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Quick algae harvesting methodologies relating optimum flocculent dose (D Opt. ), percentage harvesting efficiency (%HE) and percentage water recovery (%W Recovery ) to the in-situ hydrodynamic properties of water-algae systems are presented. Flocculation of three microalgae in single and sequential steps, using chemical (polymer and ferric chloride) and biological (egg shells) flocculants, was studied. Zeta potential and pH analysis were completed to further understand the flocculation mechanism. Polymer at D Opt. of 7.0 g/kgDS resulted in W Recovery of 90% and %HE of 96.7%. Lower %HE (92.1), %W Recovery (79) and noticeable algal cells deformation was observed for ferric chloride at D Opt. of 7.0 g/kg DS. Bio-flocculant conserved algal structure and resulted in %HE of 96.2 and %W Recovery of 90 at D Opt. of 5.4 g/kgDS. Significant % HE of 99.8, %W Recovery of 99.8%, and up to 95% reduction in D Opt. were achieved in sequential flocculation. The results established the effectiveness and suitability of sequential/ bio-flocculation for algae harvesting., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Algae are becoming a strategic source of fuels, food, feedstocks, and biologically active compounds. This potential has stimulated the development of innovative analytical methods focused on these microorganisms. Algal lipids are among the most promising potential products for fuels as well as for nutrition. The crucial parameter characterizing the algal lipids is the degree of unsaturation of the constituent fatty acids quantified by the iodine value. Here we demonstrate the capacity of the spatially resolved Raman microspectroscopy to determine the effective iodine value in lipid storage bodies of individual living algal cells. The Raman spectra were collected from three selected algal species immobilized in an agarose gel. Prior to immobilization, the algae were cultivated in the stationary phase inducing an overproduction of lipids. We employed the characteristic peaks in the Raman scattering spectra at 1,656 cm(-1) (cis C═C stretching mode) and 1,445 cm(-1) (CH(2) scissoring mode) as the markers defining the ratio of unsaturated-to-saturated carbon-carbon bonds of the fatty acids in the algal lipids. These spectral features were first quantified for pure fatty acids of known iodine value. The resultant calibration curve was then used to calculate the effective iodine value of storage lipids in the living algal cells from their Raman spectra. We demonstrated that the iodine value differs significantly for the three studied algal species. Our spectroscopic estimations of the iodine value were validated using GC-MS measurements and an excellent agreement was found for the Trachydiscus minutus species. A good agreement was also found with the earlier published data on Botryococcus braunii. Thus, we propose that Raman microspectroscopy can become technique of choice in the rapidly expanding field of algal biotechnology.

One of the reactive forms of oxygen is hydrogen peroxide (H2O2), which has been investigated as a key component of growth processes and stress responses. Different methods for the determination of H2O2 production by animal and bacterial cells exist; however, its detection in algal cell cultures is more complicated due to the presence of photosynthetic pigments in the cells and the complex structure of cell walls. Considering these issues, a reliable, quick, and simple method for H2O2 detection is needed in phycological research. The aim of this methodological study was to optimize an Amplex UltraRed method for the fluorometric detection of H2O2 produced by microalgae cells, using a wild‐type strain of Chlamydomonas reinhardtii as a model. The results showed that (i) potassium phosphate is the most suitable reaction buffer for this method, (ii) a 560 nm wavelength variant is the most appropriate as the excitation wavelength for fluorescence spectra measurement, (iii) a 50:50 ratio for the reaction mixture to sample was the most suitable, (iv) the fluorescence signal was significantly influenced by the density of the microalgae biomass, and (v) sample fortification with H2O2 allowed for an increase of the method's reliability and repeatability. The proposed protocol of the Amplex UltraRed method for the fluorometric detection of H2O2 produced by microalgae cells can yield a sensitive and accurate determination of the content of the test compound, minimizing measurement errors, eliminating chlorophyll autofluorescence problem, and compensating for the matrix effect. This method can be applied to the study of other microalgae species. [ABSTRACT FROM AUTHOR]

Microalgae with increased amount of biomass and lipid yield are crucial for biodiesel production. Mixotrophic cultivation has prominence for increasing the micro‐algal cell concentration and hence the volumetric productivity owing to independent utilization of both the photo‐assimilation of CO2 and oxidative assimilation of organic carbon sources. In this study, Ankistrodesmus sp. IFRPD 1061 was examined under various concentrations of sodium acetate for concentration and productivity of biomass and lipid, lipid contents (LCs), and fatty acid profiles. The optimum condition was obtained at Day 21 with 10 mM sodium acetate, which gave 6.940 ± 0.057 g L−1 biomass concentration, 327.619 ± 2.020 mg L−1 day−1 biomass productivity, 2.795 ± 0.191 g L−1 lipid concentration, 131.955 ± 9.275 mg L−1 day−1 lipid productivity, and 40.286 % ± 3.079 % w/w LC. The optimum condition (10 mM sodium acetate) in an open pond cultivation attained maximum values at Day 14, that is, 0.575 ± 0.004 g L−1 biomass concentration, 38.161 ± 0.076 mg L−1 day−1 biomass productivity, 0.203 ± 0.002 g L−1 lipid concentration, 13.440 ± 0.197 mg L−1 day−1 lipid productivity, and 35.219 % ± 0.585 % w/w LC. The lipids recovered from mixotrophic micro‐algae were primarily unsaturated fatty acids, which are appropriate to produce biodiesel. The results revealed that a 10 mM sodium acetate concentration can enhance lipid accumulation within algal cells. [ABSTRACT FROM AUTHOR]

Microalgae and seaweed have been consumed as food for several decades to combat starvation and food shortages worldwide. The most famous edible microalgae species are Nostoc, Spirulina, and Aphanizomenon, in addition to seaweeds, which are used in traditional medicine and food, such as Nori, which is one of the most popular foods containing Pyropia alga as a major ingredient. Recently, many applications use algae-derived polysaccharides such as agar, alginate, carrageenan, cellulose, fucoidan, mannan, laminarin, ulvan, and xylan as gelling agents in food, pharmaceuticals, and cosmetics industries. Moreover, pigments (carotenoids particularly astaxanthins, chlorophylls, and phycobilins), minerals, vitamins, polyunsaturated fatty acids, peptides, proteins, polyphenols, and diterpenes compounds are accumulated under specific cultivation and stress conditions in the algal cells to be harvested and their biomass used as a feedstock for the relevant industries and applications. No less critical is the use of algae in bioremediation, thus contributing significantly to environmental sustainability. This review will explore and discuss the various applications of microalgae and seaweeds, emphasising their role in bioremediation, recent products with algal added-value compounds that are now on the market, and novel under-developing applications such as bioplastics and nanoparticle production. Nonetheless, special attention is also drawn towards the limitations of these applications and the technologies applied, and how they may be overcome. [ABSTRACT FROM AUTHOR]

This study aimed to assess the impact of microalgal concentrations in diets on the settlement and metamorphosis stages of pediveliger larvae and spat of Crassostrea gigas oysters. Diets containing microalgal concentrations of 8, 12, and 16×104 cells mL-1 were administered for seven days during the larval settlement phase of pediveliger larvae. In the metamorphosis and postlarval cultivation phases, diets with microalgal concentrations of 8, 16, 24, and 32×104 cells mL-1 and a control group without food were tested for 14 and 21 days, respectively. Growth, yield, and survival were assessed every seven days. The diet comprised 30% Isochrysis galbana and 70% Chaetoceros muelleri microalgae. In the metamorphosis phase, the results revealed no significant differences in larval metamorphosis rate and survival across the tested diets. The concentrations exhibited similar survival in the spat with an initial average shell height of 0.657 ± 0.05 mm, with a significant difference only in growth. In the spat with an initial average shell height of 0.830 ± 0.12 mm, no differences in survival were observed among the tested concentrations. We concluded that diets of 12 and 16×104 cells mL-1 provide high rates of larval metamorphosis and spat yield during the larval settlement and metamorphosis phases. During the spat cultivation phases, diets of 32 and 24×104 cells mL-1 could optimize the cultivation time and yield of C. gigas spat in the laboratory. However, when considering survival alone, no advantage was found in providing a diet with a microalgal concentration above 8×104 cells mL-1 across all C. gigas oyster cultivation phases. [ABSTRACT FROM AUTHOR]

