Genetic remodeling in

1. An isolated Bifidobacterium animalis subsp. lactis cell comprising a genome that is customized so as to lack an operable functional gene that provides antibiotic resistance, wherein DNA coding for the functional gene is substantially deleted, and wherein the functional gene is tetW.

2. The isolated Bifidobacterium animalis subsp. lactis cell of claim 1 that is Bifidobacterium animalis subsp. lactis strain NCC 9034.

3. The isolated Bifidobacterium animalis subsp. lactis cell of claim 1 that is at least 5 times more sensitive to tetracycline than a comparable cell which contains an operable tetW gene.

4. The isolated Bifidobacterium animalis subsp. lactis cell of claim 3 that is at least 10 times more sensitive to tetracycline than a comparable cell which contains an operable tetW gene.

5. The isolated Bifidobacterium animalis subsp. lactis cell of claim 4 that is sensitive to a concentration of tetracycline greater than about 0.3 micrograms per milliter as determined using a disk diffusion assay.

6. The isolated Bifidobacterium animalis subsp. lactis cell of claim 5 which is Bifidobacterium animalis subsp. lactis strain NCC 9034.

7. The isolated Bifidobacterium animalis subsp. lactis cell of claim 1 that is substantially unchanged in a remainder of its genome.

8. A culture of Bifidobacterium animalis subsp. lactis comprising an isolated cell of claim 7 .

9. A method of producing a Bifidobacterium animalis subsp. lactis cell comprising the steps of:

obtaining upstream and downstream sequence for a predetermined functional gene from the Bifidobacterium animalis subsp. lactis;

transforming a population of the Bifidobacterium animalis subsp. lactis cells with a plasmid that is nonreplicative in the Bifidobacterium animalis subsp. lactis , the plasmid comprising the upstream and downstream flanking sequence for the functional gene and a gene encoding a selectable marker;

growing the Bifidobacterium animalis subsp. lactis cells under conditions allowing cells containing the gene encoding the selectable marker in the plasmid to grow, but not those cells without the gene encoding the selectable marker to grow, thereby selecting for transformants containing an integrated plasmid;

growing the transformants under nonselective conditions that allow growth of the cells but permit the loss of the integrated plasmid;

selecting cells that have lost the integrated plasmid by replica plating colonies onto plates with and without selective pressure and selecting those colonies that are sensitive to the selective pressure; and

confirming that the cells sensitive to the selective pressure no longer have the function of the functional gene, thereby producing a Bifidobacterium animalis subsp. lactis cell lacking an operable predetermined functional gene,

wherein DNA coding for the predetermined functional gene is substantially deleted, and wherein the predetermined functional gene is tetW.

10. The method of claim 9 wherein the selective pressure is the presence of an antibiotic.

11. The method of claim 10 wherein the antibiotic is spectinomycin.

12. The method of claim 9 wherein the plasmid integrates into the genome by homologous recombination.

13. The method of claim 12 wherein the integrated plasmid is lost through a second homologous recombination.

14. The method of claim 9 wherein the transformants are grown under nonselective conditions for at least about 100 generations.

15. The method of claim 9 wherein the Bifidobacterium cells that are transformed are B. animalis subsp. lactis NCC 2818, and the resultant cells are B. animalis subsp. lactis NCC 9034.

16. The method of claim 12 wherein the only functional gene that is rendered inoperable is the predetermined functional gene.