UV-A promotes long-term carotenoid production of Dunaliella in photobioreactors with retention of cell viability

The effect of adding UV-A radiations (320-400 nm) to photosynthetically active radiation (PAR, 400-700 nm) during the growth of Dunaliella bardawil in an air-fluidized bed photobioreactor was studied to evaluate cell growth and long-term production of carotenoids. The obtained results were compared to those obtained from D. bardawil cultures incubated under lab standard conditions for carotenoid production, this is to say, nitrogen starvation and absence of UV-A radiation. The addition of 26.5 μmol photons m-2 s-1 UV-A radiation to 1150 μmol photons m-2 s-1 PAR stimulated the growth of D. bardawil cultures grown in a full nutrient culture medium. The total carotenoid content, mostly β-carotene, was higher than that of control cultures (UV-A non added cultures) along the exponential phase. The concentration of β-carotene in UV-A added cultures after 450 h was found to be about two-fold that of control cultures. From the results of this work it can be concluded that the UV-A modulated addition to PAR could be successfully applied to long-term carotenoid production processes, whereas D. bardawil cells accumulates carotenoids with retention of its viability. It is also shown that UV-A promotes increases of both carotenoid production per culture volume unit and the specific carotenoid production rate (pg.cell-1), β-carotene being the major accumulated carotenoid

Enhancement of carotenoid production in Nannochloropsis by phosphate and sulphur limitation

Because of its value as antioxidants, food-supplements and in animal-feeding, carotenoids are among the most attractive target compounds of marine microalgae. In this contribution the influence of essential nutrients (N, S and P) limitation on the accumulation of carotenoids in the marine microalga Nannochloropsis gaditana has been studied. High and rapid biomass production, which depends on growth conditions, is the first step in a bioproduction process. In our work was observed that Nannochloropsis gaditana growth was significantly faster when using 5 % (v/v) CO2 in air instead air or HCO3 - as carbon source, at two different pH values assayed (7.2 and 8.2), as revealed from cell chlorophyll content, nitrate consumption rates and light-dependent oxygen production. Afterwards, cells grown to exponential phase were incubated in culture media containing none or limiting concentrations of either nitrate, sulphate or phosphate. The results showed that both starvation and low concentrations of nutrients (0.005 mM P, 0.2 mM N, 1.1 · 10-5 mM S) drove to increases of carotenoids/chlorophyll ratios, specially for sulphur limitation. In a general view, zeaxanthin and violaxanthin content increased in all limiting conditions tested, the increase of violaxanthin content being less pronounced

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

The Role of Microalgae in the Biogeochemical Cycling of Methylmercury (MeHg) in Aquatic Environments

Methylmercury (MeHg) is the most important and the most abundant organic Hg pollutant in the aquatic ecosystem that can affect human health through biomagnification. It is the most toxic organic Hg form, which occurs naturally and by human-induced contamination in water and is further biomagnified in the aquatic food web. MeHg is the only Hg form that accumulates in living organisms and is able to cross the blood–brain barrier, presenting an enormous health risk. Anthropogenic activity increases eutrophication of coastal waters worldwide, which promotes algae blooms. Microalgae, as primary producers, are especially sensitive to MeHg exposure in water and are an important entrance point for MeHg into the aquatic food web. MeHg assimilated by microalgae is further transferred to fish, wildlife and, eventually, humans as final consumers. MeHg biomagnifies and bioaccumulates in living organisms and has serious negative health effects on humans, especially newborns and children. Knowledge of the microalgae–MeHg interaction at the bottom of the food web provides key insights into the control and prevention of MeHg exposure in humans and wildlife. This review aims to summarize recent findings in the literature on the microalgae–MeHg interaction, which can be used to predict MeHg transfer and toxicity in the aquatic food webThis research was funded by the Spanish Ministry of Economic Transformation, Industry, Knowledge and Universities; by the European Regional Development Fund (FEDER) within the framework of the FEDER program of Andalusia (Spain) 2014–2020, grant number UHU–202065; and by Grant P20-00930 from the Andalusian Plan for Research, Development and Innovation, within the frame of the operational program “FEDER Andalucía 2014–2020” The authors wish to thank Erik Björn from Department of Chemistry, Umeå University, Sweden, for his constructive comments on the paper’s content. We wish to thank personnel from LICAH (Laboratorio de Investigación y Control Agroalimentario), University of Huelva, for their collaboration and cooperation under FEDER 2014–2020 UHU–202065 project. We also want to thank colleagues from BITAL (Algae Biotechnology Group), University of Huelva, for their kind assistance in the lab and for creating a productive working environmen

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

Study of scale-up and productivity of an acidotolerant and halotolerant microalgae (Coccomyxa onubensis) as a function of light exposure.