With increasing demand of fossil fuels and water pollution and their environmental impacts, marine green microalgae have gained special attention in both scientific and industrial fields. This is due to their fast growth in non-arable lands with high photosynthetic activity, their metabolic plasticity, as well as their high CO2 capture capacity. Tetraselmis species, green and eukaryotic microalgae, are not only considered as a valuable source of biomolecules including pigments, lipids, and starch but also widely used in biotechnological applications. Tetraselmis cultivation for high-value biomolecules and industrial use was demonstrated to be a non-cost-effective strategy because of its low demand in nutrients, such as phosphorus and nitrogen. Recently, phycoremediation of wastewater rich in nutrients, chemicals, and heavy metals has become an efficient and economic-alternative that allows the detoxification of waters and induces mechanisms in algal cells for biomolecules rich-energy synthesis to regulate their metabolic pathways. This review aims to shed light on Tetraselmis species for their different culture conditions and metabolites bioaccumulation, as well as their human health and environmental applications. Additionally, phycoremediation of contaminants associated to biofuel production in Tetraselmis cells and their different intracellular and extracellular mechanisms have also been investigated. [ABSTRACT FROM AUTHOR]

The capacity of living algal cells to efficiently eliminate metals from water is well known and achieved through the mechanisms of biosorption and bioaccumulation. These investigations highlight the potential of indigenous microalgae for the elimination of toxic elements such as cadmium (Cd), cobalt (Co), chromium (Cr), nickel (Ni), and lead (Pb) from aqueous solutions. To identify algal strains that are effective in removing heavy metals, samples of soil and water were collected from areas contaminated with industrial and municipal effluents. Among the 11 isolates obtained from various sites contaminated with heavy metals, three isolates (designated as A, I and K) were able to tolerate both the threshold and double threshold levels of the tested heavy metals. Subsequent liquid assays confirmed the efficiency of the three selected algal isolates in removing heavy metals, with isolates A and I demonstrating effectiveness in removing all tested heavy metals, exhibiting removal rates of cadmium ranging from 40% to 80%, cobalt ranging from 20% to 60%, chromium up to 90%, nickel ranging from 40% to 90%, and lead ranging from 50% to 70%. Isolate K displayed the highest efficiency in only removing lead, specifically 86.23% at 21 DAI (Days After Inoculation), and therefore was not chosen for further characterization. Through morphological and molecular characterization, isolates A and I were identified as Coelastrella thermophila AAU BR A and Chlorella sp. AAU BR I, respectively. In conclusion, the results demonstrate that the native algal isolates have the potential to serve as eco-friendly agents for remediating heavy metal-contaminated water. [ABSTRACT FROM AUTHOR]

This study introduces an evaluation methodology tailored for bioreactors, with the aim of assessing the stress experienced by algae due to harmful contaminants released from antifouling (AF) paints. We present an online monitoring system equipped with an ultra-sensitive sensor that conducts non-invasive measurements of algal culture's optical density and physiological stage through chlorophyll fluorescence signals. By coupling the ultra-sensitive sensor with flash-induced chlorophyll fluorescence, we examined the dynamic fluorescence changes in the green microalga Chlamydomonas reinhardtii when exposed to biocides. Over a 24-h observation period, increasing concentrations of biocides led to a decrease in photosynthetic activity. Notably, a substantial reduction in the maximum quantum yield of primary photochemistry (FV/FM) was observed within the first hour of exposure. Subsequently, we detected a partial recovery in FV/FM; however, this recovery remained 50% lower than that of the controls. Integrating the advanced submersible sensor with fluorescence decay kinetics offered a comprehensive perspective on the dynamic alterations in algal cells under the exposure to biocides released from antifouling coatings. The analysis of fluorescence relaxation kinetics revealed a significant shortening of the fast and middle phases, along with an increase in the duration of the slow phase, for the coating with the highest levels of biocides. Combining automated culturing and measuring methods, this approach has demonstrated its effectiveness as an ultrasensitive and non-invasive tool for monitoring the physiology of photosynthetic cultures. This is particularly valuable in the context of studying microalgae and their early responses to various environmental conditions, as well as the potential to develop an AF system with minimal harm to the environment. [ABSTRACT FROM AUTHOR]

The composition of species and the physiological status of microalgal cells serve as significant indicators for monitoring marine environments. Symbiotic with corals, Symbiodiniaceae are more sensitive to the environmental response. However, current methods for evaluating microalgae tend to be population-based indicators that cannot be focused on single-cell level, ignoring potentially heterogeneous cells as well as cell state transitions. In this study, we proposed a microalgal cell detection method based on computer vision and microfluidics, which combined microscopic image processing, microfluidic chip and convolutional neural network to achieve label-free, sheathless, automated and high-throughput microalgae identification and cell state assessment. By optimizing the data import, training process and model architecture, we solved the problem of identifying tiny objects at the micron scale, and the optimized model was able to perform the tasks of cell multi-classification and physiological state assessment with more than 95% mean average precision. We discovered a novel transition state and explored the thermal sensitivity of three clades of Symbiodiniaceae, and discovered the phenomenon of cellular heat shock at high temperatures. The evolution of the physiological state of Symbiodiniaceae cells is very important for directional cell evolution and early warning of coral ecosystem health. [ABSTRACT FROM AUTHOR]

Microalgae have rigid, complex cell walls hindering direct lipid extraction. Cell disruption techniques are used to rupture these cellular structures to increase lipid extraction. Researchers investigating the downstreamprocessing of microalgae do not always have access to microalgal cultivation systems to generate large amounts of fresh microalgal biomass. Using resuspended freeze-dried microalgal biomass as a model laboratory system for concentrated fresh biomass during cell disruption experiments offers greater flexibility in experimental planning and omits investment costs of microalgal cultivation equipment. So far, it however remains unclear whether freeze-dried resuspended biomass can be used as a model laboratory system to represent concentrated fresh biomass during cell disruption and lipid extraction experiments. This paper thus evaluated the suitability of resuspended freeze-dried Nannochloropsis as a model laboratory system for concentrated fresh Nannochloropsis during cell disruption. Ultrasound assisted cell disruption was used as example cell disruption technique and lipid extraction efficiency and free fatty acid content were investigated. Tap water and 3% sodium chloride are both suitable resuspension media for the resuspension of freeze-dried Nannochloropsis. Resuspension duration should be limited (< 120 min) to prevent the formation of free fatty acids. The condition of the biomass (concentrated fresh, or resuspended freeze-dried) prior to ultrasound assisted cell disruption did not influence the resulting lipid extraction efficiency. Resuspended freeze-dried Nannochloropsis biomass in tap water or 3% sodium chloride can thus be used as a model laboratory system for fresh microalgal biomass during research on ultrasound assisted lipid extraction. The generalization of the results to other cultivation conditions, cell disruption techniques, components of interest or microalgal species should be carefully assessed. [ABSTRACT FROM AUTHOR]

Aims This study explored the effects of slightly acidic electrolyzed water (SAEW) on algae to exploit technologies that effectively suppress algal growth in hydroponic systems and improve crop yield. Methods and Results The effects of SAEW on algal growth and the response mechanisms of algae to SAEW were investigated. Moreover, we studied whether the application of SAEW adversely affected tomato seedling growth. The results showed that SAEW significantly inhibited algal growth and destroyed the integrity of the algal cells. In addition, the intracellular oxidation−reduction system of algae was greatly influenced by SAEW. The H2O2, O2−, malondialdehyde (MDA), and reactive oxygen species (ROS) fluorescence signals were significantly induced by SAEW, and superoxide dismutase (SOD), peroxidase (POD), and glutathione reductase (GR) activities were greatly enhanced by a low SAEW concentration but significantly inhibited by SAEW with a high available chlorine concentration, which may contribute to heavy oxidative stress on algal growth and cell structure break down, eventually causing the death of algae and cell number decrease. We also found that regardless of the concentration of SAEW (from 10 to 40 mg L−1), there was no significant change in the germination index, length, or fresh weight of the hydroponic tomato seedlings. Conclusions Our findings demonstrate that SAEW can be used in hydroponic systems to restrain algae with no negative impact on tomato plants. [ABSTRACT FROM AUTHOR]

