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$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 beta-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.

No abstract

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).

No abstract

No abstract

No abstract

The effect of boron on heterocystous and nonheterocystous dinitrogen fixing Cyanobacteria was examined. The absence of boron in culture media inhibited growth and nitrogenase activity in Nodularia sp., Chlorogloeopsis sp., and Nostoc sp. cultures. Examinations of boron-deficient cultures showed changes in heterocyst morphology. However, cultures of nonheterocystous Cyanobacteria, Gloeothece sp. and Plectonema sp., grown in the absence of boron did not show any alteration in growth or nitrogenase activity. These results suggest a requirement of boron only by heterocystous Cyanobacteria. A possible role for this element in the early evolution of photosynthetic organisms is proposed.

The effect of boron on nitrogenase activity has been studied. When cells were dependent on N2 fixation, the lack of boron inhibited nitrogen-ase activity. However, under anaerobic conditions or in the presence of Na-dithionite this effect was not observed. Nitrogenase synthesis was not affected by boron deficiency. Similarly, the heterocyst number was not altered. Examination of boron-deficient cultures showed, however, some dramatic changes in heterocyst morphology. The increased activity of those enzymes related to the maintaining of the low intracellular level of toxic oxygen species (superoxide dismutase, catalase, and peroxidase) support our hypothesis of the role of boron in heterocyst envelope stabilization. The essentiality of boron has been recognized in higher plants for many years. However, there is a lack of agreement on the boron requirement of algae, fungi, and bacteria (23). Among cyanobacteria, the requirement for boron is not a general feature. In a previous paper (14), we presented evidence showing that boron is not required for the growth of Anacystis nidulans. Furthermore, Anabaena PCC 7119, a dinitrogen-fixing cyano-bacterium, cultured in presence of combined nitrogen was not affected by boron deficiency. However, when this microorganism was grown under dinitrogen-fixing conditions lacking in boron, an inhibition growth was observed (1). More direct proof that boron is involved in nitrogen fixation arises from the results measuring nitrogenase activity. In boron-deficient cells of Anabaena PCC 7119, nitrogenase activity was found to be depleted to 40% of its normal value after 2 h of deficiency, a time at which other metabolic processes were not affected by boron-deficiency (15). Nevertheless, the physiological role of boron in N2 fixation in these organisms is unclear. The role ofboron might be in the stabilization ofthe heterocyst envelope, as has been proposed for higher plant cell membranes (16). A boron deficiency could lead to a rapid modification of envelope conformation increasing the rate of oxygen diffusion into the heterocyst. A similar effect has been described for Ca2. In Gloeothece, Ca2`Ca2`deprivation causes a rapid oxygen inhibition of nitrogenase activity in light but not in the dark; this has been attributed to an effect on membranes which afford 02 protection (10). The goal of this study was to investigate the role of boron in nitrogenase synthesis and activity as well as the mechanisms for protection against 02 diffusion. 'This work was supported in part by Explosivos Rio Tinto. MATERIALS AND METHODS Culture Conditions. The cyanobacterium Anabaena PCC 7119 was grown in 1-L polyethylene bottles at 26°C in batch cultures gassed with air under a constant light intensity of 90 ,uE-m-2 e s '. Media and cells free of boron were prepared and process as previously described (15). Analytical Methods. Culture density was determined at 600 nm. For dry weight determination, cells were collected on 0.45 ,um filters, washed, and dried at 70°C for 24 h. Estimation of Heterocyst Frequenc...