Extremophilic Microalga Research Articles

Exploring Extremotolerant and Extremophilic Microalgae: New Frontiers in Sustainable Biotechnological Applications.

Exploring extremotolerant and extremophilic microalgae opens new frontiers in sustainable biotechnological applications. These microorganisms thrive in extreme environments and exhibit specialized metabolic pathways, making them valuable for various industries. The study focuses on the ecological adaptation and biotechnological potential of these microalgae, highlighting their ability to produce bioactive compounds under stress conditions. The literature reveals that extremophilic microalgae can significantly enhance biomass production, reduce contamination risks in large-scale systems, and produce valuable biomolecules such as carotenoids, lipids, and proteins. These insights suggest that extremophilic microalgae have promising applications in food, pharmaceutical, cosmetic, and biofuel industries, offering sustainable and efficient alternatives to traditional resources. The review concludes that further exploration and utilization of these unique microorganisms can lead to innovative and environmentally friendly solutions in biotechnology.

Lipid turnover through lipophagy in the newly identified extremophilic green microalga Chlamydomonas urium.

Autophagy is a central degradative pathway highly conserved among eukaryotes, including microalgae, which remains unexplored in extremophilic organisms. In this study, we described and characterized autophagy in the newly identified extremophilic green microalga Chlamydomonas urium, which was isolated from an acidic environment. The nuclear genome of C. urium was sequenced, assembled and annotated in order to identify autophagy-related genes. Transmission electron microscopy, immunoblotting, metabolomic and photosynthetic analyses were performed to investigate autophagy in this extremophilic microalga. The analysis of the C. urium genome revealed the conservation of core autophagy-related genes. We investigated the role of autophagy in C. urium by blocking autophagic flux with the vacuolar ATPase inhibitor concanamycin A. Our results indicated that inhibition of autophagic flux in this microalga resulted in a pronounced accumulation of triacylglycerols and lipid droplets (LDs). Metabolomic and photosynthetic analyses indicated that C. urium cells with impaired vacuolar function maintained an active metabolism. Such effects were not observed in the neutrophilic microalga Chlamydomonas reinhardtii. Inhibition of autophagic flux in C. urium uncovered an active recycling of LDs through lipophagy, a selective autophagy pathway for lipid turnover. This study provided the metabolic basis by which extremophilic algae are able to catabolize lipids in the vacuole.

Methylmercury Effect and Distribution in Two Extremophile Microalgae Strains Dunaliella salina and Coccomyxa onubensis from Andalusia (Spain).

The main entrance point of highly toxic organic Hg forms, including methylmercury (MeHg), into the aquatic food web is phytoplankton, which is greatly represented by various natural microalgal species. Processes associated with MeHg fate in microalgae cells such as uptake, effects on cells and toxicity, Hg biotransformation, and intracellular stability are detrimental to the process of further biomagnification and, as a consequence, have great importance for human health. The study of MeHg uptake and distribution in cultures of marine halophile Dunaliella salina and freshwater acidophilic alga Coccomyxa onubensis demonstrated that most of the MeHg is imported inside the cell, while cell surface adhesion is insignificant. Almost all MeHg is removed from the culture medium after 72 h. Significant processes in rapid MeHg removal from liquid medium are its abiotic photodegradation and volatilization associated with algal enzymatic activity. The maximum intracellular accumulation for both species was in 80 nM MeHg-exposed cultures after 24 h of exposure for D. salina (from 27 to 34 µg/gDW) and at 48 h for C. onubensis (up to 138 µg/gDW). The different Hg intakes in these two strains could be explained by the lack of a rigid cell wall in D. salina and the higher chemical ability of MeHg to pass through complex cell wall structures in C. onubensis. Electron microscopy studies on the ultrastructure of both strains demonstrated obvious microvacuolization in the form of many very small vacuoles and partial cell membrane disruption in 80 nM MeHg-exposed cultures. Results further showed that Coccomyxa onubensis is a good candidate for MeHg-contaminated water reclamation due to its great robustness at nanomolar concentrations of MeHg coupled with its very high intake and almost complete Hg removal from liquid medium at the MeHg levels tested.

