Microalgae Species Research Articles

Synthesis and utilization of biomass-derived sulfonated heterogeneous catalyst-BT-SO3H for microalgal biodiesel production

The study investigates the potential of utilizing banana trunk-derived porous activated biochar enriched with SO3H- as a catalyst for eco-friendly biodiesel production from the microalga Chlorella vulgaris. An extensive analysis, employing advanced techniques such as XRD, FTIR, TGA, XPS, NH3-TPD, BET, SEM-EDX, and TEM, was conducted to elucidate the physicochemical properties of BT-SO3H catalysts. The synthesized catalyst demonstrated its efficiency in converting the total lipids of Chlorella vulgaris into biodiesel, with varying concentrations of 3%, 5%, and 7%. Notably, using a 5% BT-SO3H concentration resulted in remarkably higher biodiesel production about 58.29%. Additionally, the fatty acid profile of C. vulgaris biodiesel indicated that C16:0 was the predominant fatty acid at 24.31%, followed by C18:1 (19.68%), C18:3 (11.45%), and C16:1 (7.56%). Furthermore, the biodiesel produced via 5% BT-SO3H was estimated to have higher levels of saturated fatty acids (SFAs) at 34.28%, monounsaturated fatty acids (MUFAs) at 30.70%, and polyunsaturated fatty acids (PUFAs) at 24.24%. These findings highlight the promising potential of BT-SO3H catalysts for efficient and environmentally friendly biodiesel production from microalgal species.

Comparing the removal efficiency of diisobutyl phthalate by Bacillariophyta, Cyanophyta and Chlorophyta

The utilization of microalgae for both removing phthalate esters (PAEs) from wastewater and producing bioenergy has become a popular research topic. However, there is a lack of studies comparing the effectiveness of different types of microalgae in removing these harmful compounds. Therefore, the present study aimed to evaluate and compare the efficiency of various processes, such as hydrolysis, photolysis, adsorption, and biodegradation, in removing diisobutyl phthalate (DiBP) using six different species of microalgae. The study indicated that the average removal efficiency of DiBP (initial concentrations of 5, 0.5, and 0.05 mg L−1) by all six microalgae (initial cell density of 1 × 106 cells mL−1) was in the order of Scenedesmus obliquus (95.39 %) > Chlorella vulgaris (94.78 %) > Chroococcus sp. (91.16 %) > Cyclotella sp. (89.32 %) > Nitzschia sp. (88.38 %) > Nostoc sp. (84.33 %). The results of both hydrolysis and photolysis experiments revealed that the removal of DiBP had minimal impact, with respective removal efficiencies of only 0.89 % and 1.82 %. The adsorption efficiency of all six microalgae decreased significantly with increasing initial DiBP concentrations, while the biodegradation efficiency was elevated. Chlorella vulgaris and Chroococcus sp. demonstrated the highest adsorption and biodegradation efficiencies among the microalgae tested. Scenedesmus obliquus was chosen for the analysis of the degradation products of DiBP due to its exceptional ability to remove DiBP. The analysis yielded valuable results, identifying monoisobutyl phthalate (MiBP), phthalic acid (PA), and salicylic acid (SA) as the possible degradation products of DiBP. The possible degradation pathways mainly included dealkylation, the addition of hydroxyl groups, and decarboxylation. This study lays a theoretical foundation for the elimination of PAEs in the aquatic environment.

