Optimization of spectral light quality for growth and product formation in different microalgae using a continuous photobioreactor

Enhancing CO2 fixation by microalgae in a Photobioreactor: Molecular mechanisms with exogenous carbonic anhydrase

Microalgae biotechnology holds great potential for mitigating CO2 emissions, yet faces challenges in commercialization due to suboptimal photosynthetic efficiency. This study presents an innovative approach to improve CO2 mass transfer efficiency in microalgae using carbonic anhydrase (CA) in an internal LED flexible air-lift photobioreactor. Optimal conditions initial inoculation with 3.55 × 106 cells/mL and 20 % CO2 concentration, complemented by white LED lighting in Chlorella sp. CA regulated intracellular composition, enhancing chlorophyll, lipid, and protein contents. Metabolomics revealed elevated malic and succinic acids, associated with increased Ribulose 1,5-bisphosphate carboxylase oxygenase (RuBisCO) and Acetoacetyl coenzyme A (Acetyl-CoA) activities, facilitating efficient carbon fixation. CA also mitigated cellular oxidative stress by reducing reactive oxygen species (ROS). Furthermore, CA improved extracellular electron acceptor with currents surpassed CK. This CA-based microalgae biotechnology provides a foundation for future commercial applications, addressing CO2 emissions.

Substrate and nutrient manipulation during continuous cultivation of extremophilic algae, Galdieria spp. RTK 37.1, substantially impacts biomass productivity and composition

The extremophilic nature and metabolic flexibility of Galdieria spp. highlights their potential for biotechnological application. However, limited research into continuous cultivation of Galdieria spp. has slowed progress towards the commercialization of these algae. The objective of this research was to investigate biomass productivity and growth yields during continuous photoautotrophic, mixotrophic and heterotrophic cultivation of Galdieria sp. RTK371; a strain recently isolated from within the Taupō Volcanic Zone in Aotearoa-New Zealand. Results indicate Galdieria sp. RTK371 grows optimally at pH 2.5 under warm white LED illumination. Photosynthetic O2 production was dependent on lighting intensity with a maximal value of (133.5 ± 12.1 nmol O2 mgbiomass -1 h-1) achieved under 100 μmol m-2 s-1 illumination. O2 production rates slowed significantly to 42 ± 1 and <0.01 nmol O2 mgbiomass -1 h-1 during mixotrophic and heterotrophic growth regimes respectively. Stable, long-term chemostat growth of Galdieria sp. RTK371 was achieved during photoautotrophic, mixotrophic and heterotrophic growth regimes. During periods of ammonium limitation, Galdieria sp. RTK371 increased its intracellular carbohydrate content (up to 37% w/w). In contrast, biomass grown in ammonium excess was composed of up to 65% protein (w/w). Results from this study demonstrate that the growth of Galdieria sp. RTK371 can be manipulated during continuous cultivation to obtain desired biomass and product yields over long cultivation periods.

Context-dependent antisense transcription from a neighboring gene interferes with the expression of mNeonGreen as a functional in vivo fluorescent reporter in the chloroplast of Chlamydomonas reinhardtii

Advancing chloroplast genetic engineering in Chlamydomonas reinhardtii remains challenging, decades after its first successful transformation. This study introduces the development of a chloroplast-optimized mNeonGreen fluorescent reporter, enabling in vivo observation through a sixfold increase in fluorescence via context-aware construct engineering. Our research highlights the influence of transcriptional readthrough and antisense mRNA pairing on post-transcriptional regulation, pointing to novel strategies for optimizing heterologous gene expression. We further demonstrate the applicability of these insights using an accessible experimentation system using glass-bead transformation and reestablishment of photosynthesis using psbH mutants, focusing on the mitigation of transcriptional readthrough effects. By characterizing heterologous expression using regulatory elements such as PrrnS, 5'atpA, and 3' rbcL in a sense-transcriptional context, we further documented up to twofold improvement in fluorescence levels. Our findings contribute new tools for molecular biology research in the chloroplast and evidence fundamental gene regulation processes that could enable the development of more effective chloroplast engineering strategies. This work not only paves the way for more efficient genetic engineering of chloroplasts but also deepens our understanding of the regulatory mechanisms at play.

