Construction and utilization of carotenoid reporter systems: identification of chromosomal integration sites that support suitable expression of biosynthetic genes and pathways.

In order to metabolically engineer microorganisms to produce compounds of interest, it is often desirable to integrate foreign genes into the chromosome of the host. However, the consequences of these genetic alterations are not always predictable. The use of a reporter system can often assist in determining chromosomal locations for optimal expression of foreign biosynthetic genes. The method described here involves the construction and utilization of promoterless carotenoid transposons, which provides a colorimetric screen for identifying the best chromosomal integration sites for the expression of the genes of interest. The transposons (pUTmTn5::392W and pUTmTn5::392) contain the carotenoid genes required for the production of canthaxanthin and astaxanthin, respectively. Thus, when promoterless transposons insert into the host's genome, the color of the colonies will vary based on their chromosomal location. There is a correlation between the color intensity of the colonies and the expression of the carotenoid transposon. The transposon insertion site can be determined via direct chromosomal sequencing. This sequence information is used to guide the site-specific integration of biosynthetic genes and pathways of interest.