Prospects for molecular farming in the green alga Chlamydomonas

Harnessing the potential of microalgae for the production of monoclonal antibodies and other recombinant proteins

Monoclonal antibodies (mAbs) have become indispensable tools in various fields, from research to therapeutics, diagnostics, and industries. However, their production, primarily in mammalian cell culture systems, is cost-intensive and resource-demanding. Microalgae, diverse photosynthetic microorganisms, are gaining attention as a favorable option for manufacturing mAbs and various other recombinant proteins. This review explores the potential of microalgae as a robust expression system for biomanufacturing high-value proteins. It also highlights the diversity of microalgae species suitable for recombinant protein. Nuclear and chloroplast genomes of some microalgae have been engineered to express mAbs and other valuable proteins. Codon optimization, vector construction, and other genetic engineering techniques have significantly improved recombinant protein expression in microalgae. These accomplishments demonstrate the potential of microalgae for biopharmaceutical manufacturing. Microalgal biotechnology holds promise for revolutionizing the production of mAbs and other therapeutic proteins, offering a sustainable and cost-effective solution to address critical healthcare needs.

An RNA thermometer in the chloroplast genome of Chlamydomonas facilitates temperature-controlled gene expression

Riboregulators such as riboswitches and RNA thermometers provide simple, protein-independent tools to control gene expression at the post-transcriptional level. In bacteria, RNA thermometers regulate protein synthesis in response to temperature shifts. Thermometers outside of the bacterial world are rare, and in organellar genomes, no RNA thermometers have been identified to date. Here we report the discovery of an RNA thermometer in a chloroplast gene of the unicellular green alga Chlamydomonas reinhardtii. The thermometer, residing in the 5' untranslated region of the psaA messenger RNA forms a hairpin-type secondary structure that masks the Shine-Dalgarno sequence at 25°C. At 40°C, melting of the secondary structure increases accessibility of the Shine-Dalgarno sequence to initiating ribosomes, thus enhancing protein synthesis. By targeted nucleotide substitutions and transfer of the thermometer into Escherichia coli, we show that the secondary structure is necessary and sufficient to confer the thermometer properties. We also demonstrate that the thermometer provides a valuable tool for inducible transgene expression from the Chlamydomonas plastid genome, in that a simple temperature shift of the algal culture can greatly increase recombinant protein yields.

Current Nuclear Engineering Strategies in the Green Microalga Chlamydomonas reinhardtii

The green model microalga Chlamydomonas reinhardtii recently emerged as a sustainable production chassis for the efficient biosynthesis of recombinant proteins and high-value metabolites. Its capacity for scalable, rapid and light-driven growth in minimal salt solutions, its simplicity for genetic manipulation and its "Generally Recognized As Safe" (GRAS) status are key features for its application in industrial biotechnology. Although nuclear transformation has typically resulted in limited transgene expression levels, recent developments now allow the design of powerful and innovative bioproduction concepts. In this review, we summarize the main obstacles to genetic engineering in C. reinhardtii and describe all essential aspects in sequence adaption and vector design to enable sufficient transgene expression from the nuclear genome. Several biotechnological examples of successful engineering serve as blueprints for the future establishment of C. reinhardtii as a green cell factory.

Antimicrobial peptides derived from microalgae for combating antibiotic resistance: Current status and prospects

Microalgae are photosynthetic cell factories that produce a spectrum of bioactive compounds extensively used for various applications. Owing to the increase in antibiotic resistance among microbial pathogens, there is a significant thrust for identifying new treatment strategies, and antimicrobial peptides (AMPs) generation is one such method. These AMPs have multiple roles and are active against bacteria, fungi, and viruses. Such peptides synthesized in microalgae have a significant role in medical application, managing aquaculture-associated diseases, and the food industry. To increase their effectiveness and novel peptides, genetically modified microalgae are used as cell factories. With the advancement of new technologies like the CRISPR-Cas system, new avenues are opened for developing novel AMPs using microalgae. This review gives us insight into the various AMPs produced by microalgae and multiple technologies involved in creating such therapeutically essential molecules.

Microalgal Carotenoids: Therapeutic Application and Latest Approaches to Enhance the Production

Microalgae are microscopic photosynthetic organisms frequently found in fresh and marine water ecosystems. Various microalgal species have been considered a reservoir of diverse health-value products, including vitamins, proteins, lipids, and polysaccharides, and are broadly utilized as food and for the treatment of human ailments such as cancer, cardiovascular diseases, allergies, and immunodeficiency. Microalgae-derived carotenoids are the type of accessory pigment that possess light-absorbing potential and play a significant role in metabolic functions. To date, nearly a thousand carotenoids have been reported, but a very less number of microalgae have been used for the commercial production of carotenoids. This review article briefly discussed the carotenoids of microalgal origin and their therapeutic application. In addition, we have briefly compiled the optimization of culture parameters used to enhance microalgal carotenoid production. In addition, the latest biotechnological approaches used to improve the yields of carotenoid has also been discussed.

