Microalga Dunaliella Salina Research Articles

Metabolic responses of the green microalga Dunaliella salina to silver nanoparticles-induced oxidative stress in the presence of salicylic acid treatment

In the present study, the biochemical responses and antioxidant enzymes activity of the Dunaliella salina, a green microalga, to the interaction of silver nanoparticles (AgNPs) and salicylic acid (SA) were investigated. Algal suspensions in the phase of logarithmic growth were subjected to the concentrations of 0, 5, 15, and 25 pM AgNPs with or without 1 mM SA. AgNPs level of 25 pM declined cell division but highly accumulated levels of chlorophyll, β-carotene, proteins, free amino acid, carbohydrates, and hydrogen peroxide, which was associated with enhanced the activity of proteolysis, lipid peroxidation, and antioxidant enzymes. SA-treated cells at 25 pM AgNPs improved cell growth but declined the activities of antioxidant enzymes and proteolytic along with a lower accumulation of metabolites except β-carotene relative to untreated controls. These results suggest that AgNPs treatment induce oxidative stress in D. salina cells, which tolerated by alga through the metabolic modifications and accumulating β-carotene, while SA induces AgNPs tolerance by the mechanisms that direct carbon flux to growth and β-carotene biosynthesis rather than the antioxidant enzymes or osmoprotectant metabolites.

Adsorption of Radioactive Materials by Green Microalgae Dunaliella salina from Aqueous Solution

Introduction: Nuclear accidents release large quantities of radioactive materials into the environment. Iodine-131 and cesium-137 are two radionuclides released during nuclear accident, which can pose the greatest cancer risks. These radionuclides can be moved to other areas through rain and wind. The aim of this study was to develop efficient and economical biological methods for the absorption of water-soluble radionuclides released after a nuclear accident. Material and Methods: The exposure of the algae to an aqueous solution of I-131 radionuclide was performed for 1, 2, and 3 h. The concentration activities of the samples were 27 μCi/ml and 270 μCi/ml. After the removal of the alga by centrifuging, the activities of the sample solutions were measured using a calibrated dose calibrator. The measured activities at the mentioned periods of time were statistically significant for both groups (P<0.05). Results: The obtained results of the current study revealed that the activity of radioiodine-131 decreased 1, 2, and 3 h after adding algae, compared to the control group at the same time (21.8, 32.33, 39.84 for 27 μCi/ml and 15.38, 21.53, and 30 for 270 μCi/ml, respectively). Furthermore, radioactive iodine is absorbed very well with this type of algae. Conclusion: It can be concluded that Dunaliella salina can be used for the decontamination of radioiodine. This method can play a significant role in the decontamination of hazardous radioiodine after nuclear accidents. © 2019, Mashhad University of Medical Sciences.

MORPHOLOGICAL AND MORPHOMETRICAL FEATURES IN DUNALIELLA SALINA (CHLAMYDOMONADALES, DUNALIELLACEAE) DURING THE TWO-PHASE CULTIVATION MODE

The paper presents studies of morphological and morphometrical characteristics of green halophilic carotenogenic microalga Dunaliella salina (Dunal) Teodoresco, 1905, from the south-west region of Crimean Peninsula. D. salina was cultivated in two-phase mode under conditions of natural illumination at the premises of A.O. Kovalevsky Institute of Biology of the Southern Seas of RAS (IBSS), Sevastopol, Russia. The maximum D. salina cell density was 1.69·106 cell/ml in the “green” phase and 0.84·106 cell/ml in the “red” growth phase. The maximum productivity by cell number reached 0.15 ∙ 106 cell/(ml·day)in the “green” phase while it was lower by 73% in the “red” phase (0.04∙106 cell/(ml·day). Along with the maximum productivity, linear growth stage in the first phase was characterized by a maximum fraction of small (up to 500 μm3 in volume) cells (about 15-29%) and a decrease in cell volume by 40-45% as compared with initial value. The mean of D. salina cell volume in the “red” phase was 30% higher than in the “green” phase. At the same time, the large cell fraction in the “red” phase was consistently high (15-35%). The patterns of change in morphological and morphometrical cell parameters were in accordance to stage and conditions of growth. Thus, cell elongation was noted in the stage of linear growth, while under unfavorable conditions at growth-declining stage cells became more round-shaped, with orange and tile-red coloration and granulation of cell content. It was shown that morphological and morphometric cell parameters can serve as additional criteria for assessment of physiological condition in D. salina culture. The experiment demonstrated the prospects for two-stage D. salina cultivation in Crimea.

