Manipulation of light wavelength at appropriate growth stage to enhance biomass productivity and fatty acid methyl ester yield using Chlorella vulgaris

Advances of microalgae-based enhancement strategies in industrial flue gas treatment: From carbon sequestration to lipid production

The acceleration of industrial development and urban expansion has led to a significant increase in flue gas emissions, posing a significant risk to human health and ecosystems. Recent studies have elucidated the significant potential of microalgae in the domain of sustainable industrial flue gas treatment. However, the inherent multifaceted factors within flue gas exert inhibitory effects on microalgal growth, thereby diminishing the overall system efficacy. Therefore, it is necessary to systematically analyze the flue gas components and propose complete intermediate treatment steps to alleviate their stressful effects on microalgae. Concurrently, to address the intrinsic limitations of the systemic functionality and enhance the applicability of microalgal biotechnology in industrial flue gas treatment, this review proposes a series of innovative solutions and strategies aimed at improving carbon fixation efficiency and lipid productivity of microalgae during flue gas treatment. In addition, the feasibility and potential limitations of these strategies in industrial applications are also discussed. Furthermore, through systematic comparative analysis, the optimal scheme and development trend of industrial flue gas emission reduction technology are explored. This comprehensive review not only establishes a theoretical foundation for the application of microalgae in industrial flue gas treatment, but also offers valuable insights for future research directions in related fields.

The effect of different light spectra on selenium bioaccumulation by Spirulina platensis cyanobacteria in flat plate photobioreactors

Selenium (Se) plays a crucial role in human health, influencing conditions such as cancer, diabetes, and neurological disorders. With global population growth and unequal nutrient distribution threatening food security, new approaches are needed to meet the nutritional needs of the world. Se is essential for immune function, metabolism, and antioxidant defense, and in regions suffering from food insecurity and malnutrition, selenium-enriched food could offer an affordable solution. Spirulina platensis, microalgae, can bioaccumulate Se from its environment, enhancing its nutritional value. This study explores how different light spectra (red, white, yellow, and blue LEDs) affect Se bioaccumulation in Spirulina when Na2SeO3 is added to the culture medium in photobioreactors. The results show that red light made the highest Se bioaccumulation (0.118 mg.L-1), followed by white, yellow, and blue light. Se addition also increased cell dry weight by 46%, 33%, 22%, and 60%, respectively, compared to photobioreactors without Se, with biomass productivity highest under red light. Furthermore, Se boosted maximum Chl α concentration, improving photosynthetic efficiency. These findings suggest that optimizing light conditions can significantly enhance the nutritional value of Spirulina, offering a potential solution to global hunger by providing a sustainable, selenium-enriched food source.

Unveiling underlying factors for optimizing light spectrum to enhance microalgae growth

Emerging research highlights the potential of specific light spectral regions to significantly enhance microalgae biomass production compared to conventional white light illumination. However, conflicting results of existing studies on the most optimal wavelengths reveal a knowledge gap regarding the underlying factors for optimal spectrum. The present paper aims to address this gap by critically analyzing existing studies on light spectral quality and its impact on microalgae growth. The analysis focuses on identifying the key factors determining an optimal light spectrum for microalgae cultivation. The study critically evaluates the effects of narrow wavelengths, assessing whether monochromatic light may be effective in maximizing biomass yield. While wavelength manipulation has a high potential, a deeper investigation into combining narrow wavelengths at varying ratios to determine the most effective spectral composition for maximizing growth is required. The study aims to provide insights into designing an optimal light spectrum for sustainable and efficient microalgae cultivation.

Current Scenario and Global Perspective of Sustainable Algal Biofuel Production

Industrialization and globalization have increased the demand for petroleum products that has increased a load on natural energy resources. The escalating fossil fuel utilization has resulted in surpassing the Earth's capacity to absorb greenhouse gases, necessitating the exploration of sustainable bioenergy alternatives to mitigate emissions. Biofuels, derived from algae, offer promising solutions to alleviate fossil fuel dependency. Algae, often regarded as third-generation biofuels, present numerous advantages owing to their high biomass production rates. While algae have been utilized for their bioactive compounds, their capability as biomass for the production of biofuel has gained traction among researchers. Various biofuels such as bio-hydrogen, bio-methane, bio-ethanol, bio-oil, and bio-butanol can be derived from algae through diverse processes like fermentation, photolysis, pyrolysis, and transesterification. Despite the enormous commercial potential of algae-derived biofuels, challenges such as high cultivation costs persist. However, leveraging the utilization of algae byproducts could improve economic viability of biofuel production. Moreover, algae derived biofuels offer environmental sustainability, cost-effectiveness, and waste reduction benefits, promising novel opportunities for a more sustainable energy future. Moreover, advancements in the field could lead to patents that drive innovation and commercialization in algae-based biofuel technologies.

Transcriptomic and Metabolomic Analysis Reveal the Effects of Light Quality on the Growth and Lipid Biosynthesis in Chlorella pyrenoidosa

Light quality has significant effects on the growth and metabolite accumulation of algal cells. However, the related mechanism has not been fully elucidated. This study reveals that both red and blue light can promote the growth and biomass accumulation of Chlorella pyrenoidosa, with the enhancing effect of blue light being more pronounced. Cultivation under blue light reduced the content of total carbohydrate in Chlorella pyrenoidosa, while increasing the content of protein and lipid. Conversely, red light decreased the content of protein and increased the content of carbohydrate and lipid. Blue light induces a shift in carbon flux from carbohydrate to protein, while red light transfers carbon flux from protein to lipid. Transcriptomic and metabolomic analysis indicated that both red and blue light positively regulate lipid synthesis in Chlorella pyrenoidosa, but they exhibited distinct impacts on the fatty acid compositions. These findings suggest that manipulating light qualities can modulate carbon metabolic pathways, potentially converting protein into lipid in Chlorella pyrenoidosa.

Effect of various light spectra on amino acids and pigment production of Arthrospira platensis using flat-plate photobioreactor

Today, the use of nutrients derived from natural bioactive compounds application in the food, pharmaceutical, and cosmetic industries is on the increase. This paper aimed to evaluate the amino acids profile (essential and non-essential) and pigments composition (chlorophyll a, carotenoids, and phycocyanin) of Arthrospira platensis (a blue-green microalga) cultivation in a flat-plate photobioreactor under various types of light-emitting diodes (red: 620-680 nm, white: 380-780 nm, yellow: 570-600nm, blue: 445-480 nm). The maximum biomass concentration (604.96 mg L-1) occurred when the red LED was applied for cultivation, and the minimum biomass concentration (279.39 mg L-1) was obtained under blue LED. The sequence of pigments and amino acids concentrations (mg L-1culture volume) was approximately in accordance with the biomass productivity. It means the red light produces the maximum concentration of pigments (chlorophyll a: 5.42, carotenoids: 2.92, phycocyanin: 67.54 mg L-1) and amino acids (essential amino acids: 110.47, nonessential amino acids: 179.10 mg L-1). Nevertheless, when these values were measured in mg per g of dry weight, the utmost contents were observed in microalgal products cultivated under blue LED. These consequences are due to the highest cell productivity and the most extended length of cells that occurred under red and blue LEDs, respectively.

