Effects of different media composition, light intensity and photoperiod on morphology and physiology of freshwater microalgae Ankistrodesmus falcatus--a potential strain for bio-fuel production

Hues of risk: investigating genotoxicity and environmental impacts of azo textile dyes

The textile industry, with its extensive use of dyes and chemicals, stands out as a significant source of water pollution. Exposure to certain textile dyes, such as azo dyes and their breakdown products like aromatic amines, has been associated with health concerns like skin sensitization, allergic reactions, and even cancer in humans. Annually, the worldwide production of synthetic dyes approximates 7 × 107 tons, of which the textile industry accounts for over 10,000 tons. Inefficient dyeing procedures result in the discharge of 15-50% of azo dyes, which do not adequately bind to fibers, into wastewater. This review delves into the genotoxic impact of azo dyes, prevalent in the textile industry, on aquatic ecosystems and human health. Examining different families of textile dye which contain azo group in their structure such as Sudan I and Sudan III Sudan IV, Basic Red 51, Basic Violet 14, Disperse Yellow 7, Congo Red, Acid Red 26, and Acid Blue 113 reveals their carcinogenic potential, which may affect both industrial workers and aquatic life. Genotoxic and carcinogenic characteristics, chromosomal abnormalities, induced physiological and neurobehavioral changes, and disruptions to spermatogenesis are evident, underscoring the harmful effects of these dyes. The review calls for comprehensive investigations into the toxic profile of azo dyes, providing essential insights to safeguard the aquatic ecosystem and human well-being. The importance of effective effluent treatment systems is underscored to mitigate adverse impacts on agricultural lands, water resources, and the environment, particularly in regions heavily reliant on wastewater irrigation for food production.

What are the growth kinetics and biochemical compositions of microalgae isolated from diverse aquatic ecosystems in Morocco, France, and Tunisia?

Thirty-six microalgae belonging to five taxonomic groups (Cyanobacteria, Chlorophyceae, Diatomophyceae, Euglenophyceae, and Eustigmatophyceae) were identified from six freshwater ecosystems in Morocco, two treatment stations in Etueffont landfill in France and three hot spring waters in Tunisia. Investigations on species growth kinetics and growth rates showed that the cyanobacterium Leptolyngbya gelatinosa exhibited both the highest biomass and growth rate with 4 g DW L-1 and 0.282 day-1, respectively. A significant protein production (more than 40% DW) was observed across the studied species. Cyanobacteria and chlorophytes stood out for their increased protein production with a maximum (66.63 ± 3.84% DW) attained by the cyanobacterium Leptolyngbya sp. Chlorophytes produced substantial amounts of carbohydrates (more than 20% DW). Euglenophytes including Phacus orbicularis and Euglena ehrenbergii along with the chlorophyte Graesiella sp. accumulated significant amounts of lipids (up to 31.12% DW).

Modelling photoperiod in enhancing hydrogen production from Chlorella vulgaris sp. while bioremediating ammonium and organic pollutants in municipal wastewater

Municipal wastewater is ubiquitously laden with myriad pollutants discharged primarily from a combination of domestic and industrial activities. These heterogeneous pollutants are threating the natural environments when the traditional activated sludge system fails sporadically to reduce the pollutants' toxicities. Besides, the activated sludge system is very energy intensive, bringing conundrums for decarbonization. This research endeavoured to employ Chlorella vulgaris sp. In converting pollutants from municipal wastewater into hydrogen via alternate light and dark fermentative process. The microalgae in attached form onto 1 cm3 of polyurethane foam cubes were adopted in optimizing light intensity and photoperiod during the light exposure duration. The highest hydrogen production was recorded at 52 mL amidst the synergistic light intensity and photoperiod of 200 μmolm-2s-1 and 12:12 h (light:dark h), respectively. At this lighting condition, the removals of chemical oxygen demand (COD) and ammoniacal nitrogen were both achieved at about 80%. The sustainability of microalgal fermentative performances was verified in recyclability study using similar immobilization support material. There were negligible diminishments of hydrogen production as well as both COD and ammoniacal nitrogen removals after five cycles, heralding inconsequential microalgal cells' washout from the polyurethane support when replacing the municipal wastewater medium at each cycle. The collected dataset was finally modelled into enhanced Monod equation aided by Python software tool of machine learning. The derived model was capable to predict the performances of microalgae to execute the fermentative process in producing hydrogen while subsisting municipal wastewater at arbitrary photoperiod. The enhanced model had a best fitting of R2 of 0.9857 as validated using an independent dataset. Concisely, the outcomes had contributed towards the advancement of municipal wastewater treatment via microalgal fermentative process in producing green hydrogen as a clean energy source to decarbonize the wastewater treatment facilities.

Impact of macronutrients and salinity stress on biomass and biochemical constituents in Monoraphidium braunii to enhance biodiesel production

Microalgal lipids are precursors to the production of biodiesel, as well as a source of valuable dietary components in the biotechnological industries. So, this study aimed to assess the effects of nutritional (nitrogen, and phosphorus) starvations and salinity stress (NaCl) on the biomass, lipid content, fatty acids profile, and predicted biodiesel properties of green microalga Monoraphidium braunii. The results showed that biomass, biomass productivity, and photosynthetic pigment contents (Chl. a, b, and carotenoids) of M. braunii were markedly decreased by nitrogen and phosphorus depletion and recorded the maximum values in cultures treated with full of N and P concentrations (control, 100%). These parameters were considerably increased at the low salinity level (up to 150 mM NaCl), while an increasing salinity level (up to 250 mM NaCl) reduces the biomass, its productivity, and pigment contents. Nutritional limitations and salt stress (NaCl) resulted in significantly enhanced accumulation of lipid and productivity of M. braunii, which represented more than twofold of the control. Furthermore, these conditions have enhanced the profile of fatty acid and biodiesel quality-related parameters. The current study exposed strategies to improve M. braunii lipid productivity for biodiesel production on a small scale in vitro in terms of fuel quality under low nutrients and salinity stress.

Microalgae biofuels: illuminating the path to a sustainable future amidst challenges and opportunities

The development of microalgal biofuels is of significant importance in advancing the energy transition, alleviating food pressure, preserving the natural environment, and addressing climate change. Numerous countries and regions across the globe have conducted extensive research and strategic planning on microalgal bioenergy, investing significant funds and manpower into this field. However, the microalgae biofuel industry has faced a downturn due to the constraints of high costs. In the past decade, with the development of new strains, technologies, and equipment, the feasibility of large-scale production of microalgae biofuel should be re-evaluated. Here, we have gathered research results from the past decade regarding microalgae biofuel production, providing insights into the opportunities and challenges faced by this industry from the perspectives of microalgae selection, modification, and cultivation. In this review, we suggest that highly adaptable microalgae are the preferred choice for large-scale biofuel production, especially strains that can utilize high concentrations of inorganic carbon sources and possess stress resistance. The use of omics technologies and genetic editing has greatly enhanced lipid accumulation in microalgae. However, the associated risks have constrained the feasibility of large-scale outdoor cultivation. Therefore, the relatively controllable cultivation method of photobioreactors (PBRs) has made it the mainstream approach for microalgae biofuel production. Moreover, adjusting the performance and parameters of PBRs can also enhance lipid accumulation in microalgae. In the future, given the relentless escalation in demand for sustainable energy sources, microalgae biofuels should be deemed a pivotal constituent of national energy planning, particularly in the case of China. The advancement of synthetic biology helps reduce the risks associated with genetically modified (GM) microalgae and enhances the economic viability of their biofuel production.

