in C. reinhardtii.     

Adaptation to Fe-deficiency requires remodeling of the photosynthetic apparatus

The molecular mechanisms underlying the onset of Fe-deficiency chlorosis and the maintenance of photosynthetic function in chlorotic chloroplasts are relevant to global photosynthetic productivity. We describe a series of graded responses of the photosynthetic apparatus to Fe-deficiency, including a novel response that occurs prior to the onset of chlorosis, namely the disconnection of the LHCI antenna from photosystem I (PSI). We propose that disconnection is mediated by a change in the physical properties of PSI-K in PSI in response to a change in plastid Fe content, which is sensed through the occupancy, and hence activity, of the Fe-containing active site in Crd1. We show further that progression of the response involves remodeling of the antenna complexes-specific degradation of existing proteins coupled to the synthesis of new ones, and establishment of a new steady state with decreased stoichiometry of electron transfer complexes. We suggest that these responses are typical of a dynamic photosynthetic apparatus where photosynthetic function is optimized and photooxidative damage is minimized in graduated responses to a combination of nutrients, light quantity and quality.     

Truncated light-harvesting chlorophyll antenna size in <Emphasis Type="Italic">Chlorella vulgaris</Emphasis> improves biomass productivity

Microalgae have been proposed as eco-friendly feedstocks for biodiesel production, because they accumulate large amounts of lipids and increase their biomass through photosynthesis. However, the photosynthetic efficiency of microalgae is too low for this strategy to be economically feasible. In an effort to overcome this issue, random mutants with reduced chlorophyll antenna size were generated by ethyl methanesulfonate (EMS)-mediated mutagenesis of Chlorella vulgaris. The antenna size mutant, herein designated E5, exhibited 56.5 and 75.8 % decreases in chlorophyll a and b contents, respectively, with significant reductions in the expression levels of peripheral light-harvesting antenna proteins in photosystem II. The saturated photosynthetic activity and electron transport rate of the E5 mutant were significantly higher and also showed reduced non-photochemical quenching (NPQ), compared to those of the wild type. Consequentially, the E5 mutant cultures achieved 44.5 % improvement in biomass productivity under high light (200 μmol photons m^?2 s^?1). These results suggest that improving the photosynthetic efficiency of microalgae could greatly enhance their biomass production, and such mutant strains can be applicable for large-scale outdoor cultivation which is typically exposed to high light intensity.     

Assembly of the light-harvesting chlorophyll antenna in the green alga Chlamydomonas reinhardtii requires expression of the TLA2-CpFTSY gene

The truncated light-harvesting antenna2 (tla2) mutant of Chlamydomonas reinhardtii showed a lighter-green phenotype, had a lower chlorophyll (Chl) per-cell content, and higher Chl a/b ratio than corresponding wild-type strains. Physiological analyses revealed a higher intensity for the saturation of photosynthesis and greater P(max) values in the tla2 mutant than in the wild type. Biochemical analyses showed that the tla2 strain was deficient in the Chl a-b light-harvesting complex, and had a Chl antenna size of the photosystems that was only about 65% of that in the wild type. Molecular and genetic analyses showed a single plasmid insertion in the tla2 strain, causing a chromosomal DNA rearrangement and deletion/disruption of five nuclear genes. The TLA2 gene, causing the tla2 phenotype, was cloned by mapping the insertion site and upon complementation with each of the genes that were deleted. Successful complementation was achieved with the C. reinhardtii TLA2-CpFTSY gene, whose occurrence and function in green microalgae has not hitherto been investigated. Functional analysis showed that the nuclear-encoded and chloroplast-localized CrCpFTSY protein specifically operates in the assembly of the peripheral components of the Chl a-b light-harvesting antenna. In higher plants, a cpftsy null mutation inhibits assembly of both the light-harvesting complex and photosystem complexes, thus resulting in a seedling-lethal phenotype. The work shows that cpftsy deletion in green algae, but not in higher plants, can be employed to generate tla mutants. The latter exhibit improved solar energy conversion efficiency and photosynthetic productivity under mass culture and bright sunlight conditions.     

