Microalga Dunaliella Research Articles

Influence of environmental factors on phosphorous content in the marine microalga Dunaliella

The effects of various combinations of environmental factors on phosphorous (P) content in the salt‐tolerant green algae Dunaliella were studied, using laboratory cultures under controlled conditions. The factors examined were the cultivation temperature, light intensity, P and NaCl concentration, and nitrogen (N): P atomic ratios in the culture, and P concentration in the preculture. The experimental system of environmental factors and the measured response of algal P content was modeled through the response surface method. The model obtained revealed that the intracellular P content in D. parva was highly dependent on the P concentration in the preculture medium under the experimental domain studied.

Adaptation of Dunaliella salina (Volvocales, Chlorophyceae) to growth on NH4+ as the sole nitrogen source

The green, wall-less microalga Dunaliella salina.(Dunal) Teodoresco (Volvocales, Chlorophyceae) UTEX 200 was cultured at air-equilibrium CO2 concentration, at 1.5 M NaCl, in the presence of either 10 mM NO3− or 10 mM NH4+ as the sole N source. The N source strongly influenced photosynthesis and C metabolism, and it altered the cell size. Growth on NH4+ caused a 20% increase of the cell volume. Chlorophyll, β-carotene, and protein content were higher by 49%, 75%, and 104%, respectively, in NH4+-grown cells compared to their NO3−-grown counterparts. By contrast, glycerol decreased by about 20% when N was supplied as NH4+ rather than as NO3−. Cells adapted to growth on NH4+ were more efficient at using light and inorganic C for photosynthesis and showed a greater affinity for photons and CO2 than cells cultured in medium containing NO3−. Ribulose bisphosphate carboxylase/oxygenase (Rubisco) protein and activity were present at about the same level in both NO3−- and NH4+-grown cells, but in vivo Rubisco activity was about three times higher in algae cultured on NH4+. Phosphoenolpyruvate (PEP) carboxylase, PEP carboxykinase, and carbonic anhydrase activities were stimulated by growth on NH4+. The mechanisms of adaptation to growth at high NH4+ concentrations are discussed.

Anti-aggregant effects on human platelets of the crude aqueous extract and polar fractions of the microalga Dunaliella tertiolecta

The crude aqueous extract of the microalga Dunaliella tertiolecta was found to have strong inhibitory effects on the aggregation of human platelets induced by thrombin, arachidonic acid and ionomycin. The extraction of the crude aqueous extract with iPrOH and posterior fractionation with solvents of increasing polarity, concentrated the activity in the more polar fractions. © 1997 John Wiley & Sons, Ltd.

Characteristics of biological NOx removal from flue gas in a Dunaliella tertiolecta culture system

A system for the biological removal of NOx from fuel flue gas was investigated using the unicellular microalga Dunaliella tertiolecta. When nitric oxide (NO), the main component of NOx in flue gas, was supplied to the algal culture in a bioreactor with a 2-m column in the light at concentrations ranging from 25 to 500 ppm, about 65% of the NO was removed. Under these conditions, cell growth was not affected by the concentration of the NO supplied, and about 1.6% O 2 was constantly evolved by photosynthesis. About 30% of the NO was removed by the medium without cells at 2% O 2, in which case the NO was probably photochemically oxidized by Fe 3+ present in the medium. In cell cultures without Fe 3+, however, 65% NO removal was achieved. In the dark, on the other hand, the rate of NO removal was governed by the amount of O 2 supplied in the inlet gas, i.e., achievement of a NO removal rate similar to that achieved in the light required the presence of O 2 at 2% or more, and NO removal did not occur without the supply of O 2. It is thus clear that both algal cells and O 2 are essential in the reactor system. NO removal is assumed to proceed as follows: NO in the gas is first dissolved in the aqueous phase, after which it is oxidized and assimilated by the algal cells. The results of investigations under various culture conditions indicate that the dissolution of NO in the aqueous phase is the rate-limiting step in this reactor system.

The uptake of organic compounds byDunaliella parvaCCAP 19/9

The feasibility of growing the unicellular green microalga Dunaliella parva heterotrophically was investigated. D. parva cells were shown to take up [14C]glycerol and [14C]glucose; the rate of uptake was fastest under illuminated conditions (photon flux density of 5–10 µmol m-2s-1), but a significant rate of uptake was maintained in the dark for at least 6 h. The uptake of both compounds was stopped when photosynthesis and respiration were inhibited by adding carbonylcyanide m-chlorophenyl hydrazone (CCCP) or Gram's iodine to the cells. Subjecting the cells to increasing salinity, which reduces the rate of photosynthesis and respiration, also reduced the rate of [14C]glycerol uptake. These results suggested that the uptake of glycerol and glucose was due to active transport. Both transport systems were saturable and they were shown to be independent systems, since there was no effect on [14C]glycerol uptake when excess cold glucose was added or vice versa. D. parva cells could also take up [14C]acetate, but it was not determined whether this was by active transport. Despite the presence of active transport systems for glycerol and glucose and evidence of acetate uptake, D. parva was not able to grow heterotrophically on any of these three potential substrates.

