Unicellular Green Alga Dunaliella Research Articles

Characterization and heterologous expression of a new matrix attachment region binding protein from the unicellular green alga Dunaliella salina

Although interactions between the nuclear matrix and special regions of chromosomal DNA called matrix attachment regions (MARs) are implicated in various nuclear functions, the understanding of the regulatory mechanism of MARs is still poor. A few MAR-binding proteins (MARBP) have been isolated from some plants and animals, but not from the unicellular algae. Here, we identify a novel MAR-binding protein, namely DMBP-1, from the halotolerant alga Dunaliella salina. The cDNA of DMBP-1 is 2322-bp long and contains a 1626 bp of an open reading frame encoding a polypeptide of 542 amino acids (59 kDa). The DMBP-1 expressed in Escherichia coli specifically binds A/T-rich MAR DNA. The DMBP-1 fused to green fluorescent protein appears only inside the nuclei of Chinese hamster ovarian cells transfected with the pEGFP-MBP, indicating that the protein is located in the nuclei. The findings mentioned above may contribute to better understanding of the nuclear matrix-MAR interactions.

Characterization of a new Dunaliella salina strain MSI-1 based on nuclear rDNA ITS sequences and its physiological response to changes in composition of growth media

Since the first formal description of the unicellular green algae Dunaliella salina, its presence in hypersaline environments worldwide and its physiological responses to different environmental conditions have been studied extensively. Moreover, due to massive carotenoid accumulation by some strains under specific growth conditions, its biotechnological applications have attracted a great deal of scientific interest. In this study, the phylogenetic relationship, growth, and carotenogenesis of a new strain of Dunaliella salina isolated from Maharlu salt lake in Shiraz (latitude 29.26°N, longitude 52.48°E), Iran were investigated. First, a phylogram based on neighbor-joining analysis of the nuclear rDNA ITS (ITS-1 + 5.8 rDNA + ITS-2) sequence data was constructed. The phylogenetic tree showed that the new isolate is part of a major clade containing several strains of D. salina and was designated as D. salina MSI-1. Then, the responses of the new isolate to the initial pH of the culture media and different concentrations of nitrate, NH4+, and citrate were examined. As with other strains of D. salina, growth and carotenogenesis were controlled by the levels of nitrate and NH4+ in the growth media. Low available nitrogen negatively affected growth but enhanced carotenoid accumulation. Insensitivity of carotenogenesis to citrate indicates a minor contribution of cytosolic IPP synthesis to the overall carotenoid production. Despite changes in the initial pH of the culture media over the experimental period, the initial pH had marked effects on the growth and carotenogenesis of the new isolate. These effects, together with the higher cell carotenoid content observed at pH 11.0, await further research. The results confirm that the analysis of the ITS sequences is a reliable basis for determination of the genetic relatedness among strains of the genus Dunaliella, and the search for strains with novel characteristics may have valuable biotechnological applications.

The dying Dead Sea: The microbiology of an increasingly extreme environment

The Dead Sea, on the border between Israel and Jordan, currently contains around 348 g salt L−1. Divalent cations (Mg2+, Ca2+) dominate over monovalent cations (Na+, K+), while Cl− and Br− are the main anions. The pH of the Sea is about 6. The water balance of the lake is negative, having dropped over 1 m year−1 over the past decade. The water is supersaturated with Na+, with massive quantities of halite precipitating to the bottom of the lake. Biological monitoring since 1980 has indicated that blooms of the unicellular green alga Dunaliella and halophilic Archaea of the family Halobacteriaceae only develop following significant dilution of the upper water layers in the lake after very rainy winters. Such events occurred in 1980, and even more dramatically in 1992, when up to 3.5 × 107 Archaea mL−1 in the diluted upper 5–10 m of the water column coloured the lake red. Species isolated from the lake include Haloferax volcanii, Haloarcula marismortui, Halorubrum sodomense and Halobaculum gomorrense. Dunaliella was no longer observed in the lake after 1996, with prokaryote numbers remaining low. To characterize the residual microbial community in the lake, biomass was collected in February 2007 for environmental genomic analyses. The results were compared with the metagenome of microbial bloom material collected in 1992. The 16S rRNA archaeal phylotypes recovered from the 2007 sample were diverse, with phylotypes distantly related to the genera Halorhabdus, Haloplanus, Natronomonas and others. Halorhabdus sp. also was recovered in culture. The 1992 bloom sample was very homogeneous, however, with a single cluster remotely related to Halobacterium salinarum. These results illustrate that the microbial communities are dynamic, even in one of the most extreme environments on Earth, and exhibit strong shifts in species composition as conditions for life become increasingly adverse.