The impact of extremely low frequency electromagnetic fields on stream periphyton: an eleven-year study

Potential effects of extremely low frequency (ELF) electromagnetic fields on periphyton were studied from 1983 to 1993 using a Before, After, Control and Impact design. The study was conducted at two sites on the Ford River, a fourth-order brown water trout stream in Dickinson County, Michigan. The Reference site received 4.9–6.5 times less exposure to ground electric fields and from 300 to 334 times less exposure to magnetic flux from 1989 to 1993 when the antenna was operational at 76 Hz than did the Antenna site. The objective of the study was to determine if ELF electromagnetic fields had caused changes in structure and/or function of algal communities in the Ford River. Significant differences in chlorophyll a standing crop and daily accumulation rate (a surrogate for primary productivity), and organic matter standing crop and daily accumulation rate were observed between the Reference and Antenna site after the antenna became operational. These four related community function variables all increased at the Antenna site with largest and most consistent increases occurring for chlorophyll measures. Compared to pre-operational data, the increase in chlorophyll at the Antenna site also occurred during a period of low amperage testing in 1986–1988, and did not increase further when the antenna became fully operational in 1989, indicating a low threshold for response. There was no significant differences between the Antenna and Reference sites in community structure variables such as diversity, evenness and the relative abundance of dominant diatoms. Thus, 76 Hz ELF electromagnetic radiation apparently did not change the basic makeup of the diatom community but did increase accumulation rates and standing crops of chlorophyll a and organic matter.     

Light-induced isomerization of the LHCII-bound xanthophyll neoxanthin: possible implications for photoprotection in plants

Light-harvesting pigment-protein complex of Photosystem II (LHCII) is the largest photosynthetic antenna complex of plants and the most abundant membrane protein in the biosphere. Plant fitness and productivity depend directly on a balance between excitations in the photosynthetic apparatus, generated by captured light quanta, and the rate of photochemical processes. Excess excitation energy leads to oxidative damage of the photosynthetic apparatus and entire organism and therefore the balance between the excitation density and photosynthesis requires precise and efficient regulation, operating also at the level of antenna complexes. We show that illumination of the isolated LHCII leads to isomerization of the protein-bound neoxanthin from conformation 9'-cis to 9',13- and 9',13'-dicis forms. At the same time light-driven excitation quenching is observed, manifested by a decrease in chlorophyll a fluorescence intensity and shortened fluorescence lifetimes. Both processes, the neoxanthin isomerization and the chlorophyll excitation quenching, are reversible in dim light. The results of the 77K florescence measurements of LHCII show that illumination is associated with appearance of the low-energy states, which can serve as energy traps in the pigment-protein complex subjected to excess excitation. Possible sequence of the molecular events is proposed, leading to a protective excess excitation energy quenching: neoxanthin photo-isomerization→formation of LHCII supramolecular structures which potentiate creation of energy traps→excitation quenching.     

Simultaneous increases in specific growth rate and specific lipid content of Chlorella vulgaris through UV‐induced reactive species

A challenge in algae‐based bio‐oil production is to simultaneously enhance specific growth rates and specific lipid content. We have demonstrated simultaneous increases in both the above in Chlorella vulgaris through reactive species (RS) induced under ultraviolet (UV) A and UVB light treatments. We postulated that the changes in photosystem (PS) stoichiometry and antenna size were responsible for the increases in specific growth rate. UVB treatment excited PSII, which resulted in a twofold to sevenfold increase in PSII/PSI ratio compared to control. An excited PSII caused a 2.7‐fold increase in the specific levels of superoxide and a twofold increase in the specific levels of hydroxyl radicals. We have established that the increased specific intracellular RS (si‐RS) levels increased the PSII antenna size by a significant 10‐fold as compared to control. In addition, the 8.2‐fold increase in specific lipid content was directly related to the si‐RS levels. We have also demonstrated that the RS induced under UVA treatment led to a 3.2‐fold increase in the saturated to unsaturated fatty acid ratio. Based on the findings, we have proposed and demonstrated a UV‐based strategy, which achieved an 8.8‐fold increase in volumetric lipid productivity. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 30:291–299, 2014     

Increased air temperature during simulated autumn conditions impairs photosynthetic electron transport between photosystem II and photosystem I

