Patent ID: 8685653

Claim:
A method for producing a bacterial cell comprising two or more amplified chromosomal copies of a gene of interest, the method comprising: a) providing a bacterial cell comprising at least one copy of an amplification unit, the unit comprising: i) at least one copy of the gene of interest, and ii) an expressible functional copy of a conditionally essential gene, which is either promoterless or transcribed from a heterologous promoter having an activity substantially lower than the endogenous promoter of said conditionally essential gene, and wherein the conditionally essential gene encodes a glutamyl-tRNA reductase, wherein the conditionally essential gene if not functional would render the cell auxotrophic for 5-amino leuvulinic acid; b) cultivating the cell under conditions suitable for growth in a medium deficient of 5-amino leuvulinic acid, thereby providing a growth advantage to a cell in which the amplification unit has been duplicated in the chromosome; and c) selecting a cell wherein the amplification unit has been duplicated in the chromosome, wherein two or more amplified chromosomal copies of the gene of interest were produced.