Current challenges of microalgae applications: exploiting the potential of non-conventional microalgae species.

The intensified attention to health, the growth of an elderly population, the changing lifestyles, and the medical discoveries have increased demand for natural and nutrient-rich foods, shaping the popularity of microalgae products. Microalgae thanks to their metabolic versatility represent a promising solution for a 'green' economy, exploiting non-arable land, non-potable water, capturing carbon dioxide (CO2) and solar energy. The interest in microalgae is justified by their high content of bioactive molecules, such as amino acids, peptides, proteins, carbohydrates, polysaccharides, polyunsaturated fatty acids (as ω-3 fatty acids), pigments (as β-carotene, astaxanthin, fucoxanthin, phycocyanin, zeaxanthin and lutein), or mineral elements. Such molecules are of interest for human and animal nutrition, cosmetic and biofuel production, for which microalgae are potential renewable sources. Microalgae, also, represent effective biological systems for treating a variety of wastewaters and can be used as a CO2 mitigation approach, helping to combat greenhouse gases and global warming emergencies. Recently a growing interest has focused on extremophilic microalgae species, which are easier to cultivate axenically and represent good candidates for open pond cultivation. In some cases, the cultivation and/or harvesting systems are still immature, but novel techniques appear as promising solutions to overcome such barriers. This review provides an overview on the actual microalgae cultivation systems and the current state of their biotechnological applications to obtain high value compounds or ingredients. Moreover, potential and future research opportunities for environment, human and animal benefits are pointed out. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Insights into Co-Cultivation of Photosynthetic Microorganisms for Novel Molecule Discovery and Enhanced Production of Specialized Metabolites

Meso- and extremophilic microalgae and cyanobacteria have a wide range of biotechnological applications. However, the industrial demand for bioactive molecules and the redundancy of these molecules has resulted in a need for new methodologies for enhanced production and the discovery of specialized metabolites. Co-cultivation has been established as a promising approach to addressing these challenges. In this context, this work aimed to describe the state of the art of the co-cultivation method involving meso- and extremophilic photosynthetic microorganisms, as well as discuss the advantages, challenges, and limitations of this approach. Co-culture is defined as an ecology-driven method in which various symbiotic interactions involving cyanobacteria and microalgae can be used to explore new compounds and enhanced production. Promising results regarding new bioactive metabolite expression and increased production through co-cultivation-based research support that idea. Also, the metabolic diversity and evolutionary adaptations of photosynthetic microorganisms to thrive in extreme environments could improve the efficiency of co-cultivation by allowing the implementation of these microorganisms. However, the complexity of ecological interactions and lack of standardization for co-cultivation protocols are obstacles to its success and scientific validation. Further research in symbiotic interplays using -omics and genetic engineering, and predictive experimental designs for co-cultures are needed to overcome these limitations.

Galdieria sulphuraria: An Extremophilic Alga as a Source of Antiviral Bioactive Compounds.

In the last decades, the interest in bioactive compounds derived from natural sources including bacteria, fungi, plants, and algae has significantly increased. It is well-known that aquatic or terrestrial organisms can produce, in special conditions, secondary metabolites with a wide range of biological properties, such as anticancer, antioxidant, anti-inflammatory, and antimicrobial activities. In this study, we focused on the extremophilic microalga Galdieria sulphuraria as a possible producer of bioactive compounds with antiviral activity. The algal culture was subjected to organic extraction with acetone. The cytotoxicity effect of the extract was evaluated by the 2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. The antiviral activity was assessed through a plaque assay against herpesviruses and coronaviruses as enveloped viruses and poliovirus as a naked one. The monolayer was treated with different concentrations of extract, ranging from 1 µg/mL to 200 µg/mL, and infected with viruses. The algal extract displayed strong antiviral activity at non-toxic concentrations against all tested enveloped viruses, in particular in the virus pre-treatment against HSV-2 and HCoV-229E, with IC50 values of 1.7 µg/mL and IC90 of 1.8 µg/mL, respectively. However, no activity against the non-enveloped poliovirus has been detected. The inhibitory effect of the algal extract was confirmed by the quantitative RT-PCR of viral genes. Preliminary chemical profiling of the extract was performed using ultra-high-performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS), revealing the enrichment in primary fatty acid amides (PFAA), such as oleamide, palmitamide, and pheophorbide A. These promising results pave the way for the further purification of the mixture to explore its potential role as an antiviral agent.