Renewal rate and nutrient concentration as tools to modify productivity and biochemical composition of cyclostat cultures of the marine microalga Dunaliella tertiolecta

Renewal rate and nutrient concentration as tools to modify productivity and biochemical composition of cyclostat cultures of the marine microalga Dunaliella tertiolecta

Renewal rate and nutrient concentration as tools to modify productivity and biochemical composition of cyclostat cultures of the marine microalga Dunaliella tertiolecta

A factorial experimental design with two nutrient concentrations (2 and 4 mmol Nl−1 in the form of NaNO3) and five rates of daily renewal of the cultures (10%, 20%, 30%, 40% and 50%) was carried out in cyclostat, light/dark-synchronized cultures of the marine microalga Dunaliella tertiolecta Butcher. Steady-state cellular density was a linear function inversely proportional to renewal rate. Maximal cellular productivity, 3 × 109 cells1−1 day−1, equivalent to 0.24 g1−1 day−1 dry weight and 0.17 g1−1 day−1 organic weight, was found with renewal rates of 20%–30% and 4mmol N1−1, but maximal protein productivity, 0.066 g1−1 day−1, was obtained with a renewal rate of 40% for both nutrient concentrations. The protein content ranged between 30% and 70% of the organic fraction depending on the culture conditions. Carbohydrates were the only fraction accumulating in response to nutrient stress, ranging from 57% to 10% of the organic fraction, meanwhile the lipid content was increased by increase of nutrient availability. Under non-nitrogen-limited conditions the C:N ratio stabilized around 5.2–5.3 and the protein content of the organic fraction around 70%, but the cell nitrogen quota decreased under these conditions with increasing renewal rates, owing to the lower organic content of cells obtained with high growth rates. The high capacity for changing the biochemical composition, demonstrated for D. tertiolecta in the cyclostat system, has interesting implications for the management of continuous cultures of microalgae and its applications in biotechnological processes.

Plant defences against excessive light studied in the microalga Dunaliella

Abstract Plants are susceptible to a variety of stresses. Among them is excessive light, and for this a number of defence mechanisms have evolved. Dunaliella is remarkable in being able to tolerate not only exceptionally saline conditions but also very high intensities of light. Investigation of the factors involved has given new insights into photoprotective mechanisms generally.

Changes in the gross chemical composition of mass cultures of the marine microalga Dunaliella tertiolecta with different aeration rates

The effect of different aeration rates, in the range 0–6·51 l of air min −1 l of culture −1, and CO 2 supply on the biochemical composition of mass cultures of the marine microalga Dunaliella tertiolecta was studied. The biochemical composition of D. tertiolecta was strongly affected by the aeration rate. There was a negative correlation between stationary-phase protein cellular content and air flow. Carbohydrate cellular content also decreased with aeration rate, a minimum being reached with 0·93 l of air min −1 l of culture −1. Maximum carbohydrate per volume unit was achieved with maximum aeration as the increase of carbohydrates per ml was directly proportional to air flow and therefore to CO 2 availability. Maximum protein per ml was achieved with 1·86 l of air min −1 l of culture −1, keeping stable with higher air flows. The cultures supplied with CO 2 showed carbohydrate and protein concentrations similar to the cultures with 1·86 l of air min −1 l of culture −1, indicating a correlation between available CO 2 and not only carbon, but also nitrogen metabolism. Different factors seemed to limit cell division and nitrogen metabolism as maximum nitrogen transformation rate was achieved with an air flow of 1·86 l of air min −1 l of culture −1, lower than the 3·72 l of air min −1 l of culture −1 needed for maximum cell density.

Improvement of growth rate and cell productivity by aeration rate in cultures of the marine microalga Dunaliella tertiolecta