Effects of food presence on microplastic ingestion and egestion in Mytilus galloprovincialis

Plastic wastes are widespread pollutants in marine environments and several studies have focused on their impacts on different ecosystems. Microplastics (MPs, < 5 mm) have been the focus of a particularly extensive investigation because of their ubiquity, large surface area, interactions with organisms, and the challenges they present in terms of disposal and management. However, studies regarding their fates and life cycle in ecosystems are still limited. This study examined the effects of presence of food (the green microalga Dunaliella salina) on egestion rate of polyethylene MPs in the mussel Mytilus galloprovincialis. Ingestion and egestion rates were calculated after 6, 12, 18, and 24 h of depuration. The results suggest that MPs exposed to algal food persisted in the mussels. A single exposure of MPs without food induced relatively rapid excretion by the mussels compared to MPs exposure with food. This could be attributed to the ability of mussels to distinguish between nutritive foods and unusable suspended particles. Thus, environmental factors, such as food abundance, can affect the cycle or fate of MPs in marine environments.

Effects of micro-sized polyethylene spheres on the marine microalga Dunaliella salina: Focusing on the algal cell to plastic particle size ratio

There is increasing concern about how microplastics (MPs) are impacting marine ecosystems. In particular, studies on how MPs impact microalgae are required because of the abundance of MPs and importance of green microalgae as primary producers. This study investigated how MPs that are larger (200 μm) than algal cells impact them, using the marine microalga Dunaliella salina as the test species. The microalga was exposed to polyethylene MPs for 6 days. Of interest, the growth and photosynthetic activity of D. salina was enhanced with exposure to MPs, while cell morphology (size and granularity) was not impacted. This phenomenon might be explained by trace concentrations of additive chemicals (endocrine disruptors, phthalates, stabilizers) that possibly leached from MPs promoting the growth and photosynthetic activity of D. salina. We also confirmed that MP size contributes towards determining how plastics affect microalgae. Specifically, as MP size shrinks compared to algal cell size, MPs have increasingly adverse effects. MPs of very small size (like nanoplastics) induce particularly adverse effects on algae. Further studies are required to establish the relationship between algal cell size and MP size.

Effect of composite additives on microwave-assisted pyrolysis of microalgae

ABSTRACT The effect of composite additives on the pyrolysis characteristics of microalgae (Dunaliella salina) was studied by microwave-assisted pyrolysis system. The composite additive was blended by SiC and CaO. The three cases, i.e. different kinds of additives (single additive and composite additive), different addition amounts (5%, 10%, 15%, 20%, and 25%) of composite additives, and different blending ratios (SiC/CaO = 0:10, 3:7, 5:5, and 7:3) were investigated. The results show that when the composite additive was 15% and the blending ratio of SiC/CaO = 5:5, the average weight loss rate (R v) and weight loss rate for the second peak (R p2) were maximum, while the final time detected as weight stabilization (t f) and the time corresponding to second peak (t p2) were minimum. Besides, SiC and CaO had a synergistic effect in this experimental condition. When the additive was 7.5% SiC, the total weight loss (M t) and the weight loss rate for the first peak (R p1) were maximum and the time corresponding to first peak (t p1) was minimum. The minimum R v and M t occurred at 7.5% CaO group.

