Abstract
Halophilic representatives of the genus Dunaliella, notably D. salina and D. viridis, are found worldwide in salt lakes and saltern evaporation and crystallizer ponds at salt concentrations up to NaCl saturation. Thanks to the biotechnological exploitation of D. salina for β-carotene production we have a profound knowledge of the physiology and biochemistry of the alga. However, relatively little is known about the ecology of the members of the genus Dunaliella in hypersaline environments, in spite of the fact that Dunaliella is often the main or even the sole primary producer present, so that the entire ecosystem depends on carbon fixed by this alga. This review paper summarizes our knowledge about the occurrence and the activities of different Dunaliella species in natural salt lakes (Great Salt Lake, the Dead Sea and others), in saltern ponds and in other salty habitats where members of the genus have been found.
Highlights
Teodoresco (Teodorescu) (1866–1949) described the habitat of the new genus of halophilic unicellular algae Dunaliella, it was known from salterns and salt lakes around the Mediterranean and the Black Sea [1,2,3]
Today we known halophilic members of the genus Dunaliella to occur in hypersaline environments worldwide as the main and often as the sole primary producer, especially at the highest salt concentrations where other oxygenic phototrophs cannot grow [2,4]
In spite of the in-depth understanding of the properties of Dunaliella strains used for the commercial production of β-carotene, often under carefully controlled conditions, we know relatively little about the behavior of these species and their closest relatives in their natural environment or in semi-natural systems such as the saltern ecosystem
Summary
While in the athalassohaline salt-saturated environment of the Dead Sea only smaller green types were found, the large-celled D. salina generally outcompetes D. viridis and D. parva in NaCl-dominated brines approaching saturation This is illustrated in a study in Hutt Lagoon, a hypersaline lagoon in Western Australia where D. salina is grown for β-carotene production. Monitoring diel changes in dissolved oxygen concentrations in mesocosms with crystallizer brine from the salterns of Eilat, Israel (1300– 2100 D. salina cells ml−1) yielded production estimates of ~0.8–1.5 μmol O2 l−1 hr−1 [51,81] These rates, equivalent to ~120–220 μg C l−1 day−1, are significantly higher than those measured in the Spanish salterns populated by denser Dunaliella communities [54]. At temperatures above 40°C, as regularly encountered in saltern evaporation ponds [55], glycerol leakage maybe significant [83]
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