Strategic Use of Extremophilic Microalgae as a Carbon Source in the Thermo-Chemical Process

Microalgal biomass has a high CO2 fixation and growth rate when using CO2 as a carbon source. Moreover, biomass can also be employed as a carbon resource to produce biofuels and chemicals. As the growth rate of extremophilic microalgae remains unaffected by harsh conditions, the present study proposes that these microalgae (such as Galdieria sulphuraria) are a rapidly growing carbon resource for syngas production. Hence, two different experiments were performed as part of this study: (1) cultivation of G. sulphuraria under outdoor conditions and (2) conversion of G. sulphuraria into syngas. The productivity of G. sulphuraria under mixotrophic condition (0.82 g L–1 d–1) was about 1.6 faster than a widely cultivated Chlorella sp. HS2. Moreover, G. sulphuraria was converted into syngas using CO2 as a co-feedstock. The simultaneous reduction of CO2 and the oxidation of volatile matter (VM) from the thermolysis of G. sulphuraria promoted syngas formation. The chemical reaction was influenced by the molecular size of the VMs. In the presence of the Ni catalyst, low-molecular-weight VMs were formed owing to chemical bond scissions. Syngas formation under CO2 doubled compared with that under inert conditions. The findings suggest that G. sulphuraria is a feasible carbon source for CO2 fixation and chemical production.

The snow alga Chloromonas kaweckae sp. nov. (Volvocales, Chlorophyta) causes green surface blooms in the high tatras (Slovakia) and tolerates high irradiance.

Seasonally slowly melting mountain snowfields are populated by extremophilic microalgae. In alpine habitats, high-light sensitive, green phytoflagellates are usually observed in subsurface layers deeper in the snowpack under dim conditions, while robust orange to reddish cyst stages can be seen exposed on the surface. In this study, uncommon surface green snow was investigated in the High Tatra Mountains (Slovakia). The monospecific community found in the green surface bloom consisted of vegetative Chloromonas cells (Volvocales, Chlorophyta). Molecular data demonstrated that the field sample and the strain isolated and established from the bloom were conspecific, and they represent a new species, Chloromonas kaweckae sp. nov., which is described based on the morphology of the vegetative cells and asexual reproduction and on molecular analyses of the strain. Cells of C. kaweckae accumulated approximately 50% polyunsaturated fatty acids, which is advantageous at low temperatures. In addition, this new species performed active photosynthesis at temperatures close to the freezing point showed a light compensation point of 126 ± 22 μmol photons·m-2 ·s-1 and some signs of photoinhibition at irradiances greater than 600 μmol photons·m-2 ·s-1 . These data indicate that the photosynthetic apparatus of C. kaweckae could be regarded as adapted to relatively high light intensities, otherwise unusual for most flagellate stages of snow algae.

