Cryptomonas

Cryptomonas is the name-giving genus of the Cryptomonads established by German biologist Christian Gottfried Ehrenberg in 1831. It is common in freshwater habitats and brackish water worldwide and often forms blooms in greater depths of lakes. The cells are usually brownish or greenish in color and are characteristic of having a slit-like furrow at the anterior. They are not known to produce any toxins. They are used to feed small zooplankton, which is the food source for small fish in fish farms. Many species of Cryptomonas can only be identified by DNA sequencing. Cryptomonas can be found in several marine ecosystems in Australia and South Korea. Cryptomonas has the meaning of hidden small flagellates from “crypto” and “monas”. Species within Cryptomonas contain four genomes: the nuclear, the nucleomorph, the plastid, and mitochondrial genomes. The plastid genome contains 118 kilobase pairs and is a result of one endosymbiosis event of ancient red alga. The study of genome structures of the genus has contributed to the life-history dependent dimorphism of Cryptomonas, which is discussed in details later in the section Dimorphism. Cryptomonas are also photolithotrophs that contribute to oxygenic carbon fixation making them greatly critical to the carbon levels of fresh water environments. Replication of Cryptomonas occurs in early summer when fresh water species are also reproducing. Cryptomonas replicates via mitosis that only takes about ten minutes. Sexual reproduction is not observed in this genus as many other genera of Cryptophytes also do not reproduce sexually. Organisms are asymmetric with a transparent membrane on the outside. The membrane is not ciliated. Cryptomonas cells are fairly large; they average about 40 micrometers in size and often take the shape of an oval or ovoid. There are two flagella present, yet the two flagella are not equally sized. One is shorter and curled and the other one is longer and straight. The two flagella are fixed to the cell by four unique microtubular roots. In addition, the flagella are lined with small hairs that allow for better movement. There are also contractile vacuoles that control the flow of water in and out. Two boat-shaped plastids are observed in the cells. In a secondary endosymbiosis event, the phagotrophic ancestor of the Cryptomonas presumably captured a red alga and reduced it to a complex plastid with four envelope membranes. The phycobilisomes of the former red algae were reduced until only phycoerythrin remained. Phycoerythrobilin, a type of red phycobilin pigment, is a chromophore discovered in cyanobacteria, chloroplasts of red algae and some Cryptomonads. Phycoerythrobilin is present in the phycobiliprotein phycoerythrin, the terminal acceptor of energy during the process of photosynthesis. The phycoerythrin was translocated into the thylakoid lumen with its chromophore composition altered; subsequently, phycobiliproteins with at least seven different absorption spectra evolved. Cryptomonas is distinguished by the purple phycoerythrin 566 as an accessory pigment, which gives the organisms a brownish color in appearance. Cryptomonas are large in size, grow rather slowly, and are limited in nutrients. It also migrates between depths of water in order to reach depths that are ideal for photosynthesis and bacteriograzing, as well avoiding organisms that are their predators. Typically, they are found at depths of up to 102 meters and in a temperature range of -1.4 to 1.5 degrees Celsius. Cryptomonas seem to grow and survive with little competition. Cryptomonas swim actively. They rotate while moving and sometimes swim in helical motion.