A comprehensive comparable study of the physiological properties of four microalgal species under different light wavelength conditions

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.

Light emitting diodes as alternative light source for growth and carotenoid enhancement in Chlorococcum humicola Cultured in airlift photobioreactors

This study compares the performance of white light emitting diodes (LEDs) and fluorescent lamps for cultivating Chlorococcum humicola (C. humicola) as aquaculture feed. Results demonstrate that daylight LEDs are seen to yield the highest biomass concentration at 1,010 ± 11 mg/L, exceeding fluorescent lamps by 36 %. Switching to daylight LEDs increased carotenoid content in algal biomass from 2.97 ± 0.23 to 3.86 ± 0.15 mg/g and carotenoid concentration from 2.21 ± 0.16 to 3.90 ± 0.27 mg/L: increases of 36 % and 76 %, respectively. Blue and daylight LEDs proved to be most effective for lutein induction, with less impact on beta-carotene. Biomass under daylight LEDs shows promising values for protein and lipid contents of 32 % and 11 % dry weight, respectively. Daylight LEDs consumed less than half the energy of fluorescent lamps. Daylight LEDs significantly enhance the growth and carotenoid content of C. humicola, offering a sustainable alternative for aquaculture feed production.

Impact of Various Visible Spectra on Attached Microalgal Growth on Palm Decanter Cake in Triggering Protein, Carbohydrate, and Lipid to Biodiesel Production

Attached microalgal growth of Chlorella vulgaris on palm decanter cake (PDC) under irradiation with various visible monochromatic and polychromatic spectra to produce biodiesel was studied in this work. The results demonstrated that the white spectrum cultivation exhibited the highest microalgal density of 1.13 g/g along with 1.213 g/L day of microalgal productivity. Correspondingly, the biodiesel obtained was comprised mainly of C16 and C18 fatty acids, possessing a high cetane number and oxidation stability from the high saturated fatty acid content (70.38%), which was appealing in terms of most biodiesel production requirements. Nevertheless, the highest lipid content (14.341%) and lipid productivity (93.428 mg/L per day) were discovered with green spectrum cultivation. Blue and white spectra led to similar protein contents (34%) as well as carbohydrate contents (61%), corroborating PDC as a feasible carbon and nutrient source for growing microalgae. Lastly, the energy feasibilities of growing the attached microalgae under visible spectra were investigated, with the highest net energy ratio (NER) of 0.302 found for the yellow spectrum. This value outweighed that in many other works which have used suspended growth systems to produce microalgal fuel feedstock. The microalgal growth attached to PDC is deemed to be a suitable alternative cultivation mode for producing sustainable microalgal feedstock for the biofuel industry.

Production, Processing, and Protection of Microalgal n-3 PUFA-Rich Oil

Microalgae have been increasingly considered as a sustainable “biofactory” with huge potentials to fill up the current and future shortages of food and nutrition. They have become an economically and technologically viable solution to produce a great diversity of high-value bioactive compounds, including n-3 polyunsaturated fatty acids (PUFA). The n-3 PUFA, especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), possess an array of biological activities and positively affect a number of diseases, including cardiovascular and neurodegenerative disorders. As such, the global market of n-3 PUFA has been increasing at a fast pace in the past two decades. Nowadays, the supply of n-3 PUFA is facing serious challenges as a result of global warming and maximal/over marine fisheries catches. Although increasing rapidly in recent years, aquaculture as an alternative source of n-3 PUFA appears insufficient to meet the fast increase in consumption and market demand. Therefore, the cultivation of microalgae stands out as a potential solution to meet the shortages of the n-3 PUFA market and provides unique fatty acids for the special groups of the population. This review focuses on the biosynthesis pathways and recombinant engineering approaches that can be used to enhance the production of n-3 PUFA, the impact of environmental conditions in heterotrophic cultivation on n-3 PUFA production, and the technologies that have been applied in the food industry to extract and purify oil in microalgae and protect n-3 PUFA from oxidation.