Electro-flotation harvesting of microalgae using a combination of electrode types

This study aims to search for a proper system for electro-flotation harvesting of microalgae Dunaliella salina with a minimization of metal contamination. The electro-flotation was realized by an application of constant electrical current via planar electrodes. An applied electrical current caused a cell aggregation and produced small bubbles which levitated cell clusters to form a foam layer containing concentrated microalgae on the top surface of the culture fluid. Since erosion induced by electrolysis did not occur for cathodes (negative electrodes), we tested the harvesting by using planar cathodes, lying in the bottom of the reactor, made from different materials and forms. For a given electrical current, all cathodes resulted in a similar harvesting efficiency as well as the energy consumption. Unlike the cathode, the anode (positive electrodes) usually erodes in the electrolytic process. To avoid contamination of released metal, we used only graphite plates as the anode. Different settings of graphite anode plates (located above the cathode) were studied. For a given electrical current, all cases of anode settings had a similar harvesting efficiency but the energy consumption increased with the distance between the anode and the cathode. For a given setup of electrodes, we showed that both the harvesting efficiency and the energy consumption increased with the applied electrical current. By considering the above results as well as the fact that the stainless steel plate is cheaper and easier to handle in comparison to the graphite plate, we suggest that a combination of graphite anode and stainless steel cathode is an appropriate set for microalgae harvesting with an avoidance of metal contamination. Furthermore, for a convenience of the collection of the levitated microalgae cells, the top surface should be leaved widely opened by setting the graphite anode plates near the wall of the reactor. Finally, we demonstrate a usage of the electrode combination for a large scale harvesting of the microalgae Dunaliella salina cultured with outdoor conditions in a salt production company located in Nakhon Ratchasima, Thailand.

Zeaxanthin Isolated from Dunaliella salina Microalgae Ameliorates Age Associated Cardiac Dysfunction in Rats through Stimulation of Retinoid Receptors.

Retinoids are essential during early cardiovascular morphogenesis. However, recent studies showed their important role in cardiac remodeling in rats with hypertension and following myocardial infarction. The present study aimed to investigate the effect of zeaxanthin heneicosylate (ZH); a carotenoid ester isolated from Dunaliella salina microalgae, on cardiac dysfunction ensuing d-galactose injection in rats. Rats injected with d-GAL (200 mg/kg; I.P) for 8 weeks were orally treated with ZH (250 μg/kg) for 28 consecutive days. Results showed that d-GAL injection caused dramatic electrocardiographic changes as well as marked elevation in serum levels of homocysteine, creatinine kinase isoenzyme and lactate dehydrogenase. A reduction in the cardiac contents of glucose transporter-4 and superoxide dismutase along with the elevation of inducible nitric oxide synthetase and interleukin-6 was also noticed. Oral administration of ZH significantly improved the above mentioned cardiac aging manifestations; this was further emphasized through histopathological examinations. The effect of ZH is mediated through the interaction with retinoid receptor alpha (RAR-α) as evidenced through a significant elevation of RAR-α expression in cardiac tissue following the lead of an in silico molecular docking study. In conclusion, zeaxanthin heneicosylate isolated from D. salina ameliorated age-associated cardiac dysfunction in rats through the activation of retinoid receptors.

Carotenoid Production by Dunaliella salina under Red Light.

The halotolerant photoautotrophic marine microalga Dunaliella salina is one of the richest sources of natural carotenoids. Here we investigated the effects of high intensity blue, red and white light from light emitting diodes (LED) on the production of carotenoids by strains of D. salina under nutrient sufficiency and strict temperature control favouring growth. Growth in high intensity red light was associated with carotenoid accumulation and a high rate of oxygen uptake. On transfer to blue light, a massive drop in carotenoid content was recorded along with very high rates of photo-oxidation. In high intensity blue light, growth was maintained at the same rate as in red or white light, but without carotenoid accumulation; transfer to red light stimulated a small increase in carotenoid content. The data support chlorophyll absorption of red light photons to reduce plastoquinone in photosystem II, coupled to phytoene desaturation by plastoquinol:oxygen oxidoreductase, with oxygen as electron acceptor. Partitioning of electrons between photosynthesis and carotenoid biosynthesis would depend on both red photon flux intensity and phytoene synthase upregulation by the red light photoreceptor, phytochrome. Red light control of carotenoid biosynthesis and accumulation reduces the rate of formation of reactive oxygen species (ROS) as well as increases the pool size of anti-oxidant.

