A biotechnological process called "Algal milking" has been established for the continuous production and extraction of glycerol as a compatible solute from the green alga Dunaliella bardawil. The quantity of glycerol increases up to 290 mg/l algal suspension with increasing the salinity of the medium to 4 M after 8 days incubation. On the other hand, the best osmotic range of alternative osmotic shocks for a continuous production and extraction of glycerol from the algal cells was (0.4 - 1.5 M NaCl). After estimation of released glycerol, subsequent reincubation in medium with 1.5 M NaCl resulted in recovery of cells and resynthesis of glycerol. After a defined regeneration time the procedure could be repeated thereby enabling the cells to be reused again. In the milking experiments which extended for >49 days; the results illustrated a remarkable increase in growth, intracellular glycerol production and release. The final volumetric productivity of glycerol was 13.47 mg/L/d algal suspension when the recovery time was seven days (total 7 cycles) and it was 18.33 mg/L/d when the recovery time was three days (total 16 cycles). Therefore, it seems that the use of D. bardawil is ideal and promising for milking in order to promote commercial production of glycerol.
Key words: Glycerol, Dunaliella bardawil, osmotic shocks, compatible solute, osmoregulation
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