Productivity of Chlorella sorokiniana in a short light-path (SLP) panel photobioreactor under high irradiance

Maximal productivity of a 14 mm light-path panel photobioreactor under high irradiance was determined. Under continuous illumination of 2100 μmol photons m-2 s-1 with red LEDs (light emitting diodes) the effect of dilution rate on photobioreactor productivity was studied. The light intensity used in this work is similar to the maximal irradiance on a horizontal surface at latitudes lower than 37º. Chlorella sorokiniana, a fast-growing green microalga, was used as a reference strain in this study. The dilution rate was varied from 0.06 h-1 to 0.26 h-1. The maximal productivity was reached at a dilution rate of 0.24 h-1, with a value of 7.7 g of dry weight m-2 h-1 (m2 of illuminated photobioreactor surface) and a volumetric productivity of 0.5 g of dry weight L-1 h- 1. At this dilution rate the biomass concentration inside the reactor was 2.1 g L-1 and the photosynthetic efficiency was 1.0 g dry weight per mol photons. This biomass yield on light energy is high but still lower than the theoretical maximal yield of 1.8 g mol photons-1 which must be related to photosaturation and thermal dissipation of absorbed light energy

Effect of abiotic stress on the production on lutein and beta-carotene by Chlamydomonas acidophila

Chlamydomonas acidophila growing autotrophically with continuous PAR light (160 µE.m-2.s-1) and 30 ºC may accumulate carotenoids which increase in response to abiotic stress, like high light intensity, UV-A radiation and temperature fluctuation. At 240 µE.m-2.s-1 the alga contains 57.5 ± 1.6 mg.l-1 of total carotenoids after 20 days of growing, which does not significantly change by an irradiance of 1000 µE.m-2.s-1. Lutein (20 ± 0.5 mg.l-1) and β-carotene (8.3 ± 0.2 mg.l-1) production were particularly high in C. acidophila, while zeaxanthine (0.2 ± 0.1 mg.l-1) was low. Enhanced production of these carotenoids was also observed in cultures illuminated with PAR light (160 µE.m-2.s-1) supplemented with moderate UV-A radiation (10 µE.m-2.s-1). Optimum algae growth takes place at 40 ºC, like the maximum amount of intracellular lutein and β-carotene. On the other hand, the presence of iron in the culture medium, in a range between 5-35 mM, significantly decreased the cell viability and the intracellular content of carotenoids, however cupper, at 1-5 mM, appears to increase the synthesis of β-carotene. The alga can growth under mixotrophic conditions, with glucose or acetate, 10 mM, as carbon source, but such conditions did not improved the intracellular content of carotenoids

Effect of pH Change on the Microalgae-Based Biogas Upgrading Process

An alternative way to remove CO2 from biogas is the use of photosynthetic microorganisms, such as microalgae. This can be achieved by the operation of an open photobioreactor, connected with a mass transfer column, such as a counterflow column. This technology provides up-graded biogas with high quality. The microalgal uptake of CO2 from the biogas in counterflow columns generates pH changes in microalgae culture. To clarify the potential effect of these dynamic pH conditions in the culture, the effect of pH change on the photosynthetic activity and PSII quantum yield was studied for microalgae Chlorella sorokiniana. Thus, assays were carried out, where the pH drop reported in the counterflow columns was replicated in batch microalgae culture through HCl addition and CO2 injection, moving the culture pH from 7.0 to 5.0 and from 7.0 to 5.8, respectively. Moreover, the effect of light/darkness on photosynthetic activity was tested when the pH decreased. The results obtained in this research showed that the photosynthetic activity decreased for the light conditions when the pH was shifted by HCl addition and CO2 injection. Despite this, the value of the PSII quantum yield remained at 0.6–0.7, which means that the microalgae culture did not suffer a negative effect on the photosynthetic system of cells because a high value of PSII efficiency remained. In the same way, the results indicated that when the pH change was corrected, the photosynthetic activity recovered. Moreover, the apparent affinity constant for dissolved inorganic carbon (KDIC) was 0.9 µM at pH 5 and 112.0 µM at pH 7, which suggests that the preferred carbon source for C.sorokniana is CO2. Finally, all the results obtained indicated that the pH drop in the counter-flow column for biogas upgrading did not cause permanent damage to the photosynthetic system, and the decrease in the photosynthetic activity as a result of the pH drop can be recovered when the pH is corrected.This research was funded by FONDECYT-ANID CHILE, grant number 1120488, CRHIAM Centre (CONICYT/FONDAP) grant number 15130015, and VRIEA-PUCV grant number 039.315/2022

Impact of microalgae-bacteria interactions on the production of algal biomass and associated compounds

