A number of important advances have occurred in microalgal biotechnology in recent years that are slowly moving the field into new areas. New products are being developed for use in the mass commercial markets as opposed to the “health food” markets. These include algal‐derived long‐chained polyunsaturated fatty acids, mainly docosahexaenoic acid, for use as supplements in human nutrition and animals. Large‐scale production of algal fatty acids is possible through the use of heterotrophic algae and the adaptation of classical fermentation systems providing consistent biomass under highly controlled conditions that result in a very high quality product. New products have also been developed for use in the development of pharmaceutical and research products. These include stable‐isotope biochemicals produced by algae in closed‐system photobioreactors and extremely bright fluorescent pigments. Cryopreservation has also had a tremendous impact on the ability of strains to be maintained for long periods of time at low cost and maintenance while preserving genetic stability.
The time course of light-induced 02 exchange by isolated intact chloroplasts and cells from spinach was determined under various conditions using isotopicaUy labeled 02 and a mass spectrometer. In dark-adapted chloroplasts and ceUs supplemented with saturating amounts of bicarbonate, 02 evolution began immediately upon ilumination. However, this initial rate of 02 evolution was counterbalanced by a simultaneous increase in the rate of 02 uptake, so that little net 02 was evolved or consumed during the first 1 I minute of illumination. After this induction (lag) phase, the rate of 02 evolution increased 3 to 4-fold while the rate of 02 uptake diminished to a very low level. Inhibition of the Calvin cycle, e.g. with DLglyceraldehyde or iodoacetamide, had negligible effects on the initial rate of 02 evolution or 02 uptake; both rates were sutained for several minutes, and about balanced so that no net 02 was produced. Uncouplers had an effect similar to that observed with Calvin cycle inhibitors, except that rates of 02 evolution and photoreduction were stimulated 40 to 50%.These results suggest that higher plant phostosynthetic preparations which retain the ability to reduce CO2 also have a significant capacity to photoreduce 02. With (5,6,12,14,15,17). Here, we determined the magnitude and kinetics of 02 evolution and reduction in isolated intact chloroplasts and whole cells obtained from spinach using a mass spectrometer with a fast mass stepper system. Significant rates of 02 reduction are shown to occur principally when CO2 fixation reactions are suboptimal. MATERIALS AND METHODSIntact chloroplasts were isolated from greenhouse-grown spinach as described previously (26). Preparations contained more than 70%/o intact chloroplasts as determined by the ferricyanide reduction method (13) and fixed CO2 at rates in excess of 100 ,umol/mg Chl * h in saturating light. Chloroplasts were routinely assayed in a 0.33 M sorbitol, 50 mm Hepes-KOH (pH 8.0) medium containing 10 mm NaHCO3, 5 mm Na4P207, 2 mm EDTA, 0.25 mM K2HPO4, and catalase (195 units/ml). Other additions are indicated in the figure legends.Intact cells were prepared from freshly harvested spinach leaves sliced into small (0.5 x 2.0 cm) strips. Approximately 2 g of leaf strips were vacuum-infiltrated in 20 ml of media containing 0.8 M sorbitol, 20 mm Mes (pH 5.8) buffer, 12.5 mm K2SO4, and 0.75% Macerase (obtained from Calbiochem). Leaf strips were digested in 75 ml of the infiltration medium (maintained at 15 C) in an apparatus similar to that described by Servaites and Ogren (23
Microalgae are a very diverse group of organisms that consist of both prokaryotic and eukaryotic forms. Although most microalgae are phototrophic, some species are also capable of heterotrophic growth. Some species of microalgae can be induced to overproduce particular fatty acids through simple manipulations of the physical and chemical properties of the culture medium. As a result of the profound differences in cellular organization and growth modes and the ability to manipulate their fatty acid content, microalgae represent a significant source of unusual and valuable lipids and fatty acids.The utilization of microalgal lipids and fatty acids as food components requires that these organisms be grown at large scale under controlled conditions. Several growth systems have been developed for large scale growth of phototrophic microalgae using either natural sunlight or artificial light, but their lack of control of culturing parameters or their high cost of operation have limited their utility for the production of food products. Instead, large scale cultivation of heterotrophic microalgae using classical fermentation systems provides consistent biomass produced under highly controlled conditions at low cost.Microalgae contain many of the major lipid classes and fatty acids found in other organisms. However, they are also the principal producers in the biosphere of some polyunsaturated fatty acids, especially docosahexaenoic acid (DHA). The high DHA content found in some algae is currently being utilized to supplement infant formula to enable it to more closely resemble human breast milk. Thus, the commercialization of DHA from microalgae demonstrates the value of these organisms as a source of useful fatty acids.
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