Changes in temperature and daylength trigger physiological and seasonal developmental processes that enable evergreen trees of the boreal forest to withstand severe winter conditions. Climate change is expected to increase the autumn air temperature in the northern latitudes, while the natural decreasing photoperiod remains unaffected. As shown previously, an increase in autumn air temperature inhibits CO2 assimilation, with a concomitant increased capacity for zeaxanthin-independent dissipation of energy exceeding the photochemical capacity in Pinus banksiana. In this study, we tested our previous model of antenna quenching and tested a limitation in intersystem electron transport in plants exposed to elevated autumn air temperatures. Using a factorial design, we dissected the effects of temperature and photoperiod on the function as well as the stoichiometry of the major components of the photosynthetic electron transport chain in P. banksiana. Natural summer conditions (16-h photoperiod/22 degrees C) and late autumn conditions (8-h photoperiod/7 degrees C) were compared with a treatment of autumn photoperiod with increased air temperature (SD/HT: 8-h photoperiod/22 degrees C) and a treatment with summer photoperiod and autumn temperature (16-h photoperiod/7 degrees C). Exposure to SD/HT resulted in an inhibition of the effective quantum yield associated with a decreased photosystem II/photosystem I stoichiometry coupled with decreased levels of Rubisco. Our data indicate that a greater capacity to keep the primary electron donor of photosystem I (P700) oxidized in plants exposed to SD/HT compared with the summer control may be attributed to a reduced rate of electron transport from the cytochrome b6f complex to photosystem I. Photoprotection under increased autumn air temperature conditions appears to be consistent with zeaxanthin-independent antenna quenching through light-harvesting complex II aggregation and a decreased efficiency in energy transfer from the antenna to the photosystem II core. We suggest that models that predict the effect of climate change on the productivity of boreal forests must take into account the interactive effects of photoperiod and elevated temperatures.     

Effects of 76 Hz electromagnetic fields on forest ecosystems in northern Michigan: Tree growth

Since 1984, the possible effects of extremely low-frequency electromagnetic (EM) fields generated by a 76 Hz communication antenna on the growth and productivity of four deciduous and one coniferous species have been studied in the Upper Peninsula of Michigan. Results from two research sites are discussed here: one site near an antenna element and a control site located 50 km from the communication system. Growth models for individual tree diameters were developed for northern red oak (Quercus rubra), paper birch (Betula papyrifera), aspen (Populus tremuloides with a few individuals ofP. grandidentata), and red maple (Acer rubrum). A growth model for individual tree height was developed for young red pine (Pinus resinosa). Average differences between the observed and predicted growth were calculated for each growing season and then compared between the study sites and across the study periods to evaluate changes in growth patterns which could be attributed to EM field effects. For aspen and red maple, the results showed a stimulation of diameter growth at magnetic flux density levels of 1 to 7 milliGauss; height growth of red pine was increased at about the same exposure levels. There are no clear indications of an EM field effect on total annual diameter growth for either of the other two species.     

The association of the antenna system to photosystem I in higher plants. Cooperative interactions stabilize the supramolecular complex and enhance red-shifted spectral forms

We report on the association of the antenna system to the reaction center in Photosystem I. Biochemical analysis of mutants depleted in antenna polypeptides showed that the binding of the antenna moiety is strongly cooperative. The minimal building block for the antenna system was shown to be a dimer. Specific protein-protein interactions play an important role in antenna association, and the gap pigments, bound at the interface between core and antenna, are proposed to mediate these interactions Gap pigments have been characterized by comparing the spectra of the Photosystem I to those of the isolated antenna and core components. CD spectroscopy showed that they are involved in pigment-pigment interactions, supporting their relevance in energy transfer from antenna to the reaction center. Moreover, gap pigments contribute to the red-shifted emission forms of Photosystem I antenna. When compared with Photosystem II, the association of peripheral antenna complexes in PSI appears to be more stable, but far less flexible and functional implications are discussed.     

Self-Organized Ag Nanorings Antenna Substrates for Surface-Enhanced Raman Spectroscopy

We investigate the surface-enhanced Raman spectroscopy of Ag nanorings antenna in both experiment and simulation. Self-organized Ag nanorings antenna were formed on quartz glass wafers by a simple chemistry reaction without any template. The three-dimensional finite-difference time-domain simulation calculations indicate that the electric field enhancement of Ag nanoring antenna is strongly dependent on the gap distance. A very strong surface plasmon coupling in the gap region of Ag nanoring antenna is observed, whose field intensity is enhanced four times compared to that for Ag nanodomes antenna with the same gap distance. Surface-enhanced Raman scattering (SERS) measurements have shown that the SERS intensity acquired from the Ag nanoring antenna is about 16 times stronger than that obtained from Ag nanodomes antenna. These results pave the way to design plasmonic nanostructures for practical applications that require coupled metallic nanoparticles with enhanced electric fields.     