Growth and phycocyanin production with Galdieria sulphuraria UTEX 2919 using xylose, glucose, and corn stover hydrolysates under heterotrophy and mixotrophy

The production of cell mass and phycocyanin (PC) was evaluated with the extremophile microalgae Galdieria sulphuraria 2919, under mixotrophic and heterotrophic conditions, in media supplemented with glucose, xylose, or a mixture of both sugars, and hemicellulosic and cellulosic hydrolysates from corn stover. Compared to xylose, cultivations with glucose under heterotrophic conditions showed 51%, 42%, and 66% higher specific growth rate, biomass volumetric productivity, and biomass yield, respectively. Glucose caused a suppression of xylose consumption and PC content was 54.4% lower when xylose was used, suggesting it inhibits the production of this pigment-protein. The use of hemicellulosic corn stover hydrolysates, hindered microalga growth because acetate at low concentrations (approximately 0.6 g L−1) caused inhibition of G. sulphuraria growth. The cellulosic fraction of corn stover was saccharified using cellulases to obtain a syrup containing glucose without acetate. When G. sulphuraria was cultivated under heterotrophic conditions on this syrup, the microalgae accumulated up to 165 mgPC gSolubleProtein−1.

Aeroterrestrial and Extremophilic Microalgae as Promising Sources for Lipids and Lipid Nanoparticles in Dermal Cosmetics

Microscopic prokaryotic and eukaryotic algae (microalgae), which can be effectively grown in mass cultures, are gaining increasing interest in cosmetics. Up to now, the main attention was on aquatic algae, while species from aeroterrestrial and extreme environments remained underestimated. In these habitats, algae accumulate high amounts of some chemical substances or develop specific compounds, which cause them to thrive in inimical conditions. Among such biologically active molecules is a large family of lipids, which are significant constituents in living organisms and valuable ingredients in cosmetic formulations. Therefore, natural sources of lipids are increasingly in demand in the modern cosmetic industry and its innovative technologies. Among novelties in skin care products is the use of lipid nanoparticles as carriers of dermatologically active ingredients, which enhance their penetration and release in the skin strata. This review is an attempt to comprehensively cover the available literature on the high-value lipids from microalgae, which inhabit aeroterrestrial and extreme habitats (AEM). Data on different compounds of 87 species, subspecies and varieties from 53 genera (represented by more than 141 strains) from five phyla are provided and, despite some gaps in the current knowledge, demonstrate the promising potential of AEM as sources of valuable lipids for novel skin care products.

Extremophilic Microalgae Galdieria Gen. for Urban Wastewater Treatment: Current State, the Case of “POWER” System, and Future Prospects

Over the past decades, wastewater research has increasingly focused on the use of microalgae as a tool to remove contaminants, entrapping nutrients, and whose biomass could provide both material and energy resources. This review covers the advances in the emerging research on the use in wastewater sector of thermoacidophilic, low-lipid microalgae of the genus Galdieria, which exhibit high content of protein, reserve carbohydrates, and other potentially extractable high-value compounds. The natural tolerance of Galdieria for high toxic environments and hot climates recently made it a key player in a single-step process for municipal wastewater treatment, biomass cultivation and production of energetic compounds using hydrothermal liquefaction. In this system developed in New Mexico, Galdieria proved to be a highly performing organism, able to restore the composition of the effluent to the standards required by the current legislation for the discharge of treated wastewater. Future research efforts should focus on the implementation, in the context of wastewater treatment, of more energetically efficient cultivation systems, potentially capable of generating water with increasingly higher purity levels.

Mechanism of gold and palladium adsorption on thermoacidophilic red alga Galdieria sulphuraria

Biosorption is a promising alternative to conventional methods for metal recovery during recycling. An extremophilic microalga Galdieria sulphuraria is suitable for use as a biosorbent with the potential for mass production and naturally high and selective adsorption capacity for gold and palladium without modification or extensive pre-treatment. However, the atomic-level understanding of how the biosorbent collects the precious metals was not known. In this study, adsorption mechanisms for G. sulphuraria-derived biosorbent in highly acidic solvents commonly found in metal wastewater were elucidated. It was indicated that the primary site of gold and palladium adsorption was the nitrogen atom on the biosorbent surface in a chlorine-rich environment where enough chlorine atoms were available for the precious metals to form chloride anionic complexes. By using several acidic solvents exhibiting different adsorption efficiency it was found that the more reduced the gold was, the higher the adsorption efficiency. Progressive gold reduction from trivalent to monovalent, then to zerovalent, which consequently produces nanoparticles with metallic gold, contributes to improved adsorption capacity by changing binding partners on the cell surface in the process, vacating adsorption positions for subsequent ionic gold. Redox reactions, including sulphur oxidation were also suggested to promote sustainable reduction of gold while palladium was shown to remain as divalent cations.