The Effect of Variable Light Source and Light Intensity on the Growth of Three Algal Species

Light is the essential energy source for autotrophically growing organisms, including microalgae. Both light intensity and light quality affect cell growth and biomass composition. Here we used three green algae—Chlamydomonas reinhardtii, Desmodesmus quadricauda, and Parachlorella kessleri—to study the effects of different light intensities and light spectra on their growth. Cultures were grown at three different light intensities (100, 250, and 500 µmol m⁻² s⁻¹) and three different light sources: fluorescent lamps, RGB LEDs, and white LEDs. Cultures of Desmodesmus quadricauda and Parachlorella kessleri were saturated at 250 µmol m⁻² s⁻¹, and further increasing the light intensity did not improve their growth. Chlamydomonas reinhardtii cultures did not reach saturation under the conditions used. All species usually divide into more than two daughter cells by a mechanism called multiple fission. Increasing light intensity resulted in an increase in maximum cell size and division into more daughter cells. In Parachlorella kessleri cells, the concentration of photosynthetic pigments decreased with light intensity. Different light sources had no effect on algal growth or photosynthetic pigments. The results show a species-specific response of algae to light intensity and support the use of any white light source for their cultivation without negative effects on growth.

Influence of Irradiance and Wavelength on the Antioxidant Activity and Carotenoids Accumulation in Muriellopsis sp. Isolated from the Antofagasta Coastal Desert

Microalgae are a valuable natural resource for a variety of biocompounds such as carotenoids. The use of different light spectra and irradiance has been considered as a promising option to improve the production of these compounds. The objective of this study was to evaluate the influence of different wavelengths (white, red, and blue) and irradiances (80 and 350 µmol photons/m2/s) on the photosynthetic state, total carotenoids and lutein productivity (HPLC), lipids (Nile red method) and antioxidant activity (DPPH) of the microalgae Muriellopsis sp. (MCH-35). This microalga, which is a potential source of lutein, was isolated from the coastal desert of Antofagasta, Chile, and adapted to grow in seawater. The results indicate that the culture exposed to high-intensity red light showed the highest biomass yield (2.5 g/L) and lutein productivity (>2.0 mg L−1day−1). However, blue light was found to have a stimulating effect on the synthesis of lutein and other carotenoids (>0.8% dry wt). Furthermore, a direct relationship between lipid accumulation and high light intensity was evidenced. Finally, the highest antioxidant activity was observed with high-intensity white light, these values have no direct relationship with lutein productivity. Therefore, the findings of this study could be utilized to obtain biocompounds of interest by altering certain culture conditions during the large-scale cultivation of MCH-35.

Physiological responses and transcriptome analysis of Spirodela polyrhiza under red, blue, and white light

Red light (RL) accelerated starch accumulation in S. polyrhiza, but higher protein content under blue light (BL) was associated with the upregulation of most DEGs enriched for specific GO terms and KEGG pathways. Red light (RL) and blue light (BL) greatly influence the growth and physiological processes of duckweed. Physiological and molecular mechanisms underlying the response of duckweed to different light qualities remain unclear. This study employed physiological and transcriptomic analyses on duckweed, Spirodela polyrhiza "5510", to elucidate its differential response mechanisms under RL, BL, and white light conditions. Changes in growth indicators, ultrastructure alterations, metabolite accumulations, and differentially expressed genes (DEGs) were measured. The results showed that BL promoted both biomass and protein accumulations, while RL promoted starch accumulation. A total of 633, 518, and 985 DEGs were found in white-vs-red, white-vs-blue, and red-vs-blue comparison groups, respectively. In Gene Ontology (GO) enrichment analysis, the DEGs in all three comparison groups were significantly enriched in two GO terms, carboxylic acid metabolic process and lyase activity. In Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, the DEGs were greatly enriched in two pathways, histidine metabolism and isoquinoline alkaloid biosynthesis. Higher protein content under BL was associated with the upregulation of most DEGs enriched with the GO terms and KEGG pathways. Furthermore, the light qualities influenced the gene expression patterns of other metabolic pathways, like carotenoid biosynthesis, and the regulation of these genes may explain the level of photosynthetic pigment content. The results revealed the physiological changes and transcriptome-level responses of duckweed to three light qualities, thereby providing bases for further research studies on the ability of duckweed as a biomass energy source.

