Gene replacement, integration, and amplification at the gdhA locus of Corynebacterium glutamicum.

Gene replacement and integration in a Corynebacterium glutamicum ATCC 21086 derivative were achieved by transformation with a nonreplicative plasmid that contains the C. glutamicum ATCC 17965 gdhA gene modified by the insertion of an aphIII cartridge. We isolated rare derivatives of the integrative transformants that have higher levels of expression of the integrated plasmid genes than the parent. Different types of such amplified clones were distinguished according to their antibiotic resistance levels, enzyme specific activities, and physical structures. All amplified clones share a structural DNA motif confined to the chromosomal gdhA locus: a variable number (up to 10) of tandem copies of a unit that includes the selected gene and one flanking repeat. A given clone contains subpopulations that differ in the number of repeats of this unit.