Technological mapping of led lighting for microalgae: a survey of patent deposits

Microalgae are a significant focus in bioprocess research due to their capacity to capture atmospheric CO2 and produce valuable secondary metabolites. Light-emitting diodes (LEDs) have gained prominence as a light source for microalgae, offering advantages over traditional lighting due to their narrowband spectrum, along with many advantages in comparison to traditional light sources. This study examines 578 patent families related to microalgae processes with LED illumination, assessing light spectrum, microalgae species, and bioproduct yield, as well as their connection to current scientific literature. The patent analysis was conducted using Orbit Intelligence® software, and scientific research was validated using the Elsevier Scopus® database, meeting specified search criteria. Both technological and scientific advancements have occurred over the past decade. Over the last two decades, the majority of patent activity has been centered in Asia, with China leading with 333 patent filings, followed by South Korea (96) and the USA (45). However, the scientific publication landscape tells a different story, with the USA leading in publications (1693), followed by China (771), and Germany (713). Most patents relate to microalgae cultivation systems. The primary microalgae species featured in the patents include Chlorella, Arthrospira (Spirulina), and Haematococcus, with biodiesel being the most prominent bioproduct. Regarding LED light quality, the patents predominantly utilize a combination of red and blue lights in various ratios. In summary, the adoption of LED lighting in microalgae production has grown significantly in both the industrial and scientific sectors. Tailoring light emissions in microalgae cultivation proves to be a smart and cost-effective method for enhancing efficiency, and this trend is expected to continue expanding in the future.

Antifungal activity of eukaryotic microalgae in dermatophytes

Introduction: Microalgae are considered a promising source of biologically active secondary metabolites, with several biotechnological properties already recorded, including antifungal activity. Objective: Thus, the properties of ethanol extracts of microalgae Ankistrodesmus falcatus, Chaetoceros neogracilis, Desmodesmus brasiliensis, Dunaliella tertiolecta, Kirchneriella lunaris and Tetraselmis gracilis were investigated in vitro for antifungal activity against dermatophytes Nannizzia gypsea, Nannizzia nana, Trichophyton mentagrophytes and Trichophyton tonsurans. Methods: The extracts were evaluated using broth microdilution methodology, with a test interval of 0.0115 to 6 mg mL-1. The antifungal itraconazole was tested at concentrations 0.0313 to 16 μg mL-1. Results: All microalgae extracts showed antifungal activity, especially extracts from C. neogracilis, D. brasiliensis and K. lunaris that totally inhibited growth of all species of dermatophytes evaluated. The lowest MIC values recorded were for the extracts of D. brasiliensis and K. lunaris (MIC 0.188 mg mL-1), against T. tonsurans e N. nana. Conclusions: This was a pioneering work about the antifungal activity of these microalgae against dermatophytes. It is expected that, from this study, further research will be carried out in order to identify and isolate the active biomolecules responsible for the antifungal activity of these microalgae species.

Environmental contamination by heavy metals and assessing the impact of inhabitant microalgae in bioremediation: a case study of urban water of Yamuna River, India

ABSTRACT A study assessed the presence of heavy metals (HMs) in Yamuna River water across different locations, seasons, and years, while also examining the efficacy of resident microalgae in HMs removal. High HM concentrations were found, with peak levels in Faridabad during the summer of 2022: Cr(II) at 132.064 µg/L, Pb(II) at 93.034 µg/L, Cu(II) at 218.6 µg/L, and Ni(II) at 347.1 µg/L. In Kalindi Kunj during the same season and year, As(lII) measured 8.05 µg/L and Cd(II) reached 31.587 µg/L. The study identified microalgae species proficient in HMs removal. Scenedesmus sp. achieved 76.11% Cr(II) and 59.83% Pb(II) removal, while Klebsormidium sp. displayed the highest rates with 78.49% Cd(II) and 64.00% As(lII) removal. Oocystis sp. and Chlorococcum sp. absorbed up to 86.53% Cu(II) and 58.54% Ni(II), respectively. This research highlights the variability of HMs in Yamuna River water and the potential of resident microalgae for HMs remediation.

Recycling Ophthalmic Lens Wastewater in a Circular Economy Context: A Case Study with Microalgae Integration.

