| 1. |
- Mamma, Diomi, et al.
(författare)
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Removal of 1,3-dichloro2-propanol and 3-chloro-1,2-propanediol by the whole cell system of Pseudomonas putida DSM 437
- 2006
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Ingår i: Journal of Environmental Science and Health. Part A. - : Informa UK Limited. - 1093-4529 .- 1532-4117. ; 41:3, s. 303-313
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Tidskriftsartikel (refereegranskat)abstract
- The removal of 1,3-dichloro-2-propanol (1,3-DCP), 3-chloro-1,2-propanediol (3-CPD) and their mixtures at concentrations up to 1000 mg · L−1 by the whole cell system of Pseudomonas putida DSM 437 was investigated. The 1,3-DCP removal rates ranged from 2.36 to 10.55 mg · L−1 · h−1; 3-CPD exhibited approximately two times higher removal rates compared to 1,3-DCP for all concentrations tested. Removal of 1,3-DCP and 3-CPD followed first-order kinetics with rate constants of 0.0109 h−1 and 0.0206 h−1, respectively. When the whole cell system of P. putida DSM 437 was applied to mixtures of the two halohdrins, complete removal of 1,3-DCP was achieved at 144 h while removal of 3-CPD was completed at times ranging from 72 to 144 h. Time to achieve 50% removal of both halohydrins depends on the initial concentration of each in the mixture. For 1,3-DCP, it ranged from 40.55 h at 200 mg · L−1 to 53.28 h at 500 mg · L−1 while the respected values for 3-CPD were 33.39 and 68.91 h.
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| 2. |
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| 3. |
- Petroutsos, Dimitris, et al.
(författare)
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Removal of p-chlorophenol by the marine microalga Tetraselmis marina
- 2007
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Ingår i: Journal of Applied Phycology. - : Springer. - 0921-8971 .- 1573-5176. ; 19:5, s. 485-490
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Tidskriftsartikel (refereegranskat)abstract
- The ability of Tetraselmis marina, a green coastal microalga, to remove chlorophenols under photoautotrophic conditions was investigated. T. marina was able to grow in the presence of 20 mg L-1 of the phenolic compounds tested. The EC50 (growth rate) value of p-chlorophenol (p-CP) to T. marina was found to be 25.5 mg L-1. The microalga was able to remove chlorophenols, showing higher efficiency for p-CP. The effect of photoregime and NaHCO3 concentration on p-CP removal was investigated. Under continuous illumination with 1 g L-1 NaHCO3 initial concentration T. marina removed 65% of 20 mg L-1 in a 10day cultivation period.
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| 4. |
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| 5. |
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| 6. |
- Allorent, Guillaume, et al.
(författare)
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A Dual Strategy to Cope with High Light in Chlamydomonas reinhardtii
- 2013
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Ingår i: The Plant Cell. - : Oxford University Press. - 1040-4651 .- 1532-298X. ; 25:2, s. 545-557
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Tidskriftsartikel (refereegranskat)abstract
- Absorption of light in excess of the capacity for photosynthetic electron transport is damaging to photosynthetic organisms. Several mechanisms exist to avoid photodamage, which are collectively referred to as nonphotochemical quenching. This term comprises at least two major processes. State transitions (qT) represent changes in the relative antenna sizes of photosystems II and I. High energy quenching (qE) is the increased thermal dissipation of light energy triggered by lumen acidification. To investigate the respective roles of qE and qT in photoprotection, a mutant (npq4 stt7-9) was generated in Chlamydomonas reinhardtii by crossing the state transition-deficient mutant (stt7-9) with a strain having a largely reduced qE capacity (npq4). The comparative phenotypic analysis of the wild type, single mutants, and double mutants reveals that both state transitions and qE are induced by high light. Moreover, the double mutant exhibits an increased photosensitivity with respect to the single mutants and the wild type. Therefore, we suggest that besides qE, state transitions also play a photoprotective role during high light acclimation of the cells, most likely by decreasing hydrogen peroxide production. These results are discussed in terms of the relative photoprotective benefit related to thermal dissipation of excess light and/or to the physical displacement of antennas from photosystem II.
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| 7. |
- Allorent, Guillaume, et al.
(författare)
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Photoreceptor-dependent regulation of photoprotection
- 2017
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Ingår i: Current opinion in plant biology. - : Elsevier BV. - 1369-5266 .- 1879-0356. ; 37, s. 102-108
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Tidskriftsartikel (refereegranskat)abstract
- In photosynthetic organisms, proteins in the light-harvesting complex (LHC) harvest light energy to fuel photosynthesis, whereas photoreceptor proteins are activated by the different wavelengths of the light spectrum to regulate cellular functions. Under conditions of excess light, blue-light photoreceptors activate chloroplast avoidance movements in sessile plants, and blue- and green-light photoreceptors cause motile algae to swim away from intense light. Simultaneously, LHCs switch from light-harvesting mode to energy-dissipation mode, which was thought to be independent of photoreceptor-signaling up until recently. Recent advances, however, indicate that energy dissipation in green algae is controlled by photoreceptors activated by blue and UV-B light, and new molecular links have been established between photoreception and photoprotection.