Distribution, screening and biochemical characterization of indigenous microalgae for bio-mass and bio-energy production potential from three districts of Pakistan

Abstract Trend of biofuel production from microalgal triacylglycerols is enhancing, because this substrate is a good sustainable and advantageous alternative to oil and gas fuel. In the present study, indigenous micro algal isolates were screened from water (n=30) and soil (n=30) samples collected from three districts of Punjab, Pakistan to evaluate their biofuel production potential. The samples were inoculated on BG – 11 agar medium plates by incubating at room temperature of 25°C providing 1000 lux for 16h light cycle followed by 8h of dark cycle for 15 d. Water samples were found to be rich in microalgae and 65.33% microalgae (49 isolates) were isolated from Faisalabad district. On the basis of microscopic morphology microalgal isolates (n=180) were selected and subjected to lipid detection by Nile red staining assay. Nile red positive isolates (n=23) were processed for biochemical (lipid, protein and carbohydrates) characterization. AIN63 isolate showed higher lipids (17.4%) content as detected by micro vanillin assay. Algal isolate AIN128 showed best protein contents (42.91%) detected by Bradford assay and AIN172 isolate showed higher carbohydrate contents (73.83%) as detected by anthrone assay. The selected algal isolates were also analyzed by Fourier transform infrared (FTIR) spectroscopy for confirmation of carbohydrate, protein and lipid analysis. These indigenous algae have the potential for in-vitro biofuel production from agricultural waste.

Biomanufacturing of glycosylated antibodies: Challenges, solutions, and future prospects

Traditionally, recombinant protein production has been done in several expression hosts of bacteria, fungi, and majorly CHO (Chinese Hamster Ovary) cells; few have high production costs and are susceptible to harmful toxin contamination. Green algae have the potential to produce recombinant proteins in a more sustainable manner. Microalgal diversity leads to offer excellent opportunities to produce glycosylated antibodies. An antibody with humanized glycans plays a crucial role in cellular communication that works to regulate cells and molecules, to control disease, and to stimulate immunity. Therefore, it becomes necessary to understand the role of abiotic factors (light, temperature, pH, etc.) in the production of bioactive molecules and molecular mechanisms of product synthesis from microalgae which would lead to harnessing the potential of algal bio-refinery. However, the potential of microalgae as the source of bio-refinery has been less explored. In the present review, omics approaches for microalgal engineering, methods of humanized glycoproteins production focusing majorly on N-glycosylation pathways, light-based regulation of glycosylation machinery, and production of antibodies with humanized glycans in microalgae with a major emphasis on modulation of post-translation machinery of microalgae which might play a role in better understanding of microalgal potential as a source for antibody production along with future perspectives.

Nitrogen and phosphorus stress as a tool to induce lipid production in microalgae

Microalgae, capable of accumulating large amounts of lipids, are of great value for biodiesel production. The high cost of such production stimulates the search for cultivation conditions that ensure their highest productivity. Reducing the content of nitrogen and phosphorus in the culture medium is widely used to change the content and productivity of lipids in microalgae. Achieving the right balance between maximum growth and maximum lipid content and productivity is the primary goal of many experimental works to ensure cost-effective biodiesel production from microalgae. The content of nitrogen and phosphorus in nutrient media for algal cultivation after converted to nitrogen (-N) and phosphorus (-P) lies in an extensive range: from 0.007 g L- 1 to 0.417 g L- 1 and from 0.0003 g L- 1 to 0.227 g L- 1 and N:P ratio from 0.12:1 to 823.33:1. When studying nutritional stress in microalgae, no single approach is used to determine the experimental concentrations of nitrogen and phosphorus. This precludes the possibility of correct interpretation of the data and may lead to erroneous conclusions. This work results from the systematisation of information on using nitrogen and phosphorus restriction to increase the lipid productivity of microalgae of different taxonomic and ecological groups to identify future research directions. The results of 301 experiments were included in the analysis using the principal components method. The investigation considered various divisions and classes: Cyanobacteria, Rhodophyta, Dinophyta, Haptophyta, Cryptophyta, Heterokontophyta/Ochrophyta (Bacillariophyceae, Eustigmatophyceae, Xanthophyceae), Chlorophyta, and also the ratio N:P, the time of the experiment, the light intensity during cultivation. Based on the concentrations of nitrogen and phosphorus existing in various nutrient media, a general scheme for designating the supply of nutrient media for nitrogen (as NO3- or NH4+, N g L- 1) and phosphorus (as РO4-, P g L- 1) has been proposed: replete -N (˃0.4 g L- 1), moderate -N (0.4-0.2), moderate N-limitation (0.19-0.1), strong N-limitation (˂0.1), without nitrogen (0), replete -Р (˃0.2), moderate -P (0.2-0.02), moderate P-limitation (0.019-0.01), strong P-limitation (˂0.01), without phosphorus (0).

Enhancing the bio-prospective of microalgae by different light systems and photoperiods

Microalgae are a source of highly valuable bioactive metabolites and a high-potential feedstock for environmentally friendly and sustainable biofuel production. Recent research has shown that microalgae benefit the environment using less water than conventional crops while increasing oxygen production and lowering CO2 emissions. Microalgae are an excellent source of value-added compounds, such as proteins, pigments, lipids, and polysaccharides, as well as a high-potential feedstock for environmentally friendly and sustainable biofuel production. Various factors, such as nutrient concentration, temperature, light, pH, and cultivation method, effect the biomass cultivation and accumulation of high-value-added compounds in microalgae. Among the aforementioned factors, light is a key and essential factor for microalgae growth. Since photoautotrophic microalgae rely on light to absorb energy and transform it into chemical energy, light has a significant impact on algal growth. During micro-algal culture, spectral quality may be tailored to improve biomass composition for use in downstream bio-refineries and boost production. The light regime, which includes changes in intensity and photoperiod, has an impact on the growth and metabolic composition of microalgae. In this review, we investigate the effects of red, blue, and UV light wavelengths, different photoperiod, and different lighting systems on micro-algal growth and their valuable compounds. It also focuses on different micro-algal growth, photosynthesis systems, cultivation methods, and current market shares.

