A retinalophototroph is one of two different types of phototrophs, and are named for retinal-binding proteins (microbial rhodopsins) they utilize for cell signaling and converting light into energy. Like all phototrophs, retinalophototrophs absorb photons to initiate their cellular processes. In contrast with chlorophototrophs, retinalophototrophs do not use chlorophyll or an electron transport chain to power their chemical reactions. This means retinalophototrophs are incapable of traditional carbon fixation, a fundamental photosynthetic process that transforms inorganic carbon (carbon contained in molecular compounds like carbon dioxide) into organic compounds. For this reason, experts consider them to be less efficient than their chlorophyll-using counterparts, chlorophototrophs.