Cytotoxicity effects of water dispersible oxidized multiwalled carbon nanotubes on marine alga, Dunaliella tertiolecta

The multiwalled carbon nanotubes (MWNTs) are novel materials with many potential applications. The ecotoxicity of these materials is not well studied, but it is essential for environmental impact assessments. In this study a commercially available MWNT material was carboxylated by microwave assisted acid oxidation. This functionalized MWNT (f-MWNT) material was examined for toxicity effects using unicellular marine green alga Dunaliella tertiolecta. D. tertiolecta was exposed to f-MWNT which had been pre-equilibrated with culture media for 24 h. Substantial growth lag phase was observed at 5 and 10 mg L −1 f-MWNT, and the resulting 50% effective concentration (EC50) on 96-h growth was 0.82 ± 0.08 mg L −1. During mid-exponential growth phase cytotoxicity was evidenced at 10 mg L −1 f-MWNT in 36% reduction in exponential growth rate, 88 mV more positive glutathione redox potential (indicative of oxidative stress), 5% and 22% reduction in photosystem II (PSII) quantum yield and functional cross section respectively, all relative to the control cultures. However, when the large f-MWNT aggregates in the media with 10 mg L −1 f-MWNT were removed by 0.2 μm filtration, D. tertiolecta did not show significant cytotoxicity effects in any of the above parameters. This suggests that the cytotoxicity effects originated predominately from the large f-MWNT aggregates. Analysis of the f-MWNT aggregation dynamics suggests active interaction between f-MWNT and algal cells or cell metabolites that promoted f-MWNT aggregation formation. The f-MWNT particles were also found absorbed on algal cell surface. The direct contact between f-MWNT and cell surface was likely responsible for reduced PSII functional cross section and oxidative stress during exponential growth.

Identification of a glucose-6-phosphate isomerase involved in adaptation to salt stress of Dunaliella salina

The unicellular green alga Dunaliella salina is a recognized model for studying plant adaptation to high salinity. To isolate some salt-induced proteins at proteomics levels and to identify their expressions at gene levels, algal cells at logarithmic phase cultured in 1.5 and 3.5 M NaCl media were harvested for protein extraction. Solubilized proteins were applied to two-dimensional gel electrophoresis (2-DE) and analyzed by ImageMaster 2D Platinum software. Twenty-one protein spots whose intensities were elevated threefold to 13-fold at 3.5 M NaCl as compared to 1.5 M NaCl were analyzed by matrix-assisted laser desorption/ionization tandem time of flight mass spectrometry. One salt-induced protein isolated from the 2-DE gels was identified as a glucose-6-phosphate isomerase (GPI) from D. salina (DsGPI). A full-length cDNA of DsGPI was obtained using rapid amplification of cDNA end technique, and it was shown by heterologous expression to encode a protein with a molecular weight consistent with the protein spot in the 2-DE gels. Real-time quantitative RT-PCR demonstrated that the mRNA of DsGPI was induced up to eightfold (P < 0.01) by 2.5 M and 14-fold higher (P < 0.01) by 3.5 M NaCl than by 1.5 M NaCl, respectively. It is concluded that the protein isolated through 2-DE is indeed DsGPI and that the DsGPI gene may be involved in adaptation to high salinity.

Nucleotide sequence and expression of the 14-3-3 from the halotolerant alga Dunaliella salina

Previously we reported the nucleotide sequence of a 14-3-3 cDNA cloned from the unicellular green alga Dunaliella salina, however, the nucleotide sequence of this gene have not been reported so far. In the present study, the cloning and characterization of the nucleotide sequence, the gene copy and expression were undertaken. The coding sequence of the gene was found to be interrupted by five introns of 132, 266, 153, 152 and 625 bp, respectively. Introns 3-5 were found in conserved positions as compared to the Chlamydomonas reinhardtii 14-3-3 gene. D. salina 14-3-3 cDNA was inserted into the prokaryotic expression plasmid pET-28 and transformed into E. coli BL21, and the recombinant expressed 14-3-3 protein was purified from E. coli and immunized the rabbit. Indirect ELISA coated with 14-3-3 illustrated that the rabbit antisera titration was 1:1.00E + 06. Western blotting assays confirmed that prepared rabbit antibodies could recognize the recombinant 14-3-3 protein. Southern blotting results showed that there was only one copy of the 14-3-3 present in the genome of D. salina and 14-3-3 expression did not change throughout the Dnualiella cell cycle.

