Phycoremediation of heavy metals using transgenic microalgae

Plummeting toxic contaminates from water through phycoremediation: Mechanism, influencing factors and future outlook to enhance the capacity of living and non-living algae

Freshwater habitats hold a unique role in the survival of all living organisms and supply water for drinking, irrigation, and life support activities. In recent decades, due to anthropogenic activities, deterioration in the water quality has been a long-lasting problem and challenge to the scientific fraternity. Although, these freshwater bodies have a bearable intrinsic capacity for pollution load however alarming increase in pollution limits the intrinsic capacities and requires additional technological interventions. The release of secondary pollutants from conventional interventions further needs revisiting the existing methodologies and asking for green interventions. Green interventions such as phycoremediation are natural, eco-friendly, economic, and energy-efficient alternatives and provide additional benefits such as nutrient recovery, biofuel production, and valuable secondary metabolites from polluted freshwater bodies. This systemic review in a nut-shell comprises the recent research insights on phycoremediation, technological implications, and influencing factors, and further discusses the associated mechanisms of metal ions biosorption by living and non-living algae, its advantages, and limitations. Besides, the article explores the possibility of future research prospects for applicability at a field scale that will help in the efficient utilization of resources, and improved ecological and health risks.

Comparative Evaluation of Chlorella vulgaris and Anabaena variabilis for Phycoremediation of Polluted River Water: Spotlighting Heavy Metals Detoxification

This study investigated the phycoremediation abilities of Chlorella vulgaris (microalga) and Anabaena variabilis (cyanobacterium) for the detoxification of polluted river water. Lab-scale phycoremediation experiments were conducted for 20 days at 30 °C using the microalgal and cyanobacterial strains and water samples collected from the Dhaleswari river in Bangladesh. The physicochemical properties such as electrical conductivity (EC), total dissolved solids (TDS), biological oxygen demand (BOD), hardness ions, and heavy metals of the collected water samples indicated that the river water is highly polluted. The results of the phycoremediation experiments demonstrated that both microalgal and cyanobacterial species significantly reduced the pollutant load and heavy metal concentrations of the river water. The pH of the river water was significantly raised from 6.97 to 8.07 and 8.28 by C. vulgaris and A. variabilis, respectively. A. variabilis demonstrated higher efficacy than C. vulgaris in reducing the EC, TDS, and BOD of the polluted river water and was more effective at reducing the pollutant load of SO₄^2- and Zn. In regard to hardness ions and heavy metal detoxification, C. vulgaris performed better at removing Ca²⁺, Mg²⁺, Cr, and Mn. These findings indicate that both microalgae and cyanobacteria have great potential to remove various pollutants, especially heavy metals, from the polluted river water as part of a low-cost, easily controllable, environmentally friendly remediation strategy. Nevertheless, the composition of polluted water should be assessed prior to the designing of microalgae- or cyanobacteria-based remediation technology, since the pollutant removal efficiency is found to be species dependent.

Review on rewiring of microalgal strategies for the heavy metal remediation - A metal specific logistics and tactics

Phycoremediation of heavy metals are gaining much attention and becoming an emerging practice for the metal removal in diverse environmental matrices. Still, the physicochemical state of metal polluted sites is often found to be complex and haphazard in nature due to the irregular discharge of wastes, that leads to the lack of conjecture on the application of microalgae for the metal bioremediation. Besides, the foresaid issues might be eventually ended up with futile effect to the polluted site. Therefore, this review is mainly focusing on interpretative assessment on pre-existing microalgal strategies and their merits and demerits for selected metal removal by microalgae through various process such as natural attenuation, nutritional amendment, chemical pretreatment, metal specific modification, immobilization and amalgamation, customization of genetic elements and integrative remediation approaches. Thus, this review provides the ideal knowledge for choosing an efficient metal remediation tactics based on the state of polluted environment. Also, this in-depth description would provide the speculative knowledge of counteractive action required for pass-over the barriers and obstacles during implementation. In addition, the most common metal removal mechanism of microalgae by adsorption was comparatively investigated with different metals through the principal component analysis by grouping various factor such as pH, temperature, initial metal concentration, adsorption capacity, removal efficiency, contact time in different microalgae. Conclusively, the suitable strategies for different heavy metals removal and addressing the complications along with their solution is comprehensively deliberated for metal removal mechanism in microalgae.