Microalgae are recognized for their versatility in providing renewable energy, biopharmaceuticals, and nutraceuticals, attributed to their sustainable, renewable, and cost-effective nature. Genetic engineering has proven highly effective in enhancing microalgae production. PCR-based genotyping is the primary method for screening genetically transformed microalgae cells. Recently, we developed a novel PCR method, namely Squash-PCR, and employed it for the molecular analysis of industrially important fungi and yeasts. In this study, we successfully implemented the Squash-PCR technique in 12 industrially significant algae species. This approach offers a quick and reliable means of obtaining DNA templates directly from squashed algal cells, eliminating the need for time-consuming and labor-intensive cultivation and genomic DNA extraction steps. Our results demonstrate the effectiveness of Squash-PCR in detecting and characterizing target genes of interest in 12 different algae species. Overall, this study establishes the Squash-PCR method as a valuable tool for molecular studies in algae, enabling researchers to rapidly screen and manipulate genetic traits in diverse algal species. [ABSTRACT FROM AUTHOR]

The present study made significant contributions to the application of a green approach for removing metals from wastewater using microalgae. Bioelimination, which involoves the use of biological material to accumulate and concentrate pollutants from aqueous solutions enables ecologically an acceptable recovery and/or elimination of these pollutants. This research specifically aimed to evaluate the efficacy of the blue-green alga/cyanobacterium Oscillatoria sp. in the wastewater treatment procedure. The growth rate was promising, especially in low concentrations of wastewater. Additionally, the study explored the potential of using algae for wastewater treatment by reducing the proportion of mineral elements in the algal culture filtrate and examining the possibility of mineral accumulation within the algal cells. Notably, minerals such as phosphate, magnesium, manganese, sodium, iron, sulfur and calcium showed significant differences (P= 0.05) at the probability level. Additionally, it was noted that the highest percentage of mineral nutrient removal was 10% with high efficiency, although in high wastewater concentrations, it was somewhat less efficient. [ABSTRACT FROM AUTHOR]

• Cell wall intact C. reinhardtii had higher EPS production and As tolerance. • Cell wall and EPS mutually contributed to the As adsorption on cell surface. • EPS enhanced the As redox transformation and methylation in and out of algal cells. • Various functional groups participated in the extracellular As complexation. Arsenic (As) pollution seriously threatens human and ecological health. Microalgal cell wall and extracellular polymeric substances (EPS) are known to interact with As, but their roles in the As resistance, accumulation and speciation in microalgae remain unclear. Here, we used two strains of Chlamydomonas reinhardtii , namely CC-125 (wild type) and CC-503 (cell wall-deficient mutant), to examine the algal growth, EPS synthesis, As adsorption, absorption and transformation under 10–1000 µg/L As(III) and As(V) treatments for 96 h. In both strains, the As absorption increased after the EPS removal, but the growth, As adsorption, and transformation of C. reinhardtii declined. The CC-125 strain was more tolerant to As stress and more efficient in EPS production, As accumulation, and redox transformation than CC-503, irrespective of EPS presence or absence. Three-dimension excitation-emission matrix (3D-EEM) and attenuated total reflectance infrared spectroscopy (ATR-IR) analyses showed that As was bound with functional groups in the EPS and cell wall, such as -COOH, NH and -OH in proteins, polysaccharides and amino acids. Together, this study demonstrated that EPS and cell wall acted as barriers to lower the As uptake by C. reinhardtii. However, the cell wall mutant strain was more susceptible to As toxicity due to lower EPS induction and higher As absorption. [Display omitted] [ABSTRACT FROM AUTHOR]

Excess nitrogen and phosphorus nutrients in the aquatic environment result in the growth of algal cells and water eutrophication, which adversely affect the aquatic environment and human health. Therefore, discovering a safe and efficient algae suppression method is necessary to ensure the ecological safety of water. Recently, the allelopathic effects of aquatic plants on algae have attracted extensive attention from researchers. This review demonstrates the current research hotspot of allelopathic algal inhibition in aquatic plants and lists the common aquatic plant species and allelochemicals. In addition, the inhibition mechanism of allelochemicals from aquatic plants on algae is systematically discussed. Moreover, the key factors affecting the inhibition of allelopathy in algae, such as pH, temperature, algal cell density, and concentration of allelochemicals, are summarized. The present utilization modes of allelochemicals on algae are also presented. Finally, the problems existing in the study of allelopathic algal inhibition of aquatic plants are highlighted, and suggestions for further research are proposed. [ABSTRACT FROM AUTHOR]

Rapid advances to industrialization and population increases have put aquatic ecosystems at high risk of pollution from various industrial and municipal effluents. The effluents consist of heavy metals (HM), micropollutants, nutrients, microorganisms, solids, particulates and dissolved matter. To this effect, pollutant remediation in such ecosystems is inevitable and of interest in global research. In this study, phycoremediation and its potential to bioremediate HM from polluted aqueous solutions is of focus. The factors influencing the process and the mechanisms involved are explored. The study established that available functional groups in microalgae, cell surfaces characteristics, type of microalgae species used, nutrient availability, size of biosorbent and metal concentration are some environmental factors, which influence phycoremediation success. Uptake of HM from contaminated water is regulated by mechanisms such as volatilization, bio-methylation, enzyme catalyzation, compartmentalization, extracellular polymeric substances-complexation, extracellular biosorption and intracellular bioaccumulation. To ensure high pollutant removal efficacy, improved adaptability of microalgae to HM-polluted systems and high resilience to attack by foreign agents, a number of mechanisms can be adopted. These include microalgal pretreatment with chemicals, bioengineering and biotechnological advances such a gene encoding, synthesis of transgenic proteins, gene overexpression, modification of microalgal cell surfaces with nanoparticles and the use of a consortium of microbes. This study noted that optimizing the discussed factors and mechanisms will promote field-scale application of phycoremediation in water treatment to remove HM. [ABSTRACT FROM AUTHOR]

Makeup water constitutes a key component in the water management of microalgal cultivation systems. However, the effect of makeup water addition on microalgal growth remains largely unexplored. This study compared two deionized water addition intervals (1 day and 4 days) for their effect on the growth of Scenedesmus dimorphus (S. dimorphus hereafter) in 2000 mL Pyrex bottles under controlled conditions. Cell counts and dry algal biomass (DAB) were measured to characterize the microalgal growth rate. Water addition intervals impacted algal cell counts but had little effect on DAB. Adding makeup water every day resulted in a higher growth rate (8.80 ± 1.46 × 105 cells mL−1 day−1; p = 0.22, though) and an earlier occurrence of the peak cell count (day 9) than adding it every 4 days (6.95 ± 1.68 × 105 cells mL−1 day−1 and day 12, respectively). It is speculated that water loss over an extended period and the following makeup water addition posed stress on S. dimorphus. Surpassing the peak cell count, S. dimorphus continued to grow in DAB, resulting in an increased cell weight as a response to nutrient starvation. Optical density at 670 nm (OD670) was also measured. Its correlation with DAB was found to be affected by water addition intervals (R2 = 0.955 for 1 day and 0.794 for 4 days), possibly due to a water loss-induced change in chlorophyll a content. This study is expected to facilitate the makeup water management of photobioreactor and open pond cultivation systems. [ABSTRACT FROM AUTHOR]