Design, construction and application of algae-bacteria synergistic system for treating wastewater

The wastewater treatment technology of algae-bacteria synergistic system (ABSS) is a promising technology which has the advantages of low energy consumption, good treatment effect and recyclable high-value products. In this treatment technology, the construction of an ABSS is a very important factor. At the same time, the emergence of some new technologies (such as microbial fuel cells and bio-carriers, etc.) has further enriched constructing the novel ABSS, which could improve the efficiency of wastewater treatment and the biomass harvesting rate. Thus, this review focuses on the construction of a novel ABSS in wastewater treatment in order to provide useful suggestions for the technology of wastewater treatment.

A modified cultivation strategy to enhance biomass production and lipid accumulation of Tetradesmus obliquus FACHB-14 with copper stress and light quality induction

In this study, a two-stage culture strategy was refined to concurrently enhance the growth and lipid accumulation of Tetradesmus obliquus. The results unveiled that, during the initial stage, the optimal conditions for biomass accumulation were achieved with 0.02 mg·L-1 Cu2+ concentration and red light. Under these conditions, biomass accumulation reached 0.628 g·L-1, marking a substantial 23.62 % increase compared to the control group. In the second stage, the optimal conditions for lipid accumulation were identified as 0.5 mg·L-1 Cu2+ concentration and red light, achieving 64.25 mg·g-1·d-1 and marking a 128.38 % increase over the control. Furthermore, the fatty acid analysis results revealed an 18.85 % increase in the saturated fatty acid content, indicating enhanced combustion performance of microalgae cultivated under the dual stress of red light and 0.5 mg·L-1 Cu2+. This study offers insights into the potential application of Tetradesmus obliquus in biofuel production.

Quantum dot-based light conversion strategy for customized cultivation of microalgae

Microalgae are photosynthetic microorganisms with the potential to mitigate the atmospheric greenhouse effect by carbon fixation. However, their growth is typically limited by light availability. A wavelength converter utilizing red, blue, and green quantum dots (QDs) was developed to optimize light quality for enhancing microalgal production. The growth, lipid content, and eicosapentaenoic acid titer of Nannochloropsis increased by 11.2%, 9.5%, and 15.5% with red QDs, respectively. The biomass and triacylglycerol content of Phaeodactylum tricornutum increased by 8.6% and 35.0%, respectively. Simultaneously, biodiesel production was accelerated in Nannochloropsis (20.2%) and P. tricornutum (11.6%), and improved with increased cetane number and reduced iodine value. Furthermore, red QDs increased the growth and biomass accumulation of Nannochloropsis under low light, while green QDs shielded Nannochloropsis from photoinhibition under high light. This customizable QD-based methodology overcomes microalgal light limitations, demonstrating a universally applicable approach to improve microalgal cultivation and biochemical component production.

Consequences of light spectra for pigment composition and gene expression in the cryptophyte Rhodomonas salina

Algae with a more diverse suite of pigments can, in principle, exploit a broader swath of the light spectrum through chromatic acclimation, the ability to maximize light capture via plasticity of pigment composition. We grew Rhodomonas salina in wide-spectrum, red, green, and blue environments and measured how pigment composition differed. We also measured expression of key light-capture and photosynthesis-related genes and performed a transcriptome-wide expression analysis. We observed the highest concentration of phycoerythrin in green light, consistent with chromatic acclimation. Other pigments showed trends inconsistent with chromatic acclimation, possibly due to feedback loops among pigments or high-energy light acclimation. Expression of some photosynthesis-related genes was sensitive to spectrum, although expression of most was not. The phycoerythrin α-subunit was expressed two-orders of magnitude greater than the β-subunit even though the peptides are needed in an equimolar ratio. Expression of genes related to chlorophyll-binding and phycoerythrin concentration were correlated, indicating a potential synthesis relationship. Pigment concentrations and expression of related genes were generally uncorrelated, implying post-transcriptional regulation of pigments. Overall, most differentially expressed genes were not related to photosynthesis; thus, examining associations between light spectrum and other organismal functions, including sexual reproduction and glycolysis, may be important.

Effects of light quality on microalgae cultivation: bibliometric analysis, mini-review, and regulation approaches

The ever-increasing concern for energy shortages and greenhouse effect has triggered the development of sustainable green technologies. Microalgae have received more attention due to the characteristics of biofuel production and CO2 fixation. From the perspective of autotrophic growth, the optimization of light quality has the potential to promote biomass production and bio-component accumulation in microalgae at low cost. In this study, bibliometric analysis was used to describe the basic features, identify the hotspots, and predict future trends of the research related to the light quality on microalgae cultivation. In addition, a mini-review referring to regulation methods of light quality was provided to optimize the framework of research. Results demonstrated that China has the greatest interest in this area. The destination of most research was to obtain biofuels and high-value-added products. Both blue and red lights were identified as the crucial spectrums for microalgae cultivation. However, sunlight is the most affordable light resource, which could not be fully utilized by microalgae through the photosynthetic process. Hence, some regulation approaches (e.g., dyes, plasmonic scattering, and carbon-based quantum dots) are proposed to increase the proportion of beneficial spectrum for enhancement of photosynthetic efficiency. In summary, this review introduces state-of-the-art research and provides theoretical guidance for light quality optimization in microalgae cultivation to obtain more benefits.

Biostimulation of green microalgae Chlorella sorokiniana using nanoparticles of MgO, Ca10(PO4)6(OH)2, and ZnO for increasing biodiesel production

Microalgae have the potential to become the primary source of biodiesel, catering to a wide range of essential applications such as transportation. This would allow for a significant reduction in dependence on conventional petroleum diesel. This study investigates the effect of biostimulation techniques utilizing nanoparticles of Magnesium oxide MgO, Calcium hydroxyapatite Ca10(PO4)6(OH)2, and Zinc oxide ZnO to enhance the biodiesel production of Chlorella sorokiniana. By enhancing cell activity, these nanoparticles have demonstrated the ability to improve oil production and subsequently increase biodiesel production. Experimentally, each nanomaterial was introduced at a concentration of 15 mg L-1. The results have shown that MgO nanoparticles yielded the highest biodiesel production, with a recorded yield of 61.5 mg L-1. Hydroxyapatite nanoparticles, on the other hand, facilitated lipid accumulation. ZnO nanoparticles showcased a multifaceted advantage by enhancing both growth and lipid content. Thus, it is suggested that these nanoparticles can be used effectively to increase the lipid content of microalgae. These findings highlight the potential of biostimulation strategies utilizing MgO, hydroxyapatite, and zinc oxide nanoparticles to bolster biodiesel production.