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.

Phycobiliproteins from microalgae: research progress in sustainable production and extraction processes

Phycobiliproteins (PBPs), one of the functional proteins from algae, are natural pigment-protein complex containing various amino acids and phycobilins. It has various activities, such as anti-inflammatory and antioxidant properties. And are potential for applications in food, cosmetics, and biomedicine. Improving their metabolic yield is of great interest. Microalgaes are one of the important sources of PBPs, with high growth rate and have the potential for large-scale production. The key to large-scale PBPs production depends on accumulation and recovery of massive productive alga in the upstream stage and the efficiency of microalgae cells breakup and extract PBPs in the downstream stage. Therefore, we reviewed the status quo in the research and development of PBPs production, summarized the advances in each stage and the feasibility of scaled-up production, and demonstrated challenges and future directions in this field.

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

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

Microalgae: A Promising Source of Bioactive Phycobiliproteins

Phycobiliproteins are photosynthetic light-harvesting pigments isolated from microalgae with fluorescent, colorimetric and biological properties, making them a potential commodity in the pharmaceutical, cosmetic and food industries. Hence, improving their metabolic yield is of great interest. In this regard, the present review aimed, first, to provide a detailed and thorough overview of the optimization of culture media elements, as well as various physical parameters, to improve the large-scale manufacturing of such bioactive molecules. The second section of the review offers systematic, deep and detailed data about the current main features of phycobiliproteins. In the ultimate section, the health and nutritional claims related to these bioactive pigments, explaining their noticeable potential for biotechnological uses in various fields, are examined.

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.

Effects of UV and UV-vis Irradiation on the Production of Microalgae and Macroalgae: New Alternatives to Produce Photobioprotectors and Biomedical Compounds

In the last decade, algae applications have generated considerable interest among research organizations and industrial sectors. Bioactive compounds, such as carotenoids, and Mycosporine-like amino acids (MAAs) derived from microalgae may play a vital role in the bio and non-bio sectors. Currently, commercial sunscreens contain chemicals such as oxybenzone and octinoxate, which have harmful effects on the environment and human health; while microalgae-based sunscreens emerge as an eco-friendly alternative to provide photo protector agents against solar radiation. Algae-based exploration ranges from staple foods to pharmaceuticals, cosmetics, and biomedical applications. This review aims to identify the effects of UV and UV-vis irradiation on the production of microalgae bioactive compounds through the assistance of different techniques and extraction methods for biomass characterization. The efficiency and results focus on the production of a blocking agent that does not damage the aquifer, being beneficial for health and possible biomedical applications.

Microalgal Biomass as Feedstock for Bacterial Production of PHA: Advances and Future Prospects

The search for biodegradable plastics has become the focus in combating the global plastic pollution crisis. Polyhydroxyalkanoates (PHAs) are renewable substitutes to petroleum-based plastics with the ability to completely mineralize in soil, compost, and marine environments. The preferred choice of PHA synthesis is from bacteria or archaea. However, microbial production of PHAs faces a major drawback due to high production costs attributed to the high price of organic substrates as compared to synthetic plastics. As such, microalgal biomass presents a low-cost solution as feedstock for PHA synthesis. Photoautotrophic microalgae are ubiquitous in our ecosystem and thrive from utilizing easily accessible light, carbon dioxide and inorganic nutrients. Biomass production from microalgae offers advantages that include high yields, effective carbon dioxide capture, efficient treatment of effluents and the usage of infertile land. Nevertheless, the success of large-scale PHA synthesis using microalgal biomass faces constraints that encompass the entire flow of the microalgal biomass production, i.e., from molecular aspects of the microalgae to cultivation conditions to harvesting and drying microalgal biomass along with the conversion of the biomass into PHA. This review discusses approaches such as optimization of growth conditions, improvement of the microalgal biomass manufacturing technologies as well as the genetic engineering of both microalgae and PHA-producing bacteria with the purpose of refining PHA production from microalgal biomass.