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| 8. |
- Arend, Marius, et al.
(författare)
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Widening the landscape of transcriptional regulation of green algal photoprotection
- 2023
-
Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- Availability of light and CO2, substrates of microalgae photosynthesis, is frequently far from optimal. Microalgae activate photoprotection under strong light, to prevent oxidative damage, and the CO2 Concentrating Mechanism (CCM) under low CO2, to raise intracellular CO2 levels. The two processes are interconnected; yet, the underlying transcriptional regulators remain largely unknown. Employing a large transcriptomic data compendium of Chlamydomonas reinhardtii’s responses to different light and carbon supply, we reconstruct a consensus genome-scale gene regulatory network from complementary inference approaches and use it to elucidate transcriptional regulators of photoprotection. We show that the CCM regulator LCR1 also controls photoprotection, and that QER7, a Squamosa Binding Protein, suppresses photoprotection- and CCM-gene expression under the control of the blue light photoreceptor Phototropin. By demonstrating the existence of regulatory hubs that channel light- and CO2-mediated signals into a common response, our study provides an accessible resource to dissect gene expression regulation in this microalga.
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| 9. |
- Bailleul, Benjamin, et al.
(författare)
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Energetic coupling between plastids and mitochondria drives CO2 assimilation in diatoms.
- 2015
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 524:7565, s. 366-9
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Tidskriftsartikel (refereegranskat)abstract
- Diatoms are one of the most ecologically successful classes of photosynthetic marine eukaryotes in the contemporary oceans. Over the past 30 million years, they have helped to moderate Earth's climate by absorbing carbon dioxide from the atmosphere, sequestering it via the biological carbon pump and ultimately burying organic carbon in the lithosphere. The proportion of planetary primary production by diatoms in the modern oceans is roughly equivalent to that of terrestrial rainforests. In photosynthesis, the efficient conversion of carbon dioxide into organic matter requires a tight control of the ATP/NADPH ratio which, in other photosynthetic organisms, relies principally on a range of plastid-localized ATP generating processes. Here we show that diatoms regulate ATP/NADPH through extensive energetic exchanges between plastids and mitochondria. This interaction comprises the re-routing of reducing power generated in the plastid towards mitochondria and the import of mitochondrial ATP into the plastid, and is mandatory for optimized carbon fixation and growth. We propose that the process may have contributed to the ecological success of diatoms in the ocean.
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| 10. |
- Bo, Davide Dal, et al.
(författare)
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Consequences of Mixotrophy on Cell Energetic Metabolism in Microchloropsis gaditana Revealed by Genetic Engineering and Metabolic Approaches
- 2021
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Ingår i: Frontiers in Plant Science. - : Frontiers Media S.A.. - 1664-462X. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Algae belonging to the Microchloropsis genus are promising organisms for biotech purposes, being able to accumulate large amounts of lipid reserves. These organisms adapt to different trophic conditions, thriving in strict photoautotrophic conditions, as well as in the concomitant presence of light plus reduced external carbon as energy sources (mixotrophy). In this work, we investigated the mixotrophic responses of Microchloropsis gaditana (formerly Nannochloropsis gaditana). Using the Biolog growth test, in which cells are loaded into multiwell plates coated with different organic compounds, we could not find a suitable substrate for Microchloropsis mixotrophy. By contrast, addition of the Lysogeny broth (LB) to the inorganic growth medium had a benefit on growth, enhancing respiratory activity at the expense of photosynthetic performances. To further dissect the role of respiration in Microchloropsis mixotrophy, we focused on the mitochondrial alternative oxidase (AOX), a protein involved in energy management in other algae prospering in mixotrophy. Knocking-out the AOX1 gene by transcription activator-like effector nuclease (TALE-N) led to the loss of capacity to implement growth upon addition of LB supporting the hypothesis that the effect of this medium was related to a provision of reduced carbon. We conclude that mixotrophic growth in Microchloropsis is dominated by respiratory rather than by photosynthetic energetic metabolism and discuss the possible reasons for this behavior in relationship with fatty acid breakdown via β-oxidation in this oleaginous alga.
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| 11. |
- Boudière, Laurence, et al.
(författare)
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Glycerolipids in photosynthesis : composition, synthesis and trafficking.
- 2014
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Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 1878-2434 .- 0005-2728. ; 1837:4, s. 470-80
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Tidskriftsartikel (refereegranskat)abstract
- Glycerolipids constituting the matrix of photosynthetic membranes, from cyanobacteria to chloroplasts of eukaryotic cells, comprise monogalactosyldiacylglycerol, digalactosyldiacylglycerol, sulfoquinovosyldiacylglycerol and phosphatidylglycerol. This review covers our current knowledge on the structural and functional features of these lipids in various cellular models, from prokaryotes to eukaryotes. Their relative proportions in thylakoid membranes result from highly regulated and compartmentalized metabolic pathways, with a cooperation, in the case of eukaryotes, of non-plastidic compartments. This review also focuses on the role of each of these thylakoid glycerolipids in stabilizing protein complexes of the photosynthetic machinery, which might be one of the reasons for their fascinating conservation in the course of evolution. This article is part of a Special Issue entitled: Dynamic and ultrastructure of bioenergetic membranes and their components.