Recent Progress on Vaccines Produced in Transgenic Plants

The development of vaccines from plants has been going on for over two decades now. Vaccine production in plants requires time and a lot of effort. Despite global efforts in plant-made vaccine development, there are still challenges that hinder the realization of the final objective of manufacturing approved and safe products. Despite delays in the commercialization of plant-made vaccines, there are some human vaccines that are in clinical trials. The novel coronavirus (SARS-CoV-2) and its resultant disease, coronavirus disease 2019 (COVID-19), have reminded the global scientific community of the importance of vaccines. Plant-made vaccines could not be more important in tackling such unexpected pandemics as COVID-19. In this review, we explore current progress in the development of vaccines manufactured in transgenic plants for different human diseases over the past 5 years. However, we first explore the different host species and plant expression systems during recombinant protein production, including their shortcomings and benefits. Lastly, we address the optimization of existing plant-dependent vaccine production protocols that are aimed at improving the recovery and purification of these recombinant proteins.

Recombinant Bovine and Human Osteopontin Generated by Chlamydomonas reinhardtii Exhibit Bioactivities Similar to Bovine Milk Osteopontin When Assessed in Mouse Pups Fed Osteopontin-Deficient Milk

SCOPE

Osteopontin (OPN), a highly phosphorylated and glycosylated protein, is present in most body fluids, including milk. OPN appears at a high concentration in human milk (130-180 mg L^-1 ), but not bovine milk (≈18 mg mL^-1 ). It is previously shown that milk OPN is involved in various biological processes and therefore may be a valuable infant formula additive.

METHODS AND RESULTS

In the present study, recombinant bovine OPN (rbOPN) and recombinant human OPN (rhOPN) are generated in a Chlamydomonas reinhardtii (C. reinhardtii) algal expression system. The rbOPN and rhOPN are phosphorylated but not glycosylated. To assess the bioactivities of rbOPN and rhOPN and compare their bioactivities to those of bovine milk OPN (bmOPN), wild-type (WT) mouse pups nursed by OPN knock-out (KO) dams are orally fed bmOPN, rbOPN, and rhOPN daily from postnatal days 1-21 (P1-21). Effects of these OPNs on development of the brain, intestine, and immune function are evaluated. The results show that rbOPN and rhOPN exhibit effects similar to those of bmOPN as well as mouse milk OPN on stimulating proliferation of the small intestine, increasing brain myelination and cognitive development, and enhancing development of immune function.

CONCLUSION

rbOPN and rhOPN are likely to provide beneficial bioactivities when added to infant diets.

The immune response and immune evasion characteristics in SARS-CoV, MERS-CoV, and SARS-CoV-2: Vaccine design strategies

The worldwide outbreak of SARS-CoV-2, severe acute respiratory syndrome coronavirus 2 as a novel human coronavirus, was the worrying news at the beginning of 2020. Since its emergence complicated more than 870,000 individuals and led to more than 43,000 deaths worldwide. Considering to the potential threat of a pandemic and transmission severity of it, there is an urgent need to evaluate and realize this new virus's structure and behavior and the immunopathology of this disease to find potential therapeutic protocols and to design and develop effective vaccines. This disease is able to agitate the response of the immune system in the infected patients, so ARDS, as a common consequence of immunopathological events for infections with Middle East respiratory syndrome coronavirus (MERS-CoV), SARS-CoV, and SARS-CoV-2, could be the main reason for death. Here, we summarized the immune response and immune evasion characteristics in SARS-CoV, MERS-CoV, and SARS-CoV-2 and therapeutic and prophylactic strategies with a focus on vaccine development and its challenges.

Nuclear transformation of Chlamydomonas reinhardtii: A review

Chlamydomonas reinhardtii is a model organism with three sequenced genomes capable of genetic transformation. C. reinhardtii has the advantages of being low cost, non-toxic, and having a post-translational modification system that ensures the recombinant proteins have the same activity as natural proteins, thus making it a great platform for application in molecular biology and other fields. In this review, we summarize the existing methods for nuclear transformation of C. reinhardtii, genes for selection, examples of foreign protein expression, and factors affecting transformation efficiency, to provide insights into effective strategies for the nuclear transformation of C. reinhardtii.

Development of an alcohol-inducible gene expression system for recombinant protein expression in Chlamydomonas reinhardtii

Microalgae have been widely considered for the production of valuable products, such as lipid-based biofuel, value-added pigments, and anti-photo aging reagents. More recently, microalgae have been considered an alternative host for recombinant protein production because of their economic benefits and ecofriendly characteristics. Additionally, many microalgal strains identified to date are generally recognized as safe (GRAS); therefore, the use of microalgae-based technology is promising. However, basic studies on the genetic engineering of microalgae are rare, despite their importance. Particularly, inducible promoter systems that can be applied for strain engineering or recombinant protein production are rarely studied; hence, a number of challenging issues remain unsolved. Therefore, in this study, we focused on the development of a convenient and compact-inducible promoter system that can be used in microalgae. Based on previous success with plant systems, we employed the alcohol-inducible AlcR-P _alcA system, which originates from the filamentous fungus, Aspergillus nidulans. This system comprises only two components, a regulatory protein, AlcR, and an inducible promoter, P _alcA. Therefore, construction and transformation of the gene cassettes can be easily performed. Ethanol-dependent gene expression was observed in the transformants with no significant growth retardation or inducer consumption observed in the cells cultivated under optimized conditions.