Investigating the impact of light quality on macromolecular composition of Chaetoceros muelleri

Diatoms (Bacillariophyceae) are important to primary productivity of aquatic ecosystems. This algal group is also a valuable source of high value compounds that are utilised as aquaculture feed. The productivity of diatoms is strongly driven by light and CO2 availability, and macro- and micronutrient concentrations. The light dependency of biomass productivity and metabolite composition is well researched in diatoms, but information on the impact of light quality, particularly the productivity return on energy invested when using different monochromatic light sources, remains scarce. In this work, the productivity return on energy invested of improving growth rate, photosynthetic activity, and metabolite productivity of the diatom Chaetoceros muelleri under defined wavelengths (blue, red, and green) as well as while light is analysed. By adjusting the different light qualities to equal photosynthetically utilisable radiation, it was found that the growth rate and photosynthetic oxygen evolution was unchanged under white, blue, and green light, but it was lower under red light. Blue light improved the productivity return on energy invested for biomass, total protein, total lipid, total carbohydrate, and in fatty acids production, which would suggest that blue light should be used for aquaculture feed production.

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.

Photobiological Effects on Biochemical Composition in Porphyridium cruentum (Rhodophyta) with a Biotechnological Application

This study describes the relation of photosynthetic capacity, growth and biochemical compounds in the microalgae Porphyridium cruentum under saturated irradiance (200 μmol m^-2  s^-1 ) by white light (WL) and low-pressure sodium vapor lamps (SOX lamps-control) and supplemented by fluorescent lamps (FLs) with different light qualities (blue: λ_max = 440 nm; green: λ_max = 560 nm; and red: λ_max = 660 nm). The maximum photosynthetic efficiency (F_v / F_m ) showed a positive correlation with the light quality by saturating light SOX in mixture with stimulating blue light than the white light (WL) at the harvest day (10 days). The production, that is maximal electron transport rate (ETR_max ), and energy dissipation, that is maximal nonphotochemical quenching (NPQ_max ), had the same pattern throughout the time (3-6 days) being the values higher under white light (WL) compared with SOX and SOX plus supplemented different light qualities. Total protein levels increased significantly in the presence of SOX light, while phycoerythrin (B-PE) showed significant differences under SOX+ blue light. Arachidonic acid (ARA) was higher under SOX and SOX plus supplemented different light qualities than that under WL, whereas eicosapentaenoic acid (EPA) was the reverse. The high photomorphogenic potential by SOX light shows promising application for microalgal biotechnology.

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.

A novel two-phase bioprocess for the production of Arthrospira (Spirulina) maxima LJGR1 at pilot plant scale during different seasons and for phycocyanin induction under controlled conditions

A two-phase outdoor cultivation bioprocess for Arthrospira maxima LJGR1 combined with phycocyanin induction in concentrated cultures under controlled conditions was evaluated using a modified low-cost Zarrouk medium. Growth was monitored during 4 cycles in 2018 and 4 cycles in 2019. Biomass was harvested and concentrated using membrane technology at the end of each cycle for further phycocyanin induction using blue LED light (controlled conditions, 24 h). The highest biomass productivity was observed during spring and summer cycles (13.63-18.97 g_DWm^-2 d^-1); during mid-fall and mid-end fall, a decrease was observed (9.93-7.76 g_DWm^-2 d^-1). Under favorable growth conditions, phycocyanin induction was successful. However, during cycles with unfavorable growth condition, phycocyanin induction was not observed. Reactive-grade phycocyanin (3.72 ± 0.14) was recovered and purified using microfiltration and ultrafiltration technologies.

Microalgae aqueous extracts exert intestinal protective effects in Caco-2 cells and dextran sodium sulphate-induced mouse colitis

Aqueous extracts from Chlorella pyrenoidosa, Spirulina platensis and Synechococcus sp. PCC 7002 showed gut protective potential in vitro and in vivo.