The inherent need to feed a growing population that is more aware of the importance of the nutritional quality of food in health has led nutraceutical products to an increasingly relevant position in the food industry. In this context microalgae acquire an essential role, due to their high nutrient content, being rich in various biomolecules, minerals, vitamins and antioxidant compounds1 . The main challenge in large-scale microalgae production is to achieve robust and economically viable growth, even under non-laboratory conditions such as those found outdoors. One promising alternative is extremophilic microalgae that have developed mechanisms that allow them to withstand these conditions2. Among them, Coccomyxa onubensis ACCV1, isolated from the acidic pH water of Río Tinto (Huelva), stands out. It is a halotolerant and acid-tolerant microalgae capable of growing in a wide range of pH values (2.5-9)3 , which potentially allows production while avoiding contamination by other microorganisms. This, together with its ability to accumulate antioxidant compounds such as carotenoids, polyphenols and polyunsaturated fatty acids make it an interesting candidate to study its scale-up for production. Thus, this project focuses on one of scale up stages by studying the variation of the productivity of this microalgae as a function of the different light exposure that occurs as a result of the different optical density of the cultures in 10 L bags. Thus, the trial consists of 3 bags maintained at different optical density (2-4, 6-8 and 10-12, respectively) by means of a repeated bath culture, with constant gassing and illumination. The incident radiation is progressively increased. In this way, the aim is to observe how productivity varies as a function of the different light exposure of the cells in each of the bags, as well as to observe their response to the increase in incident light, in terms of growth, photosynthetic efficiency and accumulation of bioactive compounds. To this end, growth is being evaluated through the quantification of parameters such as dry weight and optical density, while the measurement of quantum yield informs us of their photosynthetic state. The cell content in lipids, chlorophylls, carotenoids, flavonoids and polyphenols is being quantified

Interaction of Naturally Occurring Phytoplankton with the Biogeochemical Cycling of Mercury in Aquatic Environments and Its Effects on Global Hg Pollution and Public Health

The biogeochemical cycling of mercury in aquatic environments is a complex process driven by various factors, such as ambient temperature, seasonal variations, methylating bacteria activity, dissolved oxygen levels, and Hg interaction with dissolved organic matter (DOM). As a consequence, part of the Hg contamination from anthropogenic activity that was buried in sediments is reinserted into water columns mainly in highly toxic organic Hg forms (methylmercury, dimethylmercury, etc.). This is especially prominent in the coastal shallow waters of industrial regions worldwide. The main entrance point of these highly toxic Hg forms in the aquatic food web is the naturally occurring phytoplankton. Hg availability, intake, effect on population size, cell toxicity, eventual biotransformation, and intracellular stability in phytoplankton are of the greatest importance for human health, having in mind that such Hg incorporated inside the phytoplankton cells due to biomagnification effects eventually ends up in aquatic wildlife, fish, seafood, and in the human diet. This review summarizes recent findings on the topic of organic Hg form interaction with natural phytoplankton and offers new insight into the matter with possible directions of future research for the prevention of Hg biomagnification in the scope of climate change and global pollution increase scenarios.This research was funded by the Spanish Ministry of Economic Transformation, Industry, Knowledge and Universities; by the European Regional Development Fund (FEDER) within the framework of the FEDER program of Andalusia (Spain) 2014–2020 (grant number: UHU–202065); and by grant P20-00930 from the Andalusian Plan for Research, Development and Innovation, within the frame of the operational program “FEDER Andalucía 2014–2020”. The work of S.S. was supported by project number FCH-S-23-8330 of the Faculty of Chemistry, Brno University of Technology, Brno, Czech Republic

