Inés Garbayo

Marine Carotenoids: Biological Functions and Commercial Applications

Carotenoids are the most common pigments in nature and are synthesized by all photosynthetic organisms and fungi. Carotenoids are considered key molecules for life. Light capture, photosynthesis photoprotection, excess light dissipation and quenching of singlet oxygen are among key biological functions of carotenoids relevant for life on earth. Biological properties of carotenoids allow for a wide range of commercial applications. Indeed, recent interest in the carotenoids has been mainly for their nutraceutical properties. A large number of scientific studies have confirmed the benefits of carotenoids to health and their use for this purpose is growing rapidly. In addition, carotenoids have traditionally been used in food and animal feed for their color properties. Carotenoids are also known to improve consumer perception of quality; an example is the addition of carotenoids to fish feed to impart color to farmed salmon.

Microalgae-mediated chemicals production and wastes removal

Abstract Biotechnology of microalgae has gained importance in recent years due to the development of new production and environmental technologies. Because their growth requires unexpensive substrates such as solar light and CO 2 , microalgae can be used as cheap and effective biocatalysts to obtain high added-value compounds, from simple metabolites to complex molecules, i.e., chemicals, vitamins, carotenoids, pigments, or polysaccharides. During productive processes, the algal biomass formed may be used as a food source like proteins. On the other hand, microalgae can also be employed in contaminant bioelimination processes especially for nitrogen, phosphorus, or sulfur compounds. Particularly relevant is their use for heavy metal removal from wastewaters; upon enriching the biomass in the metal, they can be recovered, thereby providing economic advantages. The use of immobilized microalgae in these processes is very adequate and offers significant advantages in bioreactors.

STUDIES ON THE SUITABILITY OF ALGINATE-ENTRAPPED CHLAMYDOMONAS REINHARDTII CELLS FOR SUSTAINING NITRATE CONSUMPTION PROCESSES

Some aspects of the suitability of alginate beads entrapping Chlamydomonas reinhardtii cells for nitrate consumption from nitrate-containing waters were studied and discussed. Among 14 different metal cations tested as gel bead stabilizing agents, only calcium and barium formed beads showing nitrate-consuming activity. Pure calcium alginate cell entrapment resulted in the most suitable method for active cell immobilization compared to alginate-composite-gel beads based on poly-vinylcaprolactam (PVCL) and poly-vinylpyrrolidone (PVP). To perform a continuous nitrate consumption process, calcium alginate-entrapped cells were first grown in a 2.5 l airlift-loop reactor. A cell loading of about 150 microg Chl. g(-1) gel was achieved. Afterwards, five days nitrate consumption processes were performed and three different dilution rates were applied: (i) D < mu; (ii) D = mu; (iii) D > mu, where mu is the specific growth rate (h(-1)). The maximum consumption rates calculated for each dilution rate were: (i) 3.8, (ii) 6.4 and (iii) 7.2 mg nitrate mg(-1) Chl. h(-1). For low dilution rates (D < mu) some nitrite (< 300 microM) was excreted into the culture medium. However, this concentration of nitrite was not high enough to inhibit nitrate consumption.

Organic solvent toxicity in photoautotrophic unicellular microorganisms

Abstract The use of aqueous-organic two-phase systems in microalgae biocatalyzed processes can improve productivity and overcome lack of water solubility and poor extracellular excretion of many natural products produced by microalgae. In the present work the toxic effect of various solvents belonging to two different homologous series on several marine and freshwater microalgae and one cyanobacteria have been studied. Typical sigmoidal plots were obtained when plotting solvent biocompatibilty versus the Hansh parameter “log Poct” (logarithm of the solvent partition coefficient in a standard octanol/water system). Tolerance of microalgae was found to be intermediate between that reported for bacteria and for plant cell suspensions. Anabaena, a blue-green alga with more similarities with bacteria than the others algae studied, was found the most tolerant. Good correlation was found between the aqueous critical solvent concentration and the Hansh parameter for all the microalgae studied. The membrane critical solvent concentration for each microalgae was calculated applying Osborne’s model. The protective effect of cell immobilization by gel entrapment against solvent toxicity has also been investigated, and surprisingly good results were obtained even for long-term experiments.

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.