The effect of different aeration rates and CO 2 supply regimes on mass cultures of the marine microalga Dunaiella tertiolecta was studied. Eight aeration rates in the range 0–6.51 litres of air min −1 litre of culture −1 were tested. The results were compared to those obtained in non-aerated cultures into which pure CO 2 was introduced and to cultures into which air enriched with CO 2 was bubbled. The growth rate and final cellular density of D. tertiolecta in a sea-water-based medium increased with the aeration rate in the culture vessel. The maximal cellular density was 12.46×10 6 cells ml −1 under an air flow rate of 6.51 litres min −1 litre of culture −1, but evaporation and salinity increased sharply at this high aeration rate. The final cell density was proportional to the air flow rate and CO 2 following the range (figures being litres of air min −1 litre of culture −1): 6.51 = 3.72>1.86> CO 2 = (0.93+ CO 2)>0.93>0.46>0.23>0.11>0 (Mann-Whitney test p<0.05). When D. tertiolecta was grown under a CO 2 supply within the optimal pH levels but without aeration, the cultures reached a cell density of 7×10 6 cells ml −1. D. tertiolecta growth rate was inversely proportional to pH, the upper boundary for maximal growth rate being pH 9.2. Oxygen in the culture media produced by the photosynthetic activity of the microalgae did not inhibit growth. The dissolved CO 2 concentration in sea-water was the limiting factor for D. tertiolecta growth. At a pH value of 8.3, D. tertiolecta was not able to take up carbon in the form of carbonates dissolved in sea-water.

Decrease of plasma cholesterol with the marine microalga Dunaliella tertiolecta in hyper cholesterolemic rats.

Female Sprague-Dawley rats, whose plasma cholesterol level had been previously increased, were fed on a diet including 22% biomass of the marine microalga Dunaliella tertiolecta. This diet was compared to two control diets, one of casein and the other of soy flour. After 14 days of feeding, the group fed the microalgal diet exhibited the largest decrease in the plasma cholesterol concentration. The plasma cholesterol level in the group fed the microalgal diet was 45.2% of that in the control group (casein diet) and 28.4% lower than the group fed the soy flour diet. These results suggest that the marine microalga Dunaliella tertiolecta has marked anti-hypercholesterolemic activity when incorporated into the diet. High levels of cholesterol in the blood are a known risk factor for the development of atherosclerosis. High levels of cholesterol in plasma can accelerate the development of arterial disease by increasing the amount of circulating lipids available for incorporation into the arterial walls (29). Diets rich in poly­ unsaturated fatty acids reportedly reduce serum lipids by enhancing their excretion, increase membrane fluidity and reduce thrombosis by conversion of the lipids to eicosanoids (9,14,15). Lipid-lowering diets have mainly been based on an increase of linoleic acid (18 : 2 n-6) content, but the metabolites of linoleic acid (gamma-linolenic acid, 18: 3 n-6, and arachidonic acid, 20: 4 n-6) have a much greater anti-hyper choles­ terolemic activity than the parent molecule (16,27).

CO2 fixation and oil production using micro-algae

The micro-alga Dunaliella tertiolecta ATCC 30929 could be grown under highly saline conditions (6% of NaCl aqueous solution) without the need for sterilization of the bio-reactor or the culture medium which would be greatly advantageous in a scale up of the culture system. Using CO2 as a carbon source, the micro-algae growth reached 1.0g/l under non-sterilized conditions after one week. The effect of contamination by other micro-organisms on the growth was negligible. The micro-alga contained 10% glycerol, and the yield of its conversion to oil by thermo-chemical liquefaction was 36%, indicating the possibility of effective oil production by CO2 fixation using such a micro-alga.

Liquid fuel (oil) from halophilic algae: A renewable source of non-polluting energy

Liquid fuel in the form of a mixture of hydrocarbons has been produced from a renewable form of biomass, the green microalga Dunaliella, which is distributed in oceans and salt lakes throughout the world. The product is a high-quality oil low in sulfur and nitrogen and is obtained by pyrolysis of a suspension of the algal cells. Feasibility studies have determined that the total cost of oil produced from Dunaliella is $21.6 per barrel of crude oil. Allowing for a 20% profit on the investment, the price of a barrel of oil would be $26 (Zaidman, School of Applied Chemistry, The Hebrew University of Jerusalem).

Measurement of the transmembrane electrical potential of Dunaliella acidophila by microelectrodes

A method was developed to determine electrical potential differences across the plasma membrane of the microalga Dunaliella by means of potential-sensitive microelectrodes. Special emphasis was put on the measurement of the membrane potential in the acidophilic Dunaliella acidophila (optimal growth at pH 1.0), but neutrophilic, halotolerant Dunaliella species were used as reference systems. For Dunaliella acidophila positive membrane potentials (cytoplasma relative to the medium), ranging from +30 to +65mV were measured. Illumination caused a decrease of the positive potential by about 10 mV. The ATPase inhibitor omeprazole caused an increase of the positive membrane potential ranging from +60 to +100 mV, whereas the ionophore gramicidin caused a decrease of the MP to +10 to +30 mV. The salt tolerant, neutrophilic Dunaliella parva and Dunaliella bardawil exhibited negative membrane potentials in the order of -40 to -60mV, and light caused a hyperpolarization of about 10 mV. A negative membrane potential was measured also in D. acidophila cells transferred to pH 7.0. The physiological significance of a positive membrane potential for acidophilic algae is discussed.