Water pollution poses a global threat to ecosystems and human health and is driven by the presence of various contaminants in wastewater, including nano- and microplastics. Despite the magnitude of this problem, the majority of global wastewater is released untreated into water bodies. To combat this issue, a multi-strategy approach is needed. This study explores a circular economy-based solution for treating emerging pollutants, particularly wastewater from ophthalmic spectacle lens production. Our approach integrates solid waste materials into polymeric and cement matrices while also utilising wastewater for microalgae cultivation. This innovative strategy focuses on biomass generation and economic valorisation. By adopting a circular economy model, we aim to transform environmental pollutants from wastewater into valuable organic products. A key component of our approach is the utilisation of microalgae, specifically Nannochloropsis sp., known for its high lipid content and resilience. This microalgae species serves as a promising biobased feedstock, supporting the production of innovative biobased products, such as biopolymers, for ophthalmic lens manufacturing. Our interdisciplinary approach combines microalgae technology, analytical chemistry, cement production, and polymer processing to develop a sustainable circular economy model that not only addresses environmental concerns, but also offers economic benefits. This study underscores the potential of harnessing high-value products from waste streams and underscores the importance of circular economy principles in tackling pollution and resource challenges.

Evaluation on microalgae for the production of bio-chemicals and electricity

Recent advancement in biophotovoltaic systems using microalgae, coupled with biorefinery approach, would improve economy-feasibility in production. The major concern is its commercial strength in terms of scalability, strain selection and extraction procedure cost. It must compete with conventional feedstocks such as fossil fuels. This project proposes to enhance the economic feasibility of microalgae-based biorefinery by evaluating their performance for bio-electricity, bio-diesel and carotenoids production in a single cycle. The first part of the study was to construct and select a Bio-bottle Voltaic (BBV) device that would allow microalgae to grow and produce bioproducts, as well as generate the maximum current output reading derived from the microalgae's photosynthesis process. The second phase consisted of a 25-day investigation into the biorefinery performance of six different microalgal species in producing bio-electricity, bio-diesel and carotenoid in a prototype BBV device. The prototype BBV device with aluminium foil and pencil lead as its anode and cathode produced the highest carotenoid and biodiesel component production from the two microalgae tested, according to the results of the first phase of the experiment. In the second portion of the study, Scenedesmus dimorphus and Chlorella vulgaris were identified as the two microalgae most capable of maintaining their growth throughout the experiment. The maximum current reading observed for C. vulgaris was 653 mV. High Performance Liquid Chromatography analysis showed four major carotenoid compounds found which were Neoxanthin, Cantaxanthin, Astaxanthin and 9-cis antheraxanthin, and the highest carotenoid producer was C. vulgaris which recorded at 1.73 μg/mL. C. vulgaris recorded as the most alkanes producer with 22 compounds detected and Heptacosane and Heneicosane as the two major biodiesel compounds found in the extracts. Evaluation of C. vulgaris data showed that it has enormous potential for microalgal biorefinery candidates. Further ongoing research and development efforts for C. vulgaris will improve the economic viability of microalgae-based industries and reduce reliance on depleted fossil fuels.

The Role of Chlorella vulgaris in Attenuating Infertility Induced by Cadmium Chloride via Suppressing Oxidative Stress and Modulating Spermatogenesis and Steroidogenesis in Male Rats.