Phenotypic Analysis and Molecular Characterization of Enlarged Cell Size Mutant in Nannochloropsis oceanica

The cell cycle is the fundamental cellular process of eukaryotes. Although cell-cycle-related genes have been identified in microalgae, their cell cycle progression differs from species to species. Cell enlargement in microalgae is an essential biological trait. At the same time, there are various causes of cell enlargement, such as environmental factors, especially gene mutations. In this study, we first determined the phenotypic and biochemical characteristics of a previously obtained enlarged-cell-size mutant of Nannochloropsis oceanica, which was designated ECS. Whole-genome sequencing analysis of the insertion sites of ECS indicated that the insertion fragment is integrated inside the 5'-UTR of U/P-type cyclin CYCU;1 and significantly decreases the gene expression of this cyclin. In addition, the transcriptome showed that CYCU;1 is a highly expressed cyclin. Furthermore, cell cycle analysis and RT-qPCR of cell-cycle-related genes showed that ECS maintains a high proportion of 4C cells and a low proportion of 1C cells, and the expression level of CYCU;1 in wild-type (WT) cells is significantly increased at the end of the light phase and the beginning of the dark phase. This means that CYCU;1 is involved in cell division in the dark phase. Our results explain the reason for the larger ECS size. Mutation of CYCU;1 leads to the failure of ECS to fully complete cell division in the dark phase, resulting in an enlargement of the cell size and a decrease in cell density, which is helpful to understand the function of CYCU;1 in the Nannochloropsis cell cycle.

Evaluation of Growth and Production of High-Value-Added Metabolites in Scenedesmus quadricauda and Chlorella vulgaris Grown on Crude Glycerol under Heterotrophic and Mixotrophic Conditions Using Monochromatic Light-Emitting Diodes (LEDs)

This study aimed to examine the impact of crude glycerol as the main carbon source on the growth, cell morphology, and production of high-value-added metabolites of two microalgal species, namely Chlorella vulgaris and Scenedesmus quadricauda, under heterotrophic and mixotrophic conditions, using monochromatic illumination from light-emitting diodes (LEDs) emitting blue, red, yellow, and white (control) light. The findings indicated that both microalgae strains exhibited higher biomass yield on the mixotrophic growth system when compared to the heterotrophic one, while S. quadricauda generally performed better than C. vulgaris. In mixotrophic mode, the use of different monochromatic illumination affected biomass production differently on both strains. In S. quadricauda, growth rate was higher under red light (μmax = 0.89 d-1), while the highest biomass concentration and yield per gram of consumed glycerol were achieved under yellow light, reaching 1.86 g/L and Yx/s = 0.18, respectively. On the other hand, C. vulgaris demonstrated a higher growth rate on blue light (μmax = 0.45 d-1) and a higher biomass production on white (control) lighting (1.34 g/L). Regarding the production of metabolites, higher yields were achieved during mixotrophic mode in both strains. In C. vulgaris, the highest lipid (26.5% of dry cell weight), protein (63%), and carbohydrate (20.3%) contents were obtained under blue, red, and yellow light, respectively, thus indicating that different light wavelengths probably activate different metabolic pathways. Similar results were obtained for S. quadricauda with red light leading to higher lipid content, while white lighting caused higher production of proteins and carbohydrates. Overall, the study demonstrated the potential of utilizing crude glycerol as a carbon source for the growth and metabolite production of microalgae and, furthermore, revealed that the strains' behavior varied depending on lighting conditions.

The role of light wavelengths in regulating algal-bacterial granules formation, protein and lipid accumulation, and microbial functions

High value-added products recovery from algal-bacterial granular sludge (ABGS) has received great attention recently. This study aimed to explore the role of different light wavelengths in regulating granule formation, protein and lipid production, and microbial functions. Bacterial granular sludge (BGS, R0) was most conducive to forming ABGS under blue (R2) light with the highest chlorophyll a (10.2 mg/g-VSS) and diameter (1800 μm), followed by red (R1) and white (R3) lights. R0-R3 acquired high protein contents (>164.8 mg/g-VSS) with essential amino acids above 44.4%, all of which were suitable for recycling, but R2 was the best. Also, blue light significantly increased total lipid production, while red light promoted the accumulation of some unsaturated fatty acids (C18:2 and C18:3). Some unique algae and dominant bacteria (e.g., Stigeoclonium, Chlamydomonas, and Flavobacteria) enrichment and some key functions (e.g., amino acid, fatty acid, and lipid biosynthesis) up-regulation in R2 might help to improve proteins and lipids quality. Combined, this study provides valuable guidance for protein and lipid recovery from ABGS.

Stimulating carbon and nitrogen metabolism of Chlorella pyrenoidosa to treat aquaculture wastewater and produce high-quality protein in plate photobioreactors

Wastewater treatment by microalgae is the economical and environmentally friendly strategy, but is still challenged with the strict discharge standards and valuable biomass exploitations. The carbon and nitrogen metabolism of Chlorella pyrenoidosa was improved by the red LED light and starch addition to treat Tilapia aquaculture wastewater (T-AW) and produce protein simultaneously in a plate photobioreactor. The red LED light was applied to improve the nutrient removals at an outdoor temperature, but the concentrations except total nitrogen did not satisfy the discharge standards. After starch addition, the removal efficiencies of total phosphorus, total nitrogen, chemical oxygen demand, and total ammonia nitrogen were 85.15, 96.96, 88.53, and 98.01 % in a flat-plate photobioreactor, respectively, which met the discharge standards and the protein production reached 0.60 g/L. At a molecular level, the metabolic flux and transcriptome analyses showed that red light promoted carbon flux of the Embden-Meyerhof-Pranas pathway and tricarboxylic cycle, and upregulated the levels of genes encoding α-amylase, glutamine synthetase, glutamate dehydrogenase, nitrate transporter, and ammonium transporter, which facilitated nutrients removal and provided nitrogen sources for protein biosynthesis. The harvesting C. pyrenoidosa possessed the 62 % essential amino acids and great lipid composition for biofuels. This study provided a new orientation for outdoor wastewater treatment and protein production by collaboratively regulating the carbon and nitrogen metabolism of microalgae.

Ultrasonic Treatment Enhanced Astaxanthin Production of Haematococcus pluvialis

In this study, effects of ultrasonic treatment on Haematococcus pluvialis (H. pluvialis) were investigated. It has been confirmed that the ultrasonic stimulation acted as stress resources in the red cyst stage H. pluvialis cells containing astaxanthin, resulting in additional astaxanthin production. With the increase in production of astaxanthin, the average diameter of H. pluvialis cells increased accordingly. In addition, to determine how ultrasonic stimulation had an effect on the further biosynthesis of astaxanthin, genes related to astaxanthin synthesis and cellular ROS level were measured. As a result, it was confirmed that astaxanthin biosynthesis related genes and cellular ROS levels were increased, and thus ultrasonic stimulation acts as an oxidative stimulus. These results support the notion on the effect of the ultrasonic treatment, and we believe our novel approach based on the ultrasonic treatment would help to enhance the astaxanthin production from H. pluvialis.

