Construction of a gentamicin C1a-overproducing strain of Micromonospora purpurea by inactivation of the gacD gene

Gentamicin C1a is the precursor of the semi-synthetic antibiotic etimicin and has the highest antibacterial activity in the clinically important gentamicin C mixture. To obtain a gentamicin C1a-overproducing strain, we inactivated gacD gene in Micromonospora purpurea. The gacD was presumed to encode a C6′ methyltransferase by sequence analysis, and plays a role in the conversion of the gentamicin intermediate X2 to G418. So the inactivation of gacD blocks the metabolic pathways from X2 to G418 and leads to the accumulation of gentamicin C1a.The resulting recombination strain produced gentamicin C1a more than 10-fold compared to the wild type strain. Moreover, the wild-type strain produced 4 main production components, C1a, C2, C2a and C1, while the recombination strain produced only 2 components, C1a and C2b, making the purification of gentamicin C1a easier. The recombination strain was genetically stable and should be useful for the industrial production of gentamicin C1a.