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| 12. |
- Curien, Gilles, et al.
(författare)
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The Water to Water Cycles in Microalgae.
- 2016
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Ingår i: Plant and Cell Physiology. - : Oxford University Press (OUP). - 0032-0781 .- 1471-9053. ; 57:7, s. 1354-1363
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Tidskriftsartikel (refereegranskat)abstract
- In oxygenic photosynthesis, light produces ATP plus NADPH via linear electron transfer, i.e. the in-series activity of the two photosystems: PSI and PSII. This process, however, is thought not to be sufficient to provide enough ATP per NADPH for carbon assimilation in the Calvin-Benson-Bassham cycle. Thus, it is assumed that additional ATP can be generated by alternative electron pathways. These circuits produce an electrochemical proton gradient without NADPH synthesis, and, although they often represent a small proportion of the linear electron flow, they could have a huge importance in optimizing CO2 assimilation. In Viridiplantae, there is a consensus that alternative electron flow comprises cyclic electron flow around PSI and the water to water cycles. The latter processes include photosynthetic O2 reduction via the Mehler reaction at PSI, the plastoquinone terminal oxidase downstream of PSII, photorespiration (the oxygenase activity of Rubisco) and the export of reducing equivalents towards the mitochondrial oxidases, through the malate shuttle. In this review, we summarize current knowledge about the role of the water to water cycles in photosynthesis, with a special focus on their occurrence and physiological roles in microalgae.
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| 13. |
- Ezzedine, Jade A., et al.
(författare)
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Adaptive traits of cysts of the snow alga Sanguina nivaloides unveiled by 3D subcellular imaging
- 2023
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Ingår i: Nature Communications. - 2041-1723. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- Sanguina nivaloides is the main alga forming red snowfields in high mountains and Polar Regions. It is non-cultivable. Analysis of environmental samples by X-ray tomography, focused-ion-beam scanning-electron-microscopy, physicochemical and physiological characterization reveal adaptive traits accounting for algal capacity to reside in snow. Cysts populate liquid water at the periphery of ice, are photosynthetically active, can survive for months, and are sensitive to freezing. They harbor a wrinkled plasma membrane expanding the interface with environment. Ionomic analysis supports a cell efflux of K+, and assimilation of phosphorus. Glycerolipidomic analysis confirms a phosphate limitation. The chloroplast contains thylakoids oriented in all directions, fixes carbon in a central pyrenoid and produces starch in peripheral protuberances. Analysis of cells kept in the dark shows that starch is a short-term carbon storage. The biogenesis of cytosolic droplets shows that they are loaded with triacylglycerol and carotenoids for long-term carbon storage and protection against oxidative stress.
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| 14. |
- Finazzi, Giovanni, et al.
(författare)
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Ions channels/transporters and chloroplast regulation.
- 2015
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Ingår i: Cell Calcium. - : Elsevier BV. - 0143-4160 .- 1532-1991. ; 58:1, s. 86-97
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Tidskriftsartikel (refereegranskat)abstract
- Ions play fundamental roles in all living cells and their gradients are often essential to fuel transports, to regulate enzyme activities and to transduce energy within and between cells. Their homeostasis is therefore an essential component of the cell metabolism. Ions must be imported from the extracellular matrix to their final subcellular compartments. Among them, the chloroplast is a particularly interesting example because there, ions not only modulate enzyme activities, but also mediate ATP synthesis and actively participate in the building of the photosynthetic structures by promoting membrane-membrane interaction. In this review, we first provide a comprehensive view of the different machineries involved in ion trafficking and homeostasis in the chloroplast, and then discuss peculiar functions exerted by ions in the frame of photochemical conversion of absorbed light energy.
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| 15. |
- Flori, Serena, et al.
(författare)
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Plastid thylakoid architecture optimizes photosynthesis in diatoms
- 2017
-
Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Photosynthesis is a unique process that allows independent colonization of the land by plants and of the oceans by phytoplankton. Although the photosynthesis process is well understood in plants, we are still unlocking the mechanisms evolved by phytoplankton to achieve extremely efficient photosynthesis. Here, we combine biochemical, structural and in vivo physiological studies to unravel the structure of the plastid in diatoms, prominent marine eukaryotes. Biochemical and immunolocalization analyses reveal segregation of photosynthetic complexes in the loosely stacked thylakoid membranes typical of diatoms. Separation of photosystems within subdomains minimizes their physical contacts, as required for improved light utilization. Chloroplast 3D reconstruction and in vivo spectroscopy show that these subdomains are interconnected, ensuring fast equilibration of electron carriers for efficient optimum photosynthesis. Thus, diatoms and plants have converged towards a similar functional distribution of the photosystems although via different thylakoid architectures, which likely evolved independently in the land and the ocean.