Identification of Chlamydomonas reinhardtii endogenous genic flanking sequences for improved transgene expression

Chlamydomonas reinhardtii is a unicellular green alga that has attracted interest due to its potential biotechnological applications, and as a model for algal biofuel and energy metabolism. Despite all the advantages that this unicellular alga offers, poor and inconsistent expression of nuclear transgenes remains an obstacle for basic and applied research. We used a data-mining strategy to identify highly expressed genes in Chlamydomonas whose flanking sequences were tested for the ability to drive heterologous nuclear transgene expression. Candidates identified in this search included two ribosomal protein genes, RPL35a and RPL23, and ferredoxin, FDX1, whose flanking regions including promoters, terminators and untranslated sequences could drive stable luciferase transgene expression to significantly higher levels than the commonly used Hsp70A-RBCS2 (AR) hybrid promoter/terminator sequences. The RPL23 flanking sequences were further tested using the zeocin resistance gene sh-ble as a reporter in monocistronic and dicistronic constructs, and consistently yielded higher numbers of zeocin-resistant transformants and higher levels of resistance than AR- or PSAD-based vectors. Chlamydomonas RPL23 sequences also enabled transgene expression in Volvox carteri. Our study provides an additional benchmark for strong constitutive expression of transgenes in Chlamydomonas, and develops a general approach for identifying flanking sequences that can be used to drive transgene expression for any organism where transcriptome data are available.

Recombinant Hemagglutinin of Avian Influenza Virus H5 Expressed in the Chloroplast of Chlamydomonas reinhardtii and Evaluation of Its Immunogenicity in Chickens

Globally, avian influenza (AI) is a serious problem in poultry farming. Despite vaccination, the prevalence of AI in México highlights the need for new approaches to control AI and to reduce the economic losses associated with its occurrence in susceptible birds. Recombinant proteins from avian influenza virus (AIV) have been expressed in different organisms, such as plants. The present study investigated the feasibility of designing and expressing the HA protein of AIV in the transplastomic microalga Chlamydomonas reinhardtii as a novel approach for AIV control and taking advantage of culture conditions, its reproductive range, and safe use in consideration of the generally regarded as safe food ingredient regulatory classification. The results showed that the HA protein of AIV in C. reinhardtii presents antigenic activity by western blot test and through its application in chickens, demonstrating its feasibility as a recombinant antigen against AIV.

Non-conventional expression systems for the production of vaccine proteins and immunotherapeutic molecules

The increasing demand for recombinant vaccine antigens or immunotherapeutic molecules calls into question the universality of current protein expression systems. Vaccine production can require relatively low amounts of expressed materials, but represents an extremely diverse category consisting of different target antigens with marked structural differences. In contrast, monoclonal antibodies, by definition share key molecular characteristics and require a production system capable of very large outputs, which drives the quest for highly efficient and cost-effective systems. In discussing expression systems, the primary assumption is that a universal production platform for vaccines and immunotherapeutics will unlikely exist. This review provides an overview of the evolution of traditional expression systems, including mammalian cells, yeast and E.coli, but also alternative systems such as other bacteria than E. coli, transgenic animals, insect cells, plants and microalgae, Tetrahymena thermophila, Leishmania tarentolae, filamentous fungi, cell free systems, and the incorporation of non-natural amino acids.

Selenocystamine improves protein accumulation in chloroplasts of eukaryotic green algae

Eukaryotic green algae have become an increasingly popular platform for recombinant proteins production. In particular, Chlamydomonas reinhardtii, has garnered increased attention for having the necessary biochemical machinery to produce vaccines, human antibodies and next generation cancer targeting immunotoxins. While it has been shown that chloroplasts contain chaperones, peptidyl prolylisomerases and protein disulfide isomerases that facilitate these complex proteins folding and assembly, little has been done to determine which processes serve as rate-limiting steps for protein accumulation. In other expression systems, as Escherichia coli, Chinese hamster ovary cells, and insect cells, recombinant protein accumulation can be hampered by cell's inability to fold the target polypeptide into the native state, resulting in aggregation and degradation. To determine if chloroplasts' ability to oxidize proteins that require disulfide bonds into a stable conformation is a rate-limiting step of protein accumulation, three recombinant strains, each expressing a different recombinant protein, were analyzed. These recombinant proteins included fluorescent GFP, a reporter containing no disulfide bonds; Gaussia princeps luciferase, a luminescent reporter containing disulfide bonds; and an immunotoxin, an antibody-fusion protein containing disulfide bonds. Each strain was analyzed for its ability to accumulate proteins when supplemented with selenocystamine, a small molecule capable of catalyzing the formation of disulfide bonds. Selenocystamine supplementation led to an increase in luciferase and immunotoxin but not GFP accumulation. These results demonstrated that selenocystamine can increase the accumulation of proteins containing disulfide bonds and suggests that a rate-limiting step in chloroplast protein accumulation is the disulfide bonds formation in recombinant proteins native structure.