Effects of o-cresol on the growth and biochemical compositions in marine microalgae

To assess the toxic effects of o-cresol on marine organisms, Skeletonema costatum and Phaeodactylum tricornutum were chosen as test subjects to investigate its impact on growth and biochemical compositions. The results indicated that the 96-h EC50 values for o-cresol in S. costatum and P. tricornutum were 7.99 mg/L and 13.28 mg/L, respectively, demonstrating a moderate and slight toxicity level. Conversely, the maximum no-effect concentration (NOEC) for o-cresol in S. costatum and P. tricornutum were 2.43 mg/L and 0.43 mg/L, respectively, classifying their chronic toxicity grades as negligible and low toxic. Following a 96-h exposure period, the content of photosynthetic pigments in S. costatum did not significantly differ from the control group (P > 0.05). Conversely, the levels of total protein, total lipid, and carbohydrate in microalgae were significantly induced (P < 0.05) as the concentration of o-cresol increased. Higher concentrations of o-cresol generally stimulated the synthesis of biochemical compositions in algae cells, which serves as an active defense mechanism in response to pollution stress. To comprehensively evaluate the potential risk of o-cresol to marine ecosystems, it is crucial to strengthen its toxicity studies on marine fish and crustaceans in the future.

Surface properties of membrane materials and their role in cell adhesion and biofilm formation of microalgae

In this study, the effects of surface properties of membrane materials on microalgae cell adhesion and biofilm formation were investigated using Chlorella vulgaris and five different types of membrane materials under hydrodynamic conditions. The results suggest that the contact angle (hydrophobicity), surface free energy, and free energy of cohesion of membrane materials alone could not sufficiently elucidate the selectivity of microalgae cell adhesion and biofilm formation on membrane materials surfaces, and membrane surface roughness played a dominant role in controlling biofilm formation rate, under tested hydrodynamic conditions. A lower level of biofilm EPS production was generally associated with a larger amount of biofilm formation. The zeta potential of membrane materials could enhance initial microalgae cell adhesion and biofilm formation through salt bridging or charge neutralization mechanisms.

The novel chitosan-amphoteric starch dual flocculants for enhanced removal of Microcystis aeruginosa and algal organic matter

A novel flocculation strategy for simultaneously removing Microcystis aeruginosa and algal organic matter (AOM) was proposed using chitosan-amphoteric starch (C-A) dual flocculants in an efficient, cost-effective and ecologically friendly way, providing new insights for harmful algal blooms (HABs) control. A dual-functional starch-based flocculant, amphoteric starch (AS) with high anion degree of substitution (DS_A) and cation degree of substitution (DS_C), was prepared using a cationic moiety of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CTA) coupled with an anion moiety of chloroacetic acid onto the backbone of starch simultaneously. In combination of the results of FTIR, XPS, ¹H NMR, ¹³C NMR, GPC, EA, TGA and SEM, it was evidenced that the successfully synthesized AS with excellent structural characteristics contributed to the enhanced flocculation of M. aeruginosa. Furthermore, the novel C-A dual flocculants could achieve not only the removal of >99.3 % of M. aeruginosa, but also the efficacious flocculation of algal organic matter (AOM) at optimal concentration of (0.8:24) mg/L, within a wide pH range of 3-11. The analysis of zeta potential and cellular morphology revealed that the dual effects of both enhanced charge neutralization and notable netting-bridging played a vital role in efficient M. aeruginosa removal.

Platymonas helgolandica-driven nitrogen removal from mariculture wastewater under different photoperiods: Performance evaluation, enzyme activity and transcriptional response

The nitrogen removal performance and biological mechanism of Platymonas helgolandica var. Tsingtaoensis (P. helgolandica) were investigated in treating mariculture wastewater under different light: dark (L:D) photoperiods. The growth of P. helgolandica was positively correlated with the photoperiods from 6L:18D to 15L:9D, and the highest photosynthetic activity appeared under 6L:18D photoperiod on day 3. P. helgolandica exhibited the highest removal efficiencies of total nitrogen and COD at 89 % and 93 % under 15L:9D photoperiod, respectively. NH₄⁺-N assimilation was proportional to the photoperiods from 6L:18D to 15L:9D and longer illumination promoted NO₂^--N removal. However, the highest NO₃^--N reduction rate was achieved under 12L:12D photoperiod. The different nitrogen-transformed enzymatic activities were affected by photoperiod. Transcriptome revealed that unigenes were enriched in nitrogen metabolism and photosynthesis pathways, of which the functional gene expression was up-regulated significantly. This study provides insights into the optimization of photoperiod for mariculture wastewater treatment by P. helgolandica.

Microalgae on distillery wastewater treatment for improved biodiesel production and cellulose nanofiber synthesis: A sustainable biorefinery approach

Sugarcane spent wash generates waste at a large scale that impacts the environment, hence the classic waste reuse technology needs to be implemented. An integrated approach of spent wash and microalgae cultivation to produce biodiesel has gained momentum in recent times. However, the microalgae technology lacks the functional utilization of de-oiled microalgae biomass (DOB). This study proposed the development of a microalgae-based advanced process for distillery spent wash treatment, biomass recovery for biodiesel and utilizing algal residue as a step towards waste management. A novel microalga Coelastrella sp KJ-04 grown in distillery spent wash represented with high biomass (4.61g/L) and lipid production (3.6 g/L). The significant reduction in Chemical Oxygen Demand (COD, 49.3%), Total Nitrogen (TN, 49.7%), Total Phosphorous (TP, 21.8%), Total Organic Carbon (TOC, 40.2%), Total Sulphur (S, 37.2%) and Potassium (K, 42.5%) were achieved in spent wash. The extracted lipids of Coelastrella sp KJ-04 were converted to Fatty acid methyl ester (FAME) and examined by Gas chromatography -mass spectrometry (GC-MS) to observe the suitability for biodiesel prospect. The de-oiled biomass (DOB) was utilized for the synthesis of Cellulose nanofibers (CNF), purified and estimated with a diameter ranging between 20 and 27 nm. The crystalline structure and functional group of CNF were analyzed by X-ray diffraction (XRD) and Fourier Transform infrared spectroscopy (FTIR). The unprecedented work demonstrated the microalgae biorefinery approach for spent wash remediation, biodiesel synthesis and simultaneous production of biodegradable CNF from algal residue to support waste-free technology. In future, CNF can be reinforced into material for concrete as it could be the smart alternative to replace synthetic cement plastics.

Microalgae-Derived Pigments for the Food Industry

In the food industry, manufacturers and customers have paid more attention to natural pigments instead of the synthetic counterparts for their excellent coloring ability and healthy properties. Microalgae are proven as one of the major photosynthesizers of naturally derived commercial pigments, gaining higher value in the global food pigment market. Microalgae-derived pigments, especially chlorophylls, carotenoids and phycobiliproteins, have unique colors and molecular structures, respectively, and show different physiological activities and health effects in the human body. This review provides recent updates on characteristics, application fields, stability in production and extraction processes of chlorophylls, carotenoids and phycobiliproteins to standardize and analyze their commercial production from microalgae. Potential food commodities for the pigment as eco-friendly colorants, nutraceuticals, and antioxidants are summarized for the target products. Then, recent cultivation strategies, metabolic and genomic designs are presented for high pigment productivity. Technical bottlenecks of downstream processing are discussed for improved stability and bioaccessibility during production. The production strategies of microalgal pigments have been exploited to varying degrees, with some already being applied at scale while others remain at the laboratory level. Finally, some factors affecting their global market value and future prospects are proposed. The microalgae-derived pigments have great potential in the food industry due to their high nutritional value and competitive production cost.