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| 16. |
- Hochmal, Ana Karina, et al.
(författare)
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Calredoxin represents a novel type of calcium-dependent sensor-responder connected to redox regulation in the chloroplast
- 2016
-
Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 7
-
Tidskriftsartikel (refereegranskat)abstract
- Calcium (Ca2+) and redox signalling play important roles in acclimation processes from archaea to eukaryotic organisms. Herein we characterized a unique protein from Chlamydomonas reinhardtii that has the competence to integrate Ca2+- and redox-related signalling. This protein, designated as calredoxin (CRX), combines four Ca2+-binding EF-hands and a thioredoxin (TRX) domain. A crystal structure of CRX, at 1.6 Å resolution, revealed an unusual calmodulin-fold of the Ca2+-binding EF-hands, which is functionally linked via an inter-domain communication path with the enzymatically active TRX domain. CRX is chloroplast-localized and interacted with a chloroplast 2-Cys peroxiredoxin (PRX1). Ca2+-binding to CRX is critical for its TRX activity and for efficient binding and reduction of PRX1. Thereby, CRX represents a new class of Ca2+-dependent ‘sensor-responder’ proteins. Genetically engineered Chlamydomonas strains with strongly diminished amounts of CRX revealed altered photosynthetic electron transfer and were affected in oxidative stress response underpinning a function of CRX in stress acclimation.
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| 17. |
- Johnson, Xenie, et al.
(författare)
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Proton Gradient Regulation 5-Mediated Cyclic Electron Flow under ATP- or Redox-Limited Conditions : A Study of ƊATPase pgr5 and ƊrbcL pgr5 Mutants in the Green Alga Chlamydomonas reinhardtii
- 2014
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Ingår i: Plant Physiology. - : Oxford University Press. - 0032-0889 .- 1532-2548. ; 165:1, s. 438-452
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Tidskriftsartikel (refereegranskat)abstract
- The Chlamydomonas reinhardtii proton gradient regulation5 (Crpgr5) mutant shows phenotypic and functional traits similar to mutants in the Arabidopsis (Arabidopsis thaliana) ortholog, Atpgr5, providing strong evidence for conservation of PGR5-mediated cyclic electron flow (CEF). Comparing the Crpgr5 mutant with the wild type, we discriminate two pathways for CEF and determine their maximum electron flow rates. The PGR5/proton gradient regulation-like1 (PGRL1) ferredoxin (Fd) pathway, involved in recycling excess reductant to increase ATP synthesis, may be controlled by extreme photosystem I acceptor side limitation or ATP depletion. Here, we show that PGR5/PGRL1-Fd CEF functions in accordance with an ATP/redox control model. In the absence of Rubisco and PGR5, a sustained electron flow is maintained with molecular oxygen instead of carbon dioxide serving as the terminal electron acceptor. When photosynthetic control is decreased, compensatory alternative pathways can take the full load of linear electron flow. In the case of the ATP synthase pgr5 double mutant, a decrease in photosensitivity is observed compared with the single ATPase-less mutant that we assign to a decreased proton motive force. Altogether, our results suggest that PGR5/PGRL1-Fd CEF is most required under conditions when Fd becomes overreduced and photosystem I is subjected to photoinhibition. CEF is not a valve; it only recycles electrons, but in doing so, it generates a proton motive force that controls the rate of photosynthesis. The conditions where the PGR5 pathway is most required may vary in photosynthetic organisms like C. reinhardtii from anoxia to high light to limitations imposed at the level of carbon dioxide fixation.
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| 18. |
- Kukuczka, Bernadeta, et al.
(författare)
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Proton Gradient Regulation5-Like1-Mediated Cyclic Electron Flow Is Crucial for Acclimation to Anoxia and Complementary to Nonphotochemical Quenching in Stress Adaptation
- 2014
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Ingår i: Plant Physiology. - : Oxford University Press. - 0032-0889 .- 1532-2548. ; 165:4, s. 1604-1617
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Tidskriftsartikel (refereegranskat)abstract
- To investigate the functional importance of Proton Gradient Regulation5-Like1 (PGRL1) for photosynthetic performances in the moss Physcomitrella patens, we generated a pgrl1 knockout mutant. Functional analysis revealed diminished nonphotochemical quenching (NPQ) as well as decreased capacity for cyclic electron flow (CEF) in pgrl1. Under anoxia, where CEF is induced, quantitative proteomics evidenced severe down-regulation of photosystems but up-regulation of the chloroplast NADH dehydrogenase complex, plastocyanin, and Ca2+ sensors in the mutant, indicating that the absence of PGRL1 triggered a mechanism compensatory for diminished CEF. On the other hand, proteins required for NPQ, such as light-harvesting complex stress-related protein1 (LHCSR1), violaxanthin de-epoxidase, and PSII subunit S, remained stable. To further investigate the interrelation between CEF and NPQ, we generated a pgrl1 npq4 double mutant in the green alga Chlamydomonas reinhardtii lacking both PGRL1 and LHCSR3 expression. Phenotypic comparative analyses of this double mutant, together with the single knockout strains and with the P. patens pgrl1, demonstrated that PGRL1 is crucial for acclimation to high light and anoxia in both organisms. Moreover, the data generated for the C. reinhardtii double mutant clearly showed a complementary role of PGRL1 and LHCSR3 in managing high light stress response. We conclude that both proteins are needed for photoprotection and for survival under low oxygen, underpinning a tight link between CEF and NPQ in oxygenic photosynthesis. Given the complementarity of the energy-dependent component of NPQ (qE) and PGRL1-mediated CEF, we suggest that PGRL1 is a capacitor linked to the evolution of the PSII subunit S-dependent qE in terrestrial plants.