The emerging potential of natural and synthetic algae-based microbiomes for heavy metal removal and recovery from wastewaters

Heavy Metal (HM) bioremoval by microbes is a successful, environment-friendly technique, particularly at low concentrations of HMs. Studies using algae, bacteria, and fungi reveal promising capabilities in isolation and when used in consortia. Yet, few reviews have emphasized individual and collective HM removal rates and the associated mechanisms in natural or synthetic microbiomes. Besides discussing the limitations of conventional and synthetic biology approaches, this review underscores the utility of indigenous microbial taxon, i.e., algae, fungi, and bacteria, in HM removal with adsorption capacities and their synergistic role in microbiome-led studies. The detoxification mechanisms studied for certain HMs indicate distinctive removal pathways in each taxon which points to an enhanced effect when used as a microbiome. The role and higher efficacies of the designer microbiomes with complementing and mutualistic taxa are also considered, followed by recovery options for a circular bioeconomy. The citation network analysis further validates the multi-metal removal ability of microbiomes and the restricted capabilities of the individual counterparts. In precis, the study reemphasizes increased metal removal efficiencies of inter-taxon microbiomes and the mechanisms for synergistic and improved removal, eventually drawing attention to the benefits of ecological engineering approaches compared to other alternatives.

Pharmaceuticals in the Aquatic Environment: A Review on Eco-Toxicology and the Remediation Potential of Algae

The pollution of the aquatic environment has become a worldwide problem. The widespread use of pesticides, heavy metals and pharmaceuticals through anthropogenic activities has increased the emission of such contaminants into wastewater. Pharmaceuticals constitute a significant class of aquatic contaminants and can seriously threaten the health of non-target organisms. No strict legal regulations on the consumption and release of pharmaceuticals into water bodies have been implemented on a global scale. Different conventional wastewater treatments are not well-designed to remove emerging contaminants from wastewater with high efficiency. Therefore, particular attention has been paid to the phycoremediation technique, which seems to be a promising choice as a low-cost and environment-friendly wastewater treatment. This technique uses macro- or micro-algae for the removal or biotransformation of pollutants and is constantly being developed to cope with the issue of wastewater contamination. The aims of this review are: (i) to examine the occurrence of pharmaceuticals in water, and their toxicity on non-target organisms and to describe the inefficient conventional wastewater treatments; (ii) present cost-efficient algal-based techniques of contamination removal; (iii) to characterize types of algae cultivation systems; and (iv) to describe the challenges and advantages of phycoremediation.

The use of algae for environmental sustainability: trends and future prospects

Algae are photosynthetic prokaryotic or eukaryotic ubiquitously found group of organisms. Their enormous potentiality in coping up with various environmental crises has been well documented. Algae have proven to be ideal for biomonitoring of water pollution and help in removing the pollutants with their process of bioremediation apart from the production of eco-friendly sources of energy. Industries like food and pharmaceuticals are exploiting algae for producing several value-added products. The agricultural sector is also highly benefited from microalgae, as they are the good promoters of crop growth. The CO₂-removing potential of algae proves to be an asset in fighting climate change. Moreover, the relatively easy and inexpensive methods of sampling and culturing of algae make them more popular. In this paper, we review the sustainable application aspects of algae in various areas like pollution control, energy production, agriculture, and fighting climate change. Critical discussions have been made on the recent trends and advances of algal technologies indicating future prospects.

Is Genetic Engineering a Route to Enhance Microalgae-Mediated Bioremediation of Heavy Metal-Containing Effluents?

