Glycerol production by Dunaliella bioculata

Abstract

Dunaliellu bioculatu, a marine unicellular euryhaline green alga, accumulated intracellular glycerol as a response to increaed osmolality due to increased concentrations of NaCl, KCl or sucrose, but not ethylene glycol. A decrease in salinity, below the normal, of the outel medium resulted in a decrease in the intracellular glycerol. Glycerol was retained (NaCl salinization) or released (KCl salinization) by the alga. Glycerol production slightly depended on photosynthesis since it took place in the light and in the dark.Dunaliella is a genus of biflagellate unicellular green algae, the cells of which are wallless (ROUND 1973). The ability of Dunaliella cells to survive and flourish in marine environments under the influence of osmotic stresses has received considerable attention. These euryhaline organisms, because of their remarkable capacity to adjust to salinity stress, have been studied t o determine mechanisms used t o maintain osmotic equilibrium between cells and environment. Some species of Dunaliella were recorded to grow in salinities ranging from 0.3 to 12% (MCHLACHLAN 1960). The high degree of correlation between the internal concentration of glycerol and osmolarity of the clear whether the glycerol production is induced by ionic and/or osmotic stress. Thus the aim of the present work was t o study the effect of some ions and osmotica on glycerol production by D. bioculata. NaCl of KCl (osmotic and ionic components) and sucrose or ethylene glycol (osmotic components) were applied to D. bioculata cdture to elucidate the roles played by the two types of stresses on glycerol formation. Materials and methodsDunuliella bioculutu was cultivated axenically in an artifical sea water medium containing 0.5 M NaCl (BRUQOMANN et ul., 1978). The cells were illuminated with irradiation from high-pressure mercury lamps (radiant flux density 11 Wm-2, 12 h photoperiod) a t a temperature of 25 "C. Algae were used a t the late log phase of growth.Cells were harvested by centrifugation at 3500 x g for 5 min, and weie suspended, with minimal agitation, a t ten times the original cell density, in 16 mM phosphate buffer, pH 7.5, containing 2 m~. MgCl, and the same concentration of NaCl as in the growth medium. Chlorophyll was determined from methanolic extmcts of the cells (HOLDEN 1976). I n the stress experiments the osmotica were added to a medium which contained 0.5 M NaCl was taken into account in determining the final osmolality (WOLF et ul. 1977). 30

Molecular Clone and Expression of a NAD+-Dependent Glycerol-3-Phosphate Dehydrogenase Isozyme Gene from the Halotolerant alga Dunaliella salina

“…Glycerol is an important osmotically compatible solute in Dunaliella under salt stress [8], [9]. The extracellular osmotic pressure is released in Dunali ella by changing intracellular glycerol content.…”