The novel ion pump rhodopsins from Haloarcula form a family independent from both the bacteriorhodopsin and archaerhodopsin families/tribes.

Extreme halophiles newly collected from Argentine salt flats were characterized, in one of which, Haloarcula (sp. arg-1), light-driven retinal protein ion pumps were found. The proton pump, cruxrhodopsin-1, shows amino acid sequence homologies of 52% to bacteriorhodopsin and 48% to archaerhodopsin-1. The anion pump, cruxhalorhodopsin-1, identified partially as a 394bp polymerase chain reaction product, shows homologies of 70% to halorhodopsin, and 72% to pharaonis halorhodopsin. The ion pumps (and possibly sensors still to be found) in Haloarcula sp. arg-1, which constitute the cruxrhodopsin-1 family, are distinct from the bacteriorhodopsin and the archaerhodopsin families/tribes.