[7] The genus is also important in research across biological disciplines; Guillardia serves as a model organism in the study of secondary endosymbiosis and photosynthesis in cryptomonads due to its ease of culture and sequenced genome.
[6] Because it grows so well in culture, Guillardia theta is also frequently used as a model organism in modern day studies investigating cryptomonads characteristics.
In the wild, Guillardia theta is a rare planktonic marine organism, and the majority of studies have been completed from cultures.
[2] Milford Harbor includes many discrete areas such as estuaries, mud flats, marine basins, marinas, beaches, marshes, and coastal shores that provide habitats to a variety of different organisms.
[1] Additionally, ciliates are known predators of the genus in culture, suggesting the role of Guillardia as prey within aquatic systems.
Mesodinium pulex, a well studied phagotrophic ciliate common to marine, brackish, and freshwater environments ingested and grew on Guillardia theta cultures.
[1] The structure of the periplasm, a layer of thin sheets composed of irregular plates made from crystalline subunits, is a defining characteristic of the genus.
The impact of the ejectosome strands with an object such as another organism causes the uneven backwards motion of Guillardia for predator evasion.
Like other cryptomonads, Guillardia is key for understanding secondary endosymbiosis as it retains the nucleus of the algal endosymbiont in the form of a nucleomorph within a periplastidial compartment and four membranes surrounding the plastidial complex.
The small periplastidial cytoplasm is also hypothesized to retain components of its cytoskeleton, due to tubulin genes localized to the nucleomorph.
[19] While many plastidial proteins remain in the nucleomorph, those that underwent endosymbiotic gene transfer to the host nucleus are targeted back through the outermost membrane through co-translational translocation with a bipartite N-terminal signal sequence.
Also contained within the plastid are eukaryotic ribosomes and a starch granule filled pyrenoid, where CO2 fixation occurs through the enzyme RUBISCO.
[1] Like other cryptomonads, the light harvesting pigments of the plastidial chloroplasts are phycobiliproteins and chlorophyll a/c-binding proteins, homologous to those found in red algal lineages.
Motility occurs primarily through two asymmetric flagella, the longest protruding anteriorly from the gullet, while the shorter flagellum points to the back of the cell.
[11] Interestingly, the photaxis mechanisms of Guillardia theta which incorporate anion channelrhodopsins to initiate a motion response have been used in neuroscience applications as optogenetic inhibitors.
[14] Synchronization of chloroplast, nucleomorph, and host cell division is vital for the evolution of the red algal endosymbiont into an organelle.
[1] The nuclear genome is approximately 87 mega base pairs in size encoding 21,000 predicted proteins, 57% being completely unique with no known homologs in other organisms.
[1] The information gleaned from this data helped to elucidate mechanisms of secondary endosymbiosis present in protist lineages containing endosymbiotic red algal plastids.
[21] Additionally, anion channelrhodopsin proteins from Guillardia theta have been found to induce neuron hyperpolarization in optogenetic assays.
In human studies, anion channelrhodopsins can be deployed to induce chloride driven hyperpolarization, silencing targeted neurons at specific timepoints.