Identification and Utility of FdmR1 as a Streptomyces Antibiotic Regulatory Protein Activator for Fredericamycin Production in Streptomyces griseus ATCC 49344 and Heterologous Hosts

The fredericamycin (FDM) A biosynthetic gene cluster, cloned previously fromStreptomyces griseus ATCC 49344, contains three putative regulatory genes,fdmR ,fdmR1 , andfdmR2 . Their deduced gene products show high similarity to members of theStreptomyces antibiotic regulatory protein (SARP) family (FdmR1) or to MarR-like regulators (FdmR and FdmR2). Here we provide experimental data supporting FdmR1 as a SARP-type activator. Inactivation offdmR1 abolished FDM biosynthesis, and FDM production could be restored to thefdmR1 ::aac(3)IV mutant by expressingfdmR1 intrans . Reverse transcription-PCR transcriptional analyses revealed that up to 26 of the 28 genes within thefdm gene cluster, with the exception offdmR andfdmT2 , were under the positive control of FdmR1, directly or indirectly. Overexpression offdmR1 inS. griseus improved the FDM titer 5.6-fold (to about 1.36 g/liter) relative to that of wild-typeS. griseus . Cloning of the completefdm cluster into an integrative plasmid and subsequent expression in heterologous hosts revealed that considerable amounts of FDMs could be produced inStreptomyces albus but not inStreptomyces lividans . However, theS. lividans host could be engineered to produce FDMs via constitutive expression offdmR1 ; FDM production inS. lividans could be enhanced further by overexpressingfdmC , encoding a putative ketoreductase, concomitantly withfdmR1 . Taken together, these studies demonstrate the viability of engineering FDM biosynthesis and improving FDM titers in both the native producerS. griseus and heterologous hosts, such asS. albus andS. lividans . The approach taken capitalizes on FdmR1, a key activator of the FDM biosynthetic machinery.