Two-stage culture method for optimized polysaccharide production in Spirulina platensis.

BACKGROUND: The polysaccharides of Spirulina platensis possess many biological functions. Reproducing the conditions under which S. platensis produces polysaccharides is critical to furthering our understanding of the function of these polysaccharides for commercial mass production. The changes in microalgal polysaccharide production were studied under greenhouse and laboratory conditions using varying light intensities, temperatures, and NaCl concentrations. RESULTS: The polysaccharide yield was positively correlated with culturing under 192 µmol photons m(-2) s(-1) light intensity at 38 °C or in 0.75 mol L(-1) NaCl. However, NaCl reduced the total biomass productivity of S. platensis. To mitigate the negative effects of environmental stress on maximal polysaccharide production, we proposed a two-stage culture method. The first stage, designed to increase biomass production, involved culturing under 96 µmol photons m(-2) s(-1) light intensity at 28 °C. Following this, on achieving maximum biomass production, the second stage, designed to stimulate polysaccharide production, involved culturing under 192 µmol photons m(-2) s(-1) light intensity at 38 °C for 3 days or in a 0.75 mol L(-1) NaCl medium for 2 days. High-performance liquid chromatographic analysis revealed that S. platensis polysaccharides were composed of various monosaccharides, including glucose, galactose, rhamnose, mannose, fructose, and mannitol. CONCLUSION: The two-stage culture can be successfully applied to achieve the goal of polysaccharide mass production. The first stage focuses on rapidly increasing microalgal biomass. The second stage of culture conditions requires modification to maximize polysaccharide yield.

A SIMPLE METHOD FOR ISOLATING FILAMENTS AS "ALGAL SEED STOCK" FROM MONOSTROMA LATISSIMUM (CHLOROPHYTA) GERMLINGS, AND APPLICATION FOR MASS CULTIVATION(1).

Germlings were grown from Monostroma latissimum Wittr. reproductive cells on nylon ropes. Holdfast threads and some uniseriate filaments were observed to have penetrated the fibers of the dispersed ropes. The algal filaments were easily isolated and prepared for cultivation, in comparison to the methods of enzymatically isolated algal protoplasts. Under low light (60-100 µmol photons · m(-2) · s(-1) ), the algal filaments grew to form a filamentous mass. When cultivated under stronger light (300-600 µmol photons · m(-2) · s(-1) ), they grew to initially form tubular thalli and then, when cultivated under light intensities >700 µmol photons · m(-2) · s(-1) , formed foliaceous thalli. Consequently, the filaments were homogenized into small sections and then sewed on the nylon rope for algal mass cultivation. Under high-intensity natural light, they grew to form leafy thalli.

THE HORMESIS OF THE GREEN MACROALGA ULVA FASCIATA WITH LOW-DOSE (60) COBALT GAMMA RADIATION(1).

Homogenous germlings of the marine macroalga Ulva fasciata D. (synonym, Ulva lactuca L.) were used to study hormesis effects in macroalgae grown under a low dose of (60) Co γ-ray radiation. The results of this study are the first to confirm the effects of macroalgal hormesis. Here it was demonstrated that growth of U. fasciata germlings was promoted substantially under 15 Gy of (60) Co γ-ray radiation, with an average increase of algal biomass of 47.43%. The levels of polysaccharides and lipids varied among the tested material and showed no effects from the (60) Co γ-ray radiation. However, the amount of protein was higher in the irradiated algae than in the control; the highest protein content of the irradiated algae was 3.958% (dry weight), in contrast to 2.318% in nonirradiated samples. This technique was applied to a field algal mass culture, which decreased the harvest time from 90 to 60 d. The mass culture approach may facilitate the production of macroalgae under unstable weather conditions such as typhoons in the summer or strong waves in the winter. The mass-cultured macroalgae could be used as a source of bioenergy through the fermentation of algal simple sugars that derived from polysaccharides to produce ethanol.

DEVELOPMENT OF PROTOPLASTS OF ULVA FASCIATA (CHLOROPHYTA) FOR ALGAL SEED STOCK.

The aim of this study was to isolate and cultivate protoplasts of the green alga Ulva fasciata Delile and subsequently induce them to form a microthallus suspension for algal seed stock. The protoplasts were covered with secreted mucilage following 6 h of culture when viewed with SEM. The mucilage fused to form thick layers during day 1 of culture. Microfibrillar cell walls were deposited into the thick layers of mucilage on the 5th day of culture. An average of about 10% of the freshly isolated protoplasts began to divide at 6-14 days. These protoplasts subsequently developed varied morphologies, depending on the time of collection during the year. Protoplasts isolated from U. fasciata collected in March to June developed frond thalli or microthalli when they were cultured in low or high densities (cells/area), respectively. The microthallus suspension was cultured for more than two years at 10-40 µmol·m-2 ·s-1 . Frond thalli formed when the suspension was cultivated at 100-160 µmol·m-2 ·s-1 . Therefore, microthallus suspension can serve as a seed stock of U. fasciata.