Extremophile microalgae as feedstock for high‐value carotenoids: A review

AbstractThere are places in our planet where environmental conditions are beyond normal limits for growth but still harbour life. Extremophile microalgae are the candidates for large‐scale production because (i) their extreme growth conditions help to avoid unwanted contaminations, facilitating their production and (ii) in order to survive under harsh environments, these microorganisms synthesise valuable uncommon biomolecules. Extremophile microalgae include Arthrospira platensis, used as a source of phycocyanin and produced under highly alkaline conditions, and Dunaliella salina, which is industrially produced as a source of β‐carotene and can naturally resist salinity conditions exceeding 300 g L−1. Microalgae can be produced on non‐arable lands, using seawater, and within a wide range of environmental conditions, allowing their production in almost any part of the planet. The current paper aimed at highlighting the biotechnological potential of extremophile microalgae as sources for carotenoids, valuable molecules used as pigments and health‐promoters.

Cultivation of the Acidophilic Microalgae Galdieria phlegrea with Wastewater: Process Yields

Algal based wastewater treatment offers the opportunity to recover, in the form of biomass, the nutrients and internal chemical energy of wastewater. Recently, there has been a growing interest in the use of extremophilic microalgae, as they can easily adapt to difficult and often pollutant-rich environments. The thermo-acidophilic microalga Galdieria phlegrea is a species of recent discovery and great metabolic versatility, but it has still been poorly studied. Here, G. phlegrea was cultivated using raw municipal wastewater in 1 L Erlenmeyer flasks with 700 mL working volume at 37 °C for up to nine days. During the cultivation phase, biomass growth, phycocyanin content, ammonium and phosphate removal from the wastewater, lipid fraction, total carbon and nitrogen in the biomass, and variation in δ13C and δ15N isotopic ratios (a novel analytical contribution in these experiments) were monitored. Results indicated that G. phlegrea was able to grow in raw effluent, where it removed more than 50% ammonium and 20% phosphate in 24 h; total lipid content was in the range of 11–22%, while average C-N content was of 45% and 6%, respectively; isotopic analyses proved to be a useful support in identifying C and N metabolic pathways from effluent to biomass. Overall, G. phlegrea showed consistent performance with similar Cyanidiophyceae and is a potentially viable candidate for municipal wastewater valorization from a circular economy perspective.

Multiscale integration of mixotrophic microalgal cultivation, lipid synthesis, rapid biomass harvesting, and nutrient recycling in pilot-scale photobioreactors

This work presents an acetic acid mediated energy-efficient process that integrates mixotrophic cultivation of extremophilic microalga Chlorella sorokiniana at the photobioreactor (macro) scale, with algal lipid accumulation at the molecular (micro) scale, and rapid biomass harvesting at the algal particle (meso) scale, followed by multiple recycling of nutrient-rich harvested broth. Chlorella sorokiniana is grown mixotrophically in Tris-Acetate-Phosphate medium using Tris buffer as nitrogen source, CO2 and acetic acid as inorganic and organic carbon sources, respectively, at light intensities of 5600–11,000 lx and an optimized photoperiod of 18:6 (Light: Dark) in 25-l bubble-column photobioreactors for 138 h. Acetic acid is used as an organic carbon source to integrate the processes occurring at the three scales; acetic acid ionizes to acetate ions in the culture media, which are enzymatically assimilated inside the alga's cytosol to acetyl-CoA that enhance fatty acid synthesis at the molecular scale and biomass yield at the reactor scale. The excess acetate ions in the culture medium react with the ions formed by the hydrolysis of potash alum to form complexes that react with the ions on algal cell surfaces to facilitate rapid flocculation at the meso (particle) scale. This multiscale integration results in maximum biomass and overall productivity 4.16 g/L and 0.70 g/L/day, respectively, with 25.8% lipid content, obtained at 2% CO2 and 11,000 lx, while reducing the harvesting time to 18–28 min, at a harvesting efficiency and cost of 98%, and 0.064$ per kg of dry biomass, respectively. The first and the second recycles of nutrient-rich broth lower the biomass yield by 9.8% and 14.2%, respectively, while increasing the harvesting time by 8.2% and 15.3%, respectively, as compared to fresh broth. Such multiscale integration of algal growth, macromolecular synthesis and biomass harvesting, followed by broth recycling, offers a novel, cost-effective technology for mixotrophic mass cultivation of extremophilic microalgae.