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| 19. |
- Nagy, Gergely, et al.
(författare)
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Chloroplast remodeling during state transitions in Chlamydomonas reinhardtii as revealed by noninvasive techniques in vivo
- 2014
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences (PNAS). - 0027-8424 .- 1091-6490. ; 111:13, s. 5042-5047
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Tidskriftsartikel (refereegranskat)abstract
- Plants respond to changes in light quality by regulating the absorption capacity of their photosystems. These short-term adaptations use redox-controlled, reversible phosphorylation of the light-harvesting complexes (LHCIIs) to regulate the relative absorption cross-section of the two photosystems (PSs), commonly referred to as state transitions. It is acknowledged that state transitions induce substantial reorganizations of the PSs. However, their consequences on the chloroplast structure are more controversial. Here, we investigate how state transitions affect the chloroplast structure and function using complementary approaches for the living cells of Chlamydomonas reinhardtii. Using small-angle neutron scattering, we found a strong periodicity of the thylakoids in state 1, with characteristic repeat distances of ∼200 Å, which was almost completely lost in state 2. As revealed by circular dichroism, changes in the thylakoid periodicity were paralleled by modifications in the long-range order arrangement of the photosynthetic complexes, which was reduced by ∼20% in state 2 compared with state 1, but was not abolished. Furthermore, absorption spectroscopy reveals that the enhancement of PSI antenna size during state 1 to state 2 transition (∼20%) is not commensurate to the decrease in PSII antenna size (∼70%), leading to the possibility that a large part of the phosphorylated LHCIIs do not bind to PSI, but instead form energetically quenched complexes, which were shown to be either associated with PSII supercomplexes or in a free form. Altogether these noninvasive in vivo approaches allow us to present a more likely scenario for state transitions that explains their molecular mechanism and physiological consequences.
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| 20. |
- Panagiotou, Gianni, 1974, et al.
(författare)
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Fermentation characteristics of Fusarium oxysporum grown on acetate
- 2008
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Ingår i: Bioresource Technology. - : Elsevier BV. - 0960-8524 .- 1873-2976. ; :99, s. 7397-7401
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the growth characteristics of Fusarium oxysporum were evaluated in minimal medium using acetate or different mixtures of acetate and glucose as carbon source. The minimum inhibitory concentration (MIC) of acetic acid that F. oxysporum cells could tolerate was 0.8% w/v while glucose was consumed preferentially to acetate. The activity of isocitrate lyase was high when cells were grown on acetate and acetate plus glucose indicating an activation of the glyoxylate cycle. Investigation of the metabolic fingerprinting and footprinting revealed higher levels of intracellular and extracellular TCA cycle intermediates when F. oxysporum cells were grown on mixtures of acetate and glucose compared to growth on only glycose. Our data support the hypothesis that a higher flux through TCA cycle during acetate consumption could significantly increase the pool of NADH, resulting in the activation of succinate-propionate pathway which consumes reducing power (NADH) via conversion of succinate to propionyl-CoA and produce propionate.
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| 21. |
- Petroutsos, Dimitris, et al.
(författare)
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A blue-light photoreceptor mediates the feedback regulation of photosynthesis
- 2016
-
Ingår i: Nature. - : Springer Nature. - 0028-0836 .- 1476-4687. ; 537:7621, s. 563-566
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Tidskriftsartikel (refereegranskat)abstract
- In plants and algae, light serves both as the energy source for photosynthesis and a biological signal that triggers cellular responses via specific sensory photoreceptors. Red light is perceived by bilin-containing phytochromes and blue light by the flavin-containing cryptochromes and/or phototropins (PHOTs)1, the latter containing two photosensory light, oxygen, or voltage (LOV) domains2. Photoperception spans several orders of light intensity3, ranging from far below the threshold for photosynthesis to values beyond the capacity of photosynthetic CO2 assimilation. Excess light may cause oxidative damage and cell death, processes prevented by enhanced thermal dissipation via high-energy quenching (qE), a key photoprotective response4. Here we show the existence of a molecular link between photoreception, photosynthesis, and photoprotection in the green alga Chlamydomonas reinhardtii. We show that PHOT controls qE by inducing the expression of the qE effector protein LHCSR3 (light-harvesting complex stress-related protein 3) in high light intensities. This control requires blue-light perception by LOV domains on PHOT, LHCSR3 induction through PHOT kinase, and light dissipation in photosystem II via LHCSR3. Mutants deficient in the PHOT gene display severely reduced fitness under excessive light conditions, indicating that the sensing, utilization, and dissipation of light is a concerted process that plays a vital role in microalgal acclimation to environments of variable light intensities.