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.

Advances in the production of bioactive substances from marine unicellular microalgae Porphyridium spp

Porphyridium spp. are a group of unicellular marine microalgae belonging to the Rhodophyta, which evolved over one billion years and are a source of a variety of natural active components. They can naturally and efficiently accumulate phycobilin, sulfated polysaccharides, polyunsaturated fatty acids and other bioactive substances. At present, numerous attempts have been made to explore the species Porphyridium spp., whereas mainly focused on cultivation methods, metabolism regulation and the function and application of bioactive products. There is a lack of systematic summary of the existing research conclusions. In this paper, we summarized the representative results related to culture and metabolism, analyzed and discussed the existing bottleneck restrictions for their large scale application, and proposed the potential industrial development and research direction in the future. This paper is expected to provide reference and thread for research and application of Porphyridium spp..

Light Intensity and Nitrogen Concentration Impact on the Biomass and Phycoerythrin Production by Porphyridium purpureum

Several factors have the potential to influence microalgae growth. In the present study, nitrogen concentration and light intensity were evaluated in order to obtain high biomass production and high phycoerythrin accumulation from Porphyridium purpureum. The range of nitrogen concentrations evaluated in the culture medium was 0.075-0.450 g L^-1 and light intensities ranged between 30 and 100 μmol m^-2 s^-1. Surprisingly, low nitrogen concentration and high light intensity resulted in high biomass yield and phycoerythrin accumulation. Thus, the best biomass productivity (0.386 g L^-1 d^-1) and biomass yield (5.403 g L^-1) were achieved with NaNO₃ at 0.075 g L^-1 and 100 μmol m^-2 s^-1. In addition, phycoerythrin production was improved to obtain a concentration of 14.66 mg L^-1 (2.71 mg g^-1 of phycoerythrin over dry weight). The results of the present study indicate that it is possible to significantly improve biomass and pigment production in Porphyridium purpureum by limiting nitrogen concentration and light intensity.

New horizons in culture and valorization of red microalgae

Research on marine microalgae has been abundantly published and patented these last years leading to the production and/or the characterization of some biomolecules such as pigments, proteins, enzymes, biofuels, polyunsaturated fatty acids, enzymes and hydrocolloids. This literature focusing on metabolic pathways, structural characterization of biomolecules, taxonomy, optimization of culture conditions, biorefinery and downstream process is often optimistic considering the valorization of these biocompounds. However, the accumulation of knowledge associated with the development of processes and technologies for biomass production and its treatment has sometimes led to success in the commercial arena. In the history of the microalgae market, red marine microalgae are well positioned particularly for applications in the field of high value pigment and hydrocolloid productions. This review aims to establish the state of the art of the diversity of red marine microalgae, the advances in characterization of their metabolites and the developments of bioprocesses to produce this biomass.

Quantification of oxygen production and respiration rates in mixotrophic cultivation of microalgae in nonstirred photobioreactors

Online monitoring and controlling of different cellular parameters are key issues in aerobic bioprocesses. Since mixotrophic cultivation, in which we observe a mixture of cellular respiration and oxygen production has gained more popularity, there is a need for an on-process quantification of these parameters. The presented and adapted double gassing-out method applied to a mixotrophic cultivation of Galdieria sulphuraria, will be a tool for monitoring and further optimization of algal fermentation in nonstirred photobioreactors (PBR). We measured the highest net specific oxygen production rate (opr _net) as 5.73 · 10^-3 mol_O2 g^-1 h^-1 at the lowest oxygen uptake rate (OUR) of 1.00 · 10^-4 mol_O2 L^-1 h^-1. Due to higher cell densities, we also demonstrated the increasing shading effect by a decrease of opr _net, reaching the lowest value of 1.25 10^-5 mol_O2 g^-1 h^-1. Nevertheless, with this on process measurement, we can predict the relation between the zone in which oxygen is net produced to the area where cell respiration dominates in a PBR, which has a major impact to optimize cell growth along with the formation of different products of interest such as pigments.