Methanotrophic bacterial strains are provided that have been optimized for the production of carotenoid compounds through the down-regulation of one or more of the crtN1, ald, crtN2 and crtN3 genes of the carotenoid biosynthetic pathway. The resulting strains lack pigmented C.sub.30 carotenoid compounds, and show an increase in the production of C.sub.40 carotenoids. The use of the optimized host strains for the production of the C.sub.40 carotenoids canthaxanthin and astaxanthin is also described.