Saltern evaporation ponds as model systems for the study of primary production processes under hypersaline conditions

Multi-pond solar salterns, which are used worldwide for salt production along tropical and subtropical coastal areas, present an environment with increasing salt concentrations, from seawater to NaCl saturation. Characteristic salt-adapted microbial communities are found along the salinity gradient. In ponds of intermediate salinity (100 to 250 g 1- 1 ), most of the primary production occurs in benthic microbial mats dominated by different types of unicellular and filamentous Cyanobacteria (Aphanothece, Microcoleus, Phormidium and others), sometimes in association with diatoms. In crystallizer ponds, the unicellular green alga Dunaliella is the sole primary producer that lives in association with dense communities of heterotrophic halophilic Archaea that color the brines red. This basic pattern is common to all saltern systems, in spite of local variations in climate and nutrient availability. Photosynthetic activities of benthic cyanobacterial mats in the evaporation ponds and of endoevaporitic microbial communities within the gypsum crust that precipitates at intermediate salinities have been extensively studied in salterns at different locations, using oxygen microelectrodes and other techniques adapted to the study of benthic communities. These environments are generally highly productive, although most of the oxygen produced during daytime by the Cyanobacteria is recycled within the mats rather than exchanged with the overlying water and the atmosphere. Surprisingly few attempts have been made thus far to estimate the photosynthetic activity of Dunaliella, which is often present in numbers between 10 3 and 10 5 cells ml -1 in the heavily salt-stressed environment of crystallizer ponds, so that the dynamics of the system is largely unknown.

Characterization of the glucose-6-phosphate isomerase (GPI) gene from the halotolerant alga Dunaliella salina

Although glucose-6-phosphate isomerase (GPI) plays an important role in glycolysis of both the prokaryotes and eukaryotes, studies on the GPI have not been involved in the halotolerant, unicellular green alga Dunaliella salina (D. salina). In this study, a 2,338 bp of full-length cDNA cloned using rapid amplification of cDNA end (RACE) technique contained an open reading frame (ORF) of 1,980 bp encoding 660 amino acids, which has a predicted molecular weight of 73.3 kD and pI of 6.22 and shares high homology with other organisms. The cloned full-length cDNA was heterologously expressed in Escherichia coli and the recombinant GPI proteins purified using Ni-NTA His Bind column were consistent with the anticipated size of ~75 kD. Predicted 2D and 3D structures of GPI proteins possessed potential active motifs including "GEPGTNGQHSFYQLIHQG" and "VQGFIWGINSFDQWGVELGK", and critical active site residues, such as Ser 241, Ser 296, Thr 298, Thr 301, Arg 358, Glu 444, His 475 and Lys 600. Real time quantitative RT-PCR demonstrated that the expression level of the GPI gene from D. salina (DsGPI) was induced by 3.5 M NaCl with 14-fold higher than that by 1.5 M NaCl (P < 0.01), but inhibited by the light with 4-fold lower than that in the dark (P < 0.05). It is concluded that the cloned GPI gene is indeed from D. salina and may respond to salt and light.

Analysis of non-photochemical energy dissipating processes in wild type Dunaliella salina (green algae) and in zea1, a mutant constitutively accumulating zeaxanthin

Generally there is a correlation between the amount of zeaxanthin accumulated within the chloroplast of oxygenic photosynthetic organisms and the degree of non-photochemical quenching (NPQ). Although constitutive accumulation of zeaxanthin can help protect plants from photo-oxidative stress, organisms with such a phenotype have been reported to have altered rates of NPQ induction. In this study, basic fluorescence principles and the routinely used NPQ analysis technique were employed to investigate excitation energy quenching in the unicellular green alga Dunaliella salina, in both wild type (WT) and a mutant, zea1, constitutively accumulating zeaxanthin under all growth conditions. The results showed that, in D. salina, NPQ is a multi-component process consisting of energy- or DeltapH-dependent quenching (qE), state-transition quenching (qT), and photoinhibition quenching (qI). Despite the vast difference in the amount of zeaxanthin in WT and the zea1 mutant grown under low light, the overall kinetics of NPQ induction were almost the same. Only a slight difference in the relative contribution of each quenching component could be detected. Of all the NPQ subcomponents, qE seemed to be the primary NPQ operating in this alga in response to short-term exposure to excessive irradiance. Whenever qE could not operate, i.e., in the presence of nigericin, or under conditions where the level of photon flux is beyond its quenching power, qT and/or qI could adequately compensate its photoprotective function.

