Rhamnose biosynthesis pathway supplies precursors for primary and secondary metabolism in Saccharopolyspora spinosa

Rhamnose is an essential component of the insect control agent spinosad. Ho wever, the genes coding for the four enzymes involved in rhamnose biosynthe sis in Saccharopolyspora spinosa are located in three different regions of the genome, all unlinked to the cluster of other genes that are required fo r spinosyn biosynthesis. Disruption of any of the rhamnose genes resulted i n mutants with highly fragmented mycelia that could survive only in media s upplemented with an osmotic stabilizer. It appears that this single set of genes provides rhamnose for cell wall synthesis as well as for secondary me tabolite production. Duplicating the first two genes of the pathway caused a significant improvement in the yield of spinosyn fermentation products.