Enrique Torres

Effects of nitrogen source and growth phase on proximate biochemical composition, lipid classes and fatty acid profile of the marine microalga "Isochrysis Galbana"

The marine microalga Isochrysis galbana was cultured in nitrate, nitrite or urea media to examine changes in the gross biochemical composition, with special emphasis on the growth phase associated changes in the compositions of the lipid classes and fatty acids. The gross biochemical composition was affected more by the growth phase than by the nitrogen source. Protein was higher during exponential growth (about 37–45% AFDW) but the pattern changed as the cultures aged, and lipids were the main algal constituents on all nitrogen sources in the late stationary phase. In all cultures, the relative abundance of neutral lipid increased in the late stationary phase concomitant with a proportional reduction in phospholipids, whereas galactolipids only slightly changed during the growth of the cultures. Total fatty acid content was affected by nitrogen source and growth phase. Maximal PUFA values were obtained at the early stationary phase and decreased throughout the stationary phase. The highest fatty acid contents in the early stationary phase were produced in urea cultures; these cultures also had higher PUFA content, with EPA and DHA contents of 27.66% and 14.13% of total fatty acids, respectively.

Copper toxicity on the marine microalga Phaeodactylum tricornutum: effects on photosynthesis and related parameters

Abstract Essential heavy metals, as copper, can be toxic for microalgae at high concentrations. Copper affected growth and other parameters closely related to photosynthesis of the marine diatom Phaeodactylum tricornutum. A copper concentration of 0.10 mg l−1 provoked about 50% growth reduction and 1 mg l−1 inhibited the growth. Copper also interfered with photosynthesis and ATP production. A copper concentration of 0.5 mg l−1 reduced in a 50% the photosynthetic rate. Therefore, growth is more affected by copper than photosynthesis. Results of chlorophyll a fluorescence obtained by flow cytometry showed that coppers inhibitory effect on PS II activity is located on its oxidizing side. The lower copper concentration assayed provoked a significant decrease in the cellular pool of ATP. Pigment analysis by HPLC showed that copper affected the pigment pattern of P. tricornutum. Important changes were observed for chlorophyll a and its allomer: chlorophyll a proportion decreased while its allomer increased with the copper concentration, being maximum at 1 mg Cu l−1. The study of the intracellular pH by flow cytometry revealed that P. tricornutum cells exposed to 0.5 and 1 mg Cu l−1 showed an intracellular pH higher than control cultures cells, explaining the high proportion of the chlorophyll a allomer in these cells.

Production and analysis of secondary carotenoids in green algae

The microalgae Neochloris wimmeri, Scenedesmus vacuolatus, Scotiellopsisoocystiformis, Chlorella zofingiensis and Protosiphon botryoides were grown under secondarycarotenoid inductive conditions. The results indicatethat nitrogen deficiency and high light intensity arepotential inducers of astaxanthin formation in thefive microalgae studied. All these microalgaeaccumulate significant quantities of secondarycarotenoids, mainly as astaxanthin esters andcanthaxanthin. They also showed high resistance toenvironmental conditions. All these qualities makethese microalgae good candidates for successfulculture in open ponds.

Purification and characterization of phycocyanin from the marine cyanobacterium Synechococcus sp. IO9201

This paper describes a suitable method for the optimum extraction and isolation of phycocyanin from the cyanobacterium Synechococcus sp. IO9201 isolated from Caribbean waters. Phycocyanin from this microorganism was purified to homogeneity and some of its properties were investigated. The purification steps consisted of extraction, hydrophobic interaction chromatography and ion exchange chromatography. Freezing at −21°C-thawing at 4°C, using an alkaline buffer was the best method for extracting phycocyanin from Synechococcus sp. IO9201. The best extraction was obtained using butyl-sepharose resin for hydrophobic interaction chromatography and 0.05 M Tris-HCl (pH = 7) containing 10% ethanol for phycocyanin elution. Finally, phycocyanin was further purified by ion exchange chromatography using Q-sepharose and eluted with a complex isocratic system. The estimated molecular weight of the phycocyanin purified from Synechococcus sp. IO9201 was 102 000 daltons by gel filtration and the isoelectric point was 4.6. When analyzed by SDS-PAGE, Synechococcus sp. IO9201 phycocyanin migrated as two bands having an apparent molecular weight of 21 360 and 18 980 Da. The first band corresponds to β phycocyanin subunits, whereas the second corresponds to α phycocyanin subunits. So, this phycocyanin was characterized as (αCPCβCPC)3.

Potential use of flow cytometry in toxicity studies with microalgae.

Cytotoxic effects of aquatic pollutants on microalgae are very heterogeneous, and they are influenced by environmental conditions and the test species. Stress produced by copper or paraquat addition to the culture medium of two microalgae was analysed by flow cytometry. Parameters assayed were: cell volume, chlorophyll a fluorescence and cell viability. The variety of results obtained in the present study reveals that flow cytometry is a useful tool in the toxicity tests with microalgae, both marine and freshwater species, and for different kind of pollutants.