Symbiotic relationship between filamentous algae (Halomicronema sp.) and extracellular polymeric substance-producing algae (Chlamydomonas sp.) through biomimetic simulation of natural algal mats

To lower the cost of biomass harvesting, the growth of natural biofilm is considered to be an optimal alternative to microalgae aggregation. This study investigated algal mats that naturally agglomerate into a lump and float on water surfaces. Halomicronema sp., a filamentous cyanobacterium with high cell aggregation and adhesion to substrates, and Chlamydomonas sp., which grows rapidly and produces high extracellular polymeric substances (EPS) in certain environments, are the main microalgae that make up selected mats through next-generation sequencing analysis. These two species play a major role in the formation of solid mats, and showed a symbiotic relationship as the medium and nutritional source, particularly owing to the large amount of EPS formed by the reaction between EPS and calcium ions through zeta potential and Fourier-transform infrared spectroscopy analysis. This led to the formation of an ecological biomimetic algal mat (BAM) that mimics the natural algal mat system, and this is a way to reduce costs in the biomass production process as there is no separate treatment process for harvesting.

Recent advances in CO2 fixation by microalgae and its potential contribution to carbon neutrality

Many countries and regions have set their schedules to achieve the carbon neutrality between 2030 and 2070. Microalgae are capable of efficiently fixing CO₂ and simultaneously producing biomass for multiple applications, which is considered one of the most promising pathways for carbon capture and utilization. This work reviews the current research on microalgae CO₂ fixation technologies and the challenges faced by the related industries and government agencies. The technoeconomic analysis indicates that cultivation is the major cost factor. Use of waste resources such as wastewater and flue gas can significantly reduce the costs and carbon footprints. The life cycle assessment has identified fossil-based electricity use as the major contributor to the global warming potential of microalgae-based CO₂ fixation approach. Substantial efforts and investments are needed to identify and bridge the gaps among the microalgae strain development, cultivation conditions and systems, and use of renewable resources and energy.

Enhanced photoautotrophic growth of Chlorella vulgaris in starch wastewater through photo-regulation strategy

Microalgae biomass production with starch wastewater (SW) is a promising approach to realize waste recovery and cost reduction due to the inherent copious nutrients and nontoxic compounds in SW. However, the application of this technique is significantly hindered by low biomass production on account of the poor photosynthetic efficiency of microalgae. In this regard, we proposed a photo-regulation strategy characterized by the adjusting of numbers of light/dark (L/D) cycles, and compositions of light wavelength, which was proved to be an effective method for stimulating intracellular photo electron transfer and enhancing photosynthetic efficiency, to boost microalgae biomass accumulation. Additionally, responses of the microalgae photo-biochemical conversion, and the wastewater treatment performance at various number of L/D cycles and light wavelengths were discussed. The experimental results indicated that the biomass production increased when the L/D period was increased from 2 h:2 h-12 h:12 h. When the L/D period was 2 h:2 h, the biomass production reached a maximum value of 1.28 g L^-1, which was 19.6% higher than that of the control group when the L/D period was 12 h:12 h. Furthermore, with respect to microalgae growth under monochromatic light, the maximum biomass concentration (1.25 g L^-1) and lipid content (32.2%) of Chlorella were achieved under blue light; whereas, the minimum values were attained under red light (1.05 g L^-1 and 19.3%, respectively). When the red light and blue light were mixed and supplied, the microalgae biomass productivity was higher than that under white light, and the highest lipid productivity was 109.0 mg^-1 L^-1 d under a blue: red ratio of 2:1. Moreover, gas chromatography analysis demonstrated that the methyl in the range of C16-C18 in the system was higher than 70%. Fatty acid methyl esters (FAMEs) containing palmitic acid (C16:0) and oleic acid (C18:1) are beneficial for production of biodiesel, and the quality of fatty acid methyl ester used in biodiesel production can be improved using microalgae cultured under the mixed wavelengths of blue and red. Finally, Chlorella was cultured in PBR and reached the peak concentration of 2.45 g L^-1 by semi-continuous process with the HRT regulation.

Roles of illumination on distribution of phosphorus in Chlorella vulgaris under mixotrophic cultivation

Phosphorus (P) is a non-substitutable resource and global reserves of phosphate rock are limited. In this study, phosphorus recovery by Chlorella vulgaris, and the effects of different light intensities (2000 Lux, 5000 Lux, 8000 Lux, 12,000 Lux) on the phosphorus distribution in the soluble microbial product (SMP), extracellular polymeric substance (EPS) and intracellular polymeric substance (IPS) were analyzed. The results showed that the 5000 Lux was the optimum light intensity for P uptake and transformation by Chlorella vulgaris under mixotrophic cultivation. At the light intensity of 5000 Lux, the P uptake rate was 100% after 32 days of cultivation, and the concentration of intracellular organic phosphorus (OP) was 5.77 mg P/L. Moreover, EPS was the main P pool when inorganic phosphorus (IP) was depleted in bulk solution. Phosphorus recovery by microalgae is an important solution to treat P-containing wastewater.

Sulfur heterogeneity: A non-negligible factor in manipulating growth and lipid accumulation of Scenedesmus obliquus at a relatively high ratio of carbon to nitrogen

Algal biodiesel has been becoming a focus in the field of bioenergy worldwide. In this study, effects of heterogeneous sulfur (SO₄^2-, SO₃^2- and S^2-) on growth and lipid accumulation of Scenedesmus obliquus cultured in wastewater with a C/N ratio of 30 were investigated, respectively. The results shown that SO₄^2-, the optimal sulfur source, could trigger cell growth in a concentration-dependent manner. However, SO₃^2- was superior to the others in boosting carbon uptake of cells, which was subject to NH₄⁺-N concentration. Only SO₄^2- could simultaneously increase lipid content and productivity of cells with a dominant component of oleic acid (C18:1n9c) occupying approximately 40% in fatty acid profile. Additionally, the genes encoding enzymes such as CDIPT, ADPRM, DPP1, pmtA and BTA1 involved in the uppermost lipid-related pathway (glycerophospholipid metabolism) were identified facing different sulfur source regardless of the concentration changes. These findings may facilitate nutrition management efforts to enhance microalgae-based biofuel production.