Enhancement of co-production of nutritional protein and carotenoids in Dunaliella salina using a two-phase cultivation assisted by nitrogen level and light intensity

Microalga Dunaliella salina is known for its carotenogenesis. At the same time, it can also produce high-quality protein. The optimal conditions for D. salina to co-produce intracellular pools of both compounds, however, are yet unknown. This study investigated a two-phase cultivation strategy to optimize combined high-quality protein and carotenoid production of D. salina. In phase-one, a gradient of nitrogen concentrations was tested. In phase-two, effects of nitrogen pulse and high illumination were tested. Results reveal optimized protein quantity, quality (expressed as essential amino acid index EAAI) and carotenoids content in a two-phase cultivation, where short nitrogen starvation in phase-one was followed by high illumination during phase-two. Adopting this strategy, productivities of protein, EAA and carotenoids reached 22, 7 and 3 mg/L/d, respectively, with an EAAI of 1.1. The quality of this biomass surpasses FAO/WHO standard for human nutrition, and the observed level of β-carotene presents high antioxidant pro-vitamin A activity.

Recycling of Dunaliella salina cultivation medium by integrated membrane filtration and advanced oxidation

β-Carotene and other carotenoids are common food additives industrially produced by Dunaliella salina. However, the cultivation production costs are substantial and determine the economic viability of production in large-scale systems. There is a strong interest in recycling the cultivation medium in order to reduce the microalgae production costs. This work aims to study several oxidation techniques for treatment of permeate produced during harvesting of microalga Dunaliella salina by membrane filtration. The treated permeate produced is assessed for reuse as cultivation medium of Dunaliella salina. The permeate produced during membrane harvesting of Dunaliella salina was recovered and treated by ozonation and UV radiation. The different types of permeate produced were tested as cultivation media. The results obtained indicate that the permeate treated by UV with addition of H2O2 was best suited for the growth of Dunaliella salina during carotenogenesis. Nevertheless, although not performing as well as the selected cultivation medium, the use of untreated permeate seems a reasonable alternative to it, as the untreated permeate has potential to be the most cost efficient solution.

Chlorophyll and Carotenoid Content of Dunaliella salina at Various Salinity Stress and Harvesting Time

The Green halophylic species microalgae Dunaliella salina normally lives in hypersaline waters. The pigments of this algae (chlorophyll and carotenoids) have potential as nutraceutical products because of their bioactivity as natural antioxidants. This study was aimed to determine the effect of salinity stress and harvesting time on the production of chlorophyll (a and b), and carotenoids. Dunaliella salina was cultured on a laboratory scale at various levels of salinity, namely 20, 25, 30, 35, and 40 ‰ respectively. Pigment were harvested 3 times, namely during peak of logarithmic growth (P0), 24 hrs after peak (P1), and 48 hrs after peak (P2). The culture media was enriched with Walne’s solution, at pH 7 under 35 µmol quata. m-2.s-1 light intensity continuously at room temperature. The results showed that D. salina grew at given salinity. The highest and lowest growth was achieved at salinity 30 ‰ and 40 ‰, respectively. The highest chlorophyll a and b production was achieved at salinity 20 ‰ and at harvesting time the day after peak growth, while the highest production of carotenoid was obtained at salinity 25 ‰ harvested 48 hrs after the peak of growth. In conclusion, salinity stress was effective to increase chlorophyll and carotenoid production of D. salina.

Green synthesis of gold nanoparticles from Dunaliella salina, its characterization and in vitro anticancer activity on breast cancer cell line