An efficient protocol for the Agrobacterium-mediated genetic transformation of microalga Chlamydomonas reinhardtii

Algal-based recombinant protein production has gained immense interest in recent years. The development of algal expression system was earlier hindered due to the lack of efficient and cost-effective transformation techniques capable of heterologous gene integration and expression. The recent development of Agrobacterium-mediated genetic transformation method is expected to be the ideal solution for these problems. We have developed an efficient protocol for the Agrobacterium-mediated genetic transformation of microalga Chlamydomonas reinhardtii. Pre-treatment of Agrobacterium in TAP induction medium (pH 5.2) containing 100 μM acetosyringone and 1 mM glycine betaine and infection of Chlamydomonas with the induced Agrobacterium greatly improved transformation frequency. This protocol was found to double the number of transgenic events on selection media compared to that of previous reports. PCR was used successfully to amplify fragments of the hpt and GUS genes from transformed cells, while Southern blot confirmed the integration of GUS gene into the genome of C. reinhardtii. RT-PCR, Northern blot and GUS histochemical analyses confirm GUS gene expression in the transgenic cell lines of Chlamydomonas. This protocol provides a quick, efficient, economical and high-frequency transformation method for microalgae.

Future directions for the development of Chlamydomonas-based vaccines

Besides serving as a valuable model in biological sciences, Chamydomonas reinhardtii has been used during the last decade in the biotechnology arena to establish models for the low cost production of vaccines. Antigens from various pathogens including Plasmodium falciparum, foot and mouth disease virus, Staphylococcus aureus, classical swine fever virus (CSFV) as well as some auto-antigens, have been produced in C. reinhardtii. Although some of them have been functionally characterized with promising results, this review identifies future directions for the advancement in the exploitation of this robust and safe vaccine production platform. The present analysis reflects that important immunological implications exist for this system and remain unexplored, including the possible adjuvant effects of algae biomolecules, the effect of bioencapsulation on immunogenicity and the possible development of whole-cell vaccines as an approach to trigger cytotoxic immune responses. Recently described molecular strategies that aim to optimize the expression of nuclear-encoded target antigens are also discussed.

Genes involved in the endoplasmic reticulum N-glycosylation pathway of the red microalga Porphyridium sp.: a bioinformatic study

N-glycosylation is one of the most important post-translational modifications that influence protein polymorphism, including protein structures and their functions. Although this important biological process has been extensively studied in mammals, only limited knowledge exists regarding glycosylation in algae. The current research is focused on the red microalga Porphyridium sp., which is a potentially valuable source for various applications, such as skin therapy, food, and pharmaceuticals. The enzymes involved in the biosynthesis and processing of N-glycans remain undefined in this species, and the mechanism(s) of their genetic regulation is completely unknown. In this study, we describe our pioneering attempt to understand the endoplasmic reticulum N-Glycosylation pathway in Porphyridium sp., using a bioinformatic approach. Homology searches, based on sequence similarities with genes encoding proteins involved in the ER N-glycosylation pathway (including their conserved parts) were conducted using the TBLASTN function on the algae DNA scaffold contigs database. This approach led to the identification of 24 encoded-genes implicated with the ER N-glycosylation pathway in Porphyridium sp. Homologs were found for almost all known N-glycosylation protein sequences in the ER pathway of Porphyridium sp.; thus, suggesting that the ER-pathway is conserved; as it is in other organisms (animals, plants, yeasts, etc.).

Ice recrystallization inhibition mediated by a nuclear-expressed and -secreted recombinant ice-binding protein in the microalga Chlamydomonas reinhardtii

A Lolium perenne ice-binding protein (LpIBP) demonstrates superior ice recrystallization inhibition (IRI) activity and has proposed applications in cryopreservation, food texturing, as well as in being a "green" gas hydrate inhibitor. Recombinant production of LpIBP has been previously conducted in bacterial and yeast systems for studies of protein characterization, but large-scale applications have been hitherto limited due to high production costs. In this work, a codon-optimized LpIBP was recombinantly expressed and secreted in a novel one-step vector system from the nuclear genome of the green microalga Chlamydomonas reinhardtii. Both mixotrophic and photoautotrophic growth regimes supported LpIBP expression, indicating the feasibility of low-cost production using minimal medium, carbon dioxide, and light energy as input. In addition, multiple growth and bioproduct extraction cycles were performed by repetitive batch cultivation trials, demonstrating the potential for semi-continuous production and biomass harvesting. Concentrations of recombinant protein reached in this proof of concept approach were sufficient to demonstrate IRI activity in culture media without additional purification or concentration, with activity further verified by thermal hysteresis and morphology assays. The incorporation of the recombinant LpIBP into a model gas hydrate offers the promise that algal production may eventually find application as a "green" hydrate inhibitor.

