Physiological characterization and stress-induced metabolic responses of Dunaliella salina isolated from salt pan

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Abstract
A Dunaliella strain was isolated from salt crystals obtained from experimental salt farm of the institute (latitude 21.46 N, longitude 72.11°E). The comparative homology study of amplified molecular signature 18S rRNA, proves the isolated strain as D. salina. The growth pattern and metabolic responses such as proline, glycine betaine, glycerol, total protein and total sugar content to different salinity (from 0.5 to 5.5 M NaCl) were studied. The optimum growth was observed at 1.0 M NaCl and thereafter it started to decline. Maximum growth was obtained on 17th day of inoculation in all salt concentrations except 0.5 M NaCl, whereas maximum growth was observed on 13th day. There were no significant differences (P < 0.01) in chlorophyll a/b contents (1.0–1.16 ± 0.05 μg chl. a and 0.2–0.29 ± 0.01 μg chl. b per 106 cells) up to 2.0 M NaCl, however at 3.0 M NaCl a significant increase (2.5 ± 0.12 μg chl. a and 0.84 ± 0.4 μg chl. b per 106 cells) was observed which declined again at 5.5 M NaCl concentration (2.0 ± 0.1 μg chl. a and 0.52 ± 0.03 μg chl. b per 106 cells). Stress metabolites such as proline, glycine betaine, glycerol and total sugar content increased concomitantly with salt concentration. Maximum increase in proline (1.4 ± 0.07 μg), glycine betaine (5.7 ± 0.28 μg), glycerol (3.7 ± 0.18 ml) and total sugar (250 ± 12.5 μg) per 105 cells was observed in 5.5 M NaCl. A decrease in total protein with reference to 0.5 M NaCl was observed up to 3.0 M NaCl, however, a significant increase (P < 0.01) was observed at 5.5 M NaCl (0.19 ± 0.01 μg per 105 cells). Inductive coupled plasma (ICP) analysis shows that intracellular Na+ remained unchanged up to 2.0 M NaCl concentration and thereafter a significant increase was observed. No relevant increase in the intracellular level of K+ and Mg++ was observed with increasing salt concentration. Evaluation of physiological and metabolic attributes of Dunaliella salina can be used to explore its biotechnological and industrial potential.