Mercedes García-González

Outdoor cultivation of microalgae for carotenoid production: current state and perspectives.

Microalgae are a major natural source for a vast array of valuable compounds, including a diversity of pigments, for which these photosynthetic microorganisms represent an almost exclusive biological resource. Yellow, orange, and red carotenoids have an industrial use in food products and cosmetics as vitamin supplements and health food products and as feed additives for poultry, livestock, fish, and crustaceans. The growing worldwide market value of carotenoids is projected to reach over US

Conditions for open-air outdoor culture of Dunaliella salina in southern Spain

1,000 million by the end of the decade. The nutraceutical boom has also integrated carotenoids mainly on the claim of their proven antioxidant properties. Recently established benefits in human health open new uses for some carotenoids, especially lutein, an effective agent for the prevention and treatment of a variety of degenerative diseases. Consumers’ demand for natural products favors development of pigments from biological sources, thus increasing opportunities for microalgae. The biotechnology of microalgae has gained considerable progress and relevance in recent decades, with carotenoid production representing one of its most successful domains. In this paper, we review the most relevant features of microalgal biotechnology related to the production of different carotenoids outdoors, with a main focus on β-carotene from Dunaliella, astaxanthin from Haematococcus, and lutein from chlorophycean strains. We compare the current state of the corresponding production technologies, based on either open-pond systems or closed photobioreactors. The potential of scientific and technological advances for improvements in yield and reduction in production costs for carotenoids from microalgae is also discussed.

Assessment of carotenoid production by Dunaliella salina in different culture systems and operation regimes

The optimization of the operation, under the climatic conditions of southern Spain, of an experimental plant for β-carotene production by Dunaliella has been pursued. The effects of mixing, culture depth, cell density and dilution cycles on β-carotene and biomass productivity were studied under a semicontinuous culture regime in open tanks outdoors. Using 3 m2-surface containers, the highest productivity values, for both β-carotene and biomass, were recorded with a flow rate of 0.55 m s−1; 10 cm depth; 0.7 − 0.9 × 106cell ml−1, population density; and dilution cycles of two days. An average annual productivity of 1.65 g (dry wt) m−2 d−1 was estimated for Dunaliella biomass, being that for β-carotene of about 0.1 g m−2 d−1. Under these optimized conditions, experiments have been carried out at the Cadiz Bay with 20 m2-surface tanks during a whole-year cycle. The results obtained have validated this location and the operating conditions established as being most appropriate for efficient mass production of β-carotene rich D. salina.

Differential Toxicological Response to Cadmium in Anabaena strain PCC 7119 Grown with NO3- or NH4+ as Nitrogen Source

The effect of operation regime and culture system on carotenoid productivity by the halotolerant alga Dunaliella salina has been analyzed. Operation strategies tested included batch and semi continuous regime, as well as a two-stage approach run simultaneously in both, open tanks and closed reactor. The best results were obtained with the closed tubular photobioreactor. The highest carotenoid production (328.8 mg carotenoid l⁻¹ culture per month) was achieved with this culture system operated following the two-stage strategy. Also, closed tubular photobioreactor provided the highest carotenoid contents (10% of dry weight) in Dunaliella biomass and β-carotene abundance (90% of total carotenoids) as well as the highest 9-cis to all-trans β-carotene isomer ratio (1.5 at sunrise).

Sodium Requirement for Photosynthesis and Nitrate Assimilation in a Mutant of Nostoc muscorum

Summary The effect of free Cd 2+ ions on growth, photosynthesis, photosynthetic pigments (chlorophyll and phycobiliproteins), nitrate and ammonium uptake and divalent cation (Mg 2+ , Ca 2+ ) content in Anabaena PCC 7119 grown in a medium containing nitrate or ammonium was investigated. After 96 h of exposure, the metal causes an inhibition of photosynthesis in cells of Anabaena PCC 7119 growing in NH 4 + and NO 3 - media and a decrease in the photosynthetic pigments. Likewise, Cd 2+ toxicity elicited a reduction in the intracellular concentrations of Mg 2+ and Ca 2+ and an inhibition in ammonium uptake, resulting in changes in the cellular structure. The possible relation between the differential response in each culture medium and pH is discussed.

