Shoshana (Malis) Arad

Production of spirulina biomass: Effects of environmental factors and population density

The effects of environmental conditions (solar irradiance and temperature) and population density on the production of Spirulina biomass are reported for cultures grown in outdoor ponds. Both the specific rate of photosynthesis, expressed on a chlorophyll basis, and the rate of respiration, on a protein basis, decreased as algal concentration increased. Higher specific growth rates were observed at lower population densities. Lower growth rates were associated with the light limitation in dense cultures for optimum conditions in the summer. Seasonal variation was observed in productivity. In summer light was the limiting factor whereas in winter the low daytime temperature appeared to impose the major limitation. It was found that the oxygen concentration in the culture can serve as a useful indicator of limiting factors and can also be used as a means of estimating the extent of such limitations.

Antioxidant activity of the polysaccharide of the red microalga Porphyridium sp

The cells of the red microalga Porphyridium UTEX 637 are encapsulated within a sulfated polysaccharide whose external part (i.e., the soluble fraction) dissolves into the medium. It is thought that the main function of the polysaccharide is to protect the algal cells from the extreme environmental conditions, such as drought and high light, prevailing in their native sea-sand habitat. In this study, we evaluated the antioxidant properties of the water-soluble polysaccharide of Porphyridium sp. by determining the ability of a polysaccharide solution to inhibit: (1) autooxidation of linoleic acid, as determined by the standard thiobarbituric acid (TBA) and ferrous oxidation (FOX) assays; and (2) oxidative damage to 3T3 cells as determined by the dichlorofluorescein (DCFH) assay. In all three assays, the polysaccharide inhibited oxidative damage in a dose-dependent manner. Antioxidant activity was also exhibited by fractions of the polysaccharide obtained by sonication followed by separation on a reverse-phase HPLC with a C8 semi-preparative column. It is suggested that the antioxidant activity of the sulfated polysaccharide protects the alga against reactive oxygen species produced under high solar irradiation, possibly by scavenging the free radicals produced in the cell under stress conditions and transporting them from the cell to the medium.

Activity of Porphyridium sp. polysaccharide against herpes simplex viruses in vitro and in vivo

The cell wall sulfated polysaccharide of the red microalga Porphyridium sp. exhibited impressive antiviral activity against herpes simplex virus types 1 and 2 (HSV-1 and -2) both in vitro (cell culture) and in vivo (rats and rabbits). Depending on the concentration, this polysaccharide completely inhibited or slowed down the development of the cytopathic effect in HSV-infected cells, but did not show any cytotoxic effects on vero cells even when a concentration as high as 250 microg/ml was used. There was indirect evidence for a strong interaction between the polysaccharide and HSV and a weak interaction with the cell surface. When tested in vivo, Porphyridium sp. polysaccharide conferred significant and efficient protection against HSV-1 infection: at a concentration as low as 100 microg/ml, it prevented the appearance and development of symptoms of HSV-1 infection in rats and rabbits. The polysaccharide did not exhibit any cytotoxic effects at a concentration of 2 mg/ml in vivo.

Light/dark cycles in the growth of the red microalga Porphyridium sp.

The effect of light/dark cycles on the growth of the red microalga Porphyridium sp. was studied in a tubular loop bioreactor with light/dark cycles of different frequencies and in two 35-L reactors: a bubble column reactor and an air-lift reactor. Photon flux densities were in the range of 50 to 300 μE m-2 s-1, and flow rates were 1 to 10 L min-1. Under conditions of low illumination and high flow rates, similar results were obtained for the bubble column and air-lift reactors. However, higher productivities-in terms of biomass and polysaccharide-were recorded in the air-lift reactor under high light intensity and low gas flow rates. The interactions of both photosynthesis and photoinhibition with the fluid dynamics in the bioreactors was taken as the main element that allowed us to interpret the differences in performance of the bubble column and the air-lift reactor. It is suggested that the cyclic distribution of dark periods in the air-lift reactor facilitates better recovery from the photoinhibition damage suffered by the cells. Copyright 1998 John Wiley & Sons, Inc.