Growth and pigmentation of marron ( Cherax tenuimanus) fed a reference ration supplemented with the microalga Dunaliella salina

The Western Australian freshwater crayfish Cherax tenuimanus, called marron, loses dark exoskeletal colouration when fed artificial diets in indoor tanks, suggesting a carotenoid deficiency in these foods. In the present study the international Halifax crustacean inference diet (HFX CRD) was used as a control against treatments consisting of HFX CRD to which was added either a powder or fresh slurry of the carotenoid-rich microalga, Dunaliella salina. Juvenile marron housed in an indoor battery culture system were fed to the diets for 100 days. Thin layer chromatography of pigment extracts revealed that all three experimental groups contained astaxanthin, mono-esterified astaxanthin, diesterified astaxanthin and beta-carotene. However, canthaxanthin, adonirubin and esterified adonirubin were observed additionally in the algal treatment groups only. Pigment analyses of marron at 25-day intervals showed elevated levels of total carotenoid and beta-carotene in the algal treatment groups as compared to the control group. Marron on the algal slurry treatment also showed a significantly higher growth rate.

In vitro maturation, fertilization and development of mouse GV-stage oocytes after freezing and thawing

Effects on short-term (6 h) and long-term (96 h) exposure to cadmium (Cd) at 0.1, 0.5 and 2.5 mg/L in microalga Dunaliella salina were assessed using both physiological end points and gene expression analysis. Different physiological responses between the short-term and long-term exposures were observed. Upon 6 h after Cd exposure, lipid peroxidation and cell ultrastructure remained unchanged, while contents of chlorophyll a, chlorophyll b, carotenoids were increased at 0.5 and 2.5 mg/L Cd. Contrarily, 96 h after Cd exposure, lipid peroxidation levels were increased, while pigments content was decreased, and damaged cell ultrastructure was apparent at 2.5 mg/L Cd. Activities of antioxidant enzymes (APX, SOD, GST, GPX, and GR) changed differently both at 6 h and 96 h after Cd exposure. Upon 6 h after Cd exposure, SOD and GST activity increased at all three doses, GR and GPX activity increased at 0.5 mg/L Cd while APX activity increased at 0.1 mg/L Cd. Contrarily, 96 h after Cd exposure, activities of all the antioxidant enzymes increased both at 0.1 and 0.5 mg/L Cd; but there was a decrease in SOD and GR activity in D. salina exposed to 2.5 mg/L Cd. RNA-seq and qRT-PCR analyses indicated that genes involved in ROS-scavenge, photosystem, and ribosome functions were differentially expressed. The most significantly enriched function was the ribosome, in which more than 30 ribosome genes were up-regulated at 6 h but down-regulated at 96 h after Cd exposure at 2.5 mg/L. Our study indicated for the first time that genes encoding ribosomal proteins are the primary target for Cd in microalgae, which allowed gaining new insights into temporal dynamics of toxicity and adaptive response pathways in microalgae exposed to metals.

A closed system for outdoor cultivation of microalgae

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.

β-Carotene, vitamin C and vitamin E content of the marine microalga Dunaliella tertiolecta cultured with different nitrogen sources

Variations in the β-carotene, vitamin C and vitamin E content of D. tertiolecta have been shown to result from the nitrogen source used in the culture medium. Differences of 101%, 38% and 69% have been found in β-carotene, ascorbic acid and tocopherol content in mg/g of dry matter, respectively, and differences of 147%, 63% and 37% occurred in β-carotene, vitamin C and E concentrations in mg/litre of culture, respectively. Considering the β-carotene, vitamin C and vitamin E content in mg/g of chlorophyll a, maximum variations occurred in β-carotene content, with differences of 145% among the different nitrogen sources. Maximum β-carotene and vitamin C values were found in urea cultures, whereas urea cultures showed the minimum values for vitamin E.

Effects ofPhaeodactylum tricornutum and Dunaliella tertiolectaExtracts on the Central Nervous System

We report the effects of aqueous extracts of the microalgae Dunaliella tertiolecta Butcher (Chlorophyceae) and Phaeodactylum tricornutum Bohlin (Bacillariophyceae) on oxotremorin-induced cholinergic symptoms, amphetamine-induced hypermotility, pentylenetetrazole-induced convulsions, and Rota-rod test performance. Both extracts significantly reduced rectal temperature, spontaneous motor activity, and time on the Rota-rod and increased the number of mice falling off the rod before 180 s, but neither protected against pentylenetetrazole-induced convulsions or against oxotremorin-induced tremor, salivation, and diarrhoea.

Waste water treatment using saline cultures of microalgae

Survival of microorganisms (Escherichia coli has been used as an example) is affected by a combination of salinity and high pH induced by the active photosynthesis of marine microalgae (Aphanotece or Dunaliella sp.). This effect can be applied to create a more efficient wastewater treatment process using algal stabilization ponds.