Contamination of the biosphere by heavy metals has been rising, due to accelerated anthropogenic activities, and is nowadays, a matter of serious global concern. Removal of such inorganic pollutants from aquatic environments via biological processes has earned great popularity, for its cost-effectiveness and high efficiency, compared to conventional physicochemical methods. Among candidate organisms, microalgae offer several competitive advantages; phycoremediation has even been claimed as the next generation of wastewater treatment technologies. Furthermore, integration of microalgae-mediated wastewater treatment and bioenergy production adds favorably to the economic feasibility of the former process-with energy security coming along with environmental sustainability. However, poor biomass productivity under abiotic stress conditions has hindered the large-scale deployment of microalgae. Recent advances encompassing molecular tools for genome editing, together with the advent of multiomics technologies and computational approaches, have permitted the design of tailor-made microalgal cell factories, which encompass multiple beneficial traits, while circumventing those associated with the bioaccumulation of unfavorable chemicals. Previous studies unfolded several routes through which genetic engineering-mediated improvements appear feasible (encompassing sequestration/uptake capacity and specificity for heavy metals); they can be categorized as metal transportation, chelation, or biotransformation, with regulation of metal- and oxidative stress response, as well as cell surface engineering playing a crucial role therein. This review covers the state-of-the-art metal stress mitigation mechanisms prevalent in microalgae, and discusses putative and tested metabolic engineering approaches, aimed at further improvement of those biological processes. Finally, current research gaps and future prospects arising from use of transgenic microalgae for heavy metal phycoremediation are reviewed.

Emerging role of microalgae in heavy metal bioremediation

Microalgae have been publicized for their diversified dominance responsiveness and bioaccumulation potential toward pollutants in an ecosystem. Also, algal's incredible capability as biocatalysts in environmental appliances has been well elucidated owing to their robustness and simple nutritional demand. Additionally, microalgae can deliver various collections of bio-based chemical compounds helpful for diversified applications, especially as green alternatives. The environment has been contaminated with various polluting agents; one principal polluting agent is heavy metals which are carcinogenic and show toxicity even in minimal quantity, cause unsatisfactory threats to the environmental ecosystem, including human and animal health. There is a prominent tendency to apply microalgae in the phytoremediation of heavy metals compounds because of its vast benefits, including great accessibility, cost-effective, excellent toxic metal eliminating efficiency, and nontoxic to the ecosystem. This review uncovers the most recent advancements and mechanisms associated with the bioremediation process and biosorption interaction of substantial harmful synthetic compounds processing microalgae species. Furthermore, future challenges and prospects in the utilization of microalgae in heavy metals bioremediation are also explored. The current review aims to give valuable information to aid the advancement of robust and proficient future microalgae-based heavy metal bioremediation innovations and summarizing a wide range of benefits socioeconomic scope to be employed in heavy metal compound removal in environment system.

Phycoremediation mechanisms of heavy metals using living green microalgae: physicochemical and molecular approaches for enhancing selectivity and removal capacity

Heavy metal (HM) contamination of water bodies is a serious global environmental problem. Because they are not biodegradable, they can accumulate in food chains, causing various signs of toxicity to exposed organisms, including humans. Due to its effectiveness, low cost, and ecological aspect, phycoremediation, or the use of microalgae's ecological functions in the treatment of HMs contaminated wastewater, is one of the most recommended processes. This study aims to examine in depth the mechanisms involved in the phycoremediation of HMs by microalgae, it also provides an overview of the prospects for improving the productivity, selectivity, and cost-effectiveness of this bioprocess through physicochemical and genetic engineering applications. Firstly, this review proposes a detailed examination of the biosorption interactions between cell wall functional groups and HMs, and their complexation with extracellular polymeric substances released by microalgae in the extracellular environment under stress conditions. Subsequently, the metal transporters involved in the intracellular bioaccumulation of HMs as well as the main intracellular mechanisms including compartmentalization in cell organelles, enzymatic biotransformation, or photoreduction of HMs were also extensively reviewed. In the last section, future perspectives of physicochemical and genetic approaches that could be used to improve the phytoremediation process in terms of removal efficiency, selectivity for a targeted metal, or reduction of treatment time and cost are discussed, which paves the way for large-scale application of phytoremediation processes.

