It has remained relevant due to its numerous biotechnological applications, including β-carotenoid cosmetic and food products, medicine, and biofuel research.
[5] Dunaliella was originally called Haematococcus salinus by a French botanist named Michel Félix Dunal, who first sighted the organism in 1838 in saltern evaporation ponds in Montpellier, France.
However, when the organism was officially described and labelled as a new and distinct genus in 1905 Bucharest, Romania by Emanoil C. Teodorescu, the name was changed to Dunaliella in honour of the original discoverer.
To describe the genus, Teodoresco studied live samples from Romanian salt lakes and noted details like colours, movement, and general morphologies.
[6] The genus was also described by another biologist in 1905 named Clara Hamburger in Heidelberg, Germany, but unfortunately Teodoresco's paper was published first while she was in the final stages of her own article's production.
The distinct classifications came from D. salina being notably bigger in size and being red in colour due to large amounts of carotenoid pigments.
[7][6] Then, in 1921, Labbé performed a study in which he placed samples of Dunaliella from saltern brines into a lower salinity environment and observed that the organisms adapted to the new conditions of the fresh water and lost their brown-red pigment and became greener – meaning that the red colour must have originated through very euryhaline chlorophyll-filled cells changing to a red colour in extremely saline conditions after permanently damaging their chlorophyll pigments.
[1] It has been reported that in the winter months, when temperatures reach 0 °C, there is a large accumulation of round cyst-like cells that deposit themselves on the bottom of the Great Salt Lake.
This encysting property of Dunaliella must have been critical for its survival in the Dead Sea, where salt concentrations have risen to intolerable amounts, such that the organism cannot be found in the water column today.
[1] Back when the alga was found in the water column, however, population rate monitoring revealed that Dunaliella growth was inhibited by high concentrations of magnesium and calcium ions.
[6] Dunaliella blooms can therefore only occur in the Dead Sea when the waters become sufficiently diluted by winter rains and when the limiting nutrient phosphate is available.
[8] Dunaliella is a biflagellate green algal and mostly marine protist that, in its vegetative motile form and depending on the species, exhibits ellipsoid, ovoid, and cylindrical shapes that sometimes taper at the posterior end.
Olivera et al. noticed that the cell coating was affected by proteolytic enzymes and neuraminidase and concluded that its makeup must be mostly glycoprotein with some neuraminic acid residues.
[11] Instead of contractile vacuoles, marine species of Dunaliella replace the organelle's usual spot in most other Chlorophyceae cells, with two to three dictyosomes that lie in a characteristic parabasal position with their forming faces toward the plasmalemma and ER.
Secondly, when triggered by the changes in cell volumes and in levels of inorganic phosphate and pH following osmotic shock, plasma membrane sensors and various soluble metabolites activate glycerol synthesis.
Their descriptions have hardly changed since their original publications and various ones are still being debated for whether they warrant the classification as Dunaliella due to certain species having differently placed pyrenoids, missing eye spots, unusual cell division, etc.
[2][8] When conditions are unfavourable due to prolonged dryness or exposure to low salinity waters, Dunaliella cells undergo sexual reproduction.
Two haploid vegetative motile cells will touch flagella and then fuse their equal-sized gametes with one another in a very similar way to Chlamydomonas by the formation of a cytoplasmic bridge.
After this isogamous fertilization, the diploid zygote, which is red and/or green in colour, develops a thick and smooth wall and takes on a circular shape very similar to the cyst form of Dunaliella.
[3] Since 1999, molecular analysis is used as the primary tool in Dunalliela identification due to its ability to analyze data independent of environmental factors 11.
In fact, the idea for developing solutes to maintain osmotic balance in other organic matter originated from the osmoregulatory abilities of Dunaliella.