Guillardia

Guillardia is a genus of marine biflagellate cryptomonad algae with a plastid obtained through secondary endosymbiosis of a red alga.

Originally identified in Connecticut by Richard Guillard in the 1960s, Guillardia only has one described species. The genus is rare in the wild, but cultures well and has been frequently studied since its original discovery. The general morphology of the small cell is well described, and shares many similarities with other cryptomonads, though it contains a unique organization of periplasm. Guillardia is the only cryptomonad to have its entire nucleus, nucleomorph, and plastid genome sequenced. This knowledge has prompted further studies on gene transfer between chloroplast, the ancestral red algal nucleomorph, and the nucleus, as well as regulation of photosynthetic and cell cycle gene expression within the plastid. 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. Two anion channelrhodopsins have also been isolated from Guillardia theta for neurobiological research applications as optogenetic inhibitors.