Adaptation strategies of endolithic chlorophototrophs to survive the hyperarid and extreme solar radiation environment of the Atacama Desert

The Atacama Desert, northern Chile, is one of the driest deserts on Earth and, as such, a natural laboratory to explore the limits of life and the strategies evolved by microorganisms to adapt to extreme environments. Here we report the exceptional adaptation strategies of chlorophototrophic and eukaryotic algae, and chlorophototrophic and prokaryotic cyanobacteria to the hyperarid and extremely high solar radiation conditions occurring in this desert. Our approach combined several microscopy techniques, spectroscopic analytical methods, and molecular analyses. We found that the major adaptation strategy was to avoid the extreme environmental conditions by colonizing cryptoendolithic, as well as, hypoendolithic habitats within gypsum deposits. The cryptoendolithic colonization occurred a few millimeters beneath the gypsum surface and showed a succession of organized horizons of algae and cyanobacteria, which has never been reported for endolithic microbial communities. The presence of cyanobacteria beneath the algal layer, in close contact with sepiolite inclusions, and their hypoendolithic colonization suggest that occasional liquid water might persist within these sub-microhabitats. We also identified the presence of abundant carotenoids in the upper cryptoendolithic algal habitat and scytonemin in the cyanobacteria hypoendolithic habitat. This study illustrates that successful lithobiontic microbial colonization at the limit for microbial life is the result of a combination of adaptive strategies to avoid excess solar irradiance and extreme evapotranspiration rates, taking advantage of the complex structural and mineralogical characteristics of gypsum deposits—conceptually called “rock's habitable architecture.” Additionally, self-protection by synthesis and accumulation of secondary metabolites likely produces a shielding effect that prevents photoinhibition and lethal photooxidative damage to the chlorophototrophs, representing another level of adaptation. [This Document is Protected by copyright and was first published by Frontiers. All rights reserved. it is reproduced with permission.]CA, JD, OA, AD, and JW are thankful for financial support by CGL2013-42509P grant from MINECO, Spain. JD acknowledges funding from the NASA Exobiology Program (Grant EXOB08-0033) and from the National Science Foundation (Grant NSF-0918907), PV acknowledges funding from the Czech Science Foundation, project no. P210/12/P330 and ENVIMET project CZ.1.07/2.3.00/20.0246 and AD acknowledges funding from the NASA Exobiology Program (Grant NNX12AD61G) and the NASA Astrobiology Institute (NAI Grant NNX15BB01A to the SETT Institute). The authors would like to thank to the MNCN - CSIC Microscopy Service staff and A. Gonzalez (GIG - Univ. Granada) for technical assistance

Haloferax mediterranei Cells as C50 Carotenoid Factories

Haloarchaea produce C50 carotenoids such as bacterioruberin, which are of biotechnological in-terest. This study aimed to analyze the effect of different environmental and nutritional conditions on the cellular growth and dynamics of carotenoids accumulation in Haloferax mediterranei. The maximum production of carotenoids (40 µg·mL−1) was obtained during the stationary phase of growth, probably due to nutrient-limiting conditions (one-step culture). By seven days of culture, 1 mL culture produced 22.4 mg of dry weight biomass containing 0.18 % (w/w) of carotenoids. On the other hand, carbon-deficient cultures (low C/N ratio) were observed to be optimum for C50 bacterioruberin production by Hfx. mediterranei, but negatively affected the growth of cells. Thus, a two-steps process was evaluated for optimum carotenoids yield. In the first step, a nutri-ent-repleted culture medium enabled the haloarchaea to produce biomass, while in the second step, the biomass was incubated under osmotic stress and in a carbon-deficient medium. Under the conditions used, the obtained biomass contained 0.27% (w/w) of carotenoids after seven days, which accounts for 58.49 µg·mL−1 of carotenoids for a culture with turbidity 14.0.This work was funded by a research grant from MINECO Spain (RTI2018-099860-B-I00) and the University of Alicante (VIGROB-309). We are also indebted to the Andalusian Government (research project BIO-214). ZM was assisted by a pre-doctoral grant from “Plan Propio de Investigación” of the University of Huelva, Spain. MG was awarded with a pre-doctoral fellowship from the Valencian Community Government (ACIF/2019/043)