Production of unique immunotoxin cancer therapeutics in algal chloroplasts

The idea of targeted therapy, whereby drug or protein molecules are delivered to specific cells, is a compelling approach to treating disease. Immunotoxins are one such targeted therapeutic, consisting of an antibody domain for binding target cells and molecules of a toxin that inhibits the proliferation of the targeted cell. One major hurdle preventing these therapies from reaching the market has been the lack of a suitable production platform that allows the cost-effective production of these highly complex molecules. The chloroplast of the green alga Chlamydomonas reinhardtii has been shown to contain the machinery necessary to fold and assemble complex eukaryotic proteins. However, the translational apparatus of chloroplasts resembles that of a prokaryote, allowing them to accumulate eukaryotic toxins that otherwise would kill a eukaryotic host. Here we show expression and accumulation of monomeric and dimeric immunotoxin proteins in algal chloroplasts. These fusion proteins contain an antibody domain targeting CD22, a B-cell surface epitope, and the enzymatic domain of exotoxin A from Pseudomonas aeruginosa. We demonstrated that algal-produced immunotoxins accumulate as soluble and enzymatically active proteins that bind target B cells and efficiently kill them in vitro. We also show that treatment with either the mono- or dimeric immunotoxins significantly prolongs the survival of mice with implanted human B-cell tumors.

An engineered diatom acting like a plasma cell secreting human IgG antibodies with high efficiency

BACKGROUND

Although there are many different expression systems for recombinant production of pharmaceutical proteins, many of these suffer from drawbacks such as yield, cost, complexity of purification, and possible contamination with human pathogens. Microalgae have enormous potential for diverse biotechnological applications and currently attract much attention in the biofuel sector. Still underestimated, though, is the idea of using microalgae as solar-fueled expression system for the production of recombinant proteins.

RESULTS

In this study, we show for the first time that completely assembled and functional human IgG antibodies can not only be expressed to high levels in algal systems, but also secreted very efficiently into the culture medium. We engineered the diatom Phaeodactylum tricornutum to synthesize and secrete a human IgG antibody against the Hepatitis B Virus surface protein. As the diatom P. tricornutum is not known to naturally secrete many endogenous proteins, the secreted antibodies are already very pure making extensive purification steps redundant and production extremely cost efficient.

CONCLUSIONS

Microalgae combine rapid growth rates with all the advantages of eukaryotic expression systems, and offer great potential for solar-powered, low cost production of pharmaceutical proteins.

Advances in genetic engineering of marine algae

Algae are a component of bait sources for animal aquaculture, and they produce abundant valuable compounds for the chemical industry and human health. With today's fast growing demand for algae biofuels and the profitable market for cosmetics and pharmaceuticals made from algal natural products, the genetic engineering of marine algae has been attracting increasing attention as a crucial systemic technology to address the challenge of the biomass feedstock supply for sustainable industrial applications and to modify the metabolic pathway for the more efficient production of high-value products. Nevertheless, to date, only a few marine algae species can be genetically manipulated. In this article, an updated account of the research progress in marine algal genomics is presented along with methods for transformation. In addition, vector construction and gene selection strategies are reviewed. Meanwhile, a review on the progress of bioreactor technologies for marine algae culture is also revisited.

Stable expression of antibiotic-resistant gene ble from Streptoalloteichus hindustanus in the mitochondria of Chlamydomonas reinhardtii

The mitochondrial expression of exogenous antibiotic resistance genes has not been demonstrated successfully to date, which has limited the development of antibiotic resistance genes as selectable markers for mitochondrial site-directed transformation in Chlamydomonas reinhardtii. In this work, the plasmid pBSLPNCB was constructed by inserting the gene ble of Streptoalloteichus hindustanus (Sh ble), encoding a small (14-kilodalton) protective protein into the site between TERMINVREP-Left repeats and the cob gene in a fragment of mitochondrial DNA (mtDNA) of C. reinhardtii. The fusion DNA-construct, which contained TERMINVREP-Left, Sh ble, cob, and partial nd4 sequence, were introduced into the mitochondria of the respiratory deficient dum-1 mutant CC-2654 of C. reinhardtii by biolistic particle delivery system. A large number of transformants were obtained after eight weeks in the dark. Subsequent subculture of the transformants on the selection TAP media containing 3 ìg/mL Zeomycin for 12 months resulted in genetically modified transgenic algae MT-Bs. Sequencing and Southern analyses on the mitochondrial genome of the different MT-B lines revealed that Sh ble gene had been integrated into the mitochondrial genome of C. reinhardtii. Both Western blot, using the anti-BLE monoclonal antibody, and Zeomycin tolerance analysis confirmed the presence of BLE protein in the transgenic algal cells. It indicates that the Sh ble gene can be stably expressed in the mitochondria of C. reinhardtii.