Recycling of Nutrients from Dairy Wastewater by Extremophilic Microalgae with High Ammonia Tolerance.

This study explored the possibility of incorporating extremophilic algal cultivation into dairy wastewater treatment by characterizing a unique algal strain. Results showed that extremophilic microalgae Chlorella vulgaris CA1 newly isolated from dairy wastewater tolerated a high level of ammonia nitrogen (2.7 g/L), which was over 20 times the ammonia nitrogen that regular Chlorella sp. could tolerate. The isolate was mixotrophically cultured in dairy effluent treated by anaerobic digestion (AD) for recycling nutrients and polishing the wastewater. The highest biomass content of 13.3 g/L and protein content of 43.4% were achieved in the culture in AD effluent. Up to 96% of the total nitrogen and 79% of the total phosphorus were removed from the dairy AD effluent. The ability of the algae to tolerate a high level of ammonia nitrogen suggests the potential for direct nutrient recycling from dairy wastewater while producing algal biomass and high value bioproducts.

Microalgae based wastewater treatment for the removal of emerging contaminants: A review of challenges and opportunities

Emerging contaminants (ECs) are attracting considerable attention due to their potential risk to human health and ecosystem. The past decade has seen a renewed importance in microalgae for bioremediating ECs from wastewater. Several proof of concept studies have been published to rationalize the use of microalgae for bioremediating ECs at laboratory conditions. However, there has been little discussion on real world application of microalgae for bioremediation purposes. This review paper sheds new light on obstacles faced in commercial use of microalgae for bioremediating ECs. The presence of multiple ECs and their affinity for microalgae raise some concern about the validity of laboratory findings. Dynamic changes of environmental conditions and accidental contaminations can significantly influence rate of bioremediation in large scale system. Appropriate pilot scale studies may bridge the gap between the laboratory scale studies and commercial scale applications. Considering the fate of ECs in microalgal cell, more research is needed in the direction of biodegradation assisted bioremediation due to end use of algal biomass. In fact, a wide range of extremophile microalgae species can be screened for selective removal of ECs. In-depth investigations are needed to characterize the quality of wastewater effluent after the separation of microalgal biomass. Notably, life cycle analysis related studies are needed to look at the viability of microalgae assisted bioremediation of ECs.

Screening of Extremophile Microalgae Isolated from High Background Radiation Areas as Source of Bioactive Materials

Background: Microalgae are the source of various compounds with high potentials for being used in different industries. The production of such compounds can be raised under extreme conditions. In the present study, four cyanobacteria and one coccoid green alga were examined which were isolated from hot springs in high background radiation areas in Ramsar, a city in the north of Iran. Methods: Cadmium adsorption from aqueous solution, response towards cadmium stress, antioxidant activity, total phenolic compound and drought tolerance were investigated in these microalgae. Results: The results showed that these extremophile microalgae contain valuable biological compounds which can be useful in remediation of heavy metals from contaminated water and soils and pharmaceutical applications. The unicellular cyanobacterium, Chroococidiopsis thermalis IBRC-M50002, was the best strain with the highest biological activity in various testes such as cadmium adsorption (225 mg g-1), cadmium tolerance stress (100 mg ml-1), antioxidant activity (IC50= 18 μg mg-1) and total phenol content (100 μg ml-1). The coccoid green algae Grasiella emersonii IBRC-M50001, also exhibited significant antioxidant activity (IC50=10 μg mg-1) and total phenol compound (116 μg ml-1), but its cadmium adsorption, tolerance at cadmium stress and desiccation were lower than Chroococidiopsis thermalis. Conclusion: HBRAs microalgae, isolated from extreme conditions, are useful microorganisms for the production of bioactive substances and natural antioxidants. In other words, they exhibited high capacity to be used in pharmaceutical, industrial and commercial applications.

