Commercial production of intracellular microalgal metabolites requires the following: (1) largescale monoseptic production of the appropriate microalgal biomass; (2) recovery of the biomass from a relatively dilute broth; (3) extraction of the metabolite from the biomass; and (4) purification of the crude extract. This review examines the options available for recovery of the biomass and the intracellular metabolites from the biomass. Economics of monoseptic production of microalgae in photobioreactors and the downstream recovery of metabolites are discussed using eicosapentaenoic acid (EPA) recovery as a representative case study. D

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Lutein is an antioxidant that has gathered increasing attention due to its potential role in preventing or ameliorating age-related macular degeneration. Currently, it is produced from marigold oleoresin, but continuous reports of lutein-producing microalgae pose the question if those microorganisms can become an alternative source. Several microalgae have higher lutein contents than most marigold cultivars and have been shown to yield productivities hundreds of times higher than marigold crops on a per square meter basis. Microalgae and marigold are opposite alternatives in the use of resources such as land and labor and the prevalence of one or the other could change in the future as the lutein demand rises and if labor or land becomes more restricted or expensive in the producing countries. The potential of microalgae as a lutein source is analyzed and compared to marigold. It is suggested that, in the current state of the art, microalgae could compete with marigold even without counting on any of the improvements in microalgal technology that can be expected in the near future.

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A dynamic model of photosynthesis is developed, accounting for factors such as photoadaptation, photoinhibition, and the "flashing light effect." The model is shown to explain the reported photosynthesisirradiance responses observed under various conditions (constant low light, constant intense irradiance, flashing light, diurnal variation in irradiance). As significant distinguishing features, the model assumes: (1) The stored photochemical energy is consumed in an enzymemediated process that obeys Michaelis-Menten kinetics; and (2) photoinhibition has a square-root dependence on irradiance. Earlier dynamic models of photosynthesis assumed a first-order dependence of photoinhibition on irradiance and different kinetics of consumption of the stored energy than used in this work. These earlier models could not explain the photosynthesis-irradiance behavior under the full range of irradiance scenarios-a shortcoming that is overcome in the model developed in this work.

The in¯uence of culture age and nitrogen concentration on the distribution of fatty acids among the dierent acyl lipid classes has been studied in continuous cultures of the microalga Phaeodactylum tricornutum. The culture age was tested in the range of 1.15±7 days, controlled by adjusting the dilution rate of fresh medium supplied. The eect of nitrogen concentration was tested from saturating conditions to starvation by modifying nitrate concentration in the fresh medium. Culture age had almost no in¯uence on the fatty acid content; 16:0, 16:3 and 20:5 increased moderately wherein the level of 16:1 decreased when the culture age decreased. Culture age had no eect on the total fatty acid content that remained around 11% of dry weight. Conversely, culture age had a greater impact on lipid classes, producing changes in amounts of triacylglycerols (TAG) which ranged between 43% and 69%, and galactolipids (GLs) that oscillated between 20% and 40%. In general, the content of polar lipids of the biomass decreased with culture age. The other factor assayed, nitrogen content, aected the fatty acid pro®le. Saturated and monounsaturated fatty acids accumulated when the nitrogen concentration was decreased. The experiments regarding the eect of nitrogen concentration on lipid species were carried out with cells of an average age of 3.5 days. A decrease of the nitrogen concentration caused the GL fraction to decrease from 21 to 12%. Conversely, both neutral lipids (NLs) and phospolipids (PLs) increased from about 73 to 79% and from 6 to 8%, respectively. In these experiments, TAG was the lipid class with the highest increase, from 69 to 75%. 7

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In this paper, worldwide research trends in the microalgae field are analyzed based on a bibliometric study. We have looked at the number of publications and their distribution, as well as the most relevant journals and keywords, to determine the evolution and latest tendencies in this field. The results confirm that this is a fast-growing area in terms of the number of publications. The most relevant journals on this subject are Bioresource Technology and Algal Research. Although the majority of papers come out of the USA, the most relevant institutions are actually located in China, France and Spain. The most frequently cited strains are Chlorella and Chlamydomonas. The main keywords that appear in over 1,000 articles are generally related to microalgae cultivation applications such as 'biomass, biofuel, and lipids' while others are related to the methodology; for instance, 'bioreactor'. Of all the keywords, 'biomass' stands out, as it appears in almost 20% of publications. Bibliographic analysis confirms that Microalgae Biotechnology is a very active field, where scientific productivity has exponentially increased over recent years in tandem with industrial production. Therefore, expectations are high in this field for the near future.