Carlos Vílchez

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.

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 2,100 µmol photons m−2 s−1 with red light emitting diodes (LEDs) 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 37°. Chlorella sorokiniana, a fast‐growing green microalga, was used as a reference strain in this study. The dilution rate was varied from 0.06 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 dw m−2 h−1 (m2 of illuminated photobioreactor surface) and a volumetric productivity of 0.5 g dw 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 dw 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. Biotechnol. Bioeng. 2009; 104: 352–359

Horizontal or vertical photobioreactors? How to improve microalgae photosynthetic efficiency

The productivity of a vertical outdoor photobioreactor was quantitatively assessed and compared to a horizontal reactor. Daily light cycles in southern Spain were simulated and applied to grow the microalgae Chlorella sorokiniana in a flat panel photobioreactor. The maximal irradiance around noon differs from 400 μmol photons m(-2) s(-1) in the vertical position to 1800 μmol photons m(-2) s(-1) in the horizontal position. The highest volumetric productivity was achieved in the simulated horizontal position, 4 g kg culture(-1) d(-1). The highest photosynthetic efficiency was found for the vertical simulation, 1.3g of biomass produced per mol of PAR photons supplied, which compares favorably to the horizontal position (0.85 g mol(-1)) and to the theoretical maximal yield (1.8 g mol(-1)). These results prove that productivity per unit of ground area could be greatly enhanced by placing the photobioreactors vertically.

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.

Carotenoids as protective response against oxidative damage in Dunaliella bardawil

In the present work the relation between carotenoids production and cell response mechanisms to oxidative damage was studied. High light intensity and nitrogen starvation, both conditions, which may increase the oxidative damage in microalgae, significantly increased total carotenoids content in Dunaliella bardawil, the effect of N-starvation being more noticeable when acting synergetically with light on carotenoid production. S-starvation stimulated carotenoids production as much as N-starvation. The use of norflurazon, inhibitor of phytoene desaturase that blocks formation of epsilon-carotene from phytoene, caused a decrease of carotenoid content down to 5% that of the control cells incubated without the inhibitor. The decrease in the oxygen consumption rate of D. bardawil cells exposed to norflurazon suggests a connection between carotenoids desaturation and chloroplastic oxygen species dissipation processes reported in the literature for other algae. It is an indication of the carotenoids involvement in chloroplastic response mechanisms to oxidative damage.

Microalgae mediated photoproduction of β-carotene in aqueous–organic two phase systems

Improving productivity is a usual requirement for most biotechnological processes, and the utilisation of two-phase aqueous organic systems has proved to be an effective way to improve the productivity of poorly water-soluble or toxic compounds. The high hydrophobicity of beta-carotene, which is highly demanded by the pharma and agrofood industry, makes it a good candidate for aqueous/organic biphasic photoproduction. In the present work we have investigated the viability of a two-phase system for the production of beta-carotene by the marine microalgae Dunaliella salina using decane as organic phase. Decane, with a logP(octanol) value of 5.6, showed no toxicity to Dunaliella cells for more than 72 h, and its ability for beta-carotene extraction is acceptable. Transferring Dunaliella cells from standard to carotenogenic conditions caused inhibition of chlorophyll production and induced a strong synthesis of beta-carotene. The two-phase aqueous/decane system was stable and beta-carotene content of the cells was increasing during 4-days. About 8% of the total carotenoids produced were excreted and extracted into the decane phase.

β-Carotene production enhancement by UV-A radiation in Dunaliella bardawil cultivated in laboratory reactors

