Abstract: The present invention describes a process of production carotenoids in improved fermentation conditions of selected bacterial strains constitutively over-producing carotenoids or mutants thereof, purifying and isolating a specific crystalline carotenoid, preferably beta-carotene, for its use in the feed, food, cosmetic and pharmaceutical sectors. The present invention also describes a method for obtaining mutant strains constitutively overproducing carotenoids from naturally occurring bacterial strains, permitting the selection of mutants with high carotenoid yields and specificity towards a specific carotenoid. Additionally the invention describes the use of this method on obtained mutant strains for further improvement thereof.