Screening of microalgae species and evaluation of algal-lipid stimulation strategies for biodiesel production

Microalgae is considered an alternative source for biodiesel production producing renewable, sustainable and carbon-neutral energy. Microalgae property changes among species, which determines the efficiency of biodiesel production. Besides the lipid content evaluation, multi-principles (including high lipid productivity, high biomass yield, pollution resistance and desired fatty acid, etc.) for superior oil-producing species screening was proposed in this review and three microalgae species (Chlorella vulgaris, Scenedesmus obliquus and Mychonastes afer) with high bio-lipid producing prospect were screened out based on big data digging and analysis. The multilateral strategies for algal-lipid stimulating were also compared, among which, nutrient restriction, temperature control, heterotrophy and chemicals addition showed high potential in enhancing lipid accumulation; while electromagnetic field showed little effect. Interestingly, it was found that the lipid accumulation was more sensitive to nitrogen (N)-limitation other than phosphorus (P). Nutrient restriction, salinity stress etc. enhanced lipid accumulation by creating a stressed environment. Hence, optimum conditions (e.g. N:15-35 mg/L and P:4-16 mg/L) should be set to balance the lipid accumulation and biomass growth, and further guarantee the algal-lipid productivity. Otherwise, two-step cultivation could be applied during all the stressed stimulation. Different from lab study, effectiveness, operability and economy should be all considered for stimulation strategy selection. Nutrient restriction, temperature control and heterotrophy were highly feasible after the multidimensional evaluation.

Microalgae-based wastewater treatment: Mechanisms, challenges, recent advances, and future prospects

The rapid expansion of both the global economy and the human population has led to a shortage of water resources suitable for direct human consumption. As a result, water remediation will inexorably become the primary focus on a global scale. Microalgae can be grown in various types of wastewaters (WW). They have a high potential to remove contaminants from the effluents of industries and urban areas. This review focuses on recent advances on WW remediation through microalgae cultivation. Attention has already been paid to microalgae-based wastewater treatment (WWT) due to its low energy requirements, the strong ability of microalgae to thrive under diverse environmental conditions, and the potential to transform WW nutrients into high-value compounds. It turned out that microalgae-based WWT is an economical and sustainable solution. Moreover, different types of toxins are removed by microalgae through biosorption, bioaccumulation, and biodegradation processes. Examples are toxins from agricultural runoffs and textile and pharmaceutical industrial effluents. Microalgae have the potential to mitigate carbon dioxide and make use of the micronutrients that are present in the effluents. This review paper highlights the application of microalgae in WW remediation and the remediation of diverse types of pollutants commonly present in WW through different mechanisms, simultaneous resource recovery, and efficient microalgae-based co-culturing systems along with bottlenecks and prospects.

Microalgae bioreactor for nutrient removal and resource recovery from wastewater in the paradigm of circular economy

Every day, large quantities of wastewater are discharged from various sources that could be reused. Wastewater contains nutrients such as nitrogen or phosphorus, which can be recovered. Microalgae-based technologies have attracted attention in this sector, as they are able to bioremediate wastewater, harnessing its nutrients and generating algal biomass useful for different downstream uses, as well as having other advantages. There are multiple species of microalgae capable of growing in wastewater, achieving nutrient removal efficiencies surpassing 70%. On the other hand, microalgae contain lipids that can be extracted for energy recovery in biodiesel. Currently, there are several methods of lipid extraction from microalgae. Other biofuels can also be obtained from microalgae biomass, such as bioethanol, biohydrogen or biogas. This review also provides information on bioenergy products and products in the agri-food industry as well as in the field of human health based on microalgae biomass within the concept of circular bioeconomy.

Freshwater Microalgae as Promising Food Sources: Nutritional and Functional Properties

A number of researchers have predicted that the current food crisis is predicted to worsen in 2050. The prediction of this crisis is aligned with climate change causing increases in some basic foodstuff prices. Therefore, everyone should prepare to consume alternative foods at an early stage. Alternative foods have been widely developed, one of which involves microalgae. However, the type of microalgae produced by some countries on a large scale consists of only oceanic/seawater microalgae. This will have an impact on and hinder development in countries that do not have these resources. Therefore, it is necessary to explore the use of microalgae derived from freshwater. Unfortunately, freshwater microalgae are still rarely investigated for use as alternative foods. However, there is considerable potential to utilize freshwater microalgae, and these algae are very abundant and diverse. In terms of nutritional properties, compared to oceanic / seawater microalgae, freshwater microalgae contain nearly the same protein and amino acids, lipids and fatty acids, carbohydrates, and vitamins. There are even more species whose composition is similar to those currently consumed foods, such as beef, chicken, beans, eggs, and corn. In addition to dietary properties, freshwater microalgae also have functional properties, due to the presence of pigments, sterols, fatty acids, and polyphenols. Given the potential of freshwater microalgae, these aquatic resources need to be developed for potential use as future food resources.

Light induces peridinin and docosahexaenoic acid accumulation in the dinoflagellate Durusdinium glynnii

Peridinin is a light-harvesting carotenoid present in phototrophic dinoflagellates and has great potential for new drug applications and cosmetics development. Herein, the effects of irradiance mediated by light-emitting diodes on growth performance, carotenoid and fatty acid profiles, and antioxidant activity of the endosymbiotic dinoflagellate Durusdinium glynnii were investigated. The results demonstrate that D. glynnii is particularly well adapted to low-light conditions; however, it can be high-light-tolerant. In contrast to other light-harvesting carotenoids, the peridinin accumulation in D. glynnii occurred during high-light exposure. The peridinin to chlorophyll-a ratio varied as a function of irradiance, while the peridinin to total carotenoids ratio remained stable. Under optimal irradiance for growth, there was a peak in docosahexaenoic acid (DHA) bioaccumulation. This study contributes to the understanding of the photoprotective role of peridinin in endosymbiont dinoflagellates and highlights the antioxidant activity of peridinin-rich extracts. KEY POINTS: • Peridinin has a protective role against chlorophyll photo-oxidation • High light conditions induce cellular peridinin accumulation • D. glynnii accumulates high amounts of DHA under optimal light supply.