Microalgal biodiesel as a substitute for fossil energy has attracted extensive attention. However, the high cost of microalgae cultivation limits the industrial production of microalgal biodiesel. The co-culture system may offer a means to increase microalgae's biomass production. In this study, Streptomyces strains were selected to construct and optimize co-culture systems with Monoraphidium sp. HDMA-11 and the algal cell biomass, lipid content, phycocyanin content, starch content, and fatty acid composition were determined. The results showed that Streptomyces nojiriensis significantly promoted Monoraphidium sp. HDMA-11 growth and a co-culture system were established. Orthogonal experiments showed that the Monoraphidium sp. HDMA-11 biomass was further increased when the initial culture pH was 7.5, the inoculation time of Streptomyces strain supernatants was 36 h, the volume ratio of microalgal actinomycetes was 1:1, and no additional acetic acid was added. Under these conditions, compared with monocultured Monoraphidium sp. HDMA-11, the cell biomass and lipid productivity of the co-culture system increased by 525.8 and 155.1%, respectively. These results suggest that S. nojiriensis supernatant potentially enhances microalgae biomass and may represent a new method to improve microalgae growth. [ABSTRACT FROM AUTHOR]

The aim of this work is to investigate the effects of the variation in the culture parameters on the production of lipids. We first determined the best conditions to promote biomass productivity. Then, we set up a culture system in two steps: the first step is to promote the growth of the algal biomass, via the use of a culture medium enriched in nutrients, in order to have a high concentration in the cell; and the second step consisting in stimulating the production of lipids, by inducing stress to the algal cells, via the substitution of essential nutrients. Experimental results have shown that favouring growth kinetics is to the detriment of oil content. Indeed, a deficiency in essential nutrients (nitrogen and/or phosphorus) inhibits growth but favours lipid production. Lipid content tripled (51.33% dry weight) in N. gaditana grown in the total absence of nutrients (0 g/L nitrogen and phosphorus) compared to controls (12 g/L nitrogen and 5 g/L phosphorus). Nitrogen and phosphorus deficiency stimulates lipid accumulation but leads to a reduction in growth rate, which ultimately impairs lipid productivity. For better lipid productivity, a compromise must be found between growth and cellular lipid accumulation. [ABSTRACT FROM AUTHOR]

Changes in the specific growth rate, as well as fluorescent, cytometric, and morphological parameters of the green microalgae Dunaliella salina, have been evaluated in the presence of Cu2+ ions (0–3750 µg/L) in a cultivation medium. The growth rate has been found to be the most sensitive to the copper presence; it decreases at copper concentrations above 150 µg/L, while an increase in the pollutant content to 1500 µg/L or higher results in the death of a microalgal culture. The number of algal cells at the stationary growth phase decreases as the copper content in the medium increases from 150 to 3750 µg/L. According to the results of this study, the efficiency of the algal photosynthetic apparatus is not affected by copper concentrations, which do not cause the death of the culture. A decrease in the values of the maximum fluorescence quantum yield, nonphotochemical quenching, and the maximum relative electron transport rate below the optimal values can be used as an indicator of the lethal impact of the studied pollutant on D. salina. Copper concentrations in the medium equal to 750 µg/L or higher cause the following effects: an increase in cell volume, an increase in the number of spherical cells, plasmalemma deformation and perforation, the predominance of deformed cells of an irregular shape, and a double reduction in the intracellular content of chlorophyll a and the specific yield of fluorescence for chlorophyll a (μg/L). [ABSTRACT FROM AUTHOR]

Layered double hydroxide (LDH) nanomaterials are utilized extensively in numerous fields because of their distinctive structural properties. It is critical to understand the environmental behavior and toxicological effects of LDHs to address potential concerns caused by their release into the environment. In this work, the toxicological effects of two typical LDHs (Mg-Al-LDH and Zn-Al-LDH) on freshwater green algae (Scenedesmus obliquus) and the main affecting factors were examined. The Zn-Al-LDH exhibited a stronger growth inhibition toxicity than the Mg-Al-LDH in terms of median effect concentration. This toxicity difference was connected to the stability of particle dispersion in water and the metallic composition of LDHs. The contribution of the dissolved metal ions to the overall toxicity of the LDHs was lower than that of their particulate forms. Moreover, the joint toxic action of different dissolved metal ions in each LDH belonged to additive effects. The Mg-Al-LDH induced a stronger oxidative stress effect in algal cells than the Zn-Al-LDH, and mitochondrion was the main site of LDH-induced production of reactive oxygen species. Scanning electron microscope observation indicated that both LDHs caused severe damage to the algal cell surface. At environmentally relevant concentrations, the LDHs exhibited joint toxic actions with two co-occurring contaminants (oxytetracycline and nano-titanium dioxide) on S. obliquus in an additive manner mainly. These findings emphasize the impacts of the intrinsic nature of LDHs, the aqueous stability of LDHs, and other environmental contaminants on their ecotoxicological effects. [ABSTRACT FROM AUTHOR]

Microalgae shows a high potential to produce biofuel and forward osmosis (FO) has been proposed as a promising dewatering process for algal biomass separation from water. However, the effect of reverse salt flux (RSF) on algal biomass during the dewatering process using FO has not been completely explored. This study was to investigate the effect of different types of salt and their concentrations on algal biomass in terms of conductivity, settling velocity, and lipid contents in FS during a simulated FO-driven dewatering of Chlorella vulgaris microalgae. Three draw solution (DS) salts (NaCl, KCl and NH4Cl) were evaluated in RSF-simulating batch tests. The salt diffusion from the DS to the algal feed solution (FS) caused a static growth of algal biomass while increasing lipid content up to 14.8% at 8 mM NH4Cl. With the addition of the different salts, pH was maintained to the optimal algal thriving range (7.2–10.6), but the presence of salt stressed the algal cells and inhibited photosynthesis and algal growth within the experimental conditions. The settling velocity of the algal cells improved with the increase of salt content from 8 to 80 mM of each DS. It seemed that cell division could be accelerated in the presence of NH4Cl, and microscopic images showed a change in the algal cell size distribution, which may negatively affect algal settleability. DS salt in an FO-algal harvesting system should be selected based on the final algal properties and constituents required. [ABSTRACT FROM AUTHOR]

Pigmented microalgae inhabiting snow and ice environments lower the albedo of glacier and ice-sheet surfaces, significantly enhancing surface melt. Our ability to accurately predict their role in glacier and ice-sheet surface mass balance is limited by the current lack of empirical data to constrain their representation in predictive models. Here we present new empirical optical properties for snow and ice algae and incorporate them in a radiative transfer model to investigate their impact on snow and ice surface albedo. We found ice algal cells to be more efficient absorbers than snow algal cells, but their blooms had comparable impact on surface albedo due to the different photic conditions of their habitats. We then used the model to reconstruct the effect of ice algae on bare ice albedo spectra collected at our field site in southern Greenland, where blooms dropped the albedo locally by between 3 and 43%, equivalent to 1–10 L m $^{-2}$ d $^{-1}$ of melted ice. Using the newly parametrized model, future studies could investigate biological albedo reduction and algal quantification from remote hyperspectral and multispectral imagery. [ABSTRACT FROM AUTHOR]

Starch and lipids are two major carbon storage compounds in algal cells. Theoretically, switching the carbon flow from starch to lipid synthesis may be a promising approach to realize the overproduction of microalgae-derived biodiesel. However, the results in previous studies vary across algal strains. To test the hypothesis, Monoraphidium sp. mutants were generated using ethyl methane sulfonate (EMS) as a random chemical mutagen. Among the 10% survival cells after exposure to EMS (4 mM) for 30 min, 23 low-starch mutants were selected, of which only 9 strains exhibited enhanced relative fluorescence unit (RFU) compared to wild type, implying the complexity in metabolic steps underlying the re-allocation of starch and lipid in Monoraphidium. Amid these mutants, EM25 showed increased lipid content (25.1%) and moderate biomass productivity (71 mg L−1 day−1), resulting in a higher lipid productivity (17.8 mg L−1 day−1) than that of wild type. The alteration of carbon storage compounds in the mutant was attributed to changes in the activities of enzymes (AGPase, ACCase, PEPC, DGAT) related to starch and lipid synthesis. Additionally, the fatty acid composition of the mutant complied with most of the parameters defined by ASTM D6751 and EN 14,214, with a sharp decrease in cloud point compared to wild type, suggesting its application in wide geographic area and the potential to be developed as a promising candidate for biodiesel production. [ABSTRACT FROM AUTHOR]

