Proteorhodopsin (PR or pRhodopsin) belongs to the family of bacterial transmembrane rhodopsins (retinylidene proteins). In 1971, the first microbial transmembrane rhodopsin - Bacteriorhodopsin was discovered in archea domain by Dieter Oesterhelt and Walther Stoeckenius. Later in 2000, the first bacterial transmembrane rhodopsins was discovered by Oded Béjà and Edward DeLong. The Proteorhodopsin is widely expressed in various type of aquatic habitats. The light-driven proton pump gives bacteria energy in the form of adenosine triphosphate (ATP). This functionality can be used to acidify a vesicle type organelle.