Maximization of growth and lipid production of a toxic isolate of Anabaena circinalis by optimization of various parameters with mathematical modeling and computational validation

Toxic cyanobacterial blooms are recurrent for few decades throughout the globe, due to climate change, atmospheric warming and various anthropogenic activities with severe impacts of potential toxins on various ecosystems finally affecting the entire environment. These cyanobacteria are merely unexplored regarding their biochemical components except toxins. Variable influences and interactions of different factors including nitrogen, carbon, and availability of light are well known to crucially regulate cyanobacterial growth and metabolism. Thus, current research work is motivated for the evaluation and optimization of the effects of the aforementioned vital factors for improvement of biomass and lipid production of a freshwater, toxic strain of Anabaena circinalis. The modelling and optimization of factors such as nitrogen, light intensity and bicarbonate concentration (source of carbon) to maximize growth and lipid production were based on 20 design point experiments by Response Surface Methodology (RSM) and optimized values were further improved and validated by Particle Swarm Optimization (PSO) algorithm. The maximum optima were obtained 1.829 g L^-1 and 39.64 % for biomass production and lipid content respectively from PSO optimization with two different sets of optimal values of factors. It shows 0.44 % and 2.77 % higher values of responses than that of RSM optimization. These asynchronous findings pioneered the enhanced lipid accumulation as well as the growth of a toxic cyanobacterium by optimizing interaction effects of culture conditions through various statistical and computational approaches.

Individual and combined effects of diuron and light reduction on marine microalgae

Coastal ecosystems such as those in the Great Barrier Reef (GBR) lagoon, are exposed to stressors in flood plumes including low light (caused by increased turbidity) and agricultural pesticides. Photosystem II (PSII)-inhibiting herbicides are the most frequently detected pesticides in the GBR lagoon, but it is not clear how their toxicity to phototrophic species depends on light availability. This study investigated the individual and combined effects of PSII-inhibiting herbicide, diuron, and reduced light intensity (as a proxy for increased turbidity) on the marine diatom, Phaeodactylum tricornutum. Effective quantum yield (EQY) and cell density were measured to calculate responses relative to the controls over 72-h, in tests with varying stressor intensities. Individually, diuron concentrations (0.1-3 μg l^-1) were not high enough to significantly reduce growth (cell density), but led to decreased EQY; while, low light generally led to increased EQY, but only reduced growth at the lowest tested light intensity (5 μmol photons m^-2 s^-1) after 48-hours. P. tricornutum was less affected by diuron when combined with low light scenarios, with increased EQY (up to 163% of the controls) that was likely due to increased electron transport per photon, despite lesser available photons at this low light intensity. In contrast, growth was completely inhibited relative to the controls when algae were simultaneously exposed to the highest stressor levels (3 μg l^-1 diuron and 5 μmol photons m^-2 s^-1). This study highlights the importance of measuring more than one biological response variable to capture the combined effects of multiple stressors. Management of water quality stressors should consider combined impacts rather than just the impacts of individual stressors alone. Reducing suspended sediment and diuron concentrations in marine waters can decrease harmful effects and bring synergistic benefits to water quality.

Dietary Klebsormidium sp. Supplementation Improves Growth Performance, Antioxidant and Anti-Inflammatory Status, Metabolism, and Mid-Intestine Morphology of Litopenaeus Vannamei

Filamentous microalga Klebsormidium sp. has huge potential to become a natural and healthy additive in aquatic feed since it contains various bioactive nutrients, such as linoleic acid (LA), carotenoids, and chlorophylls. Therefore, an eight-week feeding experiment was performed to evaluate the effects of dietary Klebsormidium sp. on the growth performance, antioxidant and anti-inflammatory status, metabolism, and mid-intestine morphology of Litopenaeus vannamei. Two isonitrogenous and isolipid diets supplemented with and without 5% Klebsormidium sp. were prepared. Results showed that L. vannamei fed with Klebsormidium sp. had better growth performance and feed utilization by optimizing mid-intestine morphology and improving the carbohydrate metabolism. In addition, Klebsormidium sp. also enhanced the antioxidant capacity of L. vannamei by downregulating antioxidant parameters (hepatopancreas T-SOD, hepatopancreas GSH-PX, hemolymph T-SOD, hemolymph MDA) and RNA expression levels of antioxidant genes (gsh-px and cat). Furthermore, the supplementations of dietary Klebsormidium sp. significantly improved hepatopancreas health by downregulating RNA expression levels of pro-inflammatory related genes (relish and rho). Therefore, a dose of 5% Klebsormidium sp. is recommended for the daily diet of L. vannamei to improve the growth performance, antioxidant and anti-inflammatory status, metabolism, and mid-intestine morphology of shrimp.

Application of Five Different Chlorella sp. Microalgal Strains for the Treatment of Vegetation Waters Derived from Unconventional Oil Extractions Enriched with Citrus Byproducts

The Mediterranean diet has, among its cornerstones, the use of olive oil for its nutraceutical and organoleptic properties. Despite the numerous merits, olive-oil mill wastewater (OMWW), which is generated by the olive-oil extraction process, is one of the most serious environmental pollutants in the Mediterranean countries. The polluting potential of OMWW is due to its high content of tannins, polyphenols, polyalcohols, pectins and lipids. In order to close the recovery cycle of a fortified citrus olive oils previously developed, we tested the ability of five microalgae of the Chlorella group (SEC_LI_ChL_1, CL_Sc, CL_Ch, FB and Idr) in lowering the percentage of total phenolic compounds in vegetation water. This was obtained with three different extraction processes (conventional, and lemon and orange peels) at three concentrations each (10%, 25% and 50%). The results showed that strains Idr, FB and CL_Sc from the Lake Massaciuccoli can tolerate vegetation water from conventional and lemon peel extractions up to 25%; these strains can also reduce the phenolic compounds within the tests. The application of microalgae for OMWW treatment represents an interesting opportunity as well as an eco-friendly low-cost solution to be developed within companies as a full-scale approach, which could be applied to obtain a fortified microalgal biomass to be employed in nutraceutical fields.

Cultivation of Microalgae in Unsterile Malting Effluent for Biomass Production and Lipid Productivity Improvement

Microalgae have the potential to grow in nutrient-rich environments and have the ability to accumulate nutrients from wastewater. The nutrients in malting wastewater are ideal for microalgae cultivation. However, there is limited published work on the growth characteristics of freshwater microalgae grown in malting effluent. This study examined the potential of diluted malting effluent for the growth of freshwater green algae Chlorella sp. and Chlamydomonas sp. isolated from northern Ontario and subsequent biomass and lipid production. Under the 18:6 h light/dark cultivation cycle, the highest cell number counted (540 × 104 cell·mL−1 on day 20) and total chlorophyll content were found in 50% diluted malting effluents for Chlorella sp., whereas the 70% dilution concentration was the most productive for Chlamydomonas (386 × 104 cell·mL−1 on day 16). The total lipid content was higher in the 50% dilution concentration of malting effluent in both Chlorella sp. (maximum 20.5%–minimum 11.5% of dry weight) and Chlamydomonas sp. (max 39.3%–min 25.9% of dry weight). These results emphasize the suitability of using unsterile diluted malting effluent for microalgae cultivation.

