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Color changes in Dunaliella: How does the environment affect its appearance?
Dunaliella is a single-celled photosynthetic green alga known for its ability to outlast other organisms in extremely salty environments. While most Dunaliella species are found in marine environments, a few freshwater species are rare. Certain species in this genus are able to accumulate relatively large amounts of beta-carotene and glycerol under extreme growing conditions, such as high light intensity, high salt concentrations, and limited oxygen and nitrogen levels. Despite this, Dunaliella is still widely distributed in lakes and lagoons around the world. Dunaliella species are difficult to distinguish based on morphology and physiology alone because it lacks a cell wall and can change shape, plus it has different pigments that change color depending on environmental conditions. Through molecular phylogenetic analysis, it becomes crucial to identify the taxonomic system of Dunaliella.
Dunaliella has been studied for more than a hundred years and has become an important model organism for studying the salt-tolerant adaptation process of algae.
The evolution of history and knowledge
Dunaliella was first discovered in 1838 by French botanist Michel-Felix Dunal and was named Haematococcus salinus. However, when the creature was officially described and named a new genus in 1905, the name of Deluster was changed to Dunaliella in honor of the original discoverer. To describe the genus, de Lust studied living specimens from Romanian salt lakes, recording color, movement and general morphological characteristics. In the same year, another biologist, Clara Hamburg, also described the genus, but unfortunately, De Lust's paper was published before hers. Since then, various studies on Dunaliella have been gradually carried out, such as Kavala's 1906 expansion of Hamburg's salt pan research, Pierce's 1914 research on California's Salt Neck Sea, and Rabe's ecological research.
In 1906, de Lust described two species, Dunaliella salina and Dunaliella viridis, which could be distinguished by their size and color. Later research revealed that D. salina's red color came from its accumulation of large amounts of carotene, while D. viridis was a smaller, greenish variant. In 1921, Rabe conducted a study in which he placed Dunaliella in a lower salinity environment and observed that the creatures adapted to the new environment and became greener in color. This finding highlights the color changes caused by carotene accumulation at extremely high salinities.
Habitat and Ecology
Halophilic species such as Dunaliella salina thrive in extreme environments such as salt lakes, salt pans and crystallization ponds around the world. Their salt tolerance allows them to differentiate themselves from other organisms and become key primary producers in hypersaline ecosystems. What's more, Dunaliella is considered the primary food of small filter feeders and a variety of plankton.
For example, in the Great Salt Lake, Dunaliella is the dominant primary producer in the North Bay and is also an important component of the photosynthetic community in the South Bay.
In these extremely saline environments, Dunaliella can accumulate large amounts of intracellular glycerol over a long period of time to resist high external osmotic pressure. This allows them to reproduce and endure the challenges of survival in extreme environments.
Morphology and Cellular Processes
Dunaliella is an oscillating green algae that varies in shape from species to species, including oval, ovoid, and cylindrical. During certain growth stages, Dunaliella's cells can transform into round dormant bodies. The cells are usually 7 to 12 microns long and vary depending on environmental conditions, such as changes in light, salinity and nutrient supply. D. salina cells are significantly larger, usually 16 to 24 microns long.
The two equal-length flagella of these cells are approximately 1.5 to 2 times the length of the cell and can swing rapidly to propel the cell forward. Dunaliella's cell membrane has an obvious thick sticky coating and no synthetic transport vesicles, which makes it more flexible to adapt.
Under conditions of high light intensity and salinity, accumulation of beta-carotene can cause cells to appear orange to red in color.
Life cycle
Dunaliella cells reproduce sexually under adverse conditions. When two haploid motile cells come into contact, they fuse to form a thick-walled diploid zygote that can survive harsh conditions until a suitable environment returns. Thereafter, the zygote will undergo meiosis, releasing dozens of haploid daughter cells. This is an effective survival strategy when the current ecological environment changes such as high salinity or lack of moisture.
If we don’t reexamine Dunaliella’s environmental adaptability, we may miss the opportunity to understand how to respond to future environmental changes.
The color of Dunaliella is closely related to ecology. This unique appearance change makes us think deeply about the survival strategy of this algae and its interaction with the environment. How do you think environmental changes will affect algal ecosystems in the future?