The influence of ultrasound irradiation on the algal biomass productivity as well as its oil content and fatty acids profile, grown in a modified Zarrouk medium, i.e., deproteinized whey waste solution, was investigated. The algal samples (Nannochloris sp. 424-1 microalgae) were grown for 7 days in a thermostated incubator at 28 °C, shaken under continuous light. During this period, the algal biomass was subjected to induced stress by ultrasonic irradiation at different powers and sonication time. The obtained results demonstrate that ultrasound stressing of algae biomass has a positive effect on both the quantity of biomass and the oil obtained, also causing a shift in fatty acid composition by increasing the proportion of C16 and C18 polyunsaturated fatty acids. A low dosage level of exposure to the ultrasound led to algal biomass increase as well as lipid accumulation. For both types of irradiation modes which were investigated, daily and only initial irradiation, the beneficial effect of the ultrasound decreases as the exposure time increases and the excessive sonication becomes detrimental to microalgae growth. [ABSTRACT FROM AUTHOR]

• Microalgae are emerging as sustainable bioremediation platforms for Mo(V) removal. • The removal efficiency was determined at 41 % of 200 mg L−1 initial Mo(V) conc. • The optimal Mo(V) removal rate was 82.78 mg L−1 at pH 3 and 35 °C. • The maximum biomass and lipid yield of C. sorokiniana SU1 were 2.35 and 0.71 gL−1. With growing global pollution concerns, the environmental hazards posed by molybdenum (Ⅴ) discharge >10 ppm, especially from steel and semiconductor industries have escalated environmental risks. Unfortunately, sustainable methods for Mo(V) removal are limited. This study presents an environmentally friendly solution utilizing microalgae for effective Mo(V) treatment. Notably. the generated microalgal biomass serves the dual purpose of addressing molybdenum pollution and contributing to biofuel production, offering economic incentives. Selected microalgae Chlorella sorokiniana SU1 were used for treating Mo(V). The goal is to maximize Mo(V) removal over 18 days, ensuring sufficient biomass and lipid yields. Optimizing pH and temperature, directed by zeta potential analysis, improves Mo(V) removal efficiency. FTIR analysis validates Mo(V) adsorption through the reactive groups on the algal cell wall. Chlorella sorokiniana SU1 is a highly effective agent for Mo(V) removal, achieving an impressive removal rate of 82.78 mgL−1. Additionally, the resultant treatment demonstrates noteworthy microalgal biomass and lipid yields of 2.35 and 0.71 g L−1, respectively. The tactical pH and temperature optimization further augments the molybdenum removal efficiency. This innovative study addresses molybdenum pollution and also gives a sustainable route for biofuel production through generated microalgal biomass, establishing a promising technique for commercial-scale molybdenum bioremediation. [Display omitted] [ABSTRACT FROM AUTHOR]

Microplastics (MPs) are abundantly present in aquatic environments, where the phytoplankton—microalgae, are now inevitably bound to a long-term coexistence with them. While numerous studies have focused on the toxicological effects of high-concentration MPs exposure, there remains controversy over whether and how MPs affect microalgae at environmentally relevant concentrations. This study aims to draw conclusions that narrow the gap from 52 studies with varying results. Overall, MPs can inhibit growth and photosynthesis, induce oxidative damage, from which microalgae can recover after an appropriate period. Cyanobacteria exhibit greater vulnerability than chlorophyta. The relative size of MPs to algal cells potentially governs their coexistence behavior, thereby altering the mechanisms of impact. Pristine MPs may increase the production of extracellular polymeric substances (EPS) and microcystins (MCs), while aged MPs have the opposite effect. Additionally, relevant factors are systematically discussed, offering insights for future research. [Display omitted] • An environmental relevant MPs concentration has been set for analyses (< 5 mg/L). • Cyanobacteria displaying greater vulnerability compared to Chlorophyta. • Size level of MPs comparing to cells is the key factor. • The concentration-dependent inhibition exhibited temporal attenuation or even dissipation. • Aging of MPs affects the extracellular secretions. [ABSTRACT FROM AUTHOR]

Heavy metal pollution in the cold region is serious, affecting human health and aquatic ecology. This study investigated the ability of microalgae to remove heavy metals (HMs) and produce lipid at low temperature. The removal efficiency of different HMs (Cd2+, Cu2+, Cr3+ and Pb2+), cell growth and lipid synthesis of microalgae were analyzed at 15 °C. Moreover, addition of glycine betaine (GB) further enhanced the productivity of microalgae in treating HMs and lipid production, and simultaneously increased the antioxidant capacity of microalgae against environmental stresses. The results showed that the highest lipid productivity of 100.98 mg L−1 d−1 and the removal efficiency of 85.8 % were obtained under GB coupled with Cr3+. The highest glutathione content of 670.34 nmol g−1 fresh alga was achieved under GB coupled with Pb2+. In addition, lipidomics showed that GB was able to up-regulate the triglyceride and diglyceride content, influenced fatty acid composition to regulate the microalgal metabolism, and mediated lipid accumulation under 15 °C mainly through the regulation of glycerol ester metabolism. This study provided a new perspective on microalgal lipid production and the removal of HMs in cold regions and provided evidence for the use of phytohormones to improve the algal environmental resistance. [Display omitted] • GB affected algal cell growth and lipid synthesis under low temperature (15 °C). • Highest lipid productivity (100.98 mg L−1 d−1) was obtained under GB coupled Cr3+. • The removal efficiency of Cr3+ could reach 85.8 % in the presence of GB. • GB can increase algal cell resistance to external environmental stress. • Lipidomics reveal the mechanism by which GB regulated lipid accumulation in algae. [ABSTRACT FROM AUTHOR]

Pentachlorophenol (PCP) and polyethylene microplastic (PE-MP) have been designated as emerging and persistent pollutants, respectively. The combined effects of those pollutants are still unknown, especially to organisms like phytoplankton that may adsorb to their surface. Therefore, the purpose of this study was to investigate for the first time the effects of PE-MP alone and in combination with PCP on the microalgae Isochrysis galbana , clone t-ISO following 72 h of exposure. Photosynthetic pigments amounts, carotenoid, protein, carbohydrate and fatty acids have been assessed. Acute toxicity test showed that the 72 h median inhibition concentration (72 h-EC 50) was 148.2, 0.66 and 087 mg L−1 for PE-MP, PCP and their mixture. The utmost effects in growth inhibition rates were noted with 0.5 and 1.25 mg L−1 PCP (23% and 85%, respectively), and 100 and 300 mg L−1 PE-MP (49% and 64%, respectively). Moreover, it was found that those concentrations had a major impact on the photosynthetic pigments, protein, carbohydrate, and fatty acids amounts in algal cells. Furthermore, levels of H 2 O 2 and Malondialdehyde (MDA), as well as the activities of catalase (CAT), superoxide dismutase (SOD), and ascorbate peroxidase (APX), indicated the induction of an oxidative stress in algal cells. It appears that adding PE-MP at a no-effect concentration (25 mg L−1) reduces the toxicity caused by PCP due to its adsorption to polyethylene microplastics. [Display omitted] • PCP induced toxicity on Isochrysis galbana , clone t-ISO. • 25 mg L−1 of PE-MP was found with no effect. • PCP adsorption on PE-MP was evidenced. • PE-MP modulates the toxicity of PCP on Isochrysis galbana. [ABSTRACT FROM AUTHOR]