An ecofriendly and efficient method (photoinduced) has been used for green synthesis of stable gold nanoparticles (AuNPs) using aqueous extract as a reducing and stabilizing agent, derived from halotolerant microalga Dunaliella salina. Synthesis of AuNPs was confirmed by UV–Vis spectroscopy showing sharp SPR band at 560 nm after 30 min exposure of sunlight. The synthesis was optimized further as exposure(75min) to sunlight, aqueous extract of Dunaliella (AED) inoculum dose(30%) and HAuCl4.xH2O (1 mM). The presence of nearly spherical shape of AuNPs with average size of 22.4 nm and crystalline nature were confirmed by TEM, SAED and XRD analysis. The XPS analysis of AuNPs showed presence of two individual peaks at 85.17 and 88.94eV that attributed to Au 4f7/2 and Au 4f5/2 respectively. Phycochemical analysis of AED demonstrated presence of phenolics, flavonoids, tannin and proteins. AED when subjected to SDS-PAGE showed protein bands of 92 and 66 KDa. AuNPs were tested for anticancer activity on MCF7 (cancer) and MCF 10A (normal) cell lines, keeping commercial drug cisplatin as positive control. AuNPs selectively killed cancer cells and were not detrimental to the normal cell line whereas cisplatin killed normal cells also at 48 h exposure, therefore, such AuNPs may be used as an anticancer agent.

Extraction of Bioactive Compounds Using Supercritical Carbon Dioxide.

Microalgae Dunaliella salina contains useful molecules such as β-carotene and fatty acids (FAs), which are considered high value-added compounds. To extract these molecules, supercritical carbon dioxide was used at different operative conditions. The effects of mechanical pre-treatment (grinding speed at 0–600 rpm; pre-treatment time of 2.5–7.5 min) and operating parameters for extraction, such as biomass loading (2.45 and 7.53 g), pressure (100–550 bars), temperature (50–75 °C) and CO2 flow rate (7.24 and 14.48 g/min) by varying the extraction times (30–110 min) were evaluated. Results showed that the maximum cumulative recovery (25.48%) of β-carotene was achieved at 400 bars and 65 °C with a CO2 flow rate of 14.48 g/min, while the highest purity for stage (55.40%) was attained at 550 bars and 65 °C with a CO2 flow rate of 14.48 g/min. The maximum recovery of FAs, equal to 8.47 mg/g, was achieved at 550 bars and 75 °C with a CO2 flow rate of 14.48 g/min. Moreover, the lowest biomass loading (2.45 g) and the first extraction cycle (30 min) allowed the maximum extraction of β-carotene and FAs.

Design and performance of bioreactor for fermentative biogas production from marine microalgae

Novel application of marine microalgae as a new source of renewable energy production, by using anaerobic digestion route, is presented in this paper. Traditionally, biogas was produced from animal manure. Microalgae however, has a potential application to be fermented and converted into biogas. This work describes the design of bioreactor to produce biogas. The bioreactor was made of stainless steel tube of 250 ml with a thickness of 2 inches, and surrounded by a water jacket with the height of 10 cm, diameter of 8 cm. The temperaure was controlled using thermocouple and data logger. The bioreactor contains stirring system to maintain good mixing. On the top side, a hose is used as biogas outlet and the gas pressure was measure. Testing of bioreactor was done using Dunaliella salina microalgae as main subtrate and tofu wastewater as additional subtrate. The anaerobic digestion was maintained from 7, 14 and 21 days, and the biogas produced were collected. The methane content analyzed by using gas chromatography and despite its low methane prodcution, it is found that microalgae is potentially used as biogas feed.

Metabolic changes and activity pattern of antioxidant enzymes induced by salicylic acid treatment in green microalga Dunaliella salina under nitrogen deficiency

The effect of salicylic acid (SA), an endogenous plant growth regulator, on adaptation of the green microalga, Dunaliella salina to N starvation was investigated through the study of enzymatic antioxidant system and biochemical changes. Algal cells in the exponential growth phase were exposed to N deficiency with 100 μM of SA. N starvation significantly decreased cell number, chlorophyll a, and hydrogen peroxide and while highly increased levels of fresh weight, soluble sugars, starch, proteins, free amino acids, and the activity of antioxidant enzymes. N-starved cells treated with SA enhanced cell number and hydrogen peroxide content, but accumulated lower amounts of metabolites and enzymatic activities compared to untreated cultures. However, the levels of fresh weight, chlorophyll, β-carotene, and soluble proteins remained roughly unchanged relative to N starvation alone. Proteolytic activity was well correlated with accumulation of amino acids in control and other treatments. The results suggest that exogenous SA treatment can enhance adaptation to N starvation by establishing the enzymatic balance to adjust levels of metabolites and directing them to the growth processes.

