Dinophysis

Dinophysis
Scientific classification
Clade:	SAR
Infrakingdom:	Alveolata
Phylum:	Myzozoa
Superclass:	Dinoflagellata
Class:	Dinophyceae
Order:	Dinophysiales
Family:	Dinophysaceae
Genus:	Dinophysis Ehrenberg, 1839

Dinophysis is a genus of dinoflagellates^[1][2][3] common in tropical, temperate, coastal and oceanic waters.^[4] It was first described in 1839 by Christian Gottfried Ehrenberg.^[5]

Dinophysis are typically medium-sized cells (30-120 µm).^[5] The structural plan and plate tabulation are conserved within the genus.^[4] Dinophysis thecae are divided into halves by a sagittal fission suture.^[4] There are five types of thecae ornamentation in this genus,^[4] and those are a useful character for species identification.^[4] Dinophysis mainly divide by binary fission.^[4]

Dinophysis chloroplasts are usually rod-shaped or granular and yellow or brown colored.^[4] Some Dinophysis spp. take up kleptoplastids when feeding. Toxic Dinophysis produce okadaic acid, dinophysistoxins, and pectenotoxins, which inhibit protein phosphatase and cause diarrhea.^[6]

Background

The etymology of this genus name comes from Greek, Dino comes from "deinos" (δεινός)^[7] meaning terrible^[8] and "physis" (φύσις) meaning nature.^[9]

The genus was first described in 1839 by Ehrenberg, which is why the holotype species of this genus is Dinophysis acuta Ehrenberg.^[5] It has been found that what were considered different Dinophysis species might just be different life stages.^[5]

Severe diarrheic shellfish poisoning breakouts in northeast Japan led to the identification of a Dinophysis species that produces toxins, Dinophysis fortii in 1976-77.^[6] This genus is difficult to maintain in culture leading to challenges in gaining knowledge of these organisms.^[6] Some Dinophysis spp. have kleptoplastids of cryptomonad origin, specifically from the cryptomonad Teleaulax amphioxeia.^[10] Dinophysis caudata have acquired these kleptoplastids by engulfing the ciliate Mesodinium rubrum which has engulfed T. amphioxeia plastids.^[10] Cryptomonad plastids have four membranes and a nucleomorph and are a product of secondary endosymbiosis.^[10]

For years it was believed that Dinophysis did not have a sexual cycle.^[6] However, it is now apparent that gamete cells can form in Dinophysis acuminata and D. acuta; this was found when small, spherical cells seemed to form inside larger ones.^[6]

Habitat and ecology

The common habitat of Dinophysis is in tropical, temperate, coastal and oceanic waters.^[4] Although most Dinophysis are marine and planktonic, some have been found in coastal lagoons^[5]

Dinophysis caudata feed on ciliates, specifically Mesodinium rubrum through myzocytosis.^[6] Picophytoplankton, bacteria, and cryptomonads are also likely part of the diet of Dinophysis.^[6] For culture, Dinophysis are maintained on mixotrophic nutrition.^[6] Although they are mixotrophic, they are mainly phagotrophic and photosynthesis is linked to kleptoplastids.^[6]

Description of the organism

Life cycle

Dinophysis mainly divides asexually by binary fission.^[4] For years it was believed that Dinophysis did not have a sexual cycle.^[6] However, it is now apparent that gamete cells can form in D. acuminata and D. acuta; this was found when small, spherical cells seemed to form inside larger ones.^[6] While the role of a sexual cycle in Dinophysis is not fully understood yet, there is a proposed model for how this works. In the proposed model, vegetative cells give rise to small motile cells (the smaller cells previously observed within the larger cells). The smaller cells then also become vegetative and act like gametes and after conjugation the cells divide and encyst.^[13] The smaller cells that give rise to gametes tend to have thinner thecae and less developed cingular and sulcal lists.^[13] They also are flagellated and swim, they use their flagella and lists to wrap around another gamete cell for conjugation.^[13]

Although the gametes are part of a dimorphic sexual cycle, sex cysts do not play an active role in the seeding of Dinophysis populations.^[6]

Pseudogenes

While toxic species of Dinophysis such as D. acuminata have a single gene for LSU rRNA, non-toxic species seem to have two distinct classes of LSU rRNA.^[14] The difference between these two classes was a 70 bp deletion, indicating the shorter product might be a pseudogene.^[14] The pseudogene can be used as a marker of D. acuminata and might conveniently serve as a marker of toxic and non-toxic strains^[14] and bring more insight to the genetics of toxicity of Dinophysis.

Phylogenetics

Dinoflagellates are algae and according to recent phylogeny they are sister groups to ciliates and apicomplexans.^[14] Most phylogenetic studies are done with sequences of both large and small ribosomal subunits and do not always agree with morphological studies based on thecal plates.^[14] Sequencing of the small subunit of the ribosome of Dinophysis revealed very similar sequences in three species of Dinophysis (D. acuminata, D. norvegica and D. acuta), suggesting that photosynthetic Dinophysis have evolved recently.^[14]

Practical importance

Dinophysis are a threat to shellfish aquaculture due to toxic lipophilic shellfish toxins that they produce.^[6] Dinophysis have cryptophyte-like pigments and at least seven species of Dinophysis contain diarrheic shellfish toxins.^[6]

Toxic Dinophysis produce okadaic acid, dinophysistoxins, and pectenotoxins, which inhibit protein phosphatase and produce diarrhea.^[6] The more dominant the okadates are, the higher the impact on public health.^[6] Toxins are secondary metabolites, and, in some cases, a single species can produce multiple types of toxins.^[6] The production of these is controlled by both genetic factors and the environment.^[6] The enzymes produced vary due to the environment in which Dinophysis grow.^[6] The boreal seas, temperate seas and tropical seas are where most assemblages of Dinophysis that cause diarrheic shellfish poisoning occur.^[6] Common features associated with toxic Dinophysis include: large sizes, highly developed cingular and sulcal lists and hypothecal processes.^[6]

Species

References

Further reading