A greater insight on the control of the interactions between microalgae and other microorganisms, particularly bacteria, should be useful for enhancing the efficiency of microalgal biomass production and associated valuable compounds. Little attention has been paid to the controlled utilization of microalgae-bacteria consortia. However, the studies of microalgal-bacterial interactions have revealed a significant impact of the mutualistic or parasitic relationships on algal growth. The algal growth, for instance, has been shown to be enhanced by growth promoting factors produced by bacteria, such as indole-3-acetic acid. Vitamin B12 produced by bacteria in algal cultures and bacterial siderophores are also known to be involved in promoting faster microalgal growth. More interestingly, enhancement in the intracellular levels of carbohydrates, lipids and pigments of microalgae coupled with algal growth stimulation has also been reported. In this sense, massive algal production might occur in the presence of bacteria, and microalgae-bacteria interactions can be beneficial to the massive production of microalgae and algal products. This manuscript reviews the recent knowledge on the impact of the microalgae-bacteria interactions on the production of microalgae and accumulation of valuable compounds, with an emphasis on algal species having application in aquaculture

Neochloris oleoabundans oil production in an outdoor tubular photobioreactor at pilot scale

Oil production was tested with Neochloris oleoabundans in a 6 m3, horizontal soft sleeve tubular reactor from 22 October to 7 November in Matalascañas, southern Spain. Biomass productivity during the nitrogen replete phase was 7.4 g dw m−2 day−1. Maximum lipid content in the biomass was 39% and average lipid productivity during the nitrogen depletion phase was 2.0 g m−2 day−1. Nitrogen depletion of the cultures was carried out in order to enhance fatty acid formation, using the inverse nitrogen quota in the biomass to predict the fatty acid content. TFA concentration at harvest was 14%DW, compared to a value of 17%, predicted by the inverse nitrogen quota. The overall feasibility of the horizontal tubular technology for microalgal oil production, including mixing energy expenditure, was evaluated

Fe (III)-Mediated Antioxidant Response of the Acidotolerant Microalga Coccomyxa onubensis

Coccomyxa onubensis (C. onubensis) is an acidotolerant microalga isolated from Tinto River (Huelva), which contains high levels of metal cations in solution, mainly Fe (II) and (III), and Cu (II). Fe is more bioavailable at low pH, mainly because Fe (II) and Fe (III) are far more soluble, especially Fe (III). For this reason, this study aims to evaluate both physiological and biochemical responses of C. onubensis when subjected to Fe (III)-induced stress. Changes in growth, photosynthetic viability and antioxidant responses to the induced oxidative stress were determined. The results obtained suggest that the addition of moderate Fe (III) levels to C. onubensis cultures results in improved growth and photosynthetic viability. Increases in the intracellular levels of the enzyme superoxide dismutase (SOD) and flavonoids, used as antioxidant response biomarkers, a point at Fe (III)-mediated oxidative stress induction. The apparent decrease in the content of other phenolic molecules and polyunsaturated fatty acids might be understood as a sign of antioxidant molecules' involvement in reactive oxygen species (ROS) scavenging. In conclusion, a noticeable antioxidant capacity displayed by C. onubensis allows the use of moderate Fe (III) levels to trigger the accumulation of valuable antioxidant molecules, allowing the production of cell extracts with potential anti-inflammatory activity.This work was funded by the Andalusian Research, Development and Innovation Plan (Junta de Andalucía, Spain) with FEDER funds (Project P20_00930)

Ultrasound-Based Recovery of Anti-Inflammatory and Antimicrobial Extracts of the Acidophilic Microalga Coccomyxa onubensis

In the present study, the recovery of valuable molecules of proven anti-inflammatory and antimicrobial activity of the acidophilic microalga Coccomyxa onubensis (C. onubensis) were evaluated using green technologies based on ultrasound-assisted extraction (UAE). Using a factorial design (3 × 2) based on response surface methodology and Pareto charts, two types of ultrasonic equipment (bath and probe) were evaluated to recover valuable compounds, including the major terpenoid of C. onubensis, lutein, and the antimicrobial activity of the microalgal extracts obtained under optimal ultrasound conditions (desirability function) was evaluated versus conventional extraction. Significant differences in lutein recovery were observed between ultrasonic bath and ultrasonic probe and conventional extraction. Furthermore, the antimicrobial activity displayed by C. onubensis UAE-based extracts was greater than that obtained in solvent-based extracts, highlighting the effects of the extracts against pathogens such as Enterococcus hirae and Bacillus subtilis, followed by Staphylococcus aureus and Escherichia coli. In addition, gas chromatography–mass spectrometry was performed to detect valuable anti-inflammatory and antimicrobial biomolecules present in the optimal C. onubensis extracts, which revealed that phytol, sterol-like, terpenoid, and even fatty acid structures could also be responsible for the antibacterial activities of the extracts. Moreover, UAE displayed a positive effect on the recovery of valuable molecules, improving biocidal effects. Our study results facilitate the use of green technology as a good tool in algal bioprocess engineering, improving energy consumption and minimizing environmental impacts and process costs, as well as provide a valuable product for applications in the field of biotechnology.This work was partially supported by the Andalusian Research, Development and Innovation Plan (Junta de Andalucía, Spain) with FEDER funds (Project P20_00930) and by the University of Huelva through a grant obtained in the program “Requalitication of the Spanish Universitary System 2021-2023, María Zambrano” (Real Decreto 289/2021, 20 April and Order UNI/551/2021, 26 May) and “IV Convocatoria de Micro-proyectos-Cátedra de la Provincia UHU 2023”

