Two overlapping antiparallel genes encoding the iron regulator DmdR1 and the Adm proteins control sidephore and antibiotic biosynthesis in Streptomyces coelicolor A3(2)

The dmdR1 gene of Streptomyces coelicolor encodes an important regulator of iron metabolism. An antiparallel gene (adm) homologous to a development-regulated gene of Streptomyces aureofaciens has been found to overlap with dmdR1. Both proteins DmdR1 and Adm are formed in solid and liquid cultures of S. coelicolor A3(2). The purpose of this study was to assess possible interaction between the products of these two antiparallel genes. Two mutants with stop codons resulting in arrested translation of either DmdR1 or Adm were obtained by gene replacement and compared with a deletion mutant (Delta dmdR1/adm) that was defective in both genes. The deletion mutant was unable to form either protein, did not sporulate and lacked desferrioxamine, actinorhodin and undecylprodigiosin biosynthesis; biosynthesis of these compounds was recovered by complementation with dmdR1/adm genes. The mutant in which formation of Adm protein was arrested showed normal levels of DmdR1, lacked Adm and over-produced the antibiotics undecylprodigiosin and actinorhodin (in MS medium), suggesting that Adm plays an important role in secondary metabolism. The mutant in which DmdR1 formation was arrested synthesized desferrioxamines in a constitutive (deregulated) manner, and produced relatively normal levels of antibiotics. In conclusion, our results suggest that there is a fine interplay of expression of these antiparallel genes, as observed for other genes that encode lethal proteins such as the toxin/antitoxin systems. The Adm protein seems to have a major effect on the control of secondary metabolism, and its formation is probably tightly controlled, as expected for a key regulator.