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Microalgae Photobiology, Biotechnology, and Bioproduction
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Microalgae Photobiology, Biotechnology, and Bioproduction

A special issue of Plants (ISSN 2223-7747). This special issue belongs to the section "Plant Physiology and Metabolism".

Deadline for manuscript submissions: 20 January 2025 | Viewed by 11228

Special Issue Editors

Prof. Dr. Michael Hippler

E-Mail Website
Guest Editor
Institute of Plant Biology and Biotechnology, University of Münster, Münster, Germany
Interests: microalgae; Proteomics; biotechnology; Mass Spectrometry
Dr. Shin-Ichiro Ozawa

E-Mail Website
Guest Editor
Institute of Plant Science and Resources, Okayama University, Okayama, Japan
Interests: plant; photosynthesis; mass spectrometry; proteomics; structural biology

Special Issue Information

Dear Colleagues,

Photosynthetic microalgae are eukaryotic unicellular organisms that live in aquatic environments and use light energy to bind carbon dioxide (CO2) to produce biomass. Photosynthesis research on microalgal model systems whose genomes have also been sequenced, such as Chlamydomonas reinhardtii or Phaeodactylum tricornutum, has contributed significantly to our understanding of the basic principles of the photosynthetic process. The light-controlled production of microalgal biomass also holds the potential for the biotechnological use of photosynthetic microalgae for the production of biofuels and high-value raw materials. It is foreseeable that genetic engineering will further develop microalgae as biotechnological hosts for the expression of enzymes and products from natural plant substances as well as for the expression of therapeutic proteins.

In order to use microalgae for biotechnological purposes, the understanding and engineering of photosynthetic bottlenecks and the acclimatization of microalgae to the environment are important goals for the future. The understanding of how photosynthetic performance is maintained under adverse environmental conditions and of how light use efficiency versus stress acclimation responses are balanced are key for the further engineering of photosynthetic efficiency and biotechnological applications.
The purpose of this Special Issue is to discuss how microalgal research has provided insights into identifying photosynthetic bottlenecks with the potential to improve photosynthetic light-to-electron efficiency and thus photosynthetic effectiveness. In this context, aspects of light harvesting to drive photosynthetic charge separation and the dissipation of light to heat to protect the photosynthetic machinery will be addressed. Other topics include the generation, storage, and use of the proton motive force, as well as photosynthetic and alternative electron transfer processes. An additional topic is towards an understanding of how microalgae have evolved acclimation strategies to maintain photosynthetic performance under unfavorable environmental conditions. New structural insights into photosynthetic complexes are also addressed. How improvements in photosynthetic performance can be incorporated into biotechnological applications is another focus. Here, improvements in photosynthetic electron transfer to enhance H2 production and other feedstocks that require additional photosynthetic reducing power are addressed. Novel concepts for the design of photobioreactors and the engineering of microalgae growth, as well as new methods of genetic modification for biotechnological purposes, are also considered.

Prof. Dr. Michael Hippler
Dr. Shin-Ichiro Ozawa
Guest Editors

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Published Papers (8 papers)