Chlamydomonas reinhardtii as a viable platform for the production of recombinant proteins: current status and perspectives

Chlamydomonas reinhardtii has many advantages compared with traditional systems for the molecular farming of recombinant proteins. These include low production costs, rapid scalability at pilot level, absence of human pathogens and the ability to fold and assemble complex proteins accurately. Currently, the successful expression of several proteins with pharmaceutical relevance has been reported from the nuclear and the chloroplastic genome of this alga, demonstrating its usefulness for biotechnological applications. However, several factors affect the level of recombinant protein expression in Chlamydomonas such as enhancer elements, codon dependency, sensitivity to proteases and transformation-associated genotypic modification. The present review outlines a number of strategies to increase protein yields and summarizes recent achievements in algal protein production including biopharmaceuticals such as vaccines, antibodies, hormones and enzymes with implications on health-related approaches. The current status of bioreactor developments for algal culture and the challenges of scale-up and optimization processes are also discussed.

Overlapping photoprotective function of vitamin E and carotenoids in Chlamydomonas

Tocopherols (vitamin E) and carotenoids are the two most abundant groups of lipid-soluble antioxidants in the chloroplast. Carotenoids are well known for their roles in protecting against photooxidative stress, whereas the photoprotective functions of tocopherols have only recently been examined experimentally. In addition, little is known about the functional overlap of carotenoids and tocopherols in vivo. To investigate this possible overlap, Chlamydomonas reinhardtii strains were engineered to overproduce tocopherols by chloroplast transformation with non-codon-optimized and codon-optimized versions of the homogentisate phytyltransferase vitamin E2 (VTE2) from Synechocystis and by nuclear transformation with VTE2 from C. reinhardtii, which resulted in 1.6-fold, 5-fold to 10-fold, and more than 10-fold increases in total tocopherol content, respectively. To test if tocopherol overproduction can compensate for carotenoid deficiency in terms of antioxidant function, the nuclear VTE2 gene from C. reinhardtii was overexpressed in the npq1 lor1 double mutant, which lacks zeaxanthin and lutein. Following transfer to high light, the npq1 lor1 strains that overaccumulated tocopherols showed increased resistance for up to 2 d and higher efficiency of photosystem II, and they were also much more resistant to other oxidative stresses. These results suggest an overlapping functions of tocopherols and carotenoids in protection against photooxidative stress.

Green algae Chlamydomonas reinhardtii possess endogenous sialylated N-glycans

Green algae have a great potential as biofactories for the production of proteins. Chlamydomonas reinhardtii, a representative of eukaryotic microalgae, has been extensively used as a model organism to study light-induced gene expression, chloroplast biogenesis, photosynthesis, light perception, cell–cell recognition, and cell cycle control. However, little is known about the glycosylation machinery and N-linked glycan structures of green algae. In this study, we performed mass spectrometry analysis of N-linked oligosaccharides released from total extracts of Chlamydomonas reinhardtii and demonstrated that C. reinhardtii algae possess glycoproteins with mammalian-like sialylated N-linked oligosaccharides. These findings suggest that C. reinhardtii may be an attractive system for expression of target proteins.

Molecular factors affecting the accumulation of recombinant proteins in the Chlamydomonas reinhardtii chloroplast

In an effort to develop microalgae as a robust system for the production of valuable proteins, we analyzed some of the factors affecting recombinant protein expression in the chloroplast of the green alga Chlamydomonas reinhardtii. We monitored mRNA accumulation, protein synthesis, and protein turnover for three codon-optimized transgenes including GFP, bacterial luciferase, and a large single chain antibody. GFP and luciferase proteins were quite stable, while the antibody was less so. Measurements of protein synthesis, in contrast, clearly showed that translation of the three chimeric mRNAs was greatly reduced when compared to endogenous mRNAs under control of the same atpA promoter/UTR. Only in a few conditions this could be explained by limited mRNA availability since, in most cases, recombinant mRNAs accumulated quite well when compared to the atpA mRNA. In vitro toeprint and in vivo polysome analyses suggest that reduced ribosome association might contribute to limited translational efficiency. However, when recombinant polysome levels and protein synthesis are analyzed as a whole, it becomes clear that other steps, such as inefficient protein elongation, are likely to have a considerable impact. Taken together, our results point to translation as the main step limiting the expression of heterologous proteins in the C. reinhardtii chloroplast.

Improved biohydrogen production with an expression of codon-optimized hemH and lba genes in the chloroplast of Chlamydomonas reinhardtii

According to the codon bias in the chloroplast genome of Chlamydomonas reinhardtii, the codon-optimized coding regions of both the ferrochelatase gene, hemH, from Bradyrhizobium japonicum and the leghemoglobin gene, lba, from Glycine max were synthesized de novo and transferred into the chloroplast of C. reinhardtii. The expression level of hemH-lba protein was improved by 6.8 folds in the codon-optimized transgenic alga compared with the non-optimized one under both normal and anaerobic conditions. H(2) yield was 22% and the respiration rate was 44% higher in the codon-optimized transgenic algal cultures than those of the non-optimized ones, and was 450% and 134% higher than those of the control cultures, respectively. The transcript levels of hydA1 and hydA2 in the hemH-lba transgenic alga were also more stable and higher than those of the control alga. These results demonstrate that codon optimization increased the expression level of hemH-lba protein in the chloroplast of C. reinhardtii and improved algal H(2) yield by enhancing the respiration rate resulting in low O(2) content in the medium and up regulation of the expression of hydA1 and hydA2 in cells, thereby confirming the potential of the utilization of leghemoglobins for H(2) production in green algae.