Sulfated polysaccharides from red microalgae have antiinflammatory properties in vitro and in vivo.

The primary goal of the present research was to determine whether sulfated polysaccharides derived from red microalgae possess anti inflammatory properties when directed against specific parameters of human skin inflammation. These unique biopolymers were studied in both in vitro and in vivo models of skin inflammation. Human subjects were recruited to participatein a study in which the polysaccharide material was applied topically and shown to inhibit cutaneousery thema induced by a known irritant. Leukocyte migration from capillary blood intosites of inflammation is an essential component of the inflammatory process and occurs in a series of steps, two of which are adhesion and chemotaxis. In vitro, the polysaccharide material primarily inhibited the migration of polymorphonuclear leukocytes (PMNs) toward a standard chemoattractant molecule and also partially blocked adhesion of PMNs to endothelial cells. The data obtained strongly suggest that sulfated polysaccharides derived from red microalgae have significant beneficial potential for use in topical products. In addition, the data suggested that the anti inflammatory mechanism for the polysaccharide was, at least in part, due to inhibition of circulating immune cell recruitment toward inflammatory stimuli.

Chickens fed with biomass of the red microalga Porphyridium sp. have reduced blood cholesterol level and modified fatty acid composition in egg yolk.

The biomass of the red alga Porphyridium sp.constitutes a unique combination of soluble sulfatedpolysaccharide that accounts for about 70% of thealgal dry weight, and various polyunsaturatedfatty acids (PUFA) such as arachidonic andeicosapentaenoic acid (AA, 20:4 ω6 and EPA,20:5 ω3). In view of earlier results in ourlaboratory showing a reduction in serum cholesteroland triglyceride levels in rodents fed with red algalbiomass, we set out to examine the influence of algalbiomass as a feed additive on the metabolism ofchickens, with an emphasis on blood and eggcholesterol levels. For that purpose, lyophilizedalgal biomass was fed to 12–13, 30-week-old, WhiteLeghorn chickens for 10 days at a proportion of 5% or10% of the standard chicken diet. Twelve chickensfed with unsupplemented diet served as the control. No differences in body weight, egg number, and eggweight were found between the algal-fed chickens (atboth concentrations) and the control. However,chickens fed with algal biomass consumed 10% lessfood for both groups, and their serum cholesterollevels were significantly lower (by 11% and 28% forthe groups fed with 5% and 10% supplement,respectively) as compared with the respective valuesof the control group. Egg yolk of chickens fed withalgae tended to have reduced cholesterol levels (by10%) and increased linoleic acid and arachidonic acidlevels (by 29% and 24%, respectively). In addition,the color of the egg yolk was darker as a result ofthe higher carotenoid levels (2.4 fold higher) forchickens that fed with 5% supplement. Theseresults encourage the development of an improvedchicken feed having dietary fibers and polyunsaturatedfatty acids.

The extracellular polysaccharides of the red microalgae : chemistry and rheology

Abstract Cells of red microalgae encapsulated within sulphated polysaccharides, are thought to have a wide range of potential industrial applications. Our group is thus carrying out a comprehensive research program aimed at bringing these biopolymers into industrial use. The program includes physiological studies on polysaccharide production, outdoor cultivation of the microalgae, and characterisation of the polysaccharides. Chemical composition and structure and physicochemical properties were investigated for the polysaccharides of three red microalgae, Porphyridium sp., P. aerugineum and Rhodella reticulata . Differences were found among the three species in the composition of the monosugars, half ester sulphate groups and glucuronic acid content, but a disaccharide isolated was identical in all the species examined. This disaccharide is thought to be the basic building block of these polysaccharides. In addition, monosugar sulphates were isolated and characterised. Fractionation by charge showed the polysaccharides to be heterogenous and composed of at least two fractions that differed in their composition. Although the polysaccharides differed in composition, their rheological characteristics were found to be similar. Aqueous solutions of the biopolymers were stable over a wide range of pH values and temperatures and were compatible with monovalent cations. Mixtures of the algal polysaccharides with locust bean gum exhibited synergism and syneresis. When the gel strength was compared with that of agar gel at the same concentration the polysaccharide gels were found to be weaker.