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| 22. |
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| 23. |
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| 24. |
- Petroutsos, Dimitris, et al.
(författare)
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Evolution of galactoglycerolipid biosynthetic pathways--from cyanobacteria to primary plastids and from primary to secondary plastids.
- 2014
-
Ingår i: Progress in lipid research. - : Elsevier BV. - 0163-7827 .- 1873-2194. ; 54, s. 68-85
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Tidskriftsartikel (refereegranskat)abstract
- Photosynthetic membranes have a unique lipid composition that has been remarkably well conserved from cyanobacteria to chloroplasts. These membranes are characterized by a very high content in galactoglycerolipids, i.e., mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively). Galactoglycerolipids make up the bulk of the lipid matrix in which photosynthetic complexes are embedded. They are also known to fulfill specific functions, such as stabilizing photosystems, being a source of polyunsaturated fatty acids for various purposes and, in some eukaryotes, being exported to other subcellular compartments. The conservation of MGDG and DGDG suggests that selection pressures might have conserved the enzymes involved in their biosynthesis, but this does not appear to be the case. Important evolutionary transitions comprise primary endosymbiosis (from a symbiotic cyanobacterium to a primary chloroplast) and secondary endosymbiosis (from a symbiotic unicellular algal eukaryote to a secondary plastid). In this review, we compare biosynthetic pathways based on available molecular and biochemical data, highlighting enzymatic reactions that have been conserved and others that have diverged or been lost, as well as the emergence of parallel and alternative biosynthetic systems originating from other metabolic pathways. Questions for future research are highlighted.
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| 25. |
- Petroutsos, Dimitris, et al.
(författare)
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PGRL1 Participates in Iron-induced Remodeling of the Photosynthetic Apparatus and in Energy Metabolism in Chlamydomonas reinhardtii
- 2009
-
Ingår i: Journal of Biological Chemistry. - : Elsevier. - 0021-9258 .- 1083-351X. ; 284:47, s. 32770-32781
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Tidskriftsartikel (refereegranskat)abstract
- PGRL1 RNA and protein levels are increased in iron-deficient Chlamydomonas reinhardtii cells. In an RNAi strain, which accumulates lower PGRL1 levels in both iron-replete and -starved conditions, the photosynthetic electron transfer rate is decreased, respiratory capacity in iron-sufficient conditions is increased, and the efficiency of cyclic electron transfer under iron-deprivation is diminished. Pgrl1-kd cells exhibit iron deficiency symptoms at higher iron concentrations than wild-type cells, although the cells are not more depleted in cellular iron relative to wild-type cells as measured by mass spectrometry. Thiol-trapping experiments indicate iron-dependent and redox-induced conformational changes in PGRL1 that may provide a link between iron metabolism and the partitioning of photosynthetic electron transfer between linear and cyclic flow. We propose, therefore, that PGRL1 in C. reinhardtii may possess a dual function in the chloroplast; that is, iron sensing and modulation of electron transfer.
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| 26. |
- Petroutsos, Dimitris, et al.
(författare)
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The Chloroplast Calcium Sensor CAS Is Required for Photoacclimation in Chlamydomonas reinhardtii
- 2011
-
Ingår i: The Plant Cell. - : Oxford University Press. - 1040-4651 .- 1532-298X. ; 23:8, s. 2950-2963
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Tidskriftsartikel (refereegranskat)abstract
- The plant-specific calcium binding protein CAS (calcium sensor) has been localized in chloroplast thylakoid membranes of vascular plants and green algae. To elucidate the function of CAS in Chlamydomonas reinhardtii, we generated and analyzed eight independent CAS knockdown C. reinhardtii lines (cas-kd). Upon transfer to high-light (HL) growth conditions, cas-kd lines were unable to properly induce the expression of LHCSR3 protein that is crucial for nonphotochemical quenching. Prolonged exposure to HL revealed a severe light sensitivity of cas-kd lines and caused diminished activity and recovery of photosystem II (PSII). Remarkably, the induction of LHCSR3, the growth of cas-kd lines under HL, and the performance of PSII were fully rescued by increasing the calcium concentration in the growth media. Moreover, perturbing cellular Ca2+ homeostasis by application of the calmodulin antagonist W7 or the G-protein activator mastoparan impaired the induction of LHCSR3 expression in a concentration-dependent manner. Our findings demonstrate that CAS and Ca2+ are critically involved in the regulation of the HL response and particularly in the control of LHCSR3 expression.