Cadmium (Cd) is an environmental pollutant known as endocrine disruptor . Cd has been reported to induce perturbations of the testicular functions and the subsequent decline of the male fertility of both animals and humans. Chlorella vulgaris (ChV) a species of green microalga has been reported to have multiple beneficial activities such as anti-inflammatory, antioxidant, and antiapoptotic effects. Thus, this work was conducted to declare the benefits of Chlorella vulgaris (ChV) (500 mg/kg doses) against cadmium chloride CdCl2 (2 mg/kg doses) toxicity on the main and accessory reproductive organs' weight, structure, and function of male rats. Briefly, 40 adult male rats in 4 groups (n = 10) were used as follows; control, ChV, CdCl2, and CdCl2+ChV. (i) The 1st group was kept as control fed on pellet chow and water ad libitum. (ii) The second group is Chlorella vulgaris (ChV) group fed with C. vulgaris alga for 10 days (500 mg/kg BW). (iii) The third group was administrated CdCl2 (2mg/kg BW) via subcutaneous injection (S/C) daily for 10 days. (iv) The fourth group administered both CdCl2 and ChV with the abovementioned doses daily for successive 10 days. Our observations declared that cadmium exhibited an adverse influence on the testes and prostate gland architecture indicated by seminiferous tubule destruction, testicular edema, degeneration of Leydig cells, and prostate acini damage. All together affect the epididymal semen quality and quantity including sperm viability, motility, and count. Interestingly, ChV could restore the testicular architecture and spermatozoa regeneration accompanied by semen quality improvement and increased reproductive hormones including testosterone. On the other side, ChV suppresses reactive oxygen species (ROS) formation via enhancement the antioxidant-related genes in the testicular tissue including SOD, CAT, GSH, and MDA and maintaining spermatocyte survival via suppression of apoptotic related genes including caspase3 and activating steroidogenic related genes including StAR and HSD17β3 in the cadmium-treated testes. In this study, ChV could enhance male fertility under normal or stressful conditions and ameliorate the adverse effects of hazardous heavy metals that are widely distributed in our environment.

Growth of microalgae and cyanobacteria consortium in a photobioreactor treating liquid anaerobic digestate from vegetable waste

This research examines the biological treatment of undiluted vegetable waste digestate conducted in a bubble column photobioreactor. Initially, the bioreactor containing 3N-BBM medium was inoculated with Microglena sp., Tetradesmus obliquus, and Desmodesmus subspicatus mixture with a density of 1.0 × 104 cells/mL and the consortium was cultivated for 30 days. Then, the bioreactor was semi-continuously fed with liquid digestate with hydraulic retention time (HRT) of 30 days, and the treatment process was continued for the next 15 weeks. The change in the microalgal and cyanobacterial species domination was measured in regular intervals using cell counting with droplet method on a microscope slide. At the end of the experiment, Desmonostoc sp. cyanobacteria (identified with 16S ribosomal RNA genetical analysis) as well as Tetradesmus obliquus green algae along with Rhodanobacteraceae and Planococcaceae bacteria (determined with V3–V4 16sRNA metagenomic studies) dominated the microbial community in the photobioreactor. The experiment demonstrated high treatment efficiency, since nitrogen and soluble COD were removed by 89.3 ± 0.5% and 91.2 ± 1.6%, respectively, whereas for phosphates, 72.8 ± 2.1% removal rate was achieved.

Optimizing sludge retention time for sustainable photo-enhanced biological phosphorus removal systems: Insights into nutrient fate, microbial community, and bacterial phototolerance

Photo-enhanced Biological Phosphorus Removal (PEBPR) systems, promising wastewater treatment technology, offer efficient phosphorus removal without external oxygen. However, comprehending the impact of sludge retention time (SRT) on the system is crucial for successful implementation. This study investigated the SRT effect on nutrient fate, microbial community, and bacterial phototolerance in PEBPR systems. PEBPR systems exhibited good bacterial phototolerance at SRT of 10, 15, and 20 d, with optimal phosphorus-accumulation metabolism observed at SRT of 10 and 15d. However, at SRT of 5d, increased light sensitivity and glycogen-accumulating organisms (GAOs) growth resulted in poor P removal (71.9%). Accumulibacter-IIC were the dominant P accumulating organisms (PAOs) at SRT of 10, 15, and 20 d. Accumulibacter-I, IIC and IIF were the major PAOs at SRT of 5 d. The decrease in SRT promoted the microalgal population diversity, and Dictyosphaerium and Chlorella were the major microalgal species in this study. Flow cytometry results revealed high light intensity triggered intracellular Fe2+ efflux, limiting translation activity and metabolism. Moreover, PAOs had lower phototolerance than GAOs due to Poly-P bound intracellular Mg2+ affecting enzyme activity. This study provides an in-depth understanding of PEBPR systems operation strategy toward environmentally sustainable wastewater treatment.

