Regulated genetic suicide mechanism compositions and methods
Embodiments of the present invention relates to the incorporation and use of a regulated genetic suicide mechanism for use in the improved purification of biologics, including adjunct use in various eubacterial minicell production and purification methodologies. Described herein are high-yield eubacterial minicell-producing strains with genetic modifications that comprise a regulated genetic suicide mechanism that irreparably destroys the parent cell chromosome such that live parental cells in a culture can be functionally eliminated at any time during the course of a minicell production and purification run. Embodiments of the present invention also describe methods useful in the elimination of live parental cells during the production of other cell-based biologics.
1. A eubacterial minicell derived from a minicell-producing bacteria, wherein the minicell-producing bacteria comprises:
an expressible cell division gene, wherein the cell division gene is selected from the group consisting of zipA, sulA, secA, dicA, dicB, dicC, dicF, ftsA, ftsI, ftsN, ftsK, ftsL, ftsQ, ftsW, ftsZ, minC, minD, minE, seqA, ccdB, sfiC, and ddlB; and
an expressible gene encoding a homing endonuclease, wherein the homing endonuclease gene is a transgene, and wherein the chromosome of the minicell-producing bacteria comprises one or more recognition sites of the homing endonuclease.
2. The eubacterial minicell of claim 1 , wherein the minicell-producing gene is a transgene.
3. The eubacterial minicell of claim 1 , wherein the cell division gene is ftsZ, sulA, ccdB, or sfiC.
4. The eubacterial minicell of claim 1 , wherein the cell division gene is expressed under the control of an inducible promoter.
5. The eubacterial minicell of claim 4 , wherein the inducible promoter is inducible by the presence of one or more chemical compounds.
6. The eubacterial minicell of claim 1 , wherein the homing endonuclease gene is located on the chromosome of the minicell-producing bacteria.
7. The eubacterial minicell of claim 1 , wherein the homing endonuclease is selected from the group consisting of I-CeuI, PI-SceI, I-ChuI, I-CpaI, I-SceIII, I-CreI, I-MsoI, I-SceIV, I-CsmI, I-DmoI, I-PorI, PI-TliI, PI-TliII, and PI-ScpI.
8. The eubacterial minicell of claim 1 , wherein the homing endonuclease is expressed under the control of an inducible promoter.
9. The minicell-producing bacteria of claim 8 , wherein the inducible promoter is a temperature-sensitive promoter.
10. The eubacterial minicell of claim 1 , wherein the minicell-producing bacteria is a Gram-negative bacteria.
11. The eubacterial minicell of claim 10 , wherein the Gram-negative bacteria is selected from the group consisting of Campylobacter jejuni, Lactobacillus spp., Neisseria gonorrhoeae, Legionella pneumophila, Salmonella spp., Shigella spp., Pseudomonas aeruginosa , and Escherichia coli.
12. The eubacterial minicell of claim 10 , comprising a gene encoding a gene product that is involved in lipopolysaccharide synthesis, wherein the gene is genetically modified compared to a corresponding wild-type gene.
13. The eubacterial minicell of claim 12 , wherein the gene is a msbB gene that encodes a gene product that causes the bacteria to produce an altered lipid A molecule compared to lipid A molecules in a corresponding wild-type bacteria.
14. The eubacterial minicell of claim 13 , wherein the altered lipid A molecule is deficient with respect to the addition of myristolic acid to the lipid A portion of the lipopolysaccharide molecule compared to lipid A molecules in a corresponding wild-type bacteria.
15. The eubacterial minicell of claim 1 , wherein the minicell-producing bacteria is a Gram-positive bacteria.
16. A method of making minicell, comprising:
culturing a minicell-producing bacteria, wherein the minicell-producing bacteria comprises:
an expressible cell division gene, wherein the cell division gene is selected from the group consisting of zipA, sulA, secA, dicA, dicB, dicC, dicF, ftsA, ftsI, tsN, ftsK, ftsL, ftsQ, ftsW, ftsZ, minC, minD, minE, seqA, ccdB, sfiC, and ddlB; and
an expressible gene encoding a homing endonuclease, wherein the homing endonuclease gene is a transgene,
and wherein the chromosome of the minicell-producing bacteria comprises one or more recognition sites of the homing endonuclease; and
substantially separating minicells from the minicell-producing parent cells, thereby generating a composition comprising minicells.
17. The method of claim 16 , further comprising inducing expression of the gene encoding the endonuclease.
18. The method of claim 16 , further comprising inducing minicell formation from the minicell-producing parent cell.
19. The method of claim 16 , further comprising purifying the minicells from the composition.
20. The method of claim 16 , wherein the minicells are substantially separated by the parent cells by a process selected from the group consisting of centrifugation, ultracentrifugation, density gradation, immunoaffinity and immunoprecipitation.
21. A eubacterial minicell produced by the method of claim 16 .