Efficient microalgae harvesting is a great challenge hindering diverse industrial applications of microalgae. Flocculation is regarded as an effective and promising technology for microalgae harvesting. In this study, sulfate (Al2(SO4)3 and Fe2(SO4)3) and chloride flocculants (AlCl3 and FeCl3) were used to harvest Chlorella vulgaris. Flocculation conditions, including flocculant dose, flocculation time, stirring speed, stirring time, and flocculation pH, were optimized, and flocculant effects on microalgal cell status, floc characteristics, biomass composition, algal cell re-culture, and media recycling were investigated. All flocculants exhibited efficient flocculation efficiency (93.5–98.8%) with lower doses of sulfate salts (60 mg/L algal culture) and higher doses of chloride salts (100 mg/L algal culture). The tested flocculants had no obvious influence on biomass composition (including lipids, carbohydrates, proteins, and carotenoids), and microalgal cells in flocs could efficiently regrow. The spent medium of all treatments was successfully recycled for subsequent cell growth, thus reducing dependency on fresh medium. [ABSTRACT FROM AUTHOR]

Microalgal energy storage compounds (carbohydrates, lipids, etc.) can serve as renewable feedstocks for biofuels and biobased chemicals. Traditional methods of inducing the accumulation of energy storage compounds in microalgae, such as abiotic stress (high light intensity, high salinity, nutrient limitation, heavy metals, etc.), can affect the growth of microalgae and limit their efficient accumulation of energy storage materials. Plant hormones are a class of small molecular substances that act as chemical messengers to coordinate plant cell activities and regulate the physiological and metabolic activities of microalgae, including promoting microalgal cell proliferation, improving stress resistance, and enhancing photosynthetic activity, thereby increasing algal biomass and lipid, chlorophyll and protein content. This paper reviews the recent research progress on regulation of the accumulation of energy storage compounds in microalgae by adding exogenous plant hormones combined with abiotic stress, discusses the mechanism of plant hormones regarding the accumulation of energy storage compounds in microalgae, and proposes future research needs. [ABSTRACT FROM AUTHOR]

Heavy metals‐containing drinking water and wastewater are posing a severe threat to the environment, and living beings on land, air and water. Different conventional, advanced nanomaterials‐based and biological method has been employed for the treatment of heavy metals. Among the biological methods, microalgae are an important group of micro‐organisms that have numerous environmental applications and can remediate heavy metals from wastewater. Also, it has numerous advantages over conventional remediation processes. Microalgae cells can uptake the heavy metal via different physiological and biological methods and are utilized as a nutrient source to regulate its metabolic process for the production of biomass. Furthermore, the enhancement in heavy metal removal efficiency can be improved using different strategies such as immobilization of algal cells, development of algal consortia and designing of microalgae‐based nanocomposite materials. Also, it can significantly contribute towards environmental sustainability and future. Thus, the review provides a critical overview of heavy metals and their existence along with their negative effects on humans. This review provides insight on recent advanced nanomaterial approaches for the removal of heavy metals, overviews of microalgae‐based heavy metal uptake mechanisms and their potential for the amputation of different heavy metals. Furthermore, the special focus is on recent strategies that enhance heavy metal removal efficiency and contribute towards sustainability for the development of a microalgae‐based future. [ABSTRACT FROM AUTHOR]

Flow cytometry has become an indispensable tool for counting, analyzing, and sorting large cell populations in biological research and medical practice. Unfortunately, it has limitations in the analysis of non-spherically shaped cells due to the variation of their alignment with respect to the flow direction and, hence, the optical interrogation axis, resulting in unreliable cell analysis. Here, we present a simple on-chip acoustofluidic method to fix the orientation of ellipsoidal cells and focus them into a single, aligned stream. Specifically, by generating acoustic standing waves inside a 100 ⋅ 100 µm square-shaped microchannel, we successfully aligned and focused up to 97.7% of a population of Euglena gracilis (an ellipsoidal shaped microalgal species) cells in the center of the microchannel with high precision at a volume rate of 25 to 200 µL min−1. Uniform positioning of ellipsoidal cells is essential for making flow cytometry applicable to the investigation of a greater variety of cell populations and is expected to be beneficial for ecological studies and aquaculture. [ABSTRACT FROM AUTHOR]

Chlorella is one of the most well-known microalgal genera, currently comprising approximately a hundred species of single-celled green algae according to the AlgaeBase. Strains of the genus Chlorella have the ability to metabolize both inorganic and organic carbon sources in various trophic modes and synthesize valuable metabolites that are widely used in many industries. The aim of this work was to investigate the impact of three trophic modes on the growth parameters, productivities of individual cell components, and biochemical composition of Chlorella sorokiniana, Chloroidium saccharofilum, and Chlorella vulgaris cells with special consideration of protein profiles detected by SDS-PAGE gel electrophoresis and two-dimensional gel electrophoresis with MALDI-TOF/TOF MS. Mixotrophic conditions with the use of an agro-industrial by-product stimulated the growth of all Chlorella species, which was confirmed by the highest specific growth rates and the shortest biomass doubling times. The mixotrophic cultivation of all Chlorella species yielded a high amount of protein-rich biomass with reduced contents of chlorophyll a, chlorophyll b, carotenoids, and carbohydrates. Additionally, this work provides the first information about the proteome of Chloroidium saccharofilum, Chlorella sorokiniana, and Chlorella vulgaris cells cultured in molasses supplementation conditions. The proteomic analysis of the three Chlorella species growing photoheterotrophically and mixotrophically showed increased accumulation of proteins involved in the cell energy metabolism and carbon uptake, photosynthesis process, and protein synthesis, as well as proteins involved in intracellular movements and chaperone proteins. [ABSTRACT FROM AUTHOR]

Optimizing the operational parameters of the photosynthetic process is essential for effective microalgae-based CO 2 capture and fixation. This study develops and validates models that can relate the effects of CO 2 concentration and aeration rate on relevant microalgal properties, including biomass productivity and CO 2 biofixation rate. The maximum biomass concentration was predicted as 2.80 g⋅L−1 at the optimal CO 2 concentration of 10.2 % and aeration rate of 0.55 vvm. Based on the proposed models, the CO 2 biofixation rate characterized by carbon content in dry microalgal cells, and the timings of microalgae entering the exponential growth and stationary growth phases were effectively predicted. Furthermore, the lower heating value of harvested microalgal biomass was up to 21.98 kJ⋅g−1 and the dominant fatty acid methyl esters (FAME) species were C16 – C18, highlighting the potential of Chlorella vulgaris as the feedstock for microalgae-based energy production. Consequently, microalgae present a remarkable dual function for CO 2 mitigation and renewable bioenergy production. [Display omitted] • Models simulating microalgal growth and CO 2 fixation rate were developed. • Optimal CO 2 concentration and aeration rate for cell growth were determined. • High biomass of 2.80 g L−1 was achieved at the optimal operational condition. • Chlorella shows high potential on production of combustion fuel and biodiesel. [ABSTRACT FROM AUTHOR]

This study aimed to assess the ecological risks posed by sulfamethoxazole (SMX) at environmentally relevant concentrations. Specifically, its effects on the growth and biochemical components (total protein, total lipid, and total carbohydrate) of two marine microalgae species, namely Skeletonema costatum (S. costatum) and Phaeodactylum tricornutum (P. tricornutum), were investigated. Our findings revealed that concentrations of SMX below 150 ng/L stimulated the growth of both microalgae. Conversely, at higher concentrations, SMX inhibited their growth while promoting the synthesis of photosynthetic pigments, total protein, total lipid, and total carbohydrate (P < 0.05). Transmission electron microscope (TEM) observations demonstrated significant alterations in the ultrastructure of algal cells exposed to SMX, including nuclear marginalization, increased chloroplast volume, and heightened vacuolation. In addition, when SMX was lower than 250 ng/L, there was no oxidative damage in two microalgae cells. However, when SMX was higher than 250 ng/L, the antioxidant defense system of algal cells was activated to varying degrees, and the level of malondialdehyde (MDA) increased, indicating that algae cells were damaged by oxidation. From the molecular level, environmental concentration of SMX can induce microalgae cells to produce more energy substances, but there are almost no other adverse effects, indicating that the low level of SMX at the actual exposure level was unlikely to threaten P. tricornutum , but a higher concentration can significantly reduce its genetic products, which can affect the changes of its cell structure and damage P. tricornutum to some extent. Therefore, environmental concentration of SMX still has certain potential risks to microalgae. These outcomes improved current understanding of the potential ecological risks associated with SMX in marine environments. [Display omitted] • SMX can increase the contents of bioactive substances and photosynthetic pigments of two marine diatoms. • SMX above 250 ng/L will cause chloroplast damage and oxidative damage of algae cells. • SMX above 250 ng/L affects the synthesis of genetic material of P. tricornutum. [ABSTRACT FROM AUTHOR]