Lipid Enhancement in Oleaginous Nannochloropsis sp. under Nitrate Limitation for Future Bioenergy Production

Microalgae possess high oil content, exhibit rapid growth rates and biomass productivity, and leave a minimal environmental footprint, making them highly attractive for biofuel applications. Consequently, this present study is aimed at evaluating the impact of nitrogen starvation on the marine microalgae Nannochloropsis sp. to enhance lipid accumulation. The microalga culture was grown under an irradiance of 120 μmol photon m-2 s-1, temperature 25 ± 1 °C, continuous air-CO2, and with different concentrations of sodium nitrites over a 14-day cultivation period. From the results, it was found that the growth of the strain decreased under limited nitrogen conditions. After harvesting, the cells in the supernatant were regenerated by cultivating in double concentration of media. The results showed that on the 12th day, the highest lipid content was achieved, reaching 68.0 ± 2.3 wt.% of the dry weight under nitrogen limitation. The composition of the obtained lipid consisted of 18.0 wt.% saturated fatty acids, 72.38 wt.% monounsaturated fatty acids, and 8.95 wt.% polyunsaturated fatty acids. The lipid composition was dominated by monounsaturated oleic acid ( 70.97 ± 4.6 wt.%), saturated palmitic acid ( 13.68 ± 1.0 wt.%), and polyunsaturated linoleic acid ( 8.41 ± 0.4 wt.%). The findings of this study demonstrated that limiting nitrogen availability enhanced lipid accumulation in Nannochloropsis sp. Despite experiencing inhibited growth, this microalga species shows great potential for the large-scale cultivation of lipids and essential fatty acids. These results contribute to understanding the relationship between nitrogen availability and lipid metabolism in microalgae, providing valuable insights for optimizing lipid production in the context of biofuel and biotechnology applications.

Antibacterial and photocatalytic potential of bioactive compounds extracted from freshwater microalgae species (Spirogyra and Ocillatoria): A comparative analysis

Water pollution by pathogenic bacteria and organic dyes poses potential health hazards for human and aquatic life. This study aims to explore the potential of bioactive compounds extracted from two microalgae species (Spirogyra and Ocillatoria) for water pollution control. The optimization of the extraction process for bioactive compounds resulted in the highest yield at 25 min for Spirogyra and 30 min for Ocillatotia species. Further, the extracted bioactive compounds were analyzed using Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectroscopy (GC–MS). The bioactive compounds exhibited significant antibacterial activity against gram-positive and gram-negative bacteria. Notably, Spirogyra species exhibited a higher zone of inhibition (19.5–20.7 mm) than Ocillatoria species (17.0–18.0 mm) against both gram-positive and gram-negative bacterial strains. Furthermore, the photocatalytic potential of these bioactive compounds was examined by assessing the photodegradation of methylene blue (MB) and crystal violet (CV) dyes under different light sources. The findings revealed that Spirogyra species exhibited better photocatalytic activity than Ocillatoria species for MB and CV. For MB, 89.75 %, 77.82 % and 63.54 % were photodegraded when exposed to UV light, sunlight and visible light using Spirogyra extract, compared to 84.90 %, 74.70 % and 58.30 % by Ocillatoria extract. Regarding CV, Spirogyra extract achieved photodegradation efficiency of 88.94 %, 76.59 % and 64.50 % under UV light, sunlight and visible light, higher than 83.60 %, 73.60 % and 57.70 % by Ocillatoria extract. Both Spirogyra and Ocillatoria species demonstrated the best performance for dye photodegradation under UV irradiation, demonstrating great potential for nature-based water treatment.

The Alga Uronema belkae Has Two Structural Types of [FeFe]-Hydrogenases with Different Biochemical Properties.