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Research

Jump to: Review

11 pages, 813 KiB  
Article
Extraction and Concentration of Spirulina Water-Soluble Metabolites by Ultrafiltration
by Claudia Salazar-González, Carolina Mendoza Ramos, Hugo A. Martínez-Correa and Hugo Fabián Lobatón García
Plants 2024, 13(19), 2770; https://doi.org/10.3390/plants13192770 - 3 Oct 2024
Viewed by 430
Abstract
Spirulina (Arthospira platensis) is known for its rich content of natural compounds like phycocyanin, chlorophylls, carotenoids, and high protein levels, making it a nutrient-dense food. Over the past decade, research has aimed to optimize the extraction, separation, and purification of these [...] Read more.
Spirulina (Arthospira platensis) is known for its rich content of natural compounds like phycocyanin, chlorophylls, carotenoids, and high protein levels, making it a nutrient-dense food. Over the past decade, research has aimed to optimize the extraction, separation, and purification of these valuable metabolites, focusing on technologies such as high-pressure processing, ultrasound-assisted extraction, and microwave-assisted extraction as well as enzymatic treatments, chromatographic precipitation, and membrane separation. In this study, various extraction methods (conventional vs. ultrasound-assisted), solvents (water vs. phosphate buffer), solvent-to-biomass ratios (1:5 vs. 1:10), and ultrafiltration (PES membrane of MWCO 3 kDa, 2 bar) were evaluated. The quantities of total protein, phycocyanin (PC), chlorophyll a (Cla), and total carotenoids (TCC) were measured. The results showed that ultrasound-assisted extraction (UAE) with phosphate buffer at a 1:10 ratio yielded a metabolite-rich retentate (MRR) with 37.0 ± 1.9 mg/g of PC, 617 ± 15 mg/g of protein, 0.4 ± 0.2 mg/g of Cla, and 0.15 ± 0.14 mg/g of TCC. Water extraction in the concentration process achieved the highest concentrations in MRR, with approximately 76% PC, 92% total protein, 62% Cla, and 41% TCC. These findings highlight the effective extraction and concentration processes to obtain a metabolite-rich retentate from Spirulina biomass, reducing the volume tenfold and showing potential as a functional ingredient for the food, cosmetic, and pharmaceutical industries. Full article
(This article belongs to the Special Issue Microalgae Photobiology, Biotechnology, and Bioproduction)
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18 pages, 6255 KiB  
Article
Chemical Protein Crosslinking-Coupled Mass Spectrometry Reveals Interaction of LHCI with LHCII and LHCSR3 in Chlamydomonas reinhardtii
by Laura Mosebach, Shin-Ichiro Ozawa, Muhammad Younas, Huidan Xue, Martin Scholz, Yuichiro Takahashi and Michael Hippler
Plants 2024, 13(12), 1632; https://doi.org/10.3390/plants13121632 - 13 Jun 2024
Viewed by 1223
Abstract
The photosystem I (PSI) of the green alga Chlamydomonas reinhardtii associates with 10 light-harvesting proteins (LHCIs) to form the PSI-LHCI complex. In the context of state transitions, two LHCII trimers bind to the PSAL, PSAH and PSAO side of PSI to produce the [...] Read more.
The photosystem I (PSI) of the green alga Chlamydomonas reinhardtii associates with 10 light-harvesting proteins (LHCIs) to form the PSI-LHCI complex. In the context of state transitions, two LHCII trimers bind to the PSAL, PSAH and PSAO side of PSI to produce the PSI-LHCI-LHCII complex. In this work, we took advantage of chemical crosslinking of proteins in conjunction with mass spectrometry to identify protein–protein interactions between the light-harvesting proteins of PSI and PSII. We detected crosslinks suggesting the binding of LHCBM proteins to the LHCA1-PSAG side of PSI as well as protein–protein interactions of LHCSR3 with LHCA5 and LHCA3. Our data indicate that the binding of LHCII to PSI is more versatile than anticipated and imply that LHCSR3 might be involved in the regulation of excitation energy transfer to the PSI core via LHCA5/LHCA3. Full article