Diffusion characteristics of nitrate and glycerol in alginate

Diffusion characteristics of nitrate through calcium-alginate gel beads were studied and compared to diffusion of glycerol, a non-charged small molecule. Compared to the theoretical effective nitrate diffusion coefficients in gel beads of different alginate concentrations, calculated by the Mackie and Meares approach, experimental nitrate diffusion through alginate of different characteristics showed significant differences. When the residence time of gel beads in calcium chloride solution was increased from 10 to 60 min, 30% more nitrate diffused from outside to inside the polymeric matrix. When alginate concentration was varied from 3 to 6%, 25% less nitrate diffused from inside to outside alginate gel beads. In addition, experimental diffusion of a non-charged heavier molecule (glycerol) occurred faster than the one for nitrate. Significantly minor diffusion (some 30%) through alginate gel beads was found for a positive ion, ammonium. In this paper such differences mentioned above are discussed to be due to the possible electrostatic interactions between the negative charge of nitrate and calcium clusters around the polymer surface. These results could have significance in the field of inorganic nitrogen bioelimination using immobilized photosynthetic cells.

Iodine speciation in iodine-enriched microalgae Chlorella vulgaris

The characterization of iodine species in the microalgae Chlorella vulgaris after cultivation with different potassium iodide concentrations was performed using the coupling of multidimensional chromatography (size exclusion chromatography, SEC, and anion exchange chromatography, AEC) with inductively coupled plasma-mass spectrometry (ICP-MS) detection. Two iodine fractions, water-soluble and macromolecular fractions, were obtained using a sequential extraction scheme based on chemical reagents. Most iodine species separated from the water-soluble fraction with SEC-ICP-MS (mass range from 0.5 to 100 kDa) are present in inorganic forms (peak III), although the other two peaks were detected (peaks I and II). The application of AEC to the isolated peak III fraction allows the characterization of IO3– (about 25 %) and I– (about 75 %). The application of SEC-ICP-MS (mass range from 10 to 1200 kDa) to the macromolecular fraction reveals the presence of four peaks from the void volume to about 67 kDa, a peak is located about 600 kDa. The mass balance of iodine in the different fractions obtained from the microalgae raw stuff shows that the water-soluble fraction represents 66.7 % of total iodine in microalgae, but the macromolecular fraction only contains 13.3 %, both summing up for 79.9 % of the total amount of iodine, which confirms the suitability of the separation scheme. Further studies have to be focused on the purification of the isolated fractions and their identification by tandem MS.

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 “rocks 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.

Microalgae: Fast-Growth Sustainable Green Factories

Microalgae are definitely on the way to become a sustainable, fast-growing natural green source for highly demanded market products. Research is currently looking at promising outstanding applications of microalgae among which are the production of biofuels from the fatty acids present in biomass, functional foods enriched with microalgae healthy bioactive molecules, and greenhouse gas mitigation (CO2 consuming) based on high cell density microalgae cultures technology. Besides, other traditional microalgae applications are currently increasing in competitiveness in a growing market demand for green biomass, in which microalgae are widely recognized as a healthy, sustainable, and biological renewable resource. Among these traditional applications, microalgae are being used to improve the nutritional quality in animal feed, particularly in aquaculture, therapeutic agent source, and antioxidant activity. In addition, microalgae also show to be functional in waste effluents treatment to remove N and P, thus preventing eutrophication, heavy metals, and others contaminants. This review intends to offer a comprehensive overview of basic aspects of microalgae physiology, massive production of biomass, and current fields of applications at industrial scale.

IDENTIFICATION AND PHYSIOLOGICAL ASPECTS OF A NOVEL CAROTENOID-ENRICHED, METAL-RESISTANT MICROALGA ISOLATED FROM AN ACIDIC RIVER IN HUELVA (SPAIN)1

A heavy‐metal‐resistant, carotenoid‐enriched novel unicellular microalga was isolated from an acidic river in Huelva, Spain. The isolated ribosomal 18S subunit rDNA sequence showed homology with known sequences from green microalgae, the closest sequence (98% homology) belonging to the genus Coccomyxa. The isolated microalga therefore was an up to now uncultured microalga. The microalga was isolated from Tinto River area (Huelva, Spain), an acidic river that exhibits very low pH (1.7–3.1) with high concentrations of sulfuric acid and heavy metals, including Fe, Cu, Mn, Ni, and Al. Electron micrographs show that the microalga contains a large chloroplast with a presence of lipid droplets, an increased number of starch bodies as well as electron‐dense deposits and plastoglobules, the last observed only in iron‐exposed cells. Unlike other acidophile microalgae, the isolated microalga showed high growth rates when cultivated photoautotrophycally (up to 0.6 d−1) in a suitable culture medium prepared at our laboratory. The growth was shown to be iron dependent. When the microalga is grown in fluidized bed reactors, the high growth rates resulted in unexpectedly high productivities for being a microalga that naturally grows in acidic environments (0.32 g·L−1·d−1). The microalga also grows optimally on reduced carbon sources, including glucose and urea, and at an optimal temperature of 35°C. The alga pigment profile is particularly rich in carotenoids, especially lutein, suggesting that the microalga might have potential for antioxidant production, namely, xanthophylls.