Cinnamic acid, coumarin and vanillin: Alternative phenolic compounds for efficient Agrobacterium-mediated transformation of the unicellular green alga, Nannochloropsis sp

The use of acetosyringone in Agrobacterium-mediated gene transfer into plant hosts has been favored for the past few decades. The influence of other phenolic compounds and their effectiveness in Agrobacterium-mediated plant transformation systems has been neglected. In this study, the efficacy of four phenolic compounds on Agrobacterium-mediated transformation of the unicellular green alga Nannochloropsis sp. (Strain UMT-M3) was assessed by using β-glucuronidase (GUS) assay. We found that cinnamic acid, vanillin and coumarin produced higher percentages of GUS positive cells as compared to acetosyringone. These results also show that the presence of methoxy group in the phenolic compounds may not be necessary for Agrobacterium vir gene induction and receptor binding as suggested by previous studies. These findings provide possible alternative Agrobacterium vir gene inducers that are more potent as compared to the commonly used acetosyringone in achieving high efficiency of Agrobacterium-mediated transformation in microalgae and possibly for other plants.

Algal biorefinery-based industry: an approach to address fuel and food insecurity for a carbon-smart world

Food and fuel production are intricately interconnected. In a carbon-smart society, it is imperative to produce both food and fuel sustainably. Integration of the emerging biorefinery concept with other industries can bring many environmental deliverables while mitigating several sustainability-related issues with respect to greenhouse gas emissions, fossil fuel usage, land use change for fuel production and future food insufficiency. A new biorefinery-based integrated industrial ecology encompasses the different value chain of products, coproducts, and services from the biorefinery industries. This paper discusses a framework to integrate the algal biofuel-based biorefinery, a booming biofuel sector, with other industries such as livestock, lignocellulosic and aquaculture. Using the USA as an example, this paper also illustrates the benefits associated with sustainable production of fuel and food. Policy and regulatory initiatives for synergistic development of the algal biofuel sector with other industries can bring many sustainable solutions for the future existence of mankind.

Advances in plant molecular farming

Plant molecular farming (PMF) is a new branch of plant biotechnology, where plants are engineered to produce recombinant pharmaceutical and industrial proteins in large quantities. As an emerging subdivision of the biopharmaceutical industry, PMF is still trying to gain comparable social acceptance as the already established production systems that produce these high valued proteins in microbial, yeast, or mammalian expression systems. This article reviews the various cost-effective technologies and strategies, which are being developed to improve yield and quality of the plant-derived pharmaceuticals, thereby making plant-based production system suitable alternatives to the existing systems. It also attempts to overview the different novel plant-derived pharmaceuticals and non-pharmaceutical protein products that are at various stages of clinical development or commercialization. It then discusses the biosafety and regulatory issues, which are crucial (if strictly adhered to) to eliminating potential health and environmental risks, which in turn is necessary to earning favorable public perception, thus ensuring the success of the industry.

Micro-algae come of age as a platform for recombinant protein production

A complete set of genetic tools is still being developed for the micro-alga Chlamydomonas reinhardtii. Yet even with this incomplete set, this photosynthetic single-celled plant has demonstrated significant promise as a platform for recombinant protein expression. In recent years, techniques have been developed that allow for robust expression of genes from both the nuclear and plastid genome. With these advances, many research groups have examined the pliability of this and other micro-algae as biological machines capable of producing recombinant peptides and proteins. This review describes recent successes in recombinant protein production in Chlamydomonas, including production of complex mammalian therapeutic proteins and monoclonal antibodies at levels sufficient for production at economic parity with existing production platforms. These advances have also shed light on the details of algal protein production at the molecular level, and provide insight into the next steps for optimizing micro-algae as a useful platform for the production of therapeutic and industrially relevant recombinant proteins.

Micro-algae come of age as a platform for recombinant protein production

A complete set of genetic tools is still being developed for the micro-alga Chlamydomonas reinhardtii. Yet even with this incomplete set, this photosynthetic single-celled plant has demonstrated significant promise as a platform for recombinant protein expression. In recent years, techniques have been developed that allow for robust expression of genes from both the nuclear and plastid genome. With these advances, many research groups have examined the pliability of this and other micro-algae as biological machines capable of producing recombinant peptides and proteins. This review describes recent successes in recombinant protein production in Chlamydomonas, including production of complex mammalian therapeutic proteins and monoclonal antibodies at levels sufficient for production at economic parity with existing production platforms. These advances have also shed light on the details of algal protein production at the molecular level, and provide insight into the next steps for optimizing micro-algae as a useful platform for the production of therapeutic and industrially relevant recombinant proteins.

