6-Demethylchlortetracycline (6-DCT),a tetracycline antibiotic produced by Streptomyces aureofaciens,is a crucial precursor employed for the semi-synthesis of tigecycline,minocycline,and amadacyclin (PTK 0796).In this study,the 6-DCT biosynthetic gene cluster (BGC) was cloned from genomic DNA of a high 6-DCT-producing strain,S.aureofaciens DM-1,using the transformation-associated recombination method.An extra copy of the 6-DCT BGC was introduced and integrated into the chromosome of S.aureofaciens DM-1.Duplication of the 6-DCT BGC resulted in a maximum increase of the 6-DCT titer by 34％.