Regulation of Light Spectra on Cell Division of the Unicellular Green Alga Haematococcus pluvialis: Insights from Physiological and Lipidomic Analysis

Commercial scale production of natural astaxanthin is currently conducted through cultivation of the green alga Haematococcus pluvialis. This study comprehensively investigated the impact of seven different light spectra on the growth, morphology and photosynthesis of H. pluvialis vegetative cells. Further, the lipidomes of vegetative H. pluvialis grown under various light spectra were qualitatively and quantitatively analyzed using liquid chromatography/mass spectrometry (LC/MS). The results showed the existence of blue light—alone or with red light—promoted cell division, while pure red light or white light enabled increased cell sizes, cellular pigment, starch and lipid contents, and biomass production. Although the photosynthetic performance of H. pluvialis measured as chlorophyll a fluorescence was not significantly affected by light spectra, the lipid profiles, particularly chloroplast membrane lipids, showed remarkable changes with light spectra. The contents of most lipid species in the blue/red light 1/2 group, which showed the fastest cell division, remained at a moderate level compared with those under other light spectra, indicating the fastest dividing cells were featured by a fine-tuned lipid profile. From biotechnical perspective, this comprehensive study can provide insights into the development of appropriate light regimes to promote the cell density or biomass of H. pluvialis mass culture.

Effect of different wavelengths of LED light on the growth, chlorophyll, β-carotene content and proximate composition of Chlorella ellipsoidea

Chlorella ellipsoidea is a freshwater green microalga that has great prospect for the sustainable development of aquaculture industry. Microalgae require optimal lighting conditions for efficient photosynthesis. The key to cost-effective algal biomass production is to optimize algae growth conditions. This study aimed to investigate the effects of various wavelengths viz. white (380-750 nm), green (510 nm), blue (475 nm), and red (650 nm) light-emitting diodes (LEDs) on the growth, pigment content (chlorophyll-a, chlorophyll-b, and β-carotene), and proximate composition of C. ellipsoidea with a photoperiod of 12 h:12 h light: dark cycle under indoor environmental conditions. C. ellipsoidea was cultured in Bold's Basal Medium for 18 days. The cell density (125.36×10⁵ cells ml^-1), cell dry weight (58.9 ± 4.57 mg L^-1), optical density (1.66 ± 0.08 g L^-1), chlorophyll-a (7.31 ± 0.04 μg ml^-1), chlorophyll-b (2.73 ± 0.13 μg ml^-1), and β-carotene (0.39 ± 0.04 μg ml^-1) content of C. ellipsoidea were significantly (P < 0.05) higher at 15^th-day when cultured under blue LED light exposure. Significantly lower growth and nutritional values were obtained under red LED light exposure compared to the control and other LEDs spectra. In Pearson correlation analysis, the cell density and cell dry weight values showed a strong positive correlation with the values of pigment contents of C. ellipsoidea in all the treatments. The LEDs light spectra showed significant effects on proximate composition of C. ellipsoidea. Protein and lipid contents of C. ellipsoidea were significantly higher in blue LED growth conditions compared to white, green, and red LEDs. C. ellipsoidea cells were 3-7.04 μm in size and the maximum area of the cell was 38.94 μm² in blue LED treatment. Results of this study demonstrated that blue LED light spectra was the most suitable condition to induce nutritionally rich biomass production of C. ellipsoidea, which can be used as a potential source of fish feed towards sustainable aquaculture.

Cultivation and Biorefinery of Microalgae (Chlorella sp.) for Producing Biofuels and Other Byproducts: A Review

Microalgae-based carbon dioxide (CO2) biofixation and biorefinery are the most efficient methods of biological CO2 reduction and reutilization. The diversification and high-value byproducts of microalgal biomass, known as microalgae-based biorefinery, are considered the most promising platforms for the sustainable development of energy and the environment, in addition to the improvement and integration of microalgal cultivation, scale-up, harvest, and extraction technologies. In this review, the factors influencing CO2 biofixation by microalgae, including microalgal strains, flue gas, wastewater, light, pH, temperature, and microalgae cultivation systems are summarized. Moreover, the biorefinery of Chlorella biomass for producing biofuels and its byproducts, such as fine chemicals, feed additives, and high-value products, are also discussed. The technical and economic assessments (TEAs) and life cycle assessments (LCAs) are introduced to evaluate the sustainability of microalgae CO2 fixation technology. This review provides detailed insights on the adjusted factors of microalgal cultivation to establish sustainable biological CO2 fixation technology, and the diversified applications of microalgal biomass in biorefinery. The economic and environmental sustainability, and the limitations and needs of microalgal CO2 fixation, are discussed. Finally, future research directions are provided for CO2 reduction by microalgae.

LED alternating between blue and red-orange light improved the biomass and lipid productivity of Chlamydomonas reinhardtii

Light management is important for improving algae cultivation, specifically by enhancing the productivity of biomass and valued bioproducts. In this study, we present evidence that alternating blue and red-orange light can improve the algal growth kinetics and lipid production in a photobioreactor. Blue (430-445, 460-470 nm) and red-orange light (580-660 nm) from a LED were set at the light saturation point (B: 65 μmol/m²s; RO: 155 μmol/m²s) and alternated for the cultivation of the green alga Chlamydomonas reinhardtii. Growth kinetics, lipid, carbohydrate, and protein content were measured as a function of alternating illumination time. Results reveal that the first illumination light and illumination time had a significant impact on the growth kinetics and nutrient composition. When the red-orange light illumination was used at the beginning of cultivation (RO/B alternation), the biomass concentration and productivity increased 8% and 18% on average, respectively; lipid mass fraction and concentration increased 21-27% and 24-26% when 0.25-0.50 h per day of blue light illumination was used; no significant change of carbohydrate and protein content were observed. Relative to blue light alone, the improvement of growth kinetics, lipid mass fraction and concentration, and the carbohydrate concentration was significant. Under B/RO alternation (when the blue light was used first), on average, the protein content was significantly higher than RO/B alternation.

Monochromatic light filters to enhance biomass and carotenoid productivities of Dunaliella salina in raceway ponds

Monochromatic blue and red wavelengths are more efficient for light to algal biomass conversion than full-spectrum sunlight. In this study, monochromatic light filters were used to down-regulate natural sunlight to blue (400-520 nm) and red (600-700 nm) wavelengths to enhance biomass productivity of Dunaliella salina in outdoor raceway ponds. Growth indices such as cell size, pigment concentrations, biomass yield, photosynthetic efficiency, and major nutritional compositions were determined and compared against a control receiving unfiltered sunlight. Results showed that red light increased biomass productivity, lipid, and carotenoid contents but decreased cell volume, chlorophyll production, and cell weight. Conversely, blue light increased cell volume by 200%, cell weight by 68%, and enhanced chlorophyll a and protein contents by 35% and 51%, respectively, over red light. Compared to the control treatment, photoinhibition of D. salina cells at noon sunshine was decreased 60% by utilizing optical filters on the pond's surface.

