| Vitrella | |
|---|---|
 | |
Scientific classification | |
| Domain: | Eukaryota |
| Clade: | Diaphoretickes |
| Clade: | SAR |
| Clade: | Alveolata |
| Phylum: | Myzozoa |
| Class: | Chromeridophyceae |
| Order: | Colpodellales |
| Family: | Vitrellaceae |
| Genus: | Vitrella |
| Species: | V. brassicaformis |
| Binomial name | |
| Vitrella brassicaformis | |
Vitrella brassicaformis (CCMP3155) is a unicellularalga belonging to theeukaryotic supergroupAlveolata.V. brassicaformis and its closest known relative,Chromera velia, are the only two currently described members of the phylumChromerida, which in turn constitutes part of the taxonomically unranked groupColpodellida. Chromerida is phylogenetically closely related to the phylumApicomplexa, which includesPlasmodium, the agent ofmalaria.[1] Notably, bothV. brassicaformis andC. velia arephotosynthetic, each containing acomplex secondary plastid.[2] This characteristic defined the discovery of these so-called 'chromerids,' as their photosynthetic capacity positioned them to shed light upon the evolution of Apicomplexa's non-photosynthetic parasitism. Both genera lackchlorophyllb orc; these absences link the two taxonomically, as algae bearing onlychlorophylla are rare amid the biodiversity of life. Despite their similarities,V. brassicaformis differs significantly fromC. velia in morphology, lifecycle, and accessory photosynthetic pigmentation.V. brassicaformis has a green color, with a complex lifecycle involving multiple pathways and a range of sizes and morphologies, whileChromera has a brown color and cycles through a simpler process from generation to generation. The color differences are due to differences in accessory pigments.
Extant cultures ofV. brassicaformis were isolated from the coralLeptastrea purpurea in theGreat Barrier Reef.[2] These are available from the NCMA culture collection in Maine USA (cultures 3156, 3157, 3158) and are also backed up in other collections, such as NQAIF (Australia), and CCAP (UK). In 2004, the strains deposited to Culture Collection of Marine Phytoplankton (now Bigelow NCMA) by R. Moore were manually "re-isolated" (repurified) by CCMP staff. Staff worked under the assumption that the flagellate (motile) stage could be separated permanently from the benthic spherical stages, which is not so, as these are stages of a single lifecycle. The fact that this unusual peer-review process could have happened in the history of the description of the species is an example of the very unusual lifecycle/morphology combination of this organism compared to other photosynthetic eukaryotes that many culture collections were accustomed to handling. However, it is not an unusual lifecycle fordinoflagellates, which are photosynthetic relatives ofV. brassicaformis.[2]
Besides its varied somatic lifecycle,V. brassicaformis' putative gametogenesis and recombining stages have been well documented.[1]
The term "mixotrophy" defines this lifestyle which combinesphototrophy (light as energy source) andheterotrophy (predation as energy source).[2] Mixotrophicdinoflagellates are very common in the food web,[3] and "Vitrella"-like organisms may have been the ancestors of such, raising the possibility that further families of Chromerida may eventually be found in the environment.[4]
Vitrella brassicaformis was described in 2011 by Oborniket al.,[1] from type material RM11 (CCMP3155)[5] originally isolated from hostPocillopora damicornis.[2] Major differences betweenV. brassicaformis andC. velia were noted by the authors, leading to their classification into two distinct families,Vitrellaceae andChromeraceae, respectively. The plastid genome is a highly compact 85 kb-long circle.[6][7]
Just as for its sister familyChromeraceae, the familyVitrellaceae is a bridge between alternate views of protist evolution: the botanical view versus the zoological view. These views need not be opposed.Apicomplexans (all non-photosynthetic) are generally described using the zoological code, while protistan (often unicellular) algae have often been described using the botanical code. Protistologists have always been free to use whichever code they choose, and these two organisms (V. brassicaformis andC. velia) are prime examples of the need for this freedom. They possess a flagellate stage and a benthic stage.[2]
ResearcherThomas Cavalier-Smith investigating the origins of apicomplexans anddinozoans, suggested a joint categoryMyzozoa encompassing both of these superphyla, plus related groups thecolpodellids andperkinsids.[8] By morphology and lifestyle, like feeding throughmyzocytosis,[2]V. brassicaformis more closely resembles an ancestral Myzozoan thanC. velia does. These two lifestyles,autotrophy andheterotrophy, found in one organism (V. brassicaformis) represent the store of potential that was able to lead to the Myzozoan radiation.
Vitrella brassicaformis was originally isolated from the Scleractinian coralLeptastrea purpurea (tropical) using a variation of a method intended to isolateSymbiodiniaceae (algal symbionts of corals). Vitrellaceae occur globally in tropical and warm subtropical marine environments. They are associated not only with coral reef ecosystems, but also thrombolites, stromatolites and other calcifying marine environments.[4]