beta-carotene is an antioxidant molecule of commercial value that can be naturally produced by certain microalgae that mostly belong to the genus Dunaliella. So far, nitrogen starvation has been the most efficient condition for enhancing beta-carotene accumulation in Dunaliella. However, while nitrogen starvation promotes beta-carotene accumulation, the cells become non-viable; consequently under such conditions, continuous beta-carotene production is limited to less than 1 week. In this study, the use of UV-A radiation as a tool to enhance long-term beta-carotene production in Dunaliella bardawil cultures was investigated. The effect of UV-A radiation (320-400 nm) added to photosynthetically active radiation (PAR, 400-700 nm) on growth and carotenoid accumulation of D. bardawil in a laboratory air-fluidized bed photobioreactor was studied. The results were compared with those from D. bardawil control cultures incubated with PAR only. The addition of 8.7 W.m(-2) UV-A radiation to 250 Wm(-2) PAR stimulated long-term growth of D. bardawil. Throughout the exponential growth period the UV-A irradiated cultures showed enhanced carotenoid accumulation, mostly as beta-carotene. After 24 days, the concentration of beta-carotene in UV-A irradiated cultures was approximately two times that of control cultures. Analysis revealed that UV-A clearly induced major accumulation of all-trans beta-carotene. In N-starved culture media, beta-carotene biosynthesis in UV-A irradiated cultures was stimulated. We conclude that the addition of UV-A to PAR enhances carotenoid production processes, specifically all-trans beta-carotene, in D. bardawil cells without negative effects on cell growth.

Metal toxicity in Chlamydomonas reinhardtii. Effect on sulfate and nitrate assimilation

Cadmium (Cd(2+)) or copper (Cu(2+)) ions are toxic for Chlamydomonas reinhardtii growth, at 300 microM, and the alga may accumulate about 0.90+/-0.02 and 0.64+/-0.02% of its dry weight, respectively. Metal contamination changes the elemental composition of dried alga biomass, which indicates the possibility to use C. reinhardtii as biosensor and bioremediator of the aquatic contamination by heavy metals. Either, Cd(2+) or Cu(2+), inhibits about 20% of the nitrate consumption rate by the cells, while only Cd(2+) increases about 40% the sulfate consumption rate. The presence of 1 mM calcium (Ca(2+)) in the culture medium increases the C. reinhardtii productivity (about 50%), the nitrate uptake rate (about 20%) and the sulfate uptake rate (about 30%). In addition, Ca(2+) overcomes the Cd(2+) (300 microM) toxicity by decreasing (about 35%) the intracellular accumulation of metal. Sulfur-starvation induces in C. reinhardtii the expression of serine acetyltransferase and O-acetylserine(thiol)lyase activities, but decreases 50% the consumption rate of nitrate by the cells. Sulfate is also required for the full expression of the nitrate reductase (NR), nitrite reductase (NiR) and glutamate synthase activities.

Nitrite uptake by Chlamydomonas reinhardtii cells immobilized in calcium alginate

When an initial cell loading of about 30–40 µg chlorophyll (Chl)·g−1 gel and alginate suspension of 3% (w/v) were used for immobilization of Chlamydomonas reinhardtii, the resulting cell beads showed optimum nitrite uptake rate, at 30° C and pH 7.5, of 14 µmol NOinf2sup−·mg−1 Chl·h−1, the photosynthetic and respiratory activities being about 120 µmol O2 produced·mg−1 Chl·h−1, and 40 µmol O2 consumed ·mg−1 Chl·h−1, respectively. The nitrite uptake activity required CO2 in the culture and persisted after 8 days of cells immobilization, or in the presence of 0.2 mm ammonium in the medium. Our data indicate that alginate-entrapped C, reinhardtii cells may provide a stable and functional system for removing nitrogenous contaminants from waste-waters.

Luminostat operation: A tool to maximize microalgae photosynthetic efficiency in photobioreactors during the daily light cycle?

The luminostat regime has been proposed as a way to maximize light absorption and thus to increase the microalgae photosynthetic efficiency within photobioreactors. In this study, simulated outdoor light conditions were applied to a lab-scale photobioreactor in order to evaluate the luminostat control under varying light conditions. The photon flux density leaving the reactor (PFD(out)) was varied from 4 to 20 μmol photons m(-2)s(-1)and the productivity and photosynthetic efficiency of Chlorella sorokiniana were assessed. Maximal volumetric productivity (1.22g kg(-1)d(-1)) and biomass yield on PAR photons (400-700 nm) absorbed (1.27 g mol(-1)) were found when PFD(out) was maintained between 4 and 6 μmol photons m(-2)s(-1). The resultant photosynthetic efficiency was comparable to that already reported in a chemostat-controlled reactor. A strict luminostat regime could not be maintained under varying light conditions. Further modifications to the luminostat control are required before application under outdoor conditions.