Characterization of the Glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH) Gene from the Halotolerant Alga Dunaliella salina and Inhibition of Its Expression by RNAi

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) displays important functional diversity in mammalian and plants. So far, however, studies on GAPDH have not included the halotolerant, unicellular green alga Dunaliella salina. In the present study, a GAPDH cDNA was cloned and sequenced from D. salina. It was 1394 bp long, with an open reading frame of 1128 bp encoding 376 amino acid residues, and shared a high homology with other organisms. The coding region of the gene was heterologously expressed in E. coli, confirming that the gene cloned from D. salina is indeed GAPDH. Furthermore, the recombinant plasmid p7NBTFIR was constructed to express hairpin RNA (hpRNA) containing sequences homologous to the GAPDH gene to investigate the expression profile of GAPDH by RNAi in D. salina. The results of real-time quantitative PCR revealed that the relative transcription levels of the GAPDH gene in transformants G1 and G2 were reduced to 41.2% and 67.4%, respectively, of the wild-type D. salina. Observations under phase-contrast microscopy showed that the motility of the transformants cell was sluggish. The results of a photoaccumulation experiment showed that the cell motility of transformants G1 and G2 was less active than that of wild-type D. salina. The findings of this study may be useful for further studies on the subcellular localization and functional analysis of the GAPDH gene in microalgae.

Microalgae and cyanobacteria of the Dead Sea and its surrounding springs

Scientific exploration of the algal and cyanobacterial flora of the Dead Sea and its surroundings started in the 1930s. The unicellular green alga Dunaliella parva is the sole primary producer in the water column of the Dead Sea. The dynamics of the Dunaliella population and the interrelationships between the alga and the physical and chemical parameters in the lake are now well understood. Although cyanobacteria have occasionally been encountered in the Dead Sea as well, they are not known to contribute significantly to the microbial activities in the lake. Dense growth of cyanobacteria is found in various freshwater and saline, cold and warm springs in the Dead Sea area. Abundant cyanobacterial communities develop in the hot (up to 63 °C) freshwater springs of Zerka Ma'in and Zara near the eastern shore of the lake. We here report data on the diversity of these communities, based both on microscopic observations and on molecular phylogeny techniques, and on their content of UV-absorbing pigments (mycosp...

Antimicrobial Activity of Sub- and Supercritical CO2 Extracts of the Green Alga Dunaliella salina

The objective of this research was to evaluate the antimicrobial activity of carbon dioxide extracts of the unicellular biflagellated green alga Dunaliella salina against Escherichia coli, Staphylococcus aureus, Candida albicans, and Aspergillus niger. The effects of different extraction pressures ranging from 185 to 442 bar and extraction temperatures ranging from 9.8 to 45.2°C on the extracts' composition and consequently on their antimicrobial activities were investigated. The extracts were analyzed by gas chromatography–mass spectrometry in order to identify the compounds responsible for the antimicrobial activity detected. Fourteen different volatile compounds and several fatty acids were identified. The highest antimicrobial activity was obtained using 314 bar and 9.8°C. Under these conditions, the presence of an indolic derivative that had never been reported in D. salina was detected in the extract, together with polyunsaturated fatty acids and compounds related to carotene metabolism, such as β-ionone and neophytadiene, with known antimicrobial activity.

Microalgal biotechnology: Carotenoid and glycerol production by the green algae Dunaliella isolated from the Gave-Khooni salt marsh, Iran

In this study, carotenoid and glycerol production in two unicellular green algae (Dunaliella salina and D. viridis) isolated from the Gave-Khooni salt marsh grown in media containing five different salt concentrations (0.17, 1, 2, 3, and 4 M NaCl) were evaluated under sterile conditions. Algae growth decreased as the medium salinity increased. Optimum growth of D. salina and D. viridis were obtained at 2 and 1 M NaCl, respectively. As salinity increased, glycerol and carotenoid production were increased in D. salina, whereas lower values for these products were produced in D. viridis under the same conditions. Furthermore, the cell color of D. salina changed from green to orange-red following accumulation of carotenoid, but the color of D. viridis was not changed. Thereby, it seems that the Iranian D. salina may be suitable for carotenoid production (betacarotene) on a large scale. In addition, since carotenoid compounds enhance the efficiency of photosynthesis and glycerol synthesis, it appears that the pathway for glycerol production and mechanisms of salt tolerance in D. viridis are unique from those of D. salina.