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| 27. |
- Redekop, Petra, et al.
(författare)
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Transcriptional regulation of photoprotection in dark-to-light transition : More than just a matter of excess light energy
- 2022
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 8:22
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Tidskriftsartikel (refereegranskat)abstract
- In nature, photosynthetic organisms are exposed to different light spectra and intensities depending on the time of day and atmospheric and environmental conditions. When photosynthetic cells absorb excess light, they induce nonphotochemical quenching to avoid photodamage and trigger expression of “photoprotective” genes. In this work, we used the green alga Chlamydomonas reinhardtii to assess the impact of light intensity, light quality, photosynthetic electron transport, and carbon dioxide on induction of the photoprotective genes (LHCSR1, LHCSR3, and PSBS) during dark-to-light transitions. Induction (mRNA accumulation) occurred at very low light intensity and was independently modulated by blue and ultraviolet B radiation through specific photoreceptors; only LHCSR3 was strongly controlled by carbon dioxide levels through a putative enhancer function of CIA5, a transcription factor that controls genes of the carbon concentrating mechanism. We propose a model that integrates inputs of independent signaling pathways and how they may help the cells anticipate diel conditions and survive in a dynamic light environment.
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| 28. |
- Ruiz-Sola, M Águila, et al.
(författare)
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A Toolkit for the Characterization of the Photoprotective Capacity of Green Algae.
- 2018
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Ingår i: Plastids. - London : Springer. ; , s. 315-323
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Bokkapitel (refereegranskat)abstract
- While light is a crucial energy source in photosynthetic organisms, if its intensity exceeds their photosynthetic capacity it may cause light-induced damage. A dominant photoprotective mechanism in plants and algae is the qE (quenching of energy), the major component of nonphotochemical quenching (NPQ). qE is a process that dissipates absorbed excitation energy as heat, ensuring cell survival even under adverse conditions. The present protocol gathers together a set of experimental approaches (in vivo chlorophyll fluorescence, western blotting, growth and cellular chlorophyll content at very strong light) that collectively allow for the characterization of the qE capacity of the model green algae Chlamydomonas reinhardtii.
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| 29. |
- Ruiz-Sola, M. Águila, et al.
(författare)
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Light-independent regulation of algal photoprotection by CO2 availability
- 2023
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- Photosynthetic algae have evolved mechanisms to cope with suboptimal light and CO2 conditions. When light energy exceeds CO2 fixation capacity, Chlamydomonas reinhardtii activates photoprotection, mediated by LHCSR1/3 and PSBS, and the CO2 Concentrating Mechanism (CCM). How light and CO2 signals converge to regulate these processes remains unclear. Here, we show that excess light activates photoprotection- and CCM-related genes by altering intracellular CO2 concentrations and that depletion of CO2 drives these responses, even in total darkness. High CO2 levels, derived from respiration or impaired photosynthetic fixation, repress LHCSR3/CCM genes while stabilizing the LHCSR1 protein. Finally, we show that the CCM regulator CIA5 also regulates photoprotection, controlling LHCSR3 and PSBS transcript accumulation while inhibiting LHCSR1 protein accumulation. This work has allowed us to dissect the effect of CO2 and light on CCM and photoprotection, demonstrating that light often indirectly affects these processes by impacting intracellular CO2 levels.
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| 30. |
- Six, A., et al.
(författare)
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Red light induces starch accumulation in Chlorella vulgaris without affecting photosynthesis efficiency, unlike abiotic stress
- 2024
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Ingår i: Algal Research. - : Elsevier. - 2211-9264. ; 80
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Tidskriftsartikel (refereegranskat)abstract
- Microalgae show great promise as sources of starch, one of the most widely consumed macromolecules. In this study, we evaluated the impact of three starch-inducing factors, namely nitrogen deprivation, supra-optimal temperature, and red light, on the physiology and starch accumulation capacity of Chlorella vulgaris. This starch accumulation was monitored by measuring the total carbohydrate content and transmission electron microscopy (TEM) imaging. Nitrogen deprivation and a supra-optimal temperature of 39 °C resulted in carbohydrate contents of 69.7 and 64.3 % of dry weight (DW) respectively. This constituted a 5.3- and 3.3-fold increase in carbohydrate productivity compared to the control, after 4 days of cultivation. During this period, carbohydrates represented over 80 % of the produced material (DW basis). However, nitrogen deprivation and supra-optimal temperature were accompanied by extensive stress, leading to lower cell division rates and damage to the photosynthetic apparatus. Red light illumination resulted in a more moderate production of carbohydrates. After 4 days of cultivation, the carbohydrate content reached 46.8 %, representing a 3.0-fold increase in productivity compared to control. The composition of the starch formed under red light was surprisingly poor in amylose, similar to transitory-type starch rather than storage starch. Most notably, the starch accumulation under red light was sustained over 7 days without affecting the rate of cell division and quantum yield efficiency. To the best of our knowledge, red light is the only factor reported so far to induce a significant starch accumulation without hindering cell division and photosynthesis efficiency, even after long-term exposure (7 days). Furthermore, all three conditions induced a cell wall thickening, albeit without affecting the recovery of accumulated starch by high-pressure homogenization. These results highlight the potential of red light as a starch inducer in Chlorella vulgaris and open up perspectives for the production of starch-based bioplastics from microalgae.
