CrtW carotenoid ketolases are provided that are useful for the production of astaxanthin and other cyclic ketocarotenoids. The mutant ketolase genes of the present invention encode polypeptides characterized by an improvement in astaxanthin synthesis activity when converting cyclic hydroxylated carotenoid intermediates into astaxanthin. Expression of the mutant carotenoid ketolases in heterologous hosts enabled increased production of astaxanthin relative to the Sphingomonas melonis DC18 CrtW.