Influence of Light Conditions on Microalgae Growth and Content of Lipids, Carotenoids, and Fatty Acid Composition

Microalgae are a valuable natural resource for a variety of value-added products. The growth of microalgae is determined by the impact of many factors, but, from the point of view of the implementation of autotrophic growth, light is of primary importance. This work presents an overview of the influence of light conditions on the growth of microalgae, the content of lipids, carotenoids, and the composition of fatty acids in their biomass, taking into account parameters such as the intensity, duration of lighting, and use of rays of different spectral composition. The optimal light intensity for the growth of microalgae lies in the following range: 26-400 µmol photons m-2 s-1. An increase in light intensity leads to an activation of lipid synthesis. For maximum lipid productivity, various microalgae species and strains need lighting of different intensities: from 60 to 700 µmol photons m-2 s-1. Strong light preferentially increases the triacylglyceride content. The intensity of lighting has a regulating effect on the synthesis of fatty acids, carotenoids, including β-carotene, lutein and astaxanthin. In intense lighting conditions, saturated fatty acids usually accumulate, as well as monounsaturated ones, and the number of polyunsaturated fatty acids decreases. Red as well as blue LED lighting improves the biomass productivity of microalgae of various taxonomic groups. Changing the duration of the photoperiod, the use of pulsed light can stimulate microalgae growth, the production of lipids, and carotenoids. The simultaneous use of light and other stresses contributes to a stronger effect on the productivity of algae.

Effects of light-emitting diodes (LEDs) on lipid production of the aerial microalga Coccomyxa sp. KGU-D001 under liquid- and aerial-phase conditions

Algal biofuels are a promising alternative to fossil fuels, but their widespread use is hindered by problems with mass production. Light-emitting diodes (LEDs) with specific light wavelengths could be used as an energy source for algal growth and lipid synthesis. In this study, the effects of light source on the biomass and lipid production of the aerial microalga Coccomyxa sp. KGU-D001 were evaluated using LEDs. The integration of two-phase cultures, including growth and lipid production under the stress of nitrate depletion, was assessed for efficient lipid production under liquid- or aerial-phase conditions. Different wavelengths of light (blue, green, and red) were tested under liquid- and aerial-phase conditions. Under aerial-phase culture, the fatty acid contents in biofilm reached 320 mg g DWC^-1 with the red LEDs. In view of these findings, we describe a one-step culture method for growth and lipid accumulation in algal biofilm under aerial-phase culture with red LED irradiation. When Coccomyxa biofilm was cultured on wet cotton wool with BBM in a petri dish under the red LED, it was able to grow and accumulate lipids under the aerial-phase condition. Based on the results of this study, a potential method for a continuous biodiesel production system is proposed.

A comprehensive study on the effect of light quality imparted by light-emitting diodes (LEDs) on the physiological and biochemical properties of the microalgal consortia of Chlorella variabilis and Scenedesmus obliquus cultivated in dairy wastewater

The effect of light wavelengths on the physiological, biochemical and lutein content of the microalgal consortia Chlorella variabilis and Scenedesmus obliquus was evaluated using different light sources. Among different light treatments, cool-white fluorescent light produced the highest biomass of 673 mg L^-1 with a specific growth rate of 0.75 day^-1 followed by blue (500 mg L^-1; 0.73 day^-1). The chlorophyll content was enhanced under blue light (10.7 mg L^-1) followed by cool fluorescent light (9.3 mg L^-1), whereas the lutein productivity was enhanced under cool fluorescent light (7.22 mg g^-1). Protein content of the microalgal consortia was enhanced under all light treatments with the highest protein accumulation under cool-white fluorescent light (~56% of dry mass) closely followed by amber light (52% of dry mass), whereas the carbohydrate content was higher under amber light (~35% of dry mass). The results revealed that the consortia could grow well on diluted dairy wastewater thereby reducing the cost of algal production when compared with the use of inorganic media and a two-phase culture process utilizing cool fluorescent and amber light could be employed for maximizing algal biomass and nutrient composition with enhanced lutein production. The study also emphasizes on the economic efficiency of LED lights in terms of biomass produced based on the modest electricity consumed and the importance of using amber light for cultivating microalgae for its nutrient content which has seldom been studied.

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.