Autotrophic and Heterotrophic Growth Conditions Modify Biomolecole Production in the Microalga Galdieria sulphuraria (Cyanidiophyceae, Rhodophyta).

Algae have multiple similarities with fungi, with both belonging to the Thallophyte, a polyphyletic group of non-mobile organisms grouped together on the basis of similar characteristics, but not sharing a common ancestor. The main difference between algae and fungi is noted in their metabolism. In fact, although algae have chlorophyll-bearing thalloids and are autotrophic organisms, fungi lack chlorophyll and are heterotrophic, not able to synthesize their own nutrients. However, our studies have shown that the extremophilic microalga Galderia sulphuraria (GS) can also grow very well in heterotrophic conditions like fungi. This study was carried out using several approaches such as scanning electron microscope (SEM), gas chromatography/mass spectrometry (GC/MS), and infrared spectrophotometry (ATR-FTIR). Results showed that the GS, strain ACUF 064, cultured in autotrophic (AGS) and heterotrophic (HGS) conditions, produced different biomolecules. In particular, when grown in HGS, the algae (i) was 30% larger, with an increase in carbon mass that was 20% greater than AGS; (ii) produced higher quantities of stearic acid, oleic acid, monounsaturated fatty acids (MUFAs), and ergosterol; (iii) produced lower quantities of fatty acid methyl esters (FAMEs) such as methyl palmytate, and methyl linoleate, saturated fatty acids (SFAs), and poyliunsaturated fatty acids (PUFAs). ATR-FTIR and principal component analysis (PCA) statistical analysis confirmed that the macromolecular content of HGS was significantly different from AGS. The ability to produce different macromolecules by changing the trophic conditions may represent an interesting strategy to induce microalgae to produce different biomolecules that can find applications in several fields such as food, feed, nutraceutical, or energy production.

Toxicity, Physiological, and Ultrastructural Effects of Arsenic and Cadmium on the Extremophilic Microalga Chlamydomonas acidophila.

The cytotoxicity of cadmium (Cd), arsenate (As(V)), and arsenite (As(III)) on a strain of Chlamydomonas acidophila, isolated from the Rio Tinto, an acidic environment containing high metal(l)oid concentrations, was analyzed. We used a broad array of methods to produce complementary information: cell viability and reactive oxygen species (ROS) generation measures, ultrastructural observations, transmission electron microscopy energy dispersive x-ray microanalysis (TEM–XEDS), and gene expression. This acidophilic microorganism was affected differently by the tested metal/metalloid: It showed high resistance to arsenic while Cd was the most toxic heavy metal, showing an LC50 = 1.94 µM. Arsenite was almost four-fold more toxic (LC50= 10.91 mM) than arsenate (LC50 = 41.63 mM). Assessment of ROS generation indicated that both arsenic oxidation states generate superoxide anions. Ultrastructural analysis of exposed cells revealed that stigma, chloroplast, nucleus, and mitochondria were the main toxicity targets. Intense vacuolization and accumulation of energy reserves (starch deposits and lipid droplets) were observed after treatments. Electron-dense intracellular nanoparticle-like formation appeared in two cellular locations: inside cytoplasmic vacuoles and entrapped into the capsule, around each cell. The chemical nature (Cd or As) of these intracellular deposits was confirmed by TEM–XEDS. Additionally, they also contained an unexpected high content in phosphorous, which might support an essential role of poly-phosphates in metal resistance.