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| 31. |
- Terashima, Mia, et al.
(författare)
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Calcium-dependent regulation of cyclic photosynthetic electron transfer by a CAS, ANR1, and PGRL1 complex
- 2012
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences (PNAS). - 0027-8424 .- 1091-6490. ; 109:43, s. 17717-17722
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Tidskriftsartikel (refereegranskat)abstract
- Cyclic photosynthetic electron flow (CEF) is crucial to photosynthesis because it participates in the control of chloroplast energy and redox metabolism, and it is particularly induced under adverse environmental conditions. Here we report that down-regulation of the chloroplast localized Ca2+ sensor (CAS) protein by an RNAi approach in Chlamydomonas reinhardtii results in strong inhibition of CEF under anoxia. Importantly, this inhibition is rescued by an increase in the extracellular Ca2+ concentration, inferring that CEF is Ca2+-dependent. Furthermore, we identified a protein, anaerobic response 1 (ANR1), that is also required for effective acclimation to anaerobiosis. Depletion of ANR1 by artificial microRNA expression mimics the CAS-depletion phenotype, and under anaerobic conditions the two proteins coexist within a large active photosystem I-cytochrome b6/f complex. Moreover, we provide evidence that CAS and ANR1 interact with each other as well as with PGR5-Like 1 (PGRL1) in vivo. Overall our data establish a Ca2+-dependent regulation of CEF via the combined function of ANR1, CAS, and PGRL1, associated with each other in a multiprotein complex.
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| 32. |
- Tolleter, Dimitri, et al.
(författare)
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Control of Hydrogen Photoproduction by the Proton Gradient Generated by Cyclic Electron Flow in Chlamydomonas reinhardtii
- 2011
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Ingår i: The Plant Cell. - : Oxford University Press. - 1040-4651 .- 1532-298X. ; 23:7, s. 2619-2630
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen photoproduction by eukaryotic microalgae results from a connection between the photosynthetic electron transport chain and a plastidial hydrogenase. Algal H2 production is a transitory phenomenon under most natural conditions, often viewed as a safety valve protecting the photosynthetic electron transport chain from overreduction. From the colony screening of an insertion mutant library of the unicellular green alga Chlamydomonas reinhardtii based on the analysis of dark-light chlorophyll fluorescence transients, we isolated a mutant impaired in cyclic electron flow around photosystem I (CEF) due to a defect in the Proton Gradient Regulation Like1 (PGRL1) protein. Under aerobiosis, nonphotochemical quenching of fluorescence (NPQ) is strongly decreased in pgrl1. Under anaerobiosis, H2 photoproduction is strongly enhanced in the pgrl1 mutant, both during short-term and long-term measurements (in conditions of sulfur deprivation). Based on the light dependence of NPQ and hydrogen production, as well as on the enhanced hydrogen production observed in the wild-type strain in the presence of the uncoupling agent carbonyl cyanide p-trifluoromethoxyphenylhydrazone, we conclude that the proton gradient generated by CEF provokes a strong inhibition of electron supply to the hydrogenase in the wild-type strain, which is released in the pgrl1 mutant. Regulation of the trans-thylakoidal proton gradient by monitoring pgrl1 expression opens new perspectives toward reprogramming the cellular metabolism of microalgae for enhanced H2 production.
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| 33. |
- Villanova, Valeria, et al.
(författare)
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Investigating mixotrophic metabolism in the model diatom Phaeodactylum tricornutum
- 2017
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Ingår i: Philosophical Transactions of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8436 .- 1471-2970. ; 372:1728, s. 20160404-20160404
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Tidskriftsartikel (refereegranskat)abstract
- Diatoms are prominent marine microalgae, interesting not only from an ecological point of view, but also for their possible use in biotechnology applications. They can be cultivated in phototrophic conditions, using sunlight as the sole energy source. Some diatoms, however, can also grow in a mixotrophic mode, wherein both light and external reduced carbon contribute to biomass accumulation. In this study, we investigated the consequences of mixotrophy on the growth and metabolism of the pennate diatom Phaeodactylum tricornutum, using glycerol as the source of reduced carbon. Transcriptomics, metabolomics, metabolic modelling and physiological data combine to indicate that glycerol affects the central-carbon, carbon-storage and lipid metabolism of the diatom. In particular, provision of glycerol mimics typical responses of nitrogen limitation on lipid metabolism at the level of triacylglycerol accumulation and fatty acid composition. The presence of glycerol, despite provoking features reminiscent of nutrient limitation, neither diminishes photosynthetic activity nor cell growth, revealing essential aspects of the metabolic flexibility of these microalgae and suggesting possible biotechnological applications of mixotrophy.
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