Toxicity assessment of the green Dunaliella salina microalgae.

The chronic toxicity of the Dunaliella salina microalgae was examined to evaluate its toxicity by the exposure of laboratory animals to high doses of Dunaliella salina and to estimate the possibility of using it as a safe supplement. Different hematological and biochemical analysis including complete blood picture (CBC), liver function enzyme activities; aminotransferases (ALT and AST), alkaline phosphatase (ALP), total bilirubin, kidney function tests; urea, creatinine, and albumin, as well as blood glucose level, were measured. The histopathological investigation was also carried out on hepatic, renal and cardiac architectures to examine its safety. Treatment with the dose 100 mg /kg body weight of D. salina powder daily for three consecutive months did not show any signs of toxicity in both genders and in mice and rats (no mortality, no hair loss, no diarrhea, no patches of yellow color appearance, etc…..). Moreover, abnormalities on behavior, food and water intakes and health status among the treated animals were not observed. CBC profile revealed a significant increase in hemoglobin (Hb) level in treating male and female mice and rats compared to their related control levels. The biochemical analysis clearly showed an insignificant change in liver enzyme activities, blood glucose level at a dose of 100 mg/kg. Also, an insignificant reduction in total urea and creatinine levels in both genders of mice and rats were noticed. Histopathological investigation showed normal architectures of all organs. Hence we can conclude that Dunaliella salina has been proven a safe profile up to 100 mg/kg body weight, however, it succeeded to stimulate the Hb synthesis compared to control groups, showing its benifits to be used safely as food additives or protective and curative agent in different diseases in future.

Tolerance of microalgae Dunaliella salina and Phaeodactylum tricornutum to various concentrations of selenium in the medium

Cell number dynamics and growth rate of microalgaeDunaliella salina(Chlorophyta) andPhaeodactylum tricornutum(Bacillariophyta) are considered in dependence on selenium concentration in the medium. The concentrations 0.01, 0.10, and 0,50 mg/l were tested. Onetime addition of selenium did not influence on the cell number and morphology ofD. salina. Under repeatable addition of selenium (every 2 days), reliable differences in the cells number were detected for the concentration 0.10 mg/l only, but the concentrations 0.01 and 0.50 mg/l did not make any effect on the cells different from the control. Under frequent repeatable addition of selenium (every day), the concentration 0.50 mg/l caused a visible decreasing of the cell number in compare with the control sample — after 6 days the cells started to decay, settled to the flask bottom and aggregated, the suspension color turned to yellowish. Reaction of diatomPhaeodactylum tricornurumwas more complicated. Its cell number increased signifcantly against the control under both one-time addition of selenium in the concentration of 0.10 and 0.50 mg/l or the repeatable addition in every 2 days in the concentration 0.01 and 0.10 mg/l. But more frequent (every day) addition of selenium in the concentration 0.50 mg/l caused inhibition of the cells growth and decreasing of their number against the control sample — after 4 days the cells adhesion to the flask bottom was detected, apparently because of their metabolism alteration.

Light regime and growth phase affect the microalgal production of protein quantity and quality with Dunaliella salina

The microalga Dunaliella salina has been widely studied for carotenogenesis, yet its protein production for human nutrition has rarely been reported. This study unveils the effects of growth phase and light regime on protein and essential amino acid (EAA) levels in D. salina. Cultivation under 24-h continuous light was compared to 12-h/12-h light/dark cycle. The essential amino acid index (EAAI) of D. salina showed accumulating trends up to 1.53 in the stationary phase, surpassing FAO/WHO standard for human nutrition. Light/dark conditions inferred a higher light-usage efficiency, yielding 5–97% higher protein and 18–28% higher EAA mass on light energy throughout the growth, accompanied by 138% faster growth during the light phase of the light/dark cycle, compared to continuous light. The findings revealed D. salina to be especially suitable for high-quality protein production, particularly grown under light/dark conditions, with nitrogen limitation as possible trigger, and harvested in the stationary phase.

Transcriptional and physiological responses of Dunaliella salina to cadmium reveals time-dependent turnover of ribosome, photosystem, and ROS-scavenging pathways

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.