Methylomonas sp. strain 16a is an obligate methanotrophic bacterium that uses methane or methanol as the sole energy and carbon source. In order to engineer a stable strain to produce carotenoids, integration of genes or gene clusters in various nonessential locations in the chromosome is used. Construction of a canthaxanthin-producing strain involves the integration of canthaxanthin biosynthetic genes including the crtW gene for the β-carotenoid ketolase. Addition of the crtZ gene that encodes the β-carotenoid hydroxylase in this strain leads to the production of astaxanthin. Further increase in titer and yield for astaxanthin is obtained by integration of another set of astaxanthin biosynthetic gene cluster in a separate location of the chromosome.