Ephraim Cohen

A closed system for outdoor cultivation of Porphyridium

Abstract Experience accumulated during the past few years indicates that the main problems in the large-scale cultivation of algae in open ponds are low productivity and contamination. Thus, the use of closed systems can be an alternative method of cultivation. In the present study, a closed system made of polyethylene sleeves was compared with open ponds with respect to growth and polysaccharide production of two species of Porphyridium: Porphyridium sp. and P. aerugineum. For both species, cell number, biomass, and polysaccharide production were higher in the sleeves than in the ponds. It seems that polyethylene sleeves have the following advantages over open ponds: high light availability, high rate of heating and cooling, improved turbulence, relative lack of contamination, and prevention of evaporation and hence of fluctuation in salinity.

Accumulation of Secondary Carotenoids in Chlorella zofingiensis

Summary We have previously found that in Chlorella emersonii , grown under synergistic conditions of high irradiance and low nitrogen, chlorophyll and primary carotenoids were degraded, whereas secondary carotenoids were produced. In this study Chlorella zofingiensis was cultivated under similar conditions. Maximal growth was achieved in a culture growing under light irradiance of 150 μmol quanta m -2 s -1 and a nitrogen concentration of 0.5 mg/mL of KNO 3 . Higher nitrogen concentrations or higher irradiance inhibited cell division. The secondary carotenoids produced were identified as canthaxanthin (about 30 %) and astaxanthin (about 70 %) in the form of mono- and diesters. Maximal accumulation occurred in cells starved of nitrogen and grown at a light irradiance of 300 μLmol m -2 s -1 . Exposure of a thin layer of algal cells to sunlight resulted in de-esterification of the astaxanthin esters. It is suggested that secondary carotenoids have a photo-protective role, that is, under high light conditions they protect chlorophyll and other photosynthetic pigments against damage.

The effect of salt stress on the production of canthaxanthin and astaxanthin by Chlorella zofingiensis grown under limited light intensity

The fresh water green microalga Chlorella zofingiensisis known to accumulate ketocarotenoids – primarily astaxanthin but also canthaxanthin – when grown under stress conditions of high light irradiance and low nitrogen. We found that salt stress can replace light stress with respect to inducing carotenoid production: cells of C. zofingiensis grown under low light irradiance and subjected to salt and low nitrogen stress accumulated higher amounts of total secondary carotenoids than those growing under high light and low nitrogen stress. Furthermore, C. zofingiensis growing under conditions of salt stress and low light accumulated higher amounts of canthaxanthin than astaxanthin. It is suggested that for canthaxanthin accumulation under salt stress, light is not a limiting factor, but for astaxanthin accumulation high light irradiance is mandatory. These results may be applied in the future for the commercial production of canthaxanthin by C. zofingiensis in systems in which light availability is poor.

The potential of production of sulfated polysaccharides from Porphyridium

The environmental conditions prevailing in Israel make marine algae an attractive crop for the production of valuable chemicals. A marine species of Porphyridium seems to fit this purpose.

A closed system for outdoor cultivation of microalgae

Abstract The main problems in the large-scale cultivation of microalgae outdoors in open ponds are low productivity and contamination. To overcome these problems a closed system consisting of polyethylenes sleeves was developed. In a study conducted outdoors in the Negev area (Beer-Sheva, `En Yahav and Elat) the closed system was found to be superior to open ponds with respect to growth and production in a number of microalgae. In both closed and open systems, growth and production under continuous operation were higher than in batch cultivation. In continuous cultures the respective daily yields of dry matter and polysaccharides from the red microalga Porphyridium sp. were 17.7 and 7.4 g m −2 in the sleeves compared with 7.6 and 2.4 g m −2 in the ponds. With the aim of optimising growth and production the effect of sleeve diameters (10, 20 and 32 cm) on these parameters was investigated. Growth and polysaccharide production were superior in the narrow sleeves than in the wider sleeves. To scale up the system a unit of connected sleeves was developed, and the performance of various microalgae in the unit was investigated. The productivity in terms of biomass and polysaccharide production of the red microalga Rhodella reticulata was higher in sleeve units than in open ponds. β-carotene production by the green microalga Dunaliella bardawil and its isomer ratio (9- cis : all- trans ) were better in the sleeve unit than in open ponds. The sleeve system seems to have a significant advantage over open ponds, and its development and optimisation are under way.

Outdoor Cultivation of Microalgae in a Closed System for the Production of Valuable Biochemicals

A rapidly emerging area of biotechnology is the cultivation of microalgae, i.e., the use the photosynthetic machinery for the production of valuable chemicals. Attempts have been made to apply the mass culturing of microalgae for the production of biochemicals, proteins, and fuels (Soeder and Binsack, 1978; Shelef and Soeder, 1980; Barclay and Mcintosh, 1986; Richmond, 1986). However, only a few commercial successes have been reported, the most important being the production of s-carotene from the halotolerant alga Dunaliella (Ben Amotz and Avron, 1989). One of the major drawbacks limiting the mass cultivation of microalgae on a commercial scale is the problem of outdoor cultivation of these organisms on a large scale.