Glucose metabolism regulates cell growth and affects astaxanthin accumulation in the green algae Chromochloris zofingiensis. Hub gene functioning in this bioactive compound has been illustrated at the genome, transcriptome and metabolome level, but is rather limited from a proteome aspect. Microalgal cell produce an enhanced biomass (8-fold higher) but decreased lipid and astaxanthin content (~20% less) in the glucose condition compared to the control. Here, we investigate the proteomic response of C. zofingiensis grown with and without glucose using an LC-MS/MS-based Tandem Mass Tag (TMT) approach. The proteomic analysis demonstrated that glucose supplementation triggers the upregulation of 105 proteins and downregulation of 151 proteins. Thus, the carbon and energy flux might flow to cell growth, which increased the associated protein abundance, including DNA polymerase, translation initiation factor, 26S proteasome regulatory subunits, and the marker enzyme of the TCA cycle ribosomal protein. Moreover, the glucose supplement triggered the downregulation of proteins mainly involved in photosynthesis, chloroplasts, valine, leucine and isoleucine biosynthesis, 2-oxocarboxylic acid metabolism, and pantothenate and CoA biosynthesis pathways. This proteomic analysis is likely to provide new insights into algal growth and lipid or astaxanthin accumulation upon glucose supplementation, providing a foundation for further development of C. zofingiensis as oleaginous microalga for bioengineering applications. [ABSTRACT FROM AUTHOR]

Microalgal biomass and metabolites can be used as a renewable source of nutrition, pharmaceuticals and energy to maintain or improve the quality of human life. Microalgae's high volumetric productivity and low impact on the environment make them a promising raw material in terms of both ecology and economics. To optimize biotechnological processes with microalgae, improving the productivity and robustness of the cell factories is a major step towards economically viable bioprocesses. This review provides an overview of random mutagenesis techniques that are applied to microalgal cell factories, with a particular focus on physical and chemical mutagens, mutagenesis conditions and mutant characteristics. [ABSTRACT FROM AUTHOR]

The mixing of the culture medium in a photobioreactor (PBR) is very important to enhance the cultivation of microalgae since it ensures that microalgae cells can access nutrients and light radiation. In this study, a numerical model of hydrodynamic conditions was developed to investigate the mixing of the culture medium in a hybrid tubular photobioreactor under various operating conditions. The movements of microalgae cells in transparent tubes was simulated. The motion of the cells was integrated into a mechanistic model, to simulate the influence of operating parameters on the distribution of light in the culture medium and, consequently, on the production of microalgae. According to the developed multi-physical model, when the flow rate of the culture medium increases, more intensive mixing takes place in the transparent area of hybrid tubular PBR, and microalgal cells are more often exposed to light radiation. Intensification of mixing showed an increase in microalgal biomass production. However, the increase in production was very low because the concentration of microalgal biomass in the culture medium was generally low and therefore the penetration of incident light into the culture medium was not limited. [ABSTRACT FROM AUTHOR]

This review analyses the account of biological (microalgae) and synthetic (bio-polymeric adsorbents) elements to compass the treatment efficiencies of various water pollutants and mechanisms behind them. While considering pollutant removal, both techniques have their own merits and demerits. Microalgal-based methods have been dominantly used as a biological method for pollutant removal. The main limitations of microalgal methods are capacity, scale, dependence on variables of environment and duration of the process. Biopolymers on the other hand are naturally produced, abundant in nature, environmentally safe and biocompatible with cells and many times biodegradable. Algal immobilization in biopolymers has promoted the reuse of cells for further treatment and protected cells from toxic environment monitoring and controlling the external factors like pH, temperature and salinity can promote the removal process while working with the mentioned technologies. In this review, a mechanistic view of both these techniques along with integrated approaches emphasizing on their loopholes and possibilities of improvement in these techniques is represented. In addition to these, the review also discusses the post-treatment effect on algal cells which are specifically dependent on pollutant type and their concentration. All these insights will aid in developing integrated solutions to improve removal efficiencies in an environmentally safe and cost-effective manner. Novelty statement The main objective of this review is to thoroughly understand the role of micro-algal cells and synthetic adsorbents individually as well as their integrative effect in the removal of pollutants from wastewater. Many reviews have been published containing information related to either removal mechanism by algae or synthetic adsorbents. While in this review we have discussed the agents, algae and synthetic adsorbents along with their limitations and explained how these limitations can be overcome with the integration of both the moieties together in process of immobilization. We have covered both the analytical and mechanistic parts of these technologies. Along with this, the post-treatment effects on algae have been discussed which can give us a critical understanding of algal response to pollutants and by-products obtained after treatment. This review contains three different sections, their importance and also explained how these technologies can be improved in the future aspects. [ABSTRACT FROM AUTHOR]

Microalgae have evolved into a promising sustainable source of a wide range of compounds, including protein, carbohydrates, biomass, vitamins, animal feed, and cosmetic products. The process of extraction of intracellular composites in the microalgae industry is largely determined by the microalgal species, cultivation methods, cell wall disruption techniques, and extraction strategies. Various techniques have been applied to disrupt the cell wall and recover the intracellular molecules from microalgae, including non-mechanical, mechanical, and combined methods. A comprehensive understanding of the cell disruption processes in each method is essential to improve the efficiency of current technologies and further development of new methods in this field. In this review, an overview of microalgal cell disruption techniques and an analysis of their performance and challenges are provided. A number of studies on cell disruption and microalgae extraction are examined in order to highlight the key challenges facing the field of microalgae and their future prospects. In addition, the amount of product recovery for each species of microalgae and the important parameters for each technique are discussed. Finally, pulsed electric field (PEF)-assisted treatments, which are becoming an attractive option due to their simplicity and effectiveness in extracting microalgae compounds, are discussed in detail. [ABSTRACT FROM AUTHOR]

Microalgal cultivation still presents a big challenge in commercial application due to the small size and low density of microalgae. The effect of phytohormones or light spectra on enhancing microalgal growth has been individually demonstrated at the bench scale. However, the synergistic action of phytohormones and light spectra on algal growth and lipid production remains unclear. In this study, the optimal carbon and nitrogen concentrations, as well as the optimum dosage of the phytohormone indole-3-acetic acid (IAA), for the growth of Chlorella vulgaris were first evaluated under mixotrophic cultivation. A light spectrum experiment was then conducted in an incubator equipped with white and red light. Results show that optimal mixotrophic cultivation conditions were 10 g L−1 glucose, 2250 mg L−1 sodium nitrate and 10 mg L−1 IAA. Under the optimum IAA treatment and irradiation with red light, the highest biomass, lipid content and lipid productivity were 28.34%, 3.53 g L−1 and 140.04 mg L−1 d−1, respectively. As compared to white light, the synergistic action of red light and IAA stimulated biomass production and lipid accumulation by algal cell metabolism and carbon source bioconversion. Furthermore, the post-optimized C. vulgaris had the potential for biodiesel production. These results provide new insights for the highly efficient cultivation of microalgae. [Display omitted] • C & N sources were tested to optimize the conditions for mixotrophic cultivation. • IAA increased biomass production by 11% and lipid yield by 16%, versus no IAA. • Red light promoted the increase of biomass under optimal C & N source conditions. • Synergy of IAA and red light greatly enhanced algal biomass and lipid accumulation. [ABSTRACT FROM AUTHOR]

