Has no proton-pumping activity but is potentially capable of functioning as a sensory SRII-like protein. The chromophore contains 36.5% all-trans-, 7.6% 11-cis- and 56.4% 13-cis-retinal in the dark and 30.1% 11-cis- and 47.7% 13-cis-retinal upon illumination with >460 nm light. The covalent binding of retinal to the apoprotein, bacterioopsin, generates bacteriorhodopsin. Belongs to the archaeal/bacterial/fungal opsin family. Is called bop1 in PubMed:21135094.