Potential of Algae-Bacteria Synergistic Effects on Vegetable Production

Modern agriculture has become heavily dependent on chemical fertilizers, which have caused environmental pollution and the loss of soil fertility and sustainability. Microalgae and plant growth-promoting bacteria (PGPB) have been identified as alternatives to chemical fertilizers for improving soil fertility. This is because of their biofertilizing properties, through the production of bioactive compounds (e.g., phytohormones, amino acids, and carotenoids) and their ability to inhibit plant pathogens. Although treatment based on a single species of microalgae or bacteria is commonly used in agriculture, there is growing experimental evidence suggesting that a symbiotic relationship between microalgae and bacteria synergistically affects each other's physiological and metabolomic processes. Moreover, the co-culture/combination treatment of microalgae and bacteria is considered a promising approach in biotechnology for wastewater treatment and efficient biomass production, based on the advantage of the resulting synergistic effects. However, much remains unexplored regarding the microalgal-bacterial interactions for agricultural applications. In this review, we summarize the effects of microalgae and PGPB as biofertilizing agents on vegetable cultivation. Furthermore, we present the potential of the microalgae-PGPB co-culture/combination system for the environmentally compatible production of vegetables with improved quality.

Increased removal of cadmium by Chlamydomonas reinhardtii modified with a synthetic gene for γ-glutamylcysteine synthetase

Bioremediation with genetically modified microalgae is becoming an alternative to remove metalloids and metals such as cadmium, a contaminant produced in industrial processes and found in domestic waste. Its removal is important in several countries including Mexico, where the San Luis Potosi region has elevated levels of it. We generated a construct with a synthetic gene for γ-glutamylcysteine synthetase and employed it in the chloroplast transformation of Chlamydomonas reinhardtii. In dose-response kinetics with media containing from 1 to 20 mg/L of cadmium, both the transplastomic clone and the wild-type strain grew similarly, but the former removed up to 32% more cadmium. While the growth of both decreased with higher concentrations of cadmium, the transplastomic clone removed 20 ± 9% more than the wild-type strain. Compared to the wild-type strain, in the transplastomic clone the activity of glutathione S-transferase and the intracellular glutathione increased up to 2.1 and 1.9 times, respectively, in media with 2.5 and 10 mg/mL of cadmium. While 20 mg/L of cadmium inhibited the growth of both, the transplastomic clone gradually duplicated. These results confirm the expression of the synthetic gene gshA in the transformed strain as revealed in its increased removal uptake and metabolic response.

Heavy metal resistance in algae and its application for metal nanoparticle synthesis

The ungenerous release of metals from different industrial, agricultural, and anthropogenic sources has resulted in heavy metal pollution. Metals with a density larger than 5 g cm^-3 have been termed as heavy metals and have been stated to be potentially toxic to human and animals. Algae are known to be pioneer organisms with the potential to grow under extreme conditions including heavy metal-polluted sites. They have evolved efficient defense strategies to combat the toxic effects exerted by heavy metal ions. Most of the algal strains are reported to accumulate elevated metal ion concentration in cellular organelles. With respect to that, this review focuses on understanding the various strategies used by algal system for heavy metal resistance. Additionally, the application of this metal resistance in biosynthesis of metal nanoparticles and metal oxide nanoparticles has been investigated in details. We thereby conclude that algae serve as an excellent system for understanding metal uptake and accumulation. This thereby assists in the design and development of low-cost approaches for large-scale synthesis of nanoparticles and bioremediation approach, providing ample opportunities for future work.

Genetic Engineering: A Promising Tool to Engender Physiological, Biochemical, and Molecular Stress Resilience in Green Microalgae

As we march into the 21st century, the prevailing scenario of depleting energy resources, global warming and ever increasing issues of human health and food security will quadruple. In this context, genetic and metabolic engineering of green microalgae complete the quest toward a continuum of environmentally clean fuel and food production. Evolutionarily related, but unlike land plants, microalgae need nominal land or water, and are best described as unicellular autotrophs using light energy to fix atmospheric carbon dioxide (CO2) into algal biomass, mitigating fossil CO2 pollution in the process. Remarkably, a feature innate to most microalgae is synthesis and accumulation of lipids (60-65% of dry weight), carbohydrates and secondary metabolites like pigments and vitamins, especially when grown under abiotic stress conditions. Particularly fruitful, such an application of abiotic stress factors such as nitrogen starvation, salinity, heat shock, etc., can be used in a biorefinery concept for production of multiple valuable products. The focus of this mini-review underlies metabolic reorientation practices and tolerance mechanisms as applied to green microalgae under specific stress stimuli for a sustainable pollution-free future. Moreover, we entail current progress on genetic engineering as a promising tool to grasp adaptive processes for improving strains with potential biotechnological interests.