(This article belongs to the Special Issue Microalgae Photobiology, Biotechnology, and Bioproduction)
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12 pages, 1471 KiB  
Article
CRISPR/Cas9-Mediated Knockout of the Lycopene ε-Cyclase for Efficient Astaxanthin Production in the Green Microalga Chlamydomonas reinhardtii
by Jacob Sebastian Kneip, Niklas Kniepkamp, Junhwan Jang, Maria Grazia Mortaro, EonSeon Jin, Olaf Kruse and Thomas Baier
Plants 2024, 13(10), 1393; https://doi.org/10.3390/plants13101393 - 17 May 2024
Cited by 5 | Viewed by 4020
Abstract
Carotenoids are valuable pigments naturally occurring in all photosynthetic plants and microalgae as well as in selected fungi, bacteria, and archaea. Green microalgae developed a complex carotenoid profile suitable for efficient light harvesting and light protection and harbor great capacity for carotenoid production [...] Read more.
Carotenoids are valuable pigments naturally occurring in all photosynthetic plants and microalgae as well as in selected fungi, bacteria, and archaea. Green microalgae developed a complex carotenoid profile suitable for efficient light harvesting and light protection and harbor great capacity for carotenoid production through the substantial power of the endogenous 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway. Previous works established successful genome editing and induced significant changes in the cellular carotenoid content in Chlamydomonas reinhardtii. This study employs a tailored carotenoid pathway for engineered bioproduction of the valuable ketocarotenoid astaxanthin. Functional knockout of lycopene ε-cyclase (LCYE) and non-homologous end joining (NHEJ)-based integration of donor DNA at the target site inhibit the accumulation of α-carotene and consequently lutein and loroxanthin, abundant carotenoids in C. reinhardtii without changes in cellular fitness. PCR-based screening indicated that 4 of 96 regenerated candidate lines carried (partial) integrations of donor DNA and increased ß-carotene as well as derived carotenoid contents. Iterative overexpression of CrBKT, PacrtB, and CrCHYB resulted in a 2.3-fold increase in astaxanthin accumulation in mutant ΔLCYE#3 (1.8 mg/L) compared to the parental strain UVM4, which demonstrates the potential of genome editing for the design of a green cell factory for astaxanthin bioproduction. Full article
(This article belongs to the Special Issue Microalgae Photobiology, Biotechnology, and Bioproduction)
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19 pages, 2541 KiB  
Article
Heterotrophy Compared to Photoautotrophy for Growth Characteristics and Pigment Compositions in Batch Cultures of Four Green Microalgae
by Thanh Tung Le, Amélie Corato, Thomas Gerards, Stéphanie Gérin, Claire Remacle and Fabrice Franck
Plants 2024, 13(9), 1182; https://doi.org/10.3390/plants13091182 - 24 Apr 2024
Cited by 1 | Viewed by 1048
Abstract
Four strains of green microalgae (Scenedesmus acutus, Scenedesmus vacuolatus, Chlorella sorokiniana, and Chlamydomonas reinhardtii) were compared to determine growth and pigment composition under photoautotrophic or heterotrophic conditions. Batch growth experiments were performed in multicultivators with online monitoring of [...] Read more.
