Chlamydomonas nivalis, also referred to as Chloromonas typhlos,[2][1] is a unicellular red-coloured photosynthetic green alga that is found in the snowfields of the alps and polar regions all over the world.

The habitat of C. nivalis subjects the cells to environmental extremes including limited nutrients, low temperatures, and intense sunlight.

In comparison with the mesophilic C. reinhardtii, C. nivalis has special mechanisms that allow it to be cryotolerant and survive on rock surfaces as well as in soil, meltwater, and snow.

Although the seasonal mobile to dormant life cycle of C. nivalis is complex, it also helps the algae exploit its niche and survive unfavourable conditions.

When taking account of the photoprotective effect of its secondary carotenoid, astaxanthin, among the other adaptive mechanisms to its extreme habitat, it can be understood how C. nivalis became so dominant in microbial snow algae communities.

This alga is an interesting organism for researchers in various fields to study due to its possible role in lowering global albedo, ability to survive in extreme environments, and production of commercially relevant compounds.

[9][10] The seasonal life cycle of C. nivalis can be broken down to three stages based on the colour of the cell as a result of carotenoid composition, which are green, orange, and red.

Secondary carotenoid concentrations are much lower at this stage as the cells need photosynthetically active radiation for energy and growth.

[15] Later in the season, when nitrogen and nutrients becomes limited and radiation stress increases, the green cells will develop into flagellated sexual gametes that mate and produce new zygotes that have lost their flagella and are capable of surviving the winter period.

[16][14] Transformation into the zygote, or hypnoblast, is characterized by the production and accumulation of reserve materials that include sugars and lipids as well as the formation of esterified secondary carotenoids.

[14][17] In addition, the color of these pigments reduces albedo such that individual cells may melt nearby ice and snow crystals to access limiting nutrients and water in an otherwise unavailable frozen state.

It was not until the early 20th century when researchers finally began to agree on the algal nature of the organism and gave its currently known name, Chlamydomonas nivalis.

The cells can experience low nutrient availability, acidity, intense sunlight, radiation, extreme temperature regimes, and darkness.

[26] Cells that are exposed on unshaded snow may be subjected to high levels of visible light and ultraviolet radiation for an extended amount of time.

[15] Due to C. nivalis' ability to perform photosynthesis well from cold to moderate temperatures, this species is considered a cryotolerant mesophile rather than a cryophile.

[32] Another bacterium, Mesorhizobium loti, was found as contamination in a C. nivalis culture, but further testing suggested that this bacteria may be synthesizing vitamin B12 for the algae.

The orange cells mature into red cysts, the form in which it will remain for the remainder and longest portion of its life cycle.

The cell contains one central chloroplast that has a naked pyrenoid, ribosomes, starch grains, and numerous small grana stacks composed of 3-7 thylakoids within it.

[23][15] Astaxanthin protects the chloroplast from excessive light by absorbing a portion of it before it reaches the photosynthetic apparatus which subsequently prevents photoinhibition and UV damage.

[35] The absorbed radiation is converted to heat, aiding in the melt of nearby snow and ice crystals to access needed nutrients and liquid water.

[15][32] C. nivalis has one centrally located nucleus that is also oriented such that it is covered by the carotenoid globules full of astaxanthin that will provide protection against UV radiation.

[39] Due to the absorption of solar energy by the alga, albedo would be reduced and the darker areas on the snow where the blooms form would melt more rapidly.

[39] As a result, populations of C. nivalis would increase, creating a feedback loop that amplifies melting and reduces sunlight absorbance which contributes to glacier retreat and lowering albedo, as shown experimentally.