Improving carbohydrate accumulation in Chlamydomonas debaryana induced by sulfur starvation using response surface methodology

Most methods that promote carbohydrate production negatively affect cell growth and microalgal biomass production. This study explores, in a two-stage cultivation strategy, in Chlamydomonas debaryana the optimization of certain culture conditions for high carbohydrate production without loss of biomass. In the first stage, the interaction between sodium bicarbonate supplementation, aeration, and different growth periods was optimized using the response surface methodology (RMS). The 3-factor Box-Behnken design (BBD) was applied, and a second-order polynomial regression analysis was used to analyze the experimental data. The results showed that 0.45 g L^-1 of sodium bicarbonate combined with a good aerated agitation (0.6 L min^-1) and a cultivation period of 18 days are optimal to produce 5.02 g L^-1 of biomass containing 43% of carbohydrates.Under these optimized growth conditions, accumulation of carbohydrates was studied using different modes of nutritional stress. The results indicated that carbohydrate content was improved and the maximum accumulation (about 60% of the dry weight) was recorded under sulfur starvation with only a 14% reduction in biomass as compared to control. This study showed promising results as to biomass production and carbohydrate yield by the microalgae C. debaryana in view of production of third-generation biofuels.

Bright as day and dark as night: light-dependant energy for lipid biosynthesis and production in microalgae

Microalgae are photosynthetic organisms functioning as the green bio-factories for various pharmaceutical and biofuel products. To date, numerous attempts have been carried out to manipulate culture conditions to maximize the production of the desired metabolites. Because light is the energy source of microalgae for their growth and metabolites biosynthesis, it has been one of the most investigated variables emphasized on the deep understanding of how microalgae respond towards light changes as an external stimulus. This review discusses the effects of different light sources, light intensities, light wavelengths and length of photoperiod on various microalgae species, especially in terms of biomass and lipid productivity. Additionally, the relationship between photoregulation processes and lipid productivity of microalgae are also deliberated. The current available approaches of microalgae mass cultivation, including different types of open and closed systems are recapitulated with the intention to highlight the significant insights for the design of future photoreactors.

The Effects of Photobioreactor Type on Biomass and Lipid Production of the Green Microalga Monoraphidium pusillum in Laboratory Scale

Mass production of microorganisms, algae among them, for new bioactive compounds and renewable innovative products is a current issue in biotechnology. The greatest challenge of basic research on this topic is to find the best solution for both physiology and scalability. In this study, the main goal was to highlight the contradictions of physiological and technological optimization in the same, relatively small, laboratory scale. The green alga Monoraphidium pusillum (Printz) Komárková-Legnorová was cultured in a conventional Erlenmeyer flask (as air bubbled in a tank-type photobioreactor) and in a hybrid (fermenter type + helical tubular type) photobioreactor of the same volume (2.8 L). Higher cell numbers from 1.7–2.3-fold, 2–2.8-fold higher dry masses, and 1.9–2.6-fold higher total lipid contents (mg·L−1) were measured in the tank reactor than in the hybrid reactor. Cultures in the conventional tank reactor were characterized with better nutrient utilization (42.8–77.7% higher phosphate uptake) and more diverse lipid composition than in the hybrid reactor. The study highlights that well-scalable arrangements and settings could be not optimal (or unsuitable in some cases) from a physiological point of view. The results suggest certain developmental directions for complex, well-scalable devices and highlight the importance of testing the gained physiological optima on these systems.

Microalgae as Sources of High-Quality Protein for Human Food and Protein Supplements

As a result of population growth, an emerging middle-class, and a more health-conscious society concerned with overconsumption of fats and carbohydrates, dietary protein intake is on the rise. To address this rapid change in the food market, and the subsequent high demand for protein products, agriculture, aquaculture, and the food industry have been working actively in recent years to increase protein product output from both production and processing aspects. Dietary proteins derived from animal sources are of the highest quality, containing well-balanced profiles of essential amino acids that generally exceed those of other food sources. However, as a result of studies highlighting low production efficiency (e.g., feed to food conversion) and significant environmental impacts, together with the negative health impacts associated with the dietary intake of some animal products, especially red meats, the consumption of animal proteins has been remaining steady or even declining over the past few decades. To fill this gap, researchers and product development specialists at all levels have been working closely to discover new sources of protein, such as plant-based ingredients. In this regard, microalgae have been recognized as strategic crops, which, due to their vast biological diversity, have distinctive phenotypic traits and interactions with the environment in the production of biomass and protein, offering possibilities of production of large quantities of microalgal protein through manipulating growing systems and conditions and bioengineering technologies. Despite this, microalgae remain underexploited crops and research into their nutritional values and health benefits is in its infancy. In fact, only a small handful of microalgal species are being produced at a commercial scale for use as human food or protein supplements. This review is intended to provide an overview on microalgal protein content, its impact by environmental factors, its protein quality, and its associated evaluation methods. We also attempt to present the current challenges and future research directions, with a hope to enhance the research, product development, and commercialization, and ultimately meet the rapidly increasing market demand for high-quality protein products.

Thorsmoerkia curvula gen. et spec. nov. (Trebouxiophyceae, Chlorophyta), a semi-terrestrial microalga from Iceland exhibits high levels of unsaturated fatty acids

A terrestrial green alga was isolated at Iceland, and the strain (SAG 2627) was described for its morphology and phylogenetic position and tested for biotechnological capabilities. Cells had a distinctly curved, crescent shape with conical poles and a single parietal chloroplast. Phylogenetic analyses of 18S rDNA and rbcL markers placed the strain into the Trebouxiophyceae (Chlorophyta). The alga turned out to belong to an independent lineage without an obvious sister group within the Trebouxiophyceae. Based on morphological and phylogenetic data, the strain was described as a new genus and species, Thorsmoerkia curvula gen. et sp. nov. Biomass was generated in column reactors and subsequently screened for promising metabolites. Growth was optimized by pH-regulated, episodic CO₂ supplement during the logarithmic growth-phase, and half of the biomass was thereafter exposed to nitrogen and phosphate depletion. The biomass yield reached up to 53.5 mg L^-1 day^-1. Fatty acid (FA) production peaked at 24 mg L^-1 day^-1 and up to 83% of all FAs were unsaturated. At the end of the log phase, approximately 45% of dry mass were lipids, including eicosapentaenoic acid. Carotenoid production reached up to 2.94 mg L^-1 day^-1 but it was halted during the stress phase. The N-linked glycans of glycoproteins were assessed to reveal chemotaxonomic patterns. The study demonstrated that new microalgae can be found at Iceland, potentially suitable for applied purposes. The advantage of T. curvula is its robustness and that significant amounts of lipids are already accumulated during log phase, making a subsequent stress exposure dispensable.