Stable chloroplast transformation of the unicellular red alga Porphyridium species.

Red algae are extremely attractive for biotechnology because they synthesize accessory photosynthetic pigments (phycobilins and carotenoids), unsaturated fatty acids, and unique cell wall sulfated polysaccharides. We report a high-efficiency chloroplast transformation system for the unicellular red microalgaPorphyridium sp. This is the first genetic transformation system for Rhodophytes and is based on use of a mutant form of the gene encoding acetohydroxyacid synthase [AHAS(W492S)] as a dominant selectable marker. AHAS is the target enzyme of the herbicide sulfometuron methyl, which effectively inhibits growth of bacteria, fungi, plants, and algae. Biolistic transformation of synchronized Porphyridium sp. cells with the mutant AHAS(W492S) gene that confers herbicide resistance gave a high frequency of sulfomethuron methyl-resistant colonies. The mutant AHAS gene integrated into the chloroplast genome by homologous recombination. This system paves the way for expression of foreign genes in red algae and has important biotechnological implications.

Red microalgal cell-wall polysaccharides: biotechnological aspects.

The area of sugars and glycosylation is not as well developed as other fields in cell biology owing to biotechnological constraints. However, the biotechnological potential of sugars, including polysaccharides, is the driving force pushing research efforts to meet the challenge. Algae produce cell-wall sulfated polysaccharides, with those of the red unicells, which dissolve into the medium, having unique characteristics-structure, composition, fluid dynamics, and extreme stability. These characteristics, combined with polysaccharide bioactivities, offer a vast range of potential applications. Research has thus been directed toward an in-depth understanding of the molecular structure, biosynthesis, and characteristics of the red microalgal sulfated polysaccharides and to the development of molecular-genetic tools, aiming at large-scale production for applications that can benefit humanity.

Pigment and Structural Changes in Chlorella zofingiensis upon Light and Nitrogen Stress

Summary The green alga Chlorella zofingiensis was found to respond very rapidly to exposure to combined conditions of high light intensity and nitrogen deficiency by accumulation of secondary carotenoids. Accumulation of secondary carotenoids was detected as early as 60 min after induction to light stress (300 μmol·m−2. s−1) in a nitrogen-free medium. Canthaxanthin and astaxanthin (free and monoesters) were detected 2–3 h later, and after an additional 12 h an astaxanthin diester also appeared. The accumulation of total secondary carotenoids was linear in relation to time. After 24 h the main secondary carotenoids were the monoester of astaxanthin (about 50% of total secondary carotenoids) and canthaxanthin (20–25%). During the first 8 h of stress the content of the primary carotenoids β-carotene and lutein increased but subsequently the content of both chlorophyll and the primary carotenoids was reduced. The reduction in the content of the photosynthetic pigments was followed by a degradation of the thylakoids and a reduction of the potential rate of photosynthesis (α), but not of Pmax. After 3 days under light stress the chloroplast was modified to a chromoplast-like organelle, full of secondary carotenoids and free of thylakoid membranes. Twelve hours after the induction of stress, lipid bodies containing secondary carotenoids appeared around the chloroplast and accumulated at the periphery of the cell. The profile of the secondary carotenoids in the lipid bodies was similar to that in the chromoplast, both containing double the amount of astaxanthin diester and half the amount of free astaxanthin as compared with total cell carotenoids. After 3 days under stress, a hydrophobic layer rich in secondary carotenoids formed inside the cell wall. Our results suggested that the lipid layer functions as a light filter to reduce irradiation of the cell components, to prevent photooxidative damage and to reduce water losses.