Several species of microalgae can convert light energy into molecular hydrogen (H2) by employing enzymes of early phylogenetic origin, [FeFe]-hydrogenases, coupled to the photosynthetic electron transport chain. Bacterial [FeFe]-hydrogenases consist of a conserved domain that harbors the active site cofactor, the H-domain, and an additional domain that binds electron-conducting FeS clusters, the F-domain. In contrast, most algal hydrogenases characterized so far have a structurally reduced, so-termed M1-type architecture, which consists only of the H-domain that interacts directly with photosynthetic ferredoxin PetF as an electron donor. To date, only a few algal species are known to contain bacterial-type [FeFe]-hydrogenases, and no M1-type enzymes have been identified in these species. Here, we show that the chlorophycean alga Uronema belkae possesses both bacterial-type and algal-type [FeFe]-hydrogenases. Both hydrogenase genes are transcribed, and the cells produce H2 under hypoxic conditions. The biochemical analyses show that the two enzymes show features typical for each of the two [FeFe]-hydrogenase types. Most notable in the physiological context is that the bacterial-type hydrogenase does not interact with PetF proteins, suggesting that the two enzymes are integrated differently into the alga's metabolism.

Characterization of Limnospira platensis PCC 9108 R-M and CRISPR-Cas systems

The filamentous cyanobacterium Limnospira platensis, formerly known as Arthrospira platensis or spirulina, is one of the most commercially important species of microalgae. Due to its high nutritional value, pharmacological and industrial applications it is extensively cultivated on a large commercial scale. Despite its widespread use, its precise manipulation is still under development due to the lack of effective genetic protocols. Genetic transformation of Limnospira has been attempted but the methods reported have not been generally reproducible in other laboratories. Knowledge of the transformation defense mechanisms is essential for understanding its physiology and for broadening their applications. With the aim to understand more about the genetic defenses of L. platensis, in this work we have identified the restriction-modification and CRISPR-Cas systems and we have cloned and characterized thirteen methylases. In parallel, we have also characterized the methylome and orphan methyltransferases using genome-wide analysis of DNA methylation patterns and RNA-seq. The identification and characterization of these enzymes will be a valuable resource to know how this strain avoids being genetically manipulated and for further genomics studies.

Biodiesel Production by Biocatalysis using Lipids Extracted from Microalgae Oil of Chlorella vulgaris and Aurantiochytrium sp.

Microalgae are lipid-rich microscopic eukaryotic algae that can be used aiming for more sustainable biodiesel production by employing environmentally sound processes. The present work evaluates biodiesel production using a biocatalyst and two microalgae species as oil feedstock (Chlorella vulgaris and Aurantiochytrium sp.). Lipid extraction was performed using different techniques, namely, Soxhlet extractions (8 h — both species) with different solvents (hexane; hexane:ethanol (1:1 v/v); and chloroform) and room temperature hexane extraction (72 h — Aurantiochytrium sp.). Transesterification occurred for 24 h (150 rpm), using 30 % lipase loading. The results showed that high extraction temperatures cause microalgae oil degradation, focused on unsaturated fatty acids, leading to a lower biodiesel conversion yield. Using Aurantiochytrium sp. oil, it was possible to obtain around 55 %wt. of biodiesel conversion yield using oil extracted at room temperature (6:1 methanol:oil molar ratio), whereas for the oil extracted in the Soxhlet apparatus, the biodiesel conversion yield was around 30 %wt.. The low lipid content (1.0 %wt.) and biodiesel conversion yield (up to 25 %wt.) obtained using C. vulgaris show that the biomass used in the current study has low potential for biodiesel production. However, enzymatic biodiesel production from microalgae represents a promising avenue for sustainable energy generation, offering a renewable and environmentally responsible solution to the world’s energy needs. For that purpose, further studies, such as the optimisation of the extraction and transesterification of Aurantiochytrium sp. oil, should be carried out.