Modulation of Phototropin Signalosome with Artificial Illumination Holds Great Potential in the Development of Climate-Smart Crops

Changes in environmental conditions like temperature and light critically influence crop production. To deal with these changes, plants possess various photoreceptors such as Phototropin (PHOT), Phytochrome (PHY), Cryptochrome (CRY), and UVR8 that work synergistically as sensor and stress sensing receptors to different external cues. PHOTs are capable of regulating several functions like growth and development, chloroplast relocation, thermomorphogenesis, metabolite accumulation, stomatal opening, and phototropism in plants. PHOT plays a pivotal role in overcoming the damage caused by excess light and other environmental stresses (heat, cold, and salinity) and biotic stress. The crosstalk between photoreceptors and phytohormones contributes to plant growth, seed germination, photo-protection, flowering, phototropism, and stomatal opening.

Molecular genetic studies using gene targeting and synthetic biology approaches have revealed the potential role of different photoreceptor genes in the manipulation of various beneficial agronomic traits. Overexpression of PHOT2 in Fragaria ananassa leads to the increase in anthocyanin content in its leaves and fruits. Artificial illumination with blue light alone and in combination with red light influence the growth, yield, and secondary metabolite production in many plants, while in algal species, it affects growth, chlorophyll content, lipid production and also increases its bioremediation efficiency. Artificial illumination alters the morphological, developmental, and physiological characteristics of agronomic crops and algal species. This review focuses on PHOT modulated signalosome and artificial illumination-based photo-biotechnological approaches for the development of climate-smart crops.

Establishment of a resource recycling strategy by optimizing isobutanol production in engineered cyanobacteria using high salinity stress

BACKGROUND

Isobutanol is an attractive biofuel with many advantages. Third-generation biorefineries that convert CO₂ into bio-based fuels have drawn considerable attention due to their lower feedstock cost and more ecofriendly refining process. Although autotrophic cyanobacteria have been genetically modified for isobutanol biosynthesis, there is a lack of stable and convenient strategies to improve their production.

RESULTS

In this study, we first engineered Synechococcus elongatus for isobutanol biosynthesis by introducing five exogenous enzymes, reaching a production titer of 0.126 g/L at day 20. It was then discovered that high salinity stress could result in a whopping fivefold increase in isobutanol production, with a maximal in-flask titer of 0.637 g/L at day 20. Metabolomics analysis revealed that high salinity stress substantially altered the metabolic profiles of the engineered S. elongatus. A major reason for the enhanced isobutanol production is the acceleration of lipid degradation under high salinity stress, which increases NADH. The NADH then participates in the engineered isobutanol-producing pathway. In addition, increased membrane permeability also contributed to the isobutanol production titer. A cultivation system was subsequently developed by mixing synthetic wastewater with seawater to grow the engineered cyanobacteria, reaching a similar isobutanol production titer as cultivation in the medium.

CONCLUSIONS

High salinity stress on engineered cyanobacteria is a practical and feasible biotechnology to optimize isobutanol production. This biotechnology provides a cost-effective approach to biofuel production, and simultaneously recycles chemical nutrients from wastewater and seawater.

Differential responses in EPA and fucoxanthin production by the marine diatom Stauroneis sp. under varying cultivation conditions

There has been an increasing drive toward better valorising raw biological materials in the context of the sustainability of bio-based industries and the circular economy. As such, microalgae hold the ability to biosynthesise valuable metabolites, which are sought after within the bioenergy, pharmaceuticals, cosmetics or nutrition sectors. Owing to their bioactivities, the xanthophyll pigment fucoxanthin and the omega-3 polyunsaturated fatty acid eicosapentaenoic acid (EPA) have fostered increasing interests in terms of sustainably refining them from natural sources, such as microalgae. Together with the suitability of individual species to industrial cultivation, a key challenge resides in optimizing the yields of these compounds within the microalgal biomass they are retrieved from. The marine diatom Stauroneis sp. LACW24 was batch cultivated into its stationary phase of growth prior to being subjected at high cell density (1 × 10⁶  cells mL^-1 ) to seven different regimes of light exposure in replenished medium and under nutritional limitation (silica and nitrate) for 12 days. The highest EPA proportions and yields were obtained under blue LED in f/2 medium (16.5% and 4.8 mg g^-1 , respectively), double the values obtained under red LED illumination. The fucoxanthin yield was the highest when cells were subjected to blue LEDs (5.9 mg g^-1 ), a fourfold increase compared to the nitrogen-limited treatment under white LEDs. These results indicate that a two-stage approach to the batch cultivation of this diatom can be used for enhancing the production of the high-value metabolites fucoxanthin and EPA post-stationary phase.

Assessment of a Novel Oleaginous Filamentous Microalga Klebsormidium sp. Lgx80 (Streptophyta, Klebsormidiales) for Biomass and Lipid Production1

Commercial cultivation of eukaryotic microalgae has so far employed a unicellular form of species only (e.g., Chlorella pyrenoidosa, Dunaliella salina, and Haematococcus pluvialis). In this study, we assessed the feasibility of using the filamentous eukaryotic microalga Klebsormidium sp. LGX80 as a new cultivar for biomass and lipid production. The effects of different forms and concentrations of nitrogen on growth and lipid production of Klebsormidium sp. LGX80 were studied by using a glass column (ø4.5 × 60 cm) photobioreactor under laboratory conditions. Growth and lipid production of the new strain were further evaluated in an outdoor pilot-scale tubular photobioreactor. The results showed that when supplied with urea as a source of nitrogen Klebsormidium sp. LGX80 yielded a final biomass concentration of 8.49 ± 0.10 g · L^-1 in which a cellular lipid content was 59.2 ± 0.4% DW. Under such conditions, the biomass and lipid productivities were 471.7 ± 5.9 and 248.1 ± 0.0 mg · L^-1  · d^-1 , respectively. Fatty acid analysis revealed that the main fatty acids of Klebsormidium sp. LGX80 were palmitic acid (C16:0), linoleic acid (C18:2ω6), and linolenic acid (C18:3ω3), of which linoleic acid (C18:2ω6) accounted for up to 67.5 ± 0.1% of total fatty acids. When grown outdoors in a 13,000-L tubular photobioreactor with an initial nitrogen concentration of 3 mM urea, Klebsormidium sp. LGX80 reached the highest biomass concentration of 2.63 ± 0.09 g · L^-1 with the cells containing 38.0 ± 0.5% lipids (% DW), resulting in the volumetric biomass and lipid productivities of 147.2 ± 3.6 and 37.9 ± 0.9 mg · L^-1  d^-1 , respectively. The results of light:dark cycle experiment showed that a durative and prolonged light irradiation hindered the biosynthesis of chlorophyll a and chlorophyll b in the cells, but promoted the carotenoid accumulation. These results suggested that Klebsormidium sp. LGX80 can be a potential oleaginous filamentous microalga for commercial production of microalgal oils.

