In 1985, several ferredoxins and other chromophoric proteins from the halophilic phototrophic bacterium Ectothiorhodospira halophila were isolated by T. E. Meyer in Tucson, Az.1 One of the “other chromophoric proteins” he identi©ed in this screen was yellow and was named “photoactive yellow protein” (PYP) in a subsequentstudy.2 E. halophila was reclassi©ed in 1996 to its current name Halorhodospira halophila.3 H. halophila is a unicellular prokaryote, or more speci©cally, a phototrophic purple spirillum that deposits sulfur extracellularly. It was ©rst isolated and classi©ed from salt-encrusted mud taken from the shores of Summer Lake, Lake County, Oregon.4,5 Later, it was also isolated from the extremely saline lakes of the Wadi el Natrun in Egypt.6 Both locations are salt lakes, and indeed, H. halophila only thrives in extremely salty environments.