Comparison of biogas production from anaerobic digestion of microalgae species belonged to various taxonomic groups

Comparison of biogas production from anaerobic digestion of microalgae species belonged to various taxonomic groups

Development of microalgal dual-cultures for enhanced productivity in sewage: An experimental study

Microalgae polycultures can be shown greater productivity than those that characterize monocultures. Nonetheless, rapid and ready identification of optimal microalgae combinations for highly productive polyculture systems remains a challenge. By assessing the corresponding nitrogen and phosphorus utilization efficiencies, this study aimed to identify microalgal combinations that might improve productivity. Ten high-biomass-producing microalgal species in municipal sewage habitats were cultivated in an artificial municipal sewage. Four high-yielding microalgae, which additionally showed complementary nitrogen and phosphorus nutrient utilization preferences, were selected for a subsequent dual-culture experiment. The D41 dual-culture system comprising Pediastrum sp. and Micractinium sp., showed the highest biocrude yield, at 17.5 mg/L/d, which was 13 % and 69 % higher than those of A4 and A1, respectively. Additionally, D41 showed the highest total phosphorus removal rate from artificial sewage, which was 27 % higher than that of Pediastrum sp. monoculture (A4) and 22 % higher than that of the Micractinium sp. monoculture (A1). Therefore, this study demonstrated that, (a) biomass production and nitrogen and phosphorus utilization rates of the constructed microalgae dual-culture systems were higher than those of monocultures, (b) phosphorus was identified as the limiting nutrient for further enhancing microalgae productivity, and (c) the dual-culture system showed intermediate characteristics between those of the constituent monoculture systems, suggesting that microalgae can influence community structure. Through the development of adequate software packages that can integrate microalgae nutrient utilization preference of and microalgae community structure, future research will enable the development of more productive microalgae culture combinations.

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.

Construction of chitosan modified cationic lipid droplet emulsions for high-value microalgae harvesting

To reduce the risk of microalgae biomass and environmental contamination, a natural cationic lipid droplet emulsion has been constructed for harvesting microalgae. Using three different microalgae strains (Chlorella vulgaris, Scenedesmus quadricauda and Spirulina platensis), the present work studied the influence of lipid droplet dosage, chitosan concentration, pH on harvesting efficiency, and then the flotation behavior was analyzed by zeta potentials, floc size distribution, algal organic matter component, attenuated total reflectance Fourier transform infrared spectrometer and microscopic observation. The XDLVO theory was used to explain the attachment behavior during the flotation process. The experimental results showed that the maximum harvesting efficiency for two green microalgae strains was over 95% at pH 7, while the optimal dosage and ratio of lipid droplet and chitosan were depended on the microalgae species. The maximum harvesting efficiency for Spirulina platensis was less than 70% since the high salinity of growth medium weakened the bridging and netting ability of chitosan. The mechanism of capturing microalgae by the ballasting agents was mainly physical electrostatic attraction, bridging and netting. In addition, the changes of microalgae components before and after harvesting were less than 5%, indicating this method would not affect the downstream application of microalgae biomass.

Improved tolerance capacity and expression of degradation genes drive efficient removal of sulfamethizole by Chlorella pyrenoidosa

In this study, the tolerance capacities and expression of key degradation genes of a microalgal species, Chlorella pyrenoidosa prior exposure to sulfamethizole (SFT) were investigated. The results showed that acclimated microalgae had higher tolerance capacities comparing to the wild type since the half-maximum effective concentrations at 96 h increased from 31.27 mg L−1 to 51.27 mg L−1. Meanwhile, the removal of SFT was enhanced by 45.5% after acclimation, which was mainly induced by biodegradation. Bioaccumulated SFT was 17.65 and 24.61 µg g−1 in wild type and acclimated species. Gradually increased content of reactive oxygen species might act as the secondary massager to monitor the cellular metabolic pathways including synthesis of energy sources and energy metabolism. Key biodegradation genes were identified with upregulated log 2-fold change of > 6. These genes may help to biodegrade SFT in acclimation process. This study tried to unravel the underlying mechanism of acclimation process in microalgal degradation of persistent sulfonamide antibiotics, which might be useful in increasing the engineering feasibility in treatment of antibiotics’ wastewater.