Ammonium-sensitive protein kinase activity in plasma membranes of the cyanobacterium Anacystis nidulans

Summary The requirement of sodium for photosynthesis and nitrate assimilation in a mutant of Nostoc muscorum, unable to fix dinitrogen, was examined. After 24 h of culture, sodium deficient cells showed changes in the contents of photosynthetic pigments as well as in photosynthesis and nitrate assimilation. Both CO2 consumption and photosynthetic oxygen evolution were reduced when cells were cultured for 24 h in absence of sodium. Similarly nitrate uptake was inhibited in sodium deficient cells. Nitrate reductase activity however was increased by 37% under these conditions. When assays were performed after 2 h of deficiency only the photosynthetic activities (both photofixation of CO2 and photoevolution of O2) were altered by the absence of sodium. These results suggest that the impairment of nitrate assimilation is a secondary effect of sodium deficiency and that the requirement of sodium for photosynthesis is independent of its effects on nitrate assimilation.

Assessment of the CO2 fixation capacity of Anabaena sp. ATCC 33047 outdoor cultures in vertical flat-panel reactors

Cytoplasmic membranes prepared from nitrate‐grown Anacystis nidulans cells exhibit a Mg2+‐dependent protein kinase activity able to phosphorylate in vitro plasma membrane polypeptides with molecular masses of 98, 93, 83, 47, 44 and 31 kDa. The protein kinase activity was inhibited in cytoplasmic membrane preparations from nitrate‐grown cells which had been exposed to ammonium for 5 min. Parallely, ammonium exposure also resulted in a more than two‐fold activation of an alkaline phosphatase activity present in the soluble fraction. These results are discussed in relation to the well‐known inhibition by ammonium of nitrate transport activity, and a hypothesis for the regulatory mechanism involved is presented.

Continuous culture methodology for the screening of microalgae for oil.

The extent of biological CO2 fixation was evaluated for outdoor cultures of the cyanobacterium Anabaena sp. ATCC 33047. Culture conditions were optimized indoors in bubble-column photochemostats operating in continuous mode, subjected to irradiance cycles mimicking the light regime outdoors. Highest values achieved for CO2 fixation rate and biomass productivity were 1 and 0.6 g L(-1) day(-1), respectively. The comparison among different reactors operating simultaneously - open pond, horizontal tubular reactor and vertical flat-panel - allowed to assess their relative efficiency for the outdoor development of Anabaena cultures. Despite the higher volumetric CO2 fixation capacity (and biomass productivity) exhibited by the tubular photobioreactor, yield of the flat-panel reactor was 50% higher than that of the tubular option on a per area basis, reaching values over 35 g CO2 fixed m(-2) d(-1). The flat-panel reactor actually represents a most suitable system for CO2 capture coupled to the generation of valuable biomass by Anabaena cultures.

Production of Dunaliella salina biomass rich in 9-cis-β-carotene and lutein in a closed tubular photobioreactor

A basic criterion in the selection of microalgae suitable as source of oil for biodiesel should be their actual capacity to produce lipids or, more properly, the fatty acid yield. Performance assessment of 10 preselected microalgae under both batch and continuous culture points to the latter approach as the most adequate for evaluating fatty acid productivity. Differences were patent in continuous culture among strains that otherwise had analogous oil accumulation potential under batch culture. Some promising strains under batch culture (like Muriella aurantiaca and Monoraphidium braunii) exhibited, however, values for actual fatty acid productivity lower than 40 mgL(-1)d(-1) in continuous regime. The analysis performed in photochemostat under continuous culture regime revealed the great potential of Chlorococcum olefaciens, Pseudokirchneriella subcapitata and Scenedesmus almeriensis as oil producing microalgae. Fatty acid productivity levels over 90 mgL(-1)d(-1) were recorded for the latter strains under moderate nitrogen limitation, conditions which led to an enrichment in saturated and monounsaturated fatty acids, a more suitable profile as raw material for biodiesel. The continuous culture methodology employed represents a sound procedure for screening microalgae for biofuel production, providing a reliable evaluation of their fatty acid production capacity, under conditions close to those of outdoor production systems.