Illumination Policies for Stichococcus sp. Cultures in an Optimally Operating Lab-Scale PBR toward the Directed Photosynthetic Production of Desired Products

The light spectrum effect on the cultivation efficiency of the microalgae strain Stichococcus sp. is explored, as a means of potentially intensifying the biomass productivity and regulating the cellular composition. Stichococcus sp. batch culture experiments, within a 3 L bench-top photobioreactor (PBR), are designed and implemented under different light spectrum profiles (i.e., cool white light (WL), cool white combined with red light (WRL), and cool white combined with blue light, (WBL)). The obtained results indicate that the studied strain is capable of adapting its metabolite profile to the light field to which it is exposed. The highest biomass concentration (3.5 g/L), combined with intense carbohydrate accumulation activity, resulting in a respective final concentration of 1.15 g/L was achieved within 17 days using exclusively cool white light of increasing intensity. The addition of blue light emitting diodes (LED) light, combined with appropriately selected culture conditions, contributed significantly to the massive synthesis and accumulation of lipids, resulting in a concentration of 1.43 g/L and a respective content of 46.13% w/w, with a distinct impact on biomass, carbohydrates and proteins productivity. Finally, a beneficial contribution of red LED light to the protein synthesis is recognized and this can be conditionally amplified provided nitrogen sufficiency in the culture medium.

Light spectra as triggers for sorting improved strains of Tisochrysis lutea

It is known that microalgae respond to different light colors, but not at single-cell level. This work aimed to assess if different light colors could be used as triggers to sort over-producing cells. Six light spectra were used: red + green + blue (RGBL), blue (BL), red (RL), green (GL), blue + red (BRL) and blue + green (BGL). Fluorescence-activated cell sorting method was used to analyse single-cell fluorescence and sort cells. BGL and RGBL lead to the highest fucoxanthin production, while RL showed the lowest. Therefore, it was hypothesized that hyper-producing cells can be isolated efficiently under the adverse condition (RL). After exposure to all light colors for 14 days, the top 1% fucoxanthin producing cells were sorted. A sorted strain from RL showed higher (16-19%) growth rate and fucoxanthin productivity. This study showed how light spectra affected single-cell fucoxanthin and lipid contents and productivities. Also, it supplied an approach to sort for high-fucoxanthin or high-lipid cells.

Aquatic Toxicity of Photocatalyst Nanoparticles to Green Microalgae Chlorella vulgaris

In the last years, nanoparticles such as TiO2, ZnO, NiO, CuO and Fe2O3 were mainly used in wastewater applications. In addition to the positive aspects concerning using nanoparticles in the advanced oxidation process of wastewater containing pollutants, the impact of these nanoparticles on the environment must also be investigated. The toxicity of nanoparticles is generally investigated by the nanomaterials’ effect on green algae, especially on Chlorella vulgaris. In this review, several aspects are reviewed: the Chlorella vulgaris culture monitoring and growth parameters, the effect of different nanoparticles on Chlorella vulgaris, the toxicity of photocatalyst nanoparticles, and the mechanism of photocatalyst during oxidative stress on the photosynthetic mechanism of Chlorella vulgaris. The Bold basal medium (BBM) is generally recognized as an excellent standard cultivation medium for Chlorella vulgaris in the known environmental conditions such as temperature in the range 20–30 °C and light intensity of around 150 μE·m2·s−1 under a 16/8 h light/dark cycle. The nanoparticles synthesis methods influence the particle size, morphology, density, surface area to generate growth inhibition and further algal deaths at the nanoparticle-dependent concentration. Moreover, the results revealed that nanoparticles caused a more potent inhibitory effect on microalgal growth and severely disrupted algal cells’ membranes.

Astaxanthin biosynthesis promotion with pH shock in the green microalga, Haematococcus lacustris

In this study, the use of pH shock to improve astaxanthin synthesis in Haematococcus lacustris was investigated. It has been found that pH shock (pH = 4.5, 60 s) imposes stress in the cells and induces physiological changes, which result in astaxanthin accumulation. The optimal acid-base combination of pH shock was H₂SO₄-KOH, which increased the astaxanthin content per cell to 39 ± 6.92% than those of the control. In addition, pH shock can be applied simultaneously with the other inductive strategies such as high irradiance and carbon source supply. When high irradiance was applied simultaneously with pH shock, astaxanthin yield was increased 65 ± 0.541% than control. In addition, astaxanthin content per cell was increased 105 ± 6.66% than those of the control, with the concomitant application of carbon source addition with pH shock. Herein, these novel findings provide a useful technique for producing astaxanthin using H. lacustris.

The effects of exogenous cerium on photosystem II as probed by in vivo chlorophyll fluorescence and lipid production of Scenedesmus obliquus XJ002

Cerium is the most abundant rare earth metal in the earth's crust, and it has deleterious effects on aquatic ecosystems from fertilizer runoff. Scenedesmus obliquus is an oil-rich microalga that grows rapidly and is sensitive to many kinds of toxins. Given that microalgae are useful indicators of eutrophication and toxic stress, it was found that lower concentrations of cerium (0.50-5.00 mg·L^-1 ) stimulated algal growth and increased chlorophyll a content, whereas higher concentrations (above 50.00 mg·L^-1 ) had an inhibitory effect on algal growth and chlorophyll a content. The algal growth rate and chlorophyll a content peaked at a cerium concentration of 5.00 mg·L^-1 . Both the donor and acceptor sides of photosystem II (PSII) reaction centers were sensitive to cerium-induced stress. Specifically, high concentrations of cerium damaged the oxygen evolving complex and PSII reaction center and suppressed electron transport at the donor and receptor side of the reaction center, influencing the absorption, transfer, and application of light energy in S. obliquus XJ002. In addition, we established a simple method to quantify the intracellular lipid content of S. obliquus XJ002, and the optimum staining conditions for Nile red were as follows: volume percentage of dimethyl sulfoxide was 2%, the concentration of Nile red was 2.0 µg·mL^-1 , and the staining time of Nile red was 5 min. The addition of cerium resulted in a significant increase in the total lipid content of XJ002. When the concentration of cerium was 50 mg·L^-1 , the total lipid content was 16.26% higher than the control group. This information will enhance our ability to utilize microelement fertilizer in biomass accumulation programs and will help to further reveal the key regulatory factors in the lipid metabolism, and would lay the foundation for promoting the research of microalgae bioenergy.

Effects of red and blue light on leaf anatomy, CO2 assimilation and the photosynthetic electron transport capacity of sweet pepper (Capsicum annuum L.) seedlings

BACKGROUND

The red (R) and blue (B) light wavelengths are known to influence many plant physiological processes during growth and development, particularly photosynthesis. To understand how R and B light influences plant photomorphogenesis and photosynthesis, we investigated changes in leaf anatomy, chlorophyll fluorescence and photosynthetic parameters, and ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) and Calvin cycle-related enzymes expression and their activities in sweet pepper (Capsicum annuum L.) seedlings exposed to four light qualities: monochromatic white (W, control), R, B and mixed R and B (RB) light with the same photosynthetic photon flux density (PPFD) of 300 μmol/m2·s.

