The roseoflavin producer Streptomyces davaonensis has a high catalytic capacity and specific genetic adaptations with regard to the biosynthesis of riboflavin.

The bacterium Streptomyces davaonensis synthesizes the antibiotic roseoflavin in the stationary phase of growth. The starting point for roseoflavin biosynthesis is riboflavin (vitamin B2 ) and four enzymes (RibCF, RosB, RosA and RosC) are necessary to convert a vitamin (riboflavin) into a potent, broad-spectrum antibiotic (roseoflavin). In S. davaonensis, seven enzymatic functions are required to synthesize the roseoflavin precursor riboflavin from the central building blocks GTP and ribulose 5-phosphate. When compared with other bacterial and in particular Streptomyces genomes the S. davaonensis genome contains an unusual high number (21) of putative riboflavin biosynthetic genes (rib genes), including a rib gene encoding an additional riboflavin synthase originating from an Archaeon. We show by complementation analyses and enzyme assays that 17 out of these 21 putative rib genes indeed encode for riboflavin biosynthetic enzymes. Biochemical analyses of selected enzymes support this finding. Transcriptome analyses show that all of the rib genes are expressed either in the exponential or in the stationary phase of growth and thus do not represent silent genes. We conclude that the Rib enzymes produced in the stationary phase represent a physiological adaptation to support roseoflavin biosynthesis.