Advances in microalgal cell wall polysaccharides: a review focused on structure, production, and biological application

Microalgae have been shown to be useful in several biotechnological fields due to their feasible cultivation and high-value biomolecules production. Several substances of interest produced by microalgae, such as: proteins, lipids, and natural colorants, have already been explored. Based on the continuing demand for new natural molecules, microalgae could also be a valuable source of polysaccharides. Polysaccharides are extremely important in aquaculture, cosmetics, pharmaceutical, and food industries, and have great economic impact worldwide. Despite this, reviews on microalgal polysaccharide production, biological activity, and chemical structure are not abundant. Moreover, techniques of microalgal cultivation, coupled with carbohydrate production, need to be clarified in order to develop forward-looking technologies. The present review provides an overview of the main advances in microalgal cell wall polysaccharide production, as well as their associated potential biological applications and chemical structure. Several studies on future prospects, related to microalgae are presented, highlighting the key challenges in microalgal polysaccharide production.

Increasing Phosphorus Uptake Efficiency by Phosphorus-Starved Microalgae for Municipal Wastewater Post-Treatment

Four microalgal species, Chlorella vulgaris, Botryococcus braunii, Ankistrodesmus falcatus, and Tetradesmus obliquus were studied for enhanced phosphorus removal from municipal wastewater after their exposure to phosphorus starvation. Microalgae were exposed to phosphorus starvation conditions for three and five days and then used in a batch experiment to purify an effluent from a small WWTP. After 3-day P-starvation, C. vulgaris biomass growth rate increased by 50% and its PO₄ removal rate reached > 99% within 7 days. B. braunii maintained good biomass growth rate and nutrient removal regardless of the P-starvation. All species showed 2–5 times higher alkaline phosphatase activity increase for P-starved biomass than at the reference conditions, responding to the decline of PO₄ concentration in wastewater and biomass poly-P content. The overall efficiency of biomass P-starvation on enhanced phosphorus uptake was found to be dependent on the species, N/P molar ratio in the wastewater, as well as the biomass P content.

Cultivation of microalgae on unhydrolysed waste molasses syrup using mass cultivation strategy for improved biodiesel

High cultivation cost and low lipid yield are framed as a major bottleneck for the production of microalgae biodiesel. Hence, we first and foremost highlight a trophic mode transition, coupled with a combinatorial effect of organic carbon, nitrogen and light (C/N/L) on an isolated microalga Chlorococcum sp. SVF in a one pot tri-phasic intermittent feeding system by developing a lab scale Raceway tank (40L). Hitherto, waste molasses syrup without hydrolysis is unexplored in algal bioenergy arena. The direct utilisation capability of sucrose, served by waste unhydrolysed molasses syrup (WUMS), effectively modulates the intrinsic biochemical and physiological characteristics towards microalgae biomass and lipid assimilation. Response surface methodology-central composite design (RSM-CCD) tool has been employed to observe the cumulative impact of light irradiation and nutrient sources (carbon and nitrogen) on cellular stoichiometric analysis. Experimental results exhibit a potentially achievable biomass (18.88 g L^-1) and lipid accumulation (80.34%) under the light intensity of 75.5 µmol m^-2 s^-1 with stepwise light attenuation strategy. Characterisation of fatty acid methyl esters (FAME) reveals the dominance of oleic acid (32.72%) and palmitic acid methyl esters (32.49%) in mixotrophic condition, which are considered as the upmost indicators of quality biodiesel. The biofuel properties were obtained in acquiescence with American and European standard. These findings are therefore a way forward towards the effective growth of Chlorococcum sp. SVF in sucrose rich inexpensive industrial waste stream that positively influences the lipid yield for large scale sustainable biodiesel production.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02823-7.

De novo transcriptome assembly of the green alga Ankistrodesmus falcatus

Ankistrodesmus falcatus is a globally distributed freshwater chlorophyte that is a candidate for biofuel production, is used to study the effects of toxins on aquatic communities, and is used as food in zooplankton research. Each of these research fields is transitioning to genomic tools. We created a reference transcriptome for of A. falcatus using NextGen sequencing and de novo assembly methods including Trinity, Velvet-Oases, and EvidentialGene. The assembled transcriptome has a total of 17,997 contigs, an N50 value of 2,462, and a GC content of 64.8%. BUSCO analysis recovered 83.3% of total chlorophyte BUSCOs and 82.5% of the eukaryotic BUSCOs. A portion (7.9%) of these supposedly single-copy genes were found to have transcriptionally active, distinct duplicates. We annotated the assembly using the dammit annotation pipeline, resulting in putative functional annotation for 68.89% of the assembly. Using available rbcL sequences from 16 strains (10 species) of Ankistrodesmus, we constructed a neighbor-joining phylogeny to illustrate genetic distances of our A. falcatus strain to other members of the genus. This assembly will be valuable for researchers seeking to identify Ankistrodesmus sequences in metatranscriptomic and metagenomic field studies and in experiments where separating expression responses of zooplankton and their algal food sources through bioinformatics is important.

Stepwise-incremental physicochemical factors induced acclimation and tolerance in oleaginous microalgae to crucial outdoor stresses and improved properties as biodiesel feedstocks

Stress-tolerant oleaginous microalgae are promising for economical outdoor cultivation and biofuel production. This study aimed to induce acclimation and adaptive evolution of oleaginous Scenedesmus sp. SPP to tolerate crucial outdoor stresses by stepwise increasing of physicochemical factors: salinity, light intensity and temperature. The acclimatized strains showed better growth and accumulated 20-30% higher contents of lipids and chlorophylls. The adaptive-evolved strain showed greater tolerance to culture stresses by giving > 2-fold higher biomass under nitrogen rich and accumulating > 1.5-fold higher lipid content under nitrogen starvation compared to the parental strain. Moreover, stepwise increasing of multi-stresses successfully induced the multi-tolerance of the adaptive-evolved strain and gave the highest lipid content of 44.1 ± 1.5%. The extracted lipids from acclimatized/evolved strains show improved prospect fuel properties in terms of high cetane number and oxidative stability. These results show the effectiveness of stepwise-incremental physicochemical factors to intensify potential of microalgae for outdoor cultivation and as biodiesel feedstocks.

Performance Characteristics of Ankistrodesmus falcatus in Different Culture Media and Concentration

This study determined the effect of growth media and culture concentration on the growth, proximate, and microelement composition of Ankistrodesmus falcatus. The culture of A. falcatus was done using three media, namely Modified COMBO Medium (COMBO), Bold’s Basal Medium (BBM), and Bristol, at two concentrations (50% and 100%). The results obtained show that the cell density (>3.5 × 10⁷ cells/mL), optical density (>0.24), and specific growth rate (>0.429%/day) were significantly higher (p ≤ 0.05) in BBM and COMBO than in Bristol (<3.1 × 10⁷ cells/mL; <0.23; <0.416%/day, respectively) at both concentrations. However, biomass was higher in BBM (>2.20 g/L) than in COMBO (1.87–2.13 g/L), while Bristol had the lowest value observed (1.70–1.73 g/L). Biochemical and microelement composition showed variations between media and at the different concentrations, with higher values observed in BBM and COMBO. Based on the growth parameters and nutritional composition, it was concluded that BBM and COMBO were better media for the propagation of A. falcatus growth than Bristol. The study also demonstrated that the microalgae can be cultured using half of the media’s concentration to lower production costs.