Cryptomonas

From MicrobeWiki, the student-edited microbiology resource
A Cryptomonas ovata phytoplankter from a sample collected at Lake Toolik (Alaska, USA). From micro*scope

Classification

Eukaryota; Cryptophyta; Cryptomonadales; Cryptomonadaceae; Cryptomonas

Species

Cryptomonas borealis [1]

Cryptomonas commutata [2]

Cryptomonas curvata [3]

Cryptomonas erosa [4]

Cryptomonas gyropyrenoidosa [5]

Cryptomonas lundii [6]

Cryptomonas loricata [7]

Cryptomonas marssonii [8]

Cryptomonas obovoidea [9]

Cryptomonas ovata [10]

Cryptomonas paramaecium [11]

Cryptomonas phaseolus [12]

Cryptomonas pyrenoidifera [13]

Cryptomonas tetrapyrenoidosa [14]

Description and Significance

Cryptomonas is a genus of phytoplankton that inhabit freshwater aquatic systems. The genus belongs to a larger collective of organisms called "cryptomonads", which consists of of biflagellate organisms. Cells tend to be rather large, varying in shape between ovoid and elliptical, averaging 40 um in size. Cryptomonads can be either protozoans (order Cryptomonadida) or alga (class Cryptophyceae). Cryptomonas phytoplankton function as primary producers in freshwater ecosystems and contribute to the foraging base of many heterotrophs, including macroinvertibrates and fishes. While species coexist in the same habitats, they follow sequential blooms and occupy different spatial niches within the water column, which lends evidence to solve the "paradox of the plankton".

Genome Structure

The phylogenetic tree for the genus Cryptomonas. From Tree of Life Web Project

Originally this genus existed as three seperate genuses: Cryptomonas, Campylomonas, and Chilomonas. However, after the analysis of two nuclear ribosomal DNA regions and and a nucleomorph ribosomal gene, Campylomonas and Chilomonas were found to be the result of life history-dependent dimorphism in the Cryptomonas genus, and where therefore reclassified. [1]

Species within the genus Cryptomonas have 4 genomes within the cell: the nucleus, the nucleomorph, the plastid, and the mitochondrial genomes. The plastid genome is circular and contains 118 kilobase pairs. This genome is the direct result of secondary endosymbiosis via a viral phage from a red alga, which accounts for the presence of red pigments within Cryptomonas species while other related genuses lack these pigments.[2]

Cell Structure, Metabolism and Life Cycle

Interesting features of cell structure; how it gains energy; what important molecules it produces.

Cryptomonas are unique in their possession of two flagella, extending off either side of the cell. These structures are anchored within the cell by a unique configuration of four microtubular roots that work in cooperation with a striated fibrous root. The microtubular roots enter the anterior dorsal lobe of each Cryptomonas, while the striated fibrous root will be joined by five small microtubular roots surrounding the outside before anchoring.

Cryptomonas Ovata replication is dominant during the early summer bloom of fresh water species.

Ecology and Pathogenesis

Cryptomonas species are almost always found in freshwater, and function like Diatoms, a related class of algae, in that they are large, slow-growing, and are often nutrient limited in their densities as opposed to predation pressure. Their prevalence seems contrary to their slow generation times in comparison to other phytoplankton, as well as the fact that they are the primary food source of countless species of zooplankton, macroinvertibrates and fish. Indeed, there has been a study on a prevalent species of zooplantkon (Ceriodaphnia quadrangula) that demonstrated this species feeds exclusively on Cryptomonas erosa, despite being saturated by larger and more nutrient-rich diatoms. [3]

Further studies have demonstrated that Cryptomonas phytoplankton may actually migrate between layers of the water column to alternate between depths optimum for photosynthesis and bacteriograzing, and zones that deter mobile organisms that predate on the phytoplankon. Movement between these "feeding" and "refuge" zones was first observed in a study by Gasol, J. M. et al. Gasol observed that populations of C. phaseolus concentrated at the oxygen/sulfide interface within the lake, despite the fact that not only did sulfide inhibit the carbon fixation of these phytoplankton, but also that light levels were far below those that allowed for optimum growth rates. There was also a distinct lack of bacteriograzing, which is a behavior all cryptomonads demonstrate. Yet the population seemed to thrive with little competition from other species and genera of phytoplankton. [4]

References

[1] Hoef-Emden, K., Melkonian, M. "Revision of the Genus Cryptomonas (Cryptophyceae): a Combination of Molecular Phylogeny and Morphology Provides Insights into a Long-Hidden Dimorphism". Protist. 2008. Volume 159:3, p. 507

[2] Hoef-Emden, K., Tran, H., Melkonian, M. "Lineage-specific variations of congruent evolution among DNA sequences from three genomes, and relaxed selective constraints on rbcL in Cryptomonas (Cryptophyceae)". BMC Evolutionary Biology. 2005. Volume 5. p. 103-112.

[3] Gladyshev, M. I., Temerova, T. A., Dubovskaya, O. P., Kolmakov, V. I., Ivanova, E. A. "Selective grazing on Cryptomonas by Ceriodaphnia quadrangula fed a natural phytoplankton assemblage". Aquatic Ecology. 1999. Volume 33:4. p. 347-353.

[4] Gasol, J. M., Garcia-Cantizano, J., Massana, R., Guerrero, R., Pedros-Alio, C. "Physiological ecology of a metalimnetic Cryptomonas population: relationships to light, sulfide, and nutrients". Journal of Plankton Research. 1993. Volume 15:3. p. 255-275.

[5] http://www3.interscience.wiley.com/journal/119525640/abstract?CRETRY=1&SRETRY=0 Roberts, Keith R. "Structure and Significance of the Cryptomonad Flagellar Apparatus" Journal of Phycology. 2004. Volume: 20:4. p. 590-599.

Author

Page authored by Allison Cutter and Alexandra David, students of Prof. Jay Lennon at Michigan State University.