Cultivo de microalgas en una zona de alta irradancia

Microalgae are considered a promising source of high-value products (carotenoids, omega-3, DHA) as well as feedstocks for feed/food, bulk chemicals, cosmetics/pharmaceutics and biofuels. Moreover, they can be used in bioremediation tasks of polluted environments, as part of the CO2 gas mitigation process or in wastewater treatment. Light is the main substrate for the production of microalgae. Therefore, areas with high irradiances and moderated temperatures along the year are considered to be optimal for the production of microalgal biomass. However, the photosynthetic process is not a perfect process and the low efficiencies obtained in outdoor cultivation processes, especially when cultures are exposed to high irradiance conditions, are limiting the development of feasible production systems at industrial scale. Considering the excess of light hinders the photosynthetic efficiency outdoors, more knowledge on the effect of photo-saturation over the complete photosynthetic process is needed with the aim of enhancing the microalgal productivities. In this sense, simulation experiments at laboratory scale where real outdoor irradiance conditions can be simulated while keeping the rest of operational parameters optimal might result in a better understanding of the microalgal cultivation process. In this Thesis Dissertation, irradiance conditions typical from the Summer and Winter period in Huelva (south-west of Spain), geographical area with a high annual irradiance, were simulated. Different cultivation strategies leading to avoid/reduce the effects of photo-saturation and/or photo-inhibition over the microalgal cultures were evaluated and their effect over the final production of the microalgae Chlorella sorokiniana was discussed. Obtained results show the potential of such microalgae to be cultivated in a high irradiance area as Huelva, the study site, for the obtainment of biomass and high-value molecules as lutein. Moreover, the positive effect of light dilution over the photosynthetic efficiency was confirmed.Las microalgas son consideradas una fuente alternativa de productos de alto valor añadido (carotenoides, omega-3, DHA), son utilizadas en alimentación animal y humana, en el sector cosmético y farmacéutico así como en la industria química, pudiendo además ser substrato para la producción de biocombustibles o usadas en tareas de biorremediación o depuración de efluentes. La luz es el principal substrato para la producción de microalgas. Regiones con alta irradiancia y temperaturas moderadas a lo largo de todo el año son, por lo tanto, consideradas idóneas para la producción de biomasa de microalgas. Sin embargo, la fotosíntesis no es un proceso perfecto, y las bajas eficiencias fotosintéticas alcanzadas en cultivos en el exterior, especialmente bajo condiciones de alta irradiancia, limitan el desarrollo de sistemas de producción de microalgas a escala comercial. Por tanto, debido a que el exceso de luz reduce la eficiencia fotosintética en el exterior, se requiere un mayor conocimiento sobre el efecto de la foto-saturación en el proceso fotosintético con objeto de mejorar la productividad de los cultivos. En este sentido, experimentos a nivel de laboratorio donde pueden simularse condiciones reales de irradiancia, a la vez que se mantienen el resto de parámetros operacionales en sus valores óptimos, proporcionan una mejor comprensión sobre el cultivo de microalgas. En esta Tesis se simulan condiciones de irradiancia propias del periodo estival, así como del invierno, en la región de Huelva, zona geográfica de alta irradiancia anual. Se evalúan diferentes estrategias para minimizar y/o evitar los efectos de la foto-saturación y de la fotoinhibición y se discute la producción de biomasa de la microalga Chlorella sorokiniana en el lugar geográfico de estudio. Los resultados obtenidos ponen en valor el potencial de dicha microalga para ser producida en una región de alta irradiancia como Huelva (Andalucía, España) para la obtención de biomasa y de moléculas de valor añadido –luteína-, confirmando además el positivo efecto de la dilución de la luz incidente sobre la eficiencia fotosintética

Cultivation of Microalgae Chlorella Using Wine Industry by-Products

An approach of new and sustainable uses for by-products generated in the wine production industry, one of the agro-food sectors of importance, has been studied. Wine lees, a sediment obtained in different processes of decantation of wine, have been used to produce biomass of microalgae enriched in carotenoids as high added value biomolecules. Experiments to incorporate chemical components of wine lees into microalgae biomass to understand the effect of these residues on the growth and biosynthesis of carotenoids into commercial microalgae Chlorella sorokiniana have been done. Algal culture system has been optimized and preparation of culture media have been obtained by extracting in water the soluble nutrients contained in the lees at different concentrations between 5% and 50% w/v. Optimal growth was obtained using extraction of wine residues at 5% and 10% w/v. At 10% oxidative stress, measured as carotenoids production (specially lutein) and antioxidant activity (DPPH method), was more intense than the obtained using residues at 5%. Our results show that growth in culture media prepared with wine lees extracts stimulated the antioxidant activity and the production of carotenoids in C. sorokiniana cells. Preliminary information, not only to produce sustainable growth media for biomass of microalgae enriched in high value molecules, but also to reuse nutrients contained in wine industry by-products what is of particular interest in the context of a circular economy is provided