Plant-derived vaccines and other therapeutics produced in contained systems

The use of contained plant systems for the production of biopharmaceuticals represents a powerful alternative to current methods, combining the benefits of whole-plant systems and cell cultures. In vitro contained production systems include plant cell suspensions, hairy root cultures, novel plants grown in contained conditions and microalgae. These systems show intrinsic advantages, such as control over growth conditions, production in compliance with good manufacturing practice and avoidance of political resistance to the release of genetically modified field crops. At present, one of the two plant-produced vaccine-related products that have gone all the way through production and regulatory hurdles derives from tobacco cell suspensions, and the second is a human therapeutic enzyme, which is expected to reach commercial development soon and derives from carrot suspension cells. In the future, several other products from contained systems are expected to reach the clinical trial stage.

The use of single chain Fv as targeting agents for immunoliposomes: an update on immunoliposomal drugs for cancer treatment

IMPORTANCE OF THE FIELD

Targeted liposomal drugs represent the next evolution of liposomal drug delivery in cancer treatment. In various preclinical cancer models, antibody-targeted PEGylated liposomal drugs have demonstrated superior therapeutic effects over their non-targeted counterparts. Single chain Fv (scFv) has gained popularity in recent years as the targeting agent of choice over traditional targeting agents such as monoclonal antibodies (mAb) and antibody fragments (e.g., Fab').

AREAS COVERED IN THIS REVIEW

This review is focused mainly on advances in scFv-targeted liposomal drug delivery for the treatment of cancers, based on a survey of the recent literature, and on experiments done in a murine model of human B-lymphoma, using anti-CD19 targeted liposomes targeted with whole mAb, Fab' fragments and scFv fragments.

WHAT THE READER WILL GAIN

This review examines the recent advances in PEGylated immunoliposomal drug delivery, focusing on scFv fragments as targeting agents, in comparison with Fab' and mAb.

TAKE HOME MESSAGE

For clinical development, scFv are potentially preferred targeting agents for PEGylated liposomes over mAb and Fab', owing to factors such as decreased immunogenicity, and pharmacokinetics/biodistribution profiles that are similar to non-targeted PEGylated (Stealth) liposomes.

Dunaliella as an attractive candidate for molecular farming

Pharmaceutical recombinant proteins are widely used in human healthcare. At present, several protein expression systems are available to generate therapeutic proteins. These conventional systems have distinct advantages and disadvantages in protein yielding; in terms of ease of manipulation, the time required from gene transformation to protein purification, cost of production and scaling-up capitalization, proper folding and stability of active proteins. Depending on the research goal and priorities, a special system may be selected for protein expression. However, considering the limited variety of organisms currently used and their usage restrictions, there are still much more pharmaceutical proteins waiting to be economically and efficiently produced. Distinguished biological and technical features of microalgae Dunaliella such as inexpensive medium requirement, fast growth rate, the ease of manipulation, easy scaling up procedure, facility of milking in bioreactors and the ability of post-translational modifications make this microorganism an attractive candidate for molecular farming.

Synthesis and assembly of a full-length human monoclonal antibody in algal chloroplasts

Monoclonal antibodies can be effective therapeutics against a variety of human diseases, but currently marketed antibody-based drugs are very expensive compared to other therapeutic options. Here, we show that the eukaryotic green algae Chlamydomonas reinhardtii is capable of synthesizing and assembling a full-length IgG1 human monoclonal antibody (mAb) in transgenic chloroplasts. This antibody, 83K7C, is derived from a human IgG1 directed against anthrax protective antigen 83 (PA83), and has been shown to block the effects of anthrax toxin in animal models. Here we show that 83K7C heavy and light chain proteins expressed in the chloroplast accumulate as soluble proteins that assemble into complexes containing two heavy and two light chain proteins. The algal-expressed 83K7C binds PA83 in vitro with similar affinity to the mammalian-expressed 83K7C antibody. In addition, a second human IgG1 and a mouse IgG1 were also expressed and shown to properly assemble in algal chloroplast. These results show that chloroplasts have the ability to fold and assemble full-length human mAbs, and suggest the potential of algae as a platform for the cost effective production of complex human therapeutic proteins.

Generation of Chlamydomonas strains that efficiently express nuclear transgenes

The unicellular green alga Chlamydomonas reinhardtii is both an invaluable model organism for plant biology and an attractive biotechnological production system. Despite the availability of efficient methods for introduction of foreign genes into the nuclear genome of the alga, transgene expression levels are usually very poor. This is a serious limitation that has severely hampered both post-genomics research in Chlamydomonas and use of the alga in molecular farming. Here we report a solution to this problem. We have designed a genetic screen that facilitates isolation of algal strains that efficiently express introduced transgenes. The levels of accumulation of foreign protein in our expression strains are almost uniformly high in all transgenic clones and are little influenced by position effects. The possibility of expressing transgenes to high levels will greatly facilitate post-genomics research in Chlamydomonas, and will also boost exploitation of the alga as an inexpensive production host for biopharmaceuticals and other valuable compounds.