Osmotic responses of Dunaliella to the changes of salinity

Abstract

Some species in genus Dunaliella are unique in their remarkable abilities to accumulate large numbers of beta-carotene and thrive in media containing a wide range of NaCl concentrations ranging from about 0.05 M to saturation (around 5.5 M). The algae contain no rigid polysaccharide cell wall and thus have been found to be able to rapidly change their volume and shape in response to changes in the extracellular hypo- or hyper-osmotic pressure. In osmotic adjustment, the osmoregulatory response of Dunaliella functions to maintain osmotic balance at high salinities by synthesis and varying the intracellular concentration of glycerol. In this review, we describe the osmotic response process of Dunaliella under salinity stress, including the changes of cell volume, intracellular ions concentration, intracellular glycerol concentration, and the expression of some salt-induced genes. Some specific proteins and enzymes can be induced by different salinities in osmotic response process. In addition, we introduce the exogenous expression of salt-related genes of Dunaliella salina in plants and microorganisms for the purpose of confirming the functions of related genes, proteins, and enzymes. The aim of this review is to emphasize the importance of the studies on the mechanisms of osmotic adjustments of Dunaliella in order to develop its unique osmotic characteristics. It is prospected that future research should pay attention to the specific signal transduction pathway and the mechanism of osmoregulation, and to improve the salt tolerance of higher plants by using salt-tolerant genes of Dunaliella.

The relationship of glycerol and glycolysis metabolism patway under hyperosmotic stress in Dunaliella salina

“…Sources of carbon for glycerol synthesis come from photosynthetic CO 2 fixation and from the products of reserved starch decomposition [11,22,23]. Under hyperosmotic stress, glycerol is massively accumulated, and the source of carbon for glycolysis comes mainly from reserved starch decomposition [11,23]. During glycolysis, PFK converts glucose to Fructose-1,6-BP, which is then converted to DHAP and glycerol-3-phosphate (Glycerol-3-P) by glycerol-3-phosphate dehydrogenase (GPD).…”

“…The content of intracellular dihydroxyacetone phosphate determines the rate and amount of the production of glycerol. Phosphofructokinase (PFK) [8] and glycerol-3-phosphate dehydrogenase (GPD) [9][10][11] are two key enzymes of this process. PFK catalyzes the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate [12,13], and has the characteristics of allosteric modulation in bacteria, plants, and animals, keeping consistent with the activity of glycolysis [14].…”

Transcriptome sequencing and annotation of the halophytic microalga Dunaliella salina

“…An increase in salinity promotes intracellular glycerol production within two hours to maintain osmotic homeostasis. Cells recover with osmotic stress-induced gene expression and accumulation of proteins 24 h later (Chen and Jiang, 2009). The carbon for glycerol biosynthesis is obtained mainly from photosynthetic products or the degradation of stored polysaccharides with the latter dominating under 1.3.5.5), 15-cis-phytoene desaturase; ZCI (EC: 5.2.1.12), δ-carotene isomerase; ZDS (EC: 1.3.5.6), δ-carotene desaturase; PLI (EC: 5.2.1.13), prolycopene isomerase; LcyB (EC: 5.5.1.19), lycopene β-cyclase; CruP, lycopene cyclase CruP; LUT5 (EC: 1.14.−.−), cytochrome P450, family 97, subfamily A (β-ring hydroxylase); LcyE (EC: 5.5.1.18), lycopene ε-cyclase; ZEP (EC: 1.14.13.90), zeaxanthin epoxidase; LUT1 (EC:1.14.99.45), carotene ε-monooxygenase.…”

“…Excess glycerol in (Volvox carteri, Chlamydomona, Coccomyxa, Chlorella, Dunaliella, Auxenochlorella, and Micromonas), remaining algae and higher plants in the plant category cells exposed to hypo-saline stress is degraded to maintain lower osmotic pressure. This reaction is catalyzed by DHR to produce DHA (Chen and Jiang, 2009), followed by phosphorylation with dihydroxyacetone kinase (DAK, EC: 2.7.1.29) to regenerate the three-carbon metabolic intermediate DHAP.…”

Protocol for maximizing the triglycerides-enriched lipids production from <i>Dunaliella salina</i> SA32007 biomass, isolated from the Salar de Atacama (Northern Chile)

“…Different culture tests including high salinity and nutrient limitation (e.g. Mg, K, Na, NO 3 and PO 4 ) can enhance lipid synthesis and particularly triglycerides, but unfortunately these conditions produced a microalgae biomass reduction and therefore, the biodiesel yield also decreases [8][9][10][11][12][13][14][15][16]. The objective of this study was the assay of specific conditions in salinity and nitrogen deficiency and air bubbling that could stimulate the triglycerides production, while the negative effect over the biomass is mitigated.…”