Four strains of green microalgae (Scenedesmus acutus, Scenedesmus vacuolatus, Chlorella sorokiniana, and Chlamydomonas reinhardtii) were compared to determine growth and pigment composition under photoautotrophic or heterotrophic conditions. Batch growth experiments were performed in multicultivators with online monitoring of optical density. For photoautotrophic growth, light-limited (CO2-sufficient) growth was analyzed under different light intensities during the exponential and deceleration growth phases. The specific growth rate, measured during the exponential phase, and the maximal biomass productivity, measured during the deceleration phase, were not related to each other when different light intensities and different species were considered. This indicates species-dependent photoacclimation effects during cultivation time, which was confirmed by light-dependent changes in pigment content and composition when exponential and deceleration phases were compared. Except for C. reinhardtii, which does not grow on glucose, heterotrophic growth was promoted to similar extents by acetate and by glucose; however, these two substrates led to different pigment compositions. Weak light increased the pigment content during heterotrophy in the four species but was efficient in promoting growth only in S. acutus. C. sorokiniana, and S. vacuolatus exhibited the best potential for heterotrophic biomass productivities, both on glucose and acetate, with carotenoid (lutein) content being the highest in the former. Full article
(This article belongs to the Special Issue Microalgae Photobiology, Biotechnology, and Bioproduction)
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13 pages, 2609 KiB  
Article
Dysfunction of Chloroplast Protease Activity Mitigates pgr5 Phenotype in the Green Algae Chlamydomonas reinhardtii
by Shin-Ichiro Ozawa, Guoxian Zhang and Wataru Sakamoto
Plants 2024, 13(5), 606; https://doi.org/10.3390/plants13050606 - 23 Feb 2024
Viewed by 1172
Abstract
Researchers have described protection mechanisms against the photoinhibition of photosystems under strong-light stress. Cyclic Electron Flow (CEF) mitigates electron acceptor-side limitation, and thus contributes to Photosystem I (PSI) protection. Chloroplast protease removes damaged protein to assist with protein turn over, which contributes to [...] Read more.
Researchers have described protection mechanisms against the photoinhibition of photosystems under strong-light stress. Cyclic Electron Flow (CEF) mitigates electron acceptor-side limitation, and thus contributes to Photosystem I (PSI) protection. Chloroplast protease removes damaged protein to assist with protein turn over, which contributes to the quality control of Photosystem II (PSII). The PGR5 protein is involved in PGR5-dependent CEF. The FTSH protein is a chloroplast protease which effectively degrades the damaged PSII reaction center subunit, D1 protein. To investigate how the PSI photoinhibition phenotype in pgr5 would be affected by adding the ftsh mutation, we generated double-mutant pgr5ftsh via crossing, and its phenotype was characterized in the green algae Chlamydomonas reinhardtii. The cells underwent high-light incubation as well as low-light incubation after high-light incubation. The time course of Fv/Fm values in pgr5ftsh showed the same phenotype with ftsh1-1. The amplitude of light-induced P700 photo-oxidation absorbance change was measured. The amplitude was maintained at a low value in the control and pgr5ftsh during high-light incubation, but was continuously decreased in pgr5. During the low-light incubation after high-light incubation, amplitude was more rapidly recovered in pgr5ftsh than pgr5. We concluded that the PSI photoinhibition by the pgr5 mutation is mitigated by an additional ftsh1-1 mutation, in which plastoquinone pool would be less reduced due to damaged PSII accumulation. Full article
(This article belongs to the Special Issue Microalgae Photobiology, Biotechnology, and Bioproduction)
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Review