Modeling and simulation of novel antenna for the treatment of hepatocellular carcinoma using finite element method

In this article, new interstitial antenna operating at a frequency of 2.45 GHz for the treatment of hepatocellular carcinoma (HCC) using microwave ablation has been investigated. This antenna is basically an asymmetrical miniaturized choke dipole antenna with a pointed needle at the tip. A commercial finite element method (FEM) package, COMSOL Multiphysics 3.4a, has been used to simulate the performance of needle tip choke antenna. The performance of the antenna has been evaluated numerically, taking into account the specific absorption rate, antenna impedance matching and geometry of the obtained thermal lesion, and the temperature distribution plot obtained shows that maximum temperature was attained in this simulation. The antenna is also capable of creating a spherical-shaped ablation zone. The size and shape of the ablation zone can be slightly adjusted by adjusting the choke position in order to maintain spherical ablation zones.     

Insights into the evolution of the antenna domains of Type-I and Type-II photosynthetic reaction centres through homology modelling

The (bacterio)chlorophylls of photosynthetic antenna and reaction centre complexes are bound to the protein via a fifth, axial ligand to the central magnesium atom. A number of the amino acids identified as providing such ligands are conserved between the large antenna of the cyanobacterial Type-I reaction centre and smaller antennas of the Type-I reaction centres of green sulphur bacteria and heliobacteria, and these numbers match closely the estimated number of antenna bacteriochlorophylls in the latter. The possible organisation of the antenna in the latter reaction centres is discussed, as is the mechanism by which the more pigment-rich antenna of the cyanobacterial reaction centre evolved. The homology modelling approach is also extended to the six-helix antenna proteins CP47 and CP43 associated with the Photosystem II reaction centre.     

Survival strategy of photosynthetic organisms. 2. Experimental proof of the size variability of the unit building block of light-harvesting oligomeric antenna

The present series of papers is part of an integrated research program to understand the effective functional strategy of native light-harvesting molecular antennae in photosynthetic organisms. This work tackles the problem of the structural optimization of light-harvesting antennae of variable size. In vivo, the size responds to the illumination intensity, thus implying more sophisticated optimization strategies, since larger antenna size demands finer structural tuning. Earlier modeling experiments showed that the aggregation of the antenna pigments, apart from being itself a universal structural factor of functional antenna optimization with any (!) spatial lattice of light-harvesting molecules, determines the antenna performance provided that the degree of aggregation varies: the larger the unit building block, the higher the efficacy of the whole structure. It means that altering the degree of pigment aggregation in response to the antenna size is biologically expedient. In the case of the oligomeric chlorosomal antenna of green bacteria, the strategy of variable antenna structural optimization in response to the illumination intensity was demonstrated to take place in vivo and facilitate high antenna performance regardless of its size, thus allowing bacteria to survive in diverse illumination conditions.     

Light requirements in microalgal photobioreactors: an overview of biophotonic aspects

In order to enhance microalgal growth in photobioreactors (PBRs), light requirement is one of the most important parameters to be addressed; light should indeed be provided at the appropriate intensity, duration, and wavelength. Excessive intensity may lead to photo-oxidation and -inhibition, whereas low light levels will become growth-limiting. The constraint of light saturation may be overcome via either of two approaches: increasing photosynthetic efficiency by genetic engineering, aimed at changing the chlorophyll antenna size; or increasing flux tolerance, via tailoring the photonic spectrum, coupled with its intensity and temporal characteristics. These approaches will allow an increased control over the illumination features, leading to maximization of microalgal biomass and metabolite productivity. This minireview briefly introduces the nature of light, and describes its harvesting and transformation by microalgae, as well as its metabolic effects under excessively low or high supply. Optimization of the photosynthetic efficiency is discussed under the two approaches referred to above; the selection of light sources, coupled with recent improvements in light handling by PBRs, are chronologically reviewed and critically compared.