Chlamydomonas nivalis

The name Chlamydomonas nivalis is of compound Greek and Latin origin. Chlamydomonas is ultimately derived from the Ancient Greek χλαμύς (khlamús, "cloak, mantle") and μονάς (monás, "solitary"), while nivalis, from the Latin nivālis, translates to 'found growing in or near snow', as this species of algae are only found associated with snow or near snowy areas. == Morphology ==

Red snow has a variety of forms with cell development stages being considered to correspond with cell form. Cell wall structure is typically what differentiate cell types, with smooth, nippled, papillae, and wrinkled being among the most common. Cell sizes vary with red spheres being 35.96 ± 4.9 μm in diameter, ellipsoid/oval shaped cells being 20–28 mm long and 11–15 mm wide, and star shaped cells being 40–50 μm. Chlamydomonas nivalis have been observed to have primary and secondary cell walls, where the primary will be shed leaving a smooth cell wall behind. Secondary cell walls tend to constitute to more mature cysts of Chlamydomonas nivalis and being ribbed where as younger cysts were associated with being rounder, lobed, and smooth-walled. Furthermore, cell walls can be found to be 66 to 154 nm thick for smooth cell walled cysts. == Dispersal ==

While snow algae are considered to be a cosmopolitan species and Chlamydomonas nivalis has been observed across bipolar regions, the mechanisms behind their dispersal and migrations are not clear. Additional research across lattitude-ranges of red snow patches on glacial and snow fields will be advantageous in understanding the colonizing habits of snow algae. ==Description==

The seasonal life cycle of C. nivalis can be broken down to three stages based on the color of the cell as a result of carotenoid composition, which are green, orange, and red. Orange cells and red cells are the most difficult to differentiate as they look similar while the red and green cells are easiest to differentiate as they have more significant differences in composition. Cells at the red stage were previously described as a separate species than the green cells, but were later discovered to be different stages of the C. nivalis' complex life cycle. Small green coloured motile cells of the young C. nivalis at the green stage are produced in spring or early summer when temperatures are warmer and zygotes undergo meiosis in meltwater pools. The biflagellated cells are slightly oval and about 5-15 μm in diameter. In this asexually reproductive phase, the cells are sensitive to temperature and drought stress. They avoid unfavorable light and temperature by swimming in the snow until they reach more optimal conditions. 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. ==History==

The earliest documentation of red snow was made by Aristotle. While he recognized that something must be contributing to the odd colouration, red snow was also commonly mistaken as mineral deposits or pollen up until the early 1900s. In 1819, samples of 'red snow' were brought back for examination with a returning Arctic expedition under Sir John Ross. The samples were sent to Robert Brown and Francis Bauer for examination. Both men came to different conclusions on how to classify the specimens. Brown believed the specimen to be a unicellular alga while Bauer declared it a new species of fungus, Uredo nivalis. Over the next century, many researchers disputed over whether these organisms were lichen, plants, alga, or animal. 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. Unfortunately, due to the lack of sequencing techniques, reliance on visually examining similarly looking snow alga, and complicated life cycle of this species, errors continued to be made in classifying this and other species of snow algae. Today, C. nivalis has become one of the most well-studied snow algae. Although its taxonomy is still being settled, the life cycle of this snow algae is now much better understood. The historical disputes about the classification and misclassification of specimens have resulted in a number of names from older publications that all mean to refer to C. nivalis. These are: Uredo nivalis, Sphaerella nivalis, Protococcus nivalis, and Haematococcus nivalis. Furthermore, a new genus of snow algae has been proposed, Sanguina, with the predominant red snow algae found being classified as Sanguina nivaloides. Chlamydomonas nivalis is of close relation to Sanguina nivaloides. While using the name Sanguina nivaloides to be synonymous with Chlamydomonas nivalis is of interest, the two cannot be used interchangeably due to there not being a way to prove the historical species are conspecific. ==Habitat and ecology==

C. nivalis has been reported worldwide in mountainous regions, polar regions, or snowfields of every continent. It is the most abundant snow algae and typically composes the majority of cells identified in specimens taken from various sample sites. This includes, but is not limited to snow, rock surfaces, soil, meltwater, and cryoconite holes. The environmental conditions C. nivalis is typically exposed to are considered to be extreme. The cells can experience low nutrient availability, acidity, intense sunlight, radiation, extreme temperature regimes, and darkness. Red-snow algae have been shown experimentally to be limited by both nutrients (N, P, and K) and liquid water. C. nivalis spends the majority of its life in the cyst stage surrounded by snow at a depth that can range from . This can change depending on if the cell is in a mobile stage and can move, the snow melts due to the onset of warm weather, or the onset of precipitation causes more snow to fall on the cells. 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. In cryoconite holes C. nivalis can be found among bacteria, virus-like particles, ciliates, and Chlorophyte species. Infections of C. nivalis cells by chytrids, Chytridium chlamydococci, filamentous fungi, and Selenotila nivalis have also been observed. The cell wall, as the boundary that protects the inner contents of the cell from the harsh conditions in its habitat, is very rigid and hard to destroy. Negatively charged phosphatidylglycerol composes the majority of the thylakoid membranes. The thylakoid membrane lipid composition can also be changed to enhance lipid fluidity in response to lower temperatures. An undulated membrane encloses the chloroplast. Lipid bodies and carotenoid globules surround the plastid. A red secondary pigment, astaxanthin and esterified derivatives of it, accumulates up to 20 times the amount of chlorophyll a in the cytoplasmic lipid bodies of mature red spores. 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. The absorbed radiation is converted to heat, aiding in the melt of nearby snow and ice crystals to access needed nutrients and liquid water. Astaxanthin can also act as a metabolic sink for the metabolically active spores that do not divide. Within the cytoplasm there are several small cytoplasmic vacuoles with partially crystallized content within it. While mitochondria are present, they are not very obvious. Most of the cytoplasmic space is taken up by the large plastid, lipid bodies, and carotenoid globules. 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. The majority (91%) of astaxanthin derivatives are stored in its monoester form within dormant C. nivalis red cysts. Astaxanthin is the pigment that makes the cell appear deep red. Other pigments that can also be found in C. nivalis include violaxanthin and adonirubin. ==Role in environmental processes and research==

Albedo Reduction Visible algal blooms could be a crucial determinant of surface albedo. It has been suggested that algal blooms partially composed of C. nivalis may contribute to lowering ice and snow albedo. The red coloured pigments produced by the cell in combination with inorganic material could enhance the darkening over the snow and reduce the surface area of white snow. 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. However, it is also important to consider that positive feedback loops may not be a universal response to algal blooms. Duration of water melt might be a controlling factor for snow algae blooms and in the European Alps, blooms could be considered as staying stable or even being reduced. C. nivalis can be used as a model species for studying the cellular response mechanism to stressful conditions given the harsh conditions of its habitat. It is also an important organism to study adaptation to extreme environments and may become one of the leading systems for research in cold adaptation. C. nivalis could also potentially be a source for pharmaceuticals, supplements, or beauty products if the algae could be mass produced for its astaxanthin. The snow algae itself is likely safe to eat as there is no evidence supporting that it would cause diarrhea when ingested. Astrobiology Additionally, psychrophiles have also been of interest in astrobiology (exobiology) to further our understanding of life in the cosmos. With their adaptation to icy environments, these organisms can provide valuable insight into how life might evolve under similar conditions but on other cosmic bodies such as the moons Europa and Enceladus. Snow algae, specifically Chlamydomonas nivalis, has been of interest due to their production of carotenoids and secondary carotenoids (notably astaxanthin) and using them as biomarkers for habitability in the solar system. ==References==