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17 pages, 1551 KiB  
Review
Light-Driven H2 Production in Chlamydomonas reinhardtii: Lessons from Engineering of Photosynthesis
by Michael Hippler and Fatemeh Khosravitabar
Plants 2024, 13(15), 2114; https://doi.org/10.3390/plants13152114 - 30 Jul 2024
Viewed by 954
Abstract
In the green alga Chlamydomonas reinhardtii, hydrogen production is catalyzed via the [FeFe]-hydrogenases HydA1 and HydA2. The electrons required for the catalysis are transferred from ferredoxin (FDX) towards the hydrogenases. In the light, ferredoxin receives its electrons from photosystem I (PSI) so [...] Read more.
In the green alga Chlamydomonas reinhardtii, hydrogen production is catalyzed via the [FeFe]-hydrogenases HydA1 and HydA2. The electrons required for the catalysis are transferred from ferredoxin (FDX) towards the hydrogenases. In the light, ferredoxin receives its electrons from photosystem I (PSI) so that H2 production becomes a fully light-driven process. HydA1 and HydA2 are highly O2 sensitive; consequently, the formation of H2 occurs mainly under anoxic conditions. Yet, photo-H2 production is tightly coupled to the efficiency of photosynthetic electron transport and linked to the photosynthetic control via the Cyt b6f complex, the control of electron transfer at the level of photosystem II (PSII) and the structural remodeling of photosystem I (PSI). These processes also determine the efficiency of linear (LEF) and cyclic electron flow (CEF). The latter is competitive with H2 photoproduction. Additionally, the CBB cycle competes with H2 photoproduction. Consequently, an in-depth understanding of light-driven H2 production via photosynthetic electron transfer and its competition with CO2 fixation is essential for improving photo-H2 production. At the same time, the smart design of photo-H2 production schemes and photo-H2 bioreactors are challenges for efficient up-scaling of light-driven photo-H2 production. Full article
(This article belongs to the Special Issue Microalgae Photobiology, Biotechnology, and Bioproduction)
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28 pages, 1885 KiB  
Review
Regulation of Microalgal Photosynthetic Electron Transfer
by Yuval Milrad, Laura Mosebach and Felix Buchert
Plants 2024, 13(15), 2103; https://doi.org/10.3390/plants13152103 - 29 Jul 2024
Viewed by 714
Abstract
The global ecosystem relies on the metabolism of photosynthetic organisms, featuring the ability to harness light as an energy source. The most successful type of photosynthesis utilizes a virtually inexhaustible electron pool from water, but the driver of this oxidation, sunlight, varies on [...] Read more.
The global ecosystem relies on the metabolism of photosynthetic organisms, featuring the ability to harness light as an energy source. The most successful type of photosynthesis utilizes a virtually inexhaustible electron pool from water, but the driver of this oxidation, sunlight, varies on time and intensity scales of several orders of magnitude. Such rapid and steep changes in energy availability are potentially devastating for biological systems. To enable a safe and efficient light-harnessing process, photosynthetic organisms tune their light capturing, the redox connections between core complexes and auxiliary electron mediators, ion passages across the membrane, and functional coupling of energy transducing organelles. Here, microalgal species are the most diverse group, featuring both unique environmental adjustment strategies and ubiquitous protective mechanisms. In this review, we explore a selection of regulatory processes of the microalgal photosynthetic apparatus supporting smooth electron flow in variable environments. Full article
(This article belongs to the Special Issue Microalgae Photobiology, Biotechnology, and Bioproduction)
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26 pages, 1068 KiB  
Review
Getting Grip on Phosphorus: Potential of Microalgae as a Vehicle for Sustainable Usage of This Macronutrient
by Alexei Solovchenko, Maxence Plouviez and Inna Khozin-Goldberg
Plants 2024, 13(13), 1834; https://doi.org/10.3390/plants13131834 - 3 Jul 2024
Cited by 1 | Viewed by 822
Abstract
Phosphorus (P) is an important and irreplaceable macronutrient. It is central to energy and information storage and exchange in living cells. P is an element with a “broken geochemical cycle” since it lacks abundant volatile compounds capable of closing the P cycle. P [...] Read more.
Phosphorus (P) is an important and irreplaceable macronutrient. It is central to energy and information storage and exchange in living cells. P is an element with a “broken geochemical cycle” since it lacks abundant volatile compounds capable of closing the P cycle. P fertilizers are critical for global food security, but the reserves of minable P are scarce and non-evenly distributed between countries of the world. Accordingly, the risks of global crisis due to limited access to P reserves are expected to be graver than those entailed by competition for fossil hydrocarbons. Paradoxically, despite the scarcity and value of P reserves, its usage is extremely inefficient: the current waste rate reaches 80% giving rise to a plethora of unwanted consequences such as eutrophication leading to harmful algal blooms. Microalgal biotechnology is a promising solution to tackle this challenge. The proposed review briefly presents the relevant aspects of microalgal P metabolism such as cell P reserve composition and turnover, and the regulation of P uptake kinetics for maximization of P uptake efficiency with a focus on novel knowledge. The multifaceted role of polyPhosphates, the largest cell depot for P, is discussed with emphasis on the P toxicity mediated by short-chain polyPhosphates. Opportunities and hurdles of P bioremoval via P uptake from waste streams with microalgal cultures, either suspended or immobilized, are discussed. Possible avenues of P-rich microalgal biomass such as biofertilizer production or extraction of valuable polyPhosphates and other bioproducts are considered. The review concludes with a comprehensive assessment of the current potential of microalgal biotechnology for ensuring the sustainable usage of phosphorus. Full article
(This article belongs to the Special Issue Microalgae Photobiology, Biotechnology, and Bioproduction)
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