Assessing sediment quality in Spanish ports using a green alga bioassay

Coastal zones are under environmental pressure due to human activities, and ports are the areas that probably present the highest levels of contaminants in their sediments. In the present study we have combined chemical data and biological effects to determine the sediment quality of six Spanish ports. Trace metals and organic contaminants have been analyzed, and an acute bioassay was carried out in sediment elutriate using the unicellular green alga Dunaliella tertiolecta. The toxicological parameter employed was EC50, which was estimated after exposure to different concentrations of elutriates during 72 h. The development of this alga may be affected when there is a xenobiotic in the environment, and growth inhibition can be quantified and linked to the levels of contaminants in the sediment in order to determine its quality. The results showed that the metals (Cd, Cr, Hg, and Zn) and organic contaminants (PAHs and PCBs) bound to the sediments reduced the normal growth of the alga, but no alterations were detected due to the presence of Cu. The main disadvantage observed was the hormesis produced by the presence of high levels of organic material in the sediment that might hide the toxicity of xenobiotics.

Cloning and characterization of the phytoene desaturase (pds) gene — a key enzyme for carotenoids synthesis in Dunaliella (Chlorophyta)

The unicellular green alga Dunaliella is outstanding for its ability of massive accumulation of carotenoids. To elucidate the carotenoids synthesis pathway in this alga, phytoene desaturase (pds) gene cDNA together with its DNA sequences were isolated and their structures and functions analyzed. The full-length pds cDNA of 2290 bp (GenBank Accession No. DQ243892) was deduced from RACE results, including untranslated 21 bp 5′-and 520 bp 3′-flanking regions and an open reading frame of 582 amino acids, coding a protein of 64.196 kDa. The DNA sequence of 2908 bp (GenBank Accession No. DQ845248) including five introns was obtained. The fifth intron was uncompleted and complex, including two bases’ perfect repeats (GT)10 and large different-sized repeats within the last 400 bp. The Southern blot hybridization result demonstrated that this gene occurred as a single copy in this species, and the quantitative RT-PCR result showed that the transcription of this gene was constitutive. The evolutional significance of pds was discussed.

Cloning and characterization of the 14-3-3 protein gene from the halotolerant alga Dunaliella salina

Previous studies have demonstrated that 14-3-3 proteins exist in all the eukaryotic organisms studied; however, studies on the 14-3-3 proteins have not been involved in the halotolerant, unicellular green alga Dunaliella salina so far. In the present study, a cDNA encoding 14-3-3 protein of D. salina was cloned and sequenced by PCR and rapid amplification of cDNA end (RACE) technique based on homologous sequences of the 14-3-3 proteins found in other organisms. The cloned cDNA of 1485 bp in length had a 29.2 kDa of molecular weight and contained a 774 bp of open reading frame encoding a polypeptide of 258 amino acids. Like the other 14-3-3 proteins, the deduced amino acid sequences of the D. salina 14-3-3 protein also contained two putative phosphorylation sites within the N-terminal region (positions 62 and 67). Furthermore, an EF hand motif characteristic for Ca(2+)-binding sites was located within the C-terminal part of this polypeptide (positions 208-219). Analysis of bioinformatics revealed that the 14-3-3 protein of D. salina shared homology with that of other organisms. Real-time quantitative PCR demonstrated that expression of the 14-3-3 protein gene is cell cycle-dependent.

