Genes have been isolated from Rhodococcus and Deinococcus which encode a specific lycopene .beta.-cyclase capable of converting acyclic carotenoids with at least one .psi.-end group to the corresponding asymmetric carotenoid containing a single .beta.-ionone ring end group. The genes are new. Transformed host cells expressing the present genes and methods for the bio-conversion of acylic carotenoid substrates to corresponding asymmetric carotenoid are also provided.