Microalgae - A promising tool for heavy metal remediation

Biotechnology of microalgae has gained popularity due to the growing need for novel environmental technologies and the development of innovative mass-production. Inexpensive growth requirements (solar light and CO2), and, the advantage of being utilized simultaneously for multiple technologies (e.g. carbon mitigation, biofuel production, and bioremediation) make microalgae suitable candidates for several ecofriendly technologies. Microalgae have developed an extensive spectrum of mechanisms (extracellular and intracellular) to cope with heavy metal toxicity. Their wide-spread occurrence along with their ability to grow and concentrate heavy metals, ascertains their suitability in practical applications of waste-water bioremediation. Heavy metal uptake by microalgae is affirmed to be superior to the prevalent physicochemical processes employed in the removal of toxic heavy metals. In order to evaluate their potential and to fill in the loopholes, it is essential to carry out a critical assessment of the existing microalgal technologies, and realize the need for development of commercially viable technologies involving strategic multidisciplinary approaches. This review summarizes several areas of heavy metal remediation from a microalgal perspective and provides an overview of various practical avenues of this technology. It particularly details heavy metals and microalgae which have been extensively studied, and provides a schematic representation of the mechanisms of heavy metal remediation in microalgae.

Mechanisms of hexavalent chromium resistance and removal by microorganisms

Chromium has been and is extensively used worldwide in multiple industrial processes and is routinely discharged to the environment from such processes. Therefore, this heavy metal is a potential threat to the environment and to public health, primarily because it is non-biodegradable and environmentally persistent. Chromium exists in several oxidation states, the most stable of which are trivalent Cr(Ill) and hexavalent Cr(VI) species. Each species possesses its own individual chemical characteristics and produces its own biological effects. For example, Cr (Ill) is an essential oligoelement for humans, whereas Cr(VI) is carcinogenic and mutagenic. Several chemical methods are used to remove Cr(VI) from contaminated sites. Each of these methods has advantages and disadvantages. Currently, bioremediation is often the preferred method to deal with Cr contaminated sites, because it is eco-friendly, cost-effective and is a "natural" technology. Many yeast, bacterial and fungal species have been assessed for their suitability to reduce or remove Cr(VI) contamination. The mechanisms by which these microorganisms resist and reduce Cr(VI) are variable and are species dependent. There are several Cr-resistance mechanisms that are displayed by microorganisms. These include active efflux of Cr compounds, metabolic reduction of Cr(VI) to Cr (ill), and either intercellular or extracellular prec1p1tation. Microbial Cr (VI) removal typically involves three stages: binding of chromium to the cell surface, translocation of chromium into the cell, and reduction of Cr(VI) to Cr (ill). Cr(VI) reduction by microorganisms may proceed on the cell surface, outside the cell, or intracellularly, either directly via chromate reductase enzymes, or indirectly via metabolite reduction of Cr(VI). The uptake of chromium ions is a biphasic process. The primary step is known as biosorption, a metabolic energyindependent process. Thereafter, bioaccumulation occurs, but is much slower, and is dependent on cell metabolic activity. Choosing an appropriate bioremediation strategy for Cr is extremely important and must involve investigating and understanding the key mechanisms that are involved in microbial resistance to and removal of Cr(VI).

Extensive cross-environment fitness variation lies along few axes of genetic variation in the model alga, Chlamydomonas reinhardtii

Variation is essential to ecological and evolutionary dynamics, but genetic variation of quantitative traits may be concentrated in a limited number of dimensions, constraining ecoevolutionary dynamics. We describe high-dimension variation in natural accessions of the model alga, Chlamydomonas reinhardtii, and test the hypothesis that extensive fitness variation across 30 environments is constrained to a small number of axes. We used high-throughput phenotyping to investigate morphological, fitness, and genotype × environment (G × E) variation in 18 natural C. reinhardtii accessions in 30 environments. The organismal phenotypes of cell cycle, cell size, and phototactic behavior exhibited substantial genetic variation between lines, and we found up to 74-fold fitness variation across accessions and environments. Approximately 47% of the extensive G × E variation is accounted for by the first two principal components (PCs) of the G-matrix corresponding to covariation in metals response, nitrogen availability, or salt and nutrient response. The natural variation of C. reinhardtii accessions supports the hypothesis that, despite abundant genetic variation across single environments, the species' adaptive response should be constrained along few major axes of selection. These results highlight the utility of natural accessions for integrating ecoevolutionary and genetic research.

