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Concept: Dunaliella salina


Hypersaline environments pose major challenges to their microbial residents. Microorganisms have to cope with increased osmotic pressure and low water activity and therefore require specific adaptation mechanisms. Although mechanisms have already been thoroughly investigated in the green alga Dunaliella salina and some halophilic yeasts, strategies for osmoadaptation in other protistan groups (especially heterotrophs) are neither as well known nor as deeply investigated as for their prokaryotic counterpart. This is not only due to the recent awareness of the high protistan diversity and ecological relevance in hypersaline systems, but also due to methodological shortcomings. We provide the first experimental study on haloadaptation in heterotrophic microeukaryotes, using the halophilic ciliate Schmidingerothrix salinarum as a model organism. We established three approaches to investigate fundamental adaptation strategies known from prokaryotes. First, hydrogen-1 nuclear magnetic resonance (1H-NMR) spectroscopy was used for the detection, identification, and quantification of intracellular compatible solutes. Second, ion-imaging with cation-specific fluorescent dyes was employed to analyze changes in the relative ion concentrations in intact cells. Third, the effect of salt concentrations on the catalytic performance of S. salinarum malate dehydrogenase (MDH) and isocitrate dehydrogenase (ICDH) was determined. 1H-NMR spectroscopy identified glycine betaine (GB) and ectoine (Ect) as the main compatible solutes in S. salinarum. Moreover, a significant positive correlation of intracellular GB and Ect concentrations and external salinity was observed. The addition of exogenous GB, Ect, and choline (Ch) stimulated the cell growth notably, indicating that S. salinarum accumulates the solutes from the external medium. Addition of external 13C2-Ch resulted in conversion to 13C2-GB, indicating biosynthesis of GB from Ch. An increase of external salinity up to 21% did not result in an increase in cytoplasmic sodium concentration in S. salinarum. This, together with the decrease in the catalytic activities of MDH and ICDH at high salt concentration, demonstrates that S. salinarum employs the salt-out strategy for haloadaptation.

Concepts: Archaea, Bacteria, Organism, Eukaryote, Citric acid cycle, Microorganism, Halophile, Dunaliella salina


Chromium (Cr) is one of the most serious pollutants in aquatic systems. This study was performed to understand the effect of Cr (VI) on halophilic algal strains of D. salina and D. tertiolecta. The results revealed good tolerance of D. salina towards chromium (VI) up to 8 ppm concentration, whereas tolerance level in D. tertiolecta was up to 2 ppm concentration. Cr (VI) not only inhibited the growth of D. tertiolecta, but also showed increased inhibition in the level of photosynthetic pigments, protein and carbohydrate. Results have revealed that chromium (VI) induced higher increase in lipid peroxidation and H2O2 production in D. tertiolecta than the D. salina, particularly at higher concentration of chromium (VI). Chromium (VI) induced increase in the rate of RNO bleaching, loss of pigments and thiol (—SH) group was relatively higher in D. tertiolecta than the D. salina, which is indicating that D. tertiolecta was prone to Cr (VI) induced oxidative stress. Results on RNO bleaching in the presence of radical quenchers suggested that OHdeg radical played an important role in the chromium (VI)—induced general oxidative stress in D. tertiolecta.

Concepts: Algae, Photosynthesis, Oxidative stress, Vitamin C, Chromium, Halophile, Dunaliella, Dunaliella salina


The halotolerant alga Dunaliella salina is a model for stress tolerance and is used commercially for production of beta-carotene (=pro-vitamin A). The presented draft genome of the genuine strain CCAP19/18 will allow investigations into metabolic processes involved in regulation of stress responses, including carotenogenesis and adaptations to life in high-salinity environments.

Concepts: DNA, Archaea, Human Genome Project, Virus, Genome, Halophile, Dunaliella, Dunaliella salina


Energy consumption and water resource in the cultivation and harvesting steps still need to be minimized for the popularization of the microalgae-based products. An efficient electro-flocculation method for harvesting Dunaliella Salina integrated with local sand has been successfully applied. Sand was effective for speeding up the processes of flocculation and sedimentation of algal flocs and the electrolytic hydroxides was essential to bridge the sand and small flocs into large dense flocs. The maximal recovery effective improved from 95.13% in 6min to 98.09% in 4.5min and the optimal electrical energy consumption decreased 51.03% compared to conventional electro-flocculation in a laboratory ambient condition. Furthermore, reusing the flocculated medium in cultivation of the D. Salina with nitrogen supplemented performed no worse than using fresh medium. This sand enhanced electro-flocculation (SEF) technology provides a great potential for saving time and energy associated with improving microalgae harvesting.

Concepts: Algae, Agriculture, Improve, Water, Potential energy, Flocculation, Dunaliella, Dunaliella salina


S-adenosylhomocysteine hydrolase (SAHH) is an enzyme, which catalyzes the hydrolysis of S-adenosylhomocysteine (SAH) which is formed after the donation of the methyl group of S-adenosylmethionine (SAM) to a methyl acceptor in methylation reaction. As a potent regulator of methylation, SAHH plays a critical role in methylation reaction in the cells. Here we cloned the SAHH gene from unicellular green alga Dunaliella salina (dsSAHH) and investigated its effects on flagellar regeneration of D. salina, and found that dsSAHH was upregulated both at the protein and the transcription levels during pH shock-triggered flagellar regeneration of D. salina. The flagellar regeneration was accelerated when dsSAHH was overexpressed, but it was inhibited by SAHH inhibitor 3-deazaadenosine (DZA). Moreover, a receptor for activated C kinase 1 from D. salina (dsRACK1), which was identified to interact with dsSAHH, was increased when dsSAHH was overexpressed in D. salina as shown by real-time PCR. The findings of this study suggest that dsSAHH may participate in the regulation of flagellar regeneration of D. salina.

Concepts: DNA, Protein, Gene expression, Molecular biology, Adenosine triphosphate, Enzyme, RNA, Dunaliella salina