Effects of sonication and advanced chemical oxidants on the unicellular green alga Dunaliella tertiolecta and cysts, larvae and adults of the brine shrimp Artemia salina: A prospective treatment to eradicate invasive organisms from ballast water

Uptake and release of ship-borne ballast water is a major factor contributing to introductions of aquatic phytoplankton and invasive macroinvertebrates. Some invasive unicellular algae can cause harmful algal blooms and produce toxins that build up in food chains. Moreover, to date, few studies have compared the efficacy of ballast water treatments against different life history phases of aquatic macroinvertebrates. In the present study, the unicellular green alga Dunaliella tertiolecta, and three discrete life history phases of the brine shrimp Artemia salina, were independently used as model organisms to study the efficacy of sonication as well as the advanced oxidants, hydrogen peroxide and ozone, as potential ballast water treatments. Algal cells and brine shrimp cysts, nauplii, and adults were subjected to individual and combined treatments of sonication and advanced oxidants. Combined rather than individual treatments consistently yielded the highest levels of mortality in algal cells (100% over a 2 min exposure) and in brine shrimp (100% and 95% for larvae and adults, respectively, over a 2 min exposure). In contrast, mortality levels in brine shrimp cysts (66% over 2 min; increased to 92% over a 20 min exposure) were moderately high but consistently lower than that detected for larval or adult shrimp. Our results indicate that a combination of sonication and advanced chemical oxidants may be a promising method to eradicate aquatic unicellular algae and macroinvertebrates in ballast water.

Technical Note: Toxicity Tests of Typical Mutagenic Phenols on Dunaliella salina

Algal tests are the predominant methods for studying aquatic ecotoxicology. Growth inhibition effects of three phenols and combined phenols at different concentration levels on unicellular green algae (Dunaliella salina) were tested according to the OECD guidelines for testing chemicals. Using 2,4-xylenol, paracresol, and phenol as the typical mutagenic toxicants, their concentrations were set according to the Chinese national drinking water health standard (GB5749-85). Four groups of tests were designed by combining any two of the three compounds; another group was the control. D. salina was cultivated in these groups, and the EC50 of each group was obtained. Based on the 48 h EC50 values, the microalgae showed increasing inhibition effects in the following order: 2,4-xylenol < paracresol < phenol. The four groups of phenol combinations, for which the range of additive index of joint effect (AI) varied from 0.03 to 0.1, demonstrated that there were slight synergistic relationships among them.

Interrelationships between Dunaliella and halophilic prokaryotes in saltern crystallizer ponds

Thanks to their often very high population densities and their simple community structure, saltern crystallizer ponds form ideal sites to study the behavior of halophilic microorganisms in their natural environment at saturating salt concentrations. The microbial community is dominated by square red halophilic Archaea, recently isolated and described as Haloquadratum walsbyi, extremely halophilic red rod-shaped Bacteria of the genus Salinibacter, and the unicellular green alga Dunaliella as the primary producer. We review here, the information available on the microbial community structure of the saltern crystallizer brines and the interrelationships between the main components of their biota. As Dunaliella produces massive amounts of glycerol to provide osmotic stabilization, glycerol is often postulated to be the most important source of organic carbon for the heterotrophic prokaryotes in hypersaline ecosystems. We assess here, the current evidence for the possible importance of glycerol and other carbon sources in the nutrition of the Archaea and the Bacteria, the relative contribution of halophilic Bacteria and Archaea to the heterotrophic activity in the brines, and other factors that determine the nature of the microbial communities that thrive in the salt-saturated brines of saltern crystallizer ponds.

Up-Regulation of Photoprotection and PSII-Repair Gene Expression by Irradiance in the Unicellular Green Alga Dunaliella salina

The unicellular green alga Dunaliella salina is an attractive model organism for studying photoacclimation responses and the photosystem II (PSII) damage and repair process in the photosynthetic apparatus. Irradiance during cell growth defines both the photoacclimation and the PSII repair status of the cells. To identify genes specific to these processes, a cDNA library was created from irradiance-stressed D. salina. From the cDNA library, 1112 randomly selected expressed sequence tags (ESTs) were analyzed. Because ESTs constitute the expressed part of the genome, the strategy of randomly sequencing cDNA clones at their 5'-ends allowed us to obtain information about the transcript level of numerous genes in light-stressed D. salina. The results of a BLASTX search performed on the obtained total set of ESTs showed that approximately 1% of the ESTs could be assigned to genes coding for proteins that are known to be up-regulated in response to high-light stress. Specifically, after 48 h of high-light exposure of the cells, an increase in the expression level of antioxidant genes, such as Fe-SOD and APX, was observed, as well as elevated levels of the Cbr transcript, a light-harvesting Chl-protein homolog. Further, the ATP-dependent Clp protease gene was also up-regulated in D. salina cells after 48 h of exposure to high light. The results provide initial insight into the global gene regulation process in response to irradiance.