RESULTS

The results revealed that seedlings grown under R light had lower biomass accumulation, CO2 assimilation and photosystem II (PSII) electron transportation compared to plants grown under other treatments. These changes are probably due to inactivation of the photosystem (PS). Biomass accumulation and CO2 assimilation were significantly enriched in B- and RB-grown plants, especially the latter treatment. Their leaves were also thicker, and photosynthetic electron transport capacity, as well as the photosynthetic rate were enhanced. The up-regulation of the expression and activities of Rubisco, fructose-1, 6-bisphosphatase (FBPase) and glyceraldehyde-phosphate dehydrogenase (GAPDH), which involved in the Calvin cycle and are probably the main enzymatic factors contributing to RuBP (ribulose-1, 5-bisphosphate) synthesis, were also increased.

CONCLUSIONS

Mixed R and B light altered plant photomorphogenesis and photosynthesis, mainly through its effects on leaf anatomy, photosynthetic electron transportation and the expression and activities of key Calvin cycle enzymes.

Campus Sewage Treatment by Golenkinia SDEC-16 and Biofuel Production under Monochromic Light

The integration of microalgal cultivation in wastewater can fulfill the dual roles of pollutant degradation and biomass output. Meanwhile, the LED lights with different wavelengths have a great effect on the growth and metabolism of microalgae. In this study, Golenkinia SDEC-16, a strain isolated for biofuel production, was evaluated to verify its potentials for campus sewage treatment and lipid accumulation under the red, green, and blue lights. The results indicated that the treated campus sewage met the first grade level in the Chinese pollutant discharge standards for municipal wastewater treatment plants within seven days under both red and blue light. The green light failed to exhibit excellent performance in nutrient removal, but facilitated the lipid synthesis as high as 42.99 ± 3.48%. The increased lipid content was achieved along with low biomass accumulation owing to low effective light utilization, indicating that the green light could be merely used as a stimulus strategy. The red light benefited the photosynthesis of Golenkinia SDEC-16, with the maximal biomass concentration of 0.80 ± 0.03 g/L and lipid content of 36.90 ± 3.62%, which can attain the optimal balance between biomass production and lipid synthesis.

High density long-term cultivation of Chlorella vulgaris SAG 211-12 in a novel microgravity-capable membrane raceway photobioreactor for future bioregenerative life support in SPACE

Hybrid life support systems are of great interest for future far-distant space exploration missions to planetary surfaces, e.g. Mars, planned until 2050. By synergistically combining physicochemical and biotechnological algae-based subsystems, an essential step towards the closure of the carbon loop in environmental control and life support systems (ECLSS) shall be accomplished, offering a wide beneficial potential for ECLSS through the utilization of oxygenic photosynthesis: O₂ and potential human food can be formed in-situ from CO₂ and water. The wild type green alga Chlorella vulgaris strain SAG 211-12 was selected as model microorganism due to its photoautotrophic growth, high biomass yield, cultivation flexibility and long-term cultivation robustness. The current study presents for the first time a stable xenic long-term processing of microalgae in a novel microgravity capable membrane raceway photobioreactor for 188 days with the focus on algal growth kinetics and gas evolution. In particular, culture homogeneity and viability were monitored and evaluated during the whole cultivation process due to their putative crucial impact on long-term functionality and efficiency of a closed cultivation system. Based on a specially designed cyclic batch cultivation process for SAG 211-12, a successive biomass growth up to a maximum of 12.2 g l^-1 with a max. global volumetric productivity of 1.3 g l^-1 d^-1 was reached within the closed loop system. The photosynthetic capacity was assessed to a global molar photosynthetic quotient of 0.31. Furthermore, cultivation parameters for a change from batch to continuous processing at high biomass densities and proliferation rates are introduced. The presented µgPBR miniature plant and the developed high throughput cultivation process are planned to be tested under real space conditions within the PBR@LSR project (microgravity and cosmic radiation) aboard the International Space Station with an operation period of up to 180 days to investigate the impact on long-term system stability.

Influence of spectral intensity and quality of LED lighting on photoacclimation, carbon allocation and high-value pigments in microalgae

Tailoring spectral quality during microalgal cultivation can provide a means to increase productivity and enhance biomass composition for downstream biorefinery. Five microalgae strains from three distinct lineages were cultivated under varying spectral intensities and qualities to establish their effects on pigments and carbon allocation. Light intensity significantly impacted pigment yields and carbon allocation in all strains, while the effects of spectral quality were mostly species-specific. High light conditions induced chlorophyll photoacclimation and resulted in an increase in xanthophyll cycle pigments in three of the five strains. High-intensity blue LEDs increased zeaxanthin tenfold in Rhodella sp. APOT_15 relative to medium or low light conditions. White light however was optimal for phycobiliprotein content (11.2 mg mL^-1) for all tested light intensities in this strain. The highest xanthophyll pigment yields for the Chlorophyceae were associated with medium-intensity blue and green lights for Brachiomonas submarina APSW_11 (5.6 mg g^-1 lutein and 2.0 mg g^-1 zeaxanthin) and Kirchneriella aperta DMGFW_21 (1.5 mg g^-1 lutein and 1 mg g^-1 zeaxanthin), respectively. The highest fucoxanthin content in both Heterokontophyceae strains (2.0 mg g^-1) was associated with medium and high white light for Stauroneis sp. LACW_24 and Phaeothamnion sp. LACW_34, respectively. This research provides insights into the application of LEDs to influence microalgal physiology, highlighting the roles of low light on lipid metabolism in Rhodella sp. APOT_15, of blue and green lights for carotenogenesis in Chlorophyceae and red light-induced photoacclimation in diatoms.

Control of a toxic cyanobacterial bloom species, Microcystis aeruginosa, using the peptide HPA3NT3-A2

Microcystis aeruginosa, a species of freshwater cyanobacteria, is known to be one of the dominant species causing cyanobacterial harmful algal blooms (CyanoHABs). M. aeruginosa blooms have the potential to produce neurotoxins and peptide hepatotoxins, such as microcystins and lipopolysaccharides (LPSs). Currently, technologies for CyanoHAB control do not provide any ultimate solution because of the secondary pollution associated with the control measures. In this study, we attempted to use the peptide HPA3NT3-A2, which has been reported to be nontoxic and has antimicrobial properties, for the development of an eco-friendly control against CyanoHABs. HPA3NT3-A2 displayed significant algicidal effects against M. aeruginosa cells. HPA3NT3-A2 induced cell aggregation and flotation (thereby facilitating harvest), inhibited cell growth through sedimentation, and eventually destroyed the cells. HPA3NT3-A2 had no algicidal effect on other microalgal species such as Haematococcus pluvialis and Chlorella vulgaris. Additionally, HPA3NT3-A2 was not toxic to Daphnia magna. The algicidal mechanism of HPA3NT3-A2 was intracellular penetration. The results of this study suggest the novel possibility of controlling CyanoHABs using HPA3NT3-A2.