Isotherm studies for the determination of Cd (II) ions removal capacity in living biomass of a microalga with high tolerance to cadmium toxicity

The biosorption characteristics of Cd (II) ions using the living biomass of the marine diatom Phaeodactylum tricornutum were investigated. This microalga is a highly tolerant species to cadmium toxicity; for this reason, it is interesting to know its potential for use in the removal of this metal. The use of living biomass offers better possibilities than that of dead biomass since cadmium can also be bioaccumulated inside the cells. For this purpose, tolerant species are necessary. P. tricornutum is within this category with an EC50,96h of 19.1 ± 3.5 mg Cd (II)/L, and in the present manuscript, it is demonstrated that this microalga has a very good potential for bioremediation of Cd (II) ions in saline habitats. Cadmium removed by the cells was divided into three fractions: total, intracellular and bioadsorbed. The experiments were conducted for 96 h in natural seawater with a concentration range of 1-100 mg Cd (II)/L. Each fraction was characterized every 24 h by sorption isotherms. The experimental isotherm data were analyzed using the Langmuir, Freundlich, Dubinin-Radushkevich and Temkin equations. The biosorption was well described by Langmuir isotherm followed by Freundlich. The worst model was Temkin. The biosorption capacity of this microalga for Cd (II) ions was found to be 67.1 ± 3.2 mg/g after 96 h with approximately 40 % of this capacity in the intracellular fraction. The bioconcentration factor determined was 2,204.7 after 96 h and with an initial Cd (II) concentration of 1 mg/L.

The potential of transgenic green microalgae; a robust photobioreactor to produce recombinant therapeutic proteins

Microalgae have been used in food, cosmetic, and biofuel industries as a natural source of lipids, vitamins, pigments and antioxidants for a long time. Green microalgae, as potent photobioreactors, can be considered as an economical expression system to produce recombinant therapeutical proteins at large-scale due to low cost of production and scaling-up capitalization owning to the inexpensive medium requirement, fast growth rate, and the ease of manipulation. These microalgae possess all benefit eukaryotic expression systems including the ability of post-translational modifications required for proper folding and stability of active proteins. Among the many items regarded as recombinant protein production, this review compares the different expression systems with green microalgae like Dunaliella by viewing the nuclear/chloroplast transformation challenges/benefits, related selection markers/reporter genes, and crucial factors/strategies affecting the increase of foreign protein expression in microalgae transformants. Some important factors were discussed regarding the increase of protein yielding in microalgae transformants including: transformation-associated genotypic modifications, endogenous regulatory factors, promoters, codon optimization, enhancer elements, and milking of recombinant protein.

The Chlorella variabilis NC64A genome reveals adaptation to photosymbiosis, coevolution with viruses, and cryptic sex

Chlorella variabilis NC64A, a unicellular photosynthetic green alga (Trebouxiophyceae), is an intracellular photobiont of Paramecium bursaria and a model system for studying virus/algal interactions. We sequenced its 46-Mb nuclear genome, revealing an expansion of protein families that could have participated in adaptation to symbiosis. NC64A exhibits variations in GC content across its genome that correlate with global expression level, average intron size, and codon usage bias. Although Chlorella species have been assumed to be asexual and nonmotile, the NC64A genome encodes all the known meiosis-specific proteins and a subset of proteins found in flagella. We hypothesize that Chlorella might have retained a flagella-derived structure that could be involved in sexual reproduction. Furthermore, a survey of phytohormone pathways in chlorophyte algae identified algal orthologs of Arabidopsis thaliana genes involved in hormone biosynthesis and signaling, suggesting that these functions were established prior to the evolution of land plants. We show that the ability of Chlorella to produce chitinous cell walls likely resulted from the capture of metabolic genes by horizontal gene transfer from algal viruses, prokaryotes, or fungi. Analysis of the NC64A genome substantially advances our understanding of the green lineage evolution, including the genomic interplay with viruses and symbiosis between eukaryotes.

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.