Investigation of virus-induced microalgal host lysis and the associated infection dynamics typically requires sampling of infected cultures at multiple timepoints, visually monitoring the state of infected cells, or determining virus titration within the culture media. Such approaches require intensive effort and are prone to low sensitivity and high error rates. Furthermore, natural physiological variations can become magnified by poor environmental control, which is often compounded by variability in virus stock efficacy and relatively long infection cycles. We introduce a new method that closely monitors host health and integrity to learn about the infection strategy of Chloroviruses. Our approach combines aspects of spectrometry, plaque assays, and infection dose assessment to monitor algal cells under conditions more representative of the natural environment. Our automated method exploits the continuous monitoring of infected microalgae cultures in highly controlled lab-scale photobioreactors that provide the opportunity for environmental control, technical replication, and intensive culture monitoring without external intervention or culture disruption. This approach has enabled the development of a protocol to investigate molecular signalling impacting the virus life cycle and particle release, accurate determination of virus lysis time under multiple environmental conditions, and assessment of the functional diversity of multiple virus isolates. [ABSTRACT FROM AUTHOR]

Oleaginous microalgae have been considered promising sources of biodiesel due to their high lipid content. Nitrogen limitation/starvation is one of the most prominent strategies to induce lipid accumulation in microalgae. Nonetheless, despite numerous studies, the mechanism underlying this approach is not well understood. The aim of this study was to investigate the effect of nitrogen limitation and starvation on biochemical and morphological changes in the microalga Chlorella vulgaris FACHB-1068, thereby obtaining the optimal nitrogen stress strategy for maximizing the lipid productivity of microalgal biomass. The results showed that nitrogen limitation (nitrate concentration < 21.66 mg/L) and starvation enhanced the lipid content but generally decreased the biomass productivity, pigment concentration, and protein content in algal cells. Comparatively, 3-day nitrogen starvation was found to be a more suitable strategy to produce lipid-rich biomass. It resulted in an increased biomass production and satisfactory lipid content of 266 mg/L and 31.33%, respectively. Besides, nitrogen starvation caused significant changes in cell morphology, with an increase in numbers and total size of lipid droplets and starch granules. Under nitrogen starvation, saturated fatty acids (C-16:0, C-20:0, and C-18:0) accounted for the majority of the total fatty acids (~80%), making C. vulgaris FACHB-1068 a potential feedstock for biodiesel production. Our work may contribute to a better understanding of the biochemical and morphological changes in microalgae under nitrogen stress. Besides, our work may provide valuable information on increasing the lipid productivity of oleaginous microalgae by regulating nitrogen supply. [ABSTRACT FROM AUTHOR]

Ionic liquids (ILs) are new green solvents, which are widely used in lignocellulosic and microalgal biorefineries. However, high-temperature operating conditions limit their application in the extraction of heat-labile algal products, such as bioactive astaxanthin. In this study, we report the technical feasibility of room-temperature astaxanthin extraction from Haematococcus lacustris cysts with a thick and complex cell wall structure, by combining ultrathin α-quartz nanoplates (NPLs) with ethyl-3-methylimidazolium ([Emim])-based ILs. When four different [Emim]-based ILs with thiocyanate (SCN), diethylphosphate (DEP), HSO4, and Cl anions were applied to 90-day-old H. lacustris cysts at room temperature (~28 °C), the astaxanthin extraction efficiency was as low as 9.6–14.2%. Under sonication, α-quartz NPLs disrupted the cyst cell wall for a short duration (5 min). The astaxanthin extraction efficacies of a subsequent IL treatment improved significantly to 49.8% for [Emim] SCN, 60.0% for [Emim] DEP, 80.7% for [Emim] HSO4, and 74.3% for [Emim] Cl ions, which were 4.4, 6.1, 8.4, and 5.2 times higher than the extraction efficacy of only ILs, respectively. This finding suggests that α-quartz NPLs can serve as powerful cell-wall-disrupting agents for the room-temperature IL-mediated extraction of astaxanthin from robust algal cyst cells. [ABSTRACT FROM AUTHOR]

We investigated the transfer of radiocesium and its behavior in living cells and cellular debris in a Chlamydomonas spp. bloom in a pond located approximately 5 km from the Fukushima Dai-ichi Nuclear Power Plant. A microalgal bloom in the pond was the dominant factor in determining the radiocesium concentration (Bq/L) of the > 0.45 μm pond water fraction. The water-to-algae transfer factor [(137Cs concentration Bq/kg>0.45 μm fraction) × (137Cs concentration Bq/L<0.45 μm water)−1] was 1.6 × 103. The transfer factor was similar for filamentous algae attached to the wall of the pond, and suggesting that radiocesium transfer to algae was through water, not directly from sediment. Intact microalgal cells and cellular debris displayed nearly equal 137Cs concentrations, and radiocesium was also transferred in cellular debris as well as living algal cells. The water-to-algae transfer factor in this study is two to three orders of magnitude lower than previously reported radiocesium concentration ratio of suspended solid (> 0.45 μm) and water in rivers in Fukushima [(137Cs concentration Bq/kg>0.45 μm fraction) × (137Cs concentration Bq/L<0.45 μm water)−1]. [ABSTRACT FROM AUTHOR]

A fundamentally new microfluorimeter is designed to assess the functional state of primary photosynthesis in individual phytoplanktonic cells. The device is tested during a sea expedition. It allows estimation of the amount of photosynthetic pigments, the primary photosynthetic efficiency, the light slope of the linear electron-transfer rate (light response curve) as well as the degree of nonphotochemical quenching of excited pigment molecules in every cell found in a studied phytoplankton community. This data enables plotting of the distribution diagrams of algal cells for each of the listed characteristics within the population of every algal species. The microfluorimeter has a convenient graphic interface where a user can save the measurement results to spreadsheets. The detection limit of the device is equal to 1 pg of chlorophyll inside the photometric volume. This sensitivity is high enough for the reliable quantification of chlorophyll-fluorescence parameters of individual algal cells. The microfluorimeter is equipped with a system that maintains the object temperature constant over a wide temperature range limited from below by the dew point and water condensation on the cover-glass surface. [ABSTRACT FROM AUTHOR]

In this work, a label-free and inexpensive method for the monitoring of water pollutants is demonstrated. We introduce a localized surface plasmon resonance (LSPR) based plasmonic capillary optical biosensor to detect microalgae cells. Here, the plasmonic capillary biosensor was prepared by decorating the inner walls of a glass capillary with gold nanoparticles that were employed for investigations. Since the gold nanoparticle has the potential to sense pollutants in water rapidly with high sensitivity and they are expected to perform a significant role in environmental monitoring. Our proposed plasmonic capillary sensor has a detection limit of 25 algal cells (Chlorella sp. CB4). Furthermore, the plasmonic capillary sensing platform significantly simplifies sensor fabrication and reduces the cost of the device. We believe that the presented plasmonic sensor could stand as a potential candidate for developing a cost-effective, label-free, and rapid sensing platform to detect microalgae pollutants present in the water at very low concentrations. [ABSTRACT FROM AUTHOR]

The possibility of using fluorochrome dye fluorescein diacetate (FDA) in combination with flow cytometry and the variable fluorescence coefficient of chlorophyll a has been investigated to assess the functional state of microalgae cells under conditions of cumulative growth of cultures and with variability of light and temperature from optimal to extreme levels. It has been shown that the FDA fluorescence value is a more conservative parameter in comparison with the relative variable fluorescence of chlorophyll a, and its noticeable changes are associated with the irreversible loss of the functional activity of algal cells and their death, which makes it possible to use this indicator as a marker of the viability of algae under extreme cultivation conditions. A noticeable decrease in FDA fluorescence values is associated with the onset of a deep stationary phase (death phase) of algal growth and is also observed when the cells of the studied cultures are exposed to high temperature (>25°C) and inhibitory light intensity (1200 μE/(m2 s)). [ABSTRACT FROM AUTHOR]