The effect of medium and light wavelength towards Stichococcus bacillaris fatty acid production and composition

Introduction of novel species will highlight technical feasibility of microalgae-based biofuels for commercial applications. This paper reports the effect of culture medium and light wavelength on biomass and fatty acid production of S. bacillaris which holds some advantages as short life cycle, easy cultivation, high lipid content, diversity of fatty acids and stability under harsh environmental conditions. The results displayed that, soil extract (SE) greatly enhance growth rate of cultures. Maximum biomass and lipid productivity were achieved in TAP medium as 81 mg/L·day, 19.44 mg/L·day; respectively. Light wavelength didn't significantly change growth kinetics but played a critical role on chlorophyll-a accumulation. C14:0, C16:0 and C18:0 fatty acids were abundant which are suitable for biodiesel conversion. Interestingly, blue and red light increased longer chain fatty acids content. These results indicated that; S. bacillaris holds potential for further development of biodiesel production and feasibility of algal biodiesel for fundamental and applied sciences.

Night illumination using monochromatic light-emitting diodes for enhanced microalgal growth and biodiesel production

The present study investigated the effect of monochromatic light-emitting diodes (LEDs) on the growth and biodiesel yield of the green microalga Scenedesmus obliquus. Different LEDs were applied individually or in combination during the night period. Among different individual treatments, red and blue illumination showed the highest biomass and lipid productivity due to stimulation of pigmentation and photosystem II, respectively. Microalgal growth, lipid production and biodiesel recovery significantly increased under combined blue-red illumination. In addition, saturated and monounsaturated fatty acids proportions increased in favor of polyunsaturated ones. Moreover, blue-red LEDs enhanced the net biodiesel energy output over the control. The total increase in net energy output represented 5.1, 3.8 and 10.8 MJ using red, blue and blue-red light, respectively. In conclusion, application of blue-red LEDs during the night period is an economical technology for microalgae cultivation, which might have a potential impact on the future of commercial biodiesel production from microalgae.

Enhancement of CO2 biofixation and lipid production by Chlorella vulgaris using coloured polypropylene film

Chlorella vulgaris was cultivated with light at different wavelengths (λ_max) and irradiation intensities (I) by applying a coloured tape (CT) as a simple, inexpensive light filter. C. vulgaris was cultivated in a standard medium using blue (CT_B), green (CT_G), red (CT_R), yellow (CT_Y) and white (CT_W) CT to filter the light, as well the unfiltered light (U). The influence of λ_max and I on specific growth rate (μ), nutrient removal efficiency (% RE of total nitrogen, TN, and phosphorus, TP), CO₂ fixation rate (RC) and lipid productivity (P_lipid) were evaluated. The highest biomass concentration X_max of 2.26 g L^-1 was measured for CT_W with corresponding μ, TN and TP RE, RC and P_lipid values of 0.95 d^-1, 92% and 100%, 0.67 g L^-1 d^-1 and 83.6 mg L^-1 d^-1, respectively. The normalised μ and P_lipid for U were significantly lower than in CT_W of 33-50% and 75%, respectively. The corresponding non-normalised parameter values for CT_B were significantly lower at 0.45 d^-1, 0.18 g L^-1, 15% and 37%, 0.03 g L^-1 d^-1 and 1.2 mg L^-1 d^-1. Results suggest a significant impact of I and λ_max, with up to a 50% increase in growth and nutrient RE from optimising these parameters.

Study of the Persistence of the Phytotoxicity Induced by Graphene Oxide Quantum Dots and of the Specific Molecular Mechanisms by Integrating Omics and Regular Analyses

Although increasing attention has been paid to the nanotoxicity of graphene oxide quantum dots (GOQDs) due to their broad range of applications, the persistence and recoverability associated with GOQDs had been widely ignored. Interestingly, stress-response hormesis for algal growth was observed for Chlorella vulgaris as a single-celled model organism. Few physiological parameters, such as algal density, plasmolysis, and levels of reactive oxygen species, exhibited facile recovery. In contrast, the effects on chlorophyll a levels, permeability, and starch grain accumulation exhibited persistent toxicity. In the exposure stage, the downregulation of genes related to unsaturated fatty acid biosynthesis, carotenoid biosynthesis, phenylpropanoid biosynthesis, and binding contributed to toxic effects on photosynthesis. In the recovery stage, downregulation of genes related to the cis-Golgi network, photosystem I, photosynthetic membrane, and thylakoid was linked to the persistence of toxic effects on photosynthesis. The upregulated galactose metabolism and downregulated aminoacyl-tRNA biosynthesis also indicated toxicity persistence in the recovery stage. The downregulation and upregulation of phenylalanine metabolism in the exposure and recovery stages, respectively, reflected the tolerance of the algae to GOQDs. The present study highlights the importance of studying nanotoxicity by elucidation of stress and recovery patterns with metabolomics and transcriptomics.

Critical light-related gene expression varies in two different strains of the dinoflagellate Karlodinium veneficum in response to the light spectrum and light intensity

The toxic dinoflagellate Karlodinium veneficum is widely distributed in cosmopolitan estuaries and is responsible for massive fish mortality worldwide. Intraspecific biodiversity is important for the spread to various habitats, interspecific competition to dominate a population, and bloom formation and density maintenance. Strategies for light adaptation may help determine the ecological niches of different ecotypes. However, the mechanism of phenotypic biodiversity is still unclear. In this study, intraspecific differences in genetic regulatory mechanisms in response to varied light intensities and qualities were comparatively researched on two different strains isolated from coastal areas of the East China Sea, namely, GM2 and GM3. In GM2, the expression of genes in the Calvin cycle, namely, rbcL and SBPase, and a light-related gene that correlated with cellular motility, rhodopsin, were significantly inhibited under high light intensities. Thus, this strain was adapted to low light. In contrast, the gene expression levels were promoted by high light conditions in GM3. These upregulated genes in the GM3 strain probably compensated for the negative effects on the maximum quantum yields of PSII (Fv/Fm) under high light stress, which inhibited both strains, enabling GM3 to maintain a constant growth rate. Thus, this strain was adapted to high light. Compared with white light, monochromatic blue light had negative effects on Fv/Fm and the relative electron transfer rate (ETR) in both strains. Under blue light, gene expression levels of rbcL and SBPase in GM2 were inhibited; in contrast, the levels of these genes, especially rbcL, were promoted in GM3. rbcL was significantly upregulated in the blue light groups. Monochromatic red light promoted rhodopsin gene expression in the two strains in a similar manner. These intraspecific diverse responses to light play important roles in the motor characteristics, diel vertical migration, interspecific relationships and photosynthetic or phagotrophic activities of K. veneficum and can determine the population distribution, population maintenance and bloom formation.