Long-chain class III metallothioneins as a mechanism of cadmium tolerance in the marine diatom Phaeodactylum tricornutum Bohlin

Abstract Cadmium tolerance of the marine diatom Phaeodactylum tricornutum Bohlin was studied. P. tricornutum growth was significantly reduced by cadmium concentrations of 5 mg l −1 or higher. The EC 50 value was 22.39 mg l −1 of cadmium after four days of exposure. Therefore, P. tricornutum is more tolerant to cadmium than other microalgal cells. In response to exposure to cadmium, P. tricornutum synthesize class III metallothioneins which sequester the metal in a harmless form. However, cadmium tolerance of P. tricornutum cells is not only due to the ability of this microalga to synthesize class III metallothioneins (γ-Glu-Cys) n -Gly, but also because these metallothioneins are composed of long-chain polypeptides. The cadmium-metallothionein complexes of P. tricornutum cells contain predominantly polypeptides of n = 4−9. Long-chain metallothioneins are more efficient in binding heavy metals. Capillary electrophoresis was used to separate class III metallothioneins. This is a recent technique used to separate many molecules. With this technique, the length of the separated polypeptides can also be estimated.

Removal of cadmium ions by the marine diatom Phaeodactylum tricornutum Bohlin accumulation and long-term kinetics of uptake

Abstract The marine diatom Phaeodactylum tricornutum Bohlin was exposed to different cadmium concentrations (1–100 mg l−1) for 4 days. The amount of cadmium removed was recorded, with particular attention paid to long-term uptake kinetics, and to the cellular location of cadmium. Cadmium accumulation occurred at all concentrations assayed. The EC50 of cadmium to P. tricornutum was 22·39 mg l−1 after 4 days of exposure. Cadmium uptake followed a saturation kinetic at cadmium concentrations ≥25 mg l−1. However, at lower cadmium concentrations, the uptake of this metal followed a linear trend for all days of culture. At cadmium concentrations in the medium lower than 25 mg l−1, P. tricornutum removed cadmium mainly within the cell. At higher cadmium concentrations, the amount of cadmium removed by adsorption to the cell surface was higher than intracellular cadmium, because of the toxic effects of cadmium on P. tricornutum cells. This toxicity reduced the cadmium accumulation within the cells.

Effect of cadmium on growth, ATP content, carbon fixation and ultrastructure in the marine diatom Phaeodactylum Tricornutum Bohlin

Cadmium toxicity to the diatom Phaeodactylum tricornutum Bohlin has been studied on the basis of the effect of this metal on growth, ATP content, 14C uptake and cellular ultrastructure. The microalga was exposed to 1, 5, 10, 25, 50, 75 and 100 mg l-1 of cadmium and showed a concentration-dependent inhibition in those physiological parameters. At cadmium concentrations of 5 mg l-1 or higher, a significant effect on growth of P. tricornutum was observed. After 8 hours of exposure to the different cadmium concentrations, the decrease in the ATP content was significant only at cadmium concentrations of 25 mg l-1 or higher. 14C uptake was more susceptible to cadmium than the decrease in the ATP content, as 5 mg l-1 of cadmium caused a severe decrease in this parameter. Cadmium also caused ultrastructural changes in P. tricornutum cells: deposition of cadmium on the surface of cell, increase in the chloroplast size, appearance of electrodense granulations, and reduction in lipid inclusions.

Dunaliella salina as marine microalga highly tolerant to but a poor remover of cadmium

Cadmium tolerance and removal in the marine microalga Dunaliella salina were studied in cultures exposed to different metal concentrations (5-120 mg Cd l(-1)) for 96h. This microalga can be included in the group of microalgal species most tolerant to cadmium due to the high value of EC50 that it possesses (48.9 mg Cd l(-1) at 96 h of culture). The greater percentage of cadmium removed was obtained in cultures exposed to 5 mg Cd l(-1) at 96h, but removing only 11.3% of the added cadmium. In all cultures, the quantity of cadmium removed intracellularly was much lower than the bioadsorbed quantity and it was proportional to the sulfhydryl group levels. Both the Freundlich and Langmuir adsorption models were suitable for describing the short-term biosorption of cadmium by living cells of D. salina.

Response of the marine microalga Dunaliella tertiolecta (Chlorophyceae) to copper toxicity in short time experiments

Heavy metals are introduced into aquatic ecosystems from industrial wastes, agricultural runoff and mining activities. The toxicity of heavy metal ions in solution to microalgae is well known. The essentiality and toxicity of heavy metals has been a subject of extensive research (Stokes 1983). From a biological point of view, heavy metals can be divided into two categories: essential and non-essential. However, essential heavy metals also have been reported to be toxic at high concentrations. Many of these metals have a direct influence on various physiological and biochemical processes including reduction in growth, photosynthesis, and chlorophyll content or inhibition of enzyme activities (Reddy and Prasad 1990).