Compositions and methods for biocontainment of microorganisms
Methods and strategies for introducing genetic safeguards into microorganisms, genetically modified organisms (GMO) including the safeguards, and methods of use thereof are provided. The genetic safeguards generally impart a low escape frequency, are robust, and are modular. Safeguards with low escape frequency prevent the rise of mutants escaping defined media and limit growth in the wild. Robust safeguards retain wild-type levels of fitness while also maintaining containment in diverse growth conditions.
1. A genomically recoded organism (GRO) comprising a genome wherein at least one codon is reassigned creating an available sense codon for a recombinant tRNA;
wherein at least one instance of the available sense codon is present as a sense codon in the coding region of at least one endogenous essential gene of interest that encodes a protein whose expression is needed for the GRO's viability;
wherein the at least one instance of the available sense codon encodes a conserved amino acid residue at a functional site of the protein; and
wherein the recombinant tRNA can be charged by a paired recombinant aminoacyl-tRNA synthetase (aaRS) to permit site-specific incorporation of a synthetic amino acid (sAA) or non-standard amino acid (nsAA) into a nascent peptide chain of the protein during translation of the transcribed essential gene in the GRO.
2. The GRO of claim 1 , wherein
all genomic instances of a first stop codon sequence have been reassigned to a second stop codon sequence and the available sense codon consists of the sequence of the first stop codon, or
all genomic instances of an endogenous sense codon sequence have been reassigned to a synonymous codon sequence and the available sense codon consists of the sequence of the endogenous sense codon;
and wherein the anticodon sequence for the recombinant tRNA recognizes the available sense codon sequence.
3. The GRO of claim 2 , wherein the genomic sequence of the first stop codon sequence is TAG and the second stop codon sequence is TAA or TGA.
4. The GRO of claim, 3 wherein the GRO is a variant of E. coli strain C321.A A (GenBank accession CP006698).
5. The GRO of claim 1 further comprising a nucleic acid encoding an expression control sequence operably linked to a sequence encoding the recombinant aminoacyl-tRNA synthetase (aaRS) and the recombinant tRNA,
wherein the GRO has reduced viability in non-permissive media that does not include the synthetic amino acid (sAA) or non-standard amino acid (nsAA) compared to permissive media including the synthetic amino acid (sAA) or non-standard amino acid (nsAA),
wherein the escape frequency of the GRO in the non-permissive media is about 10 −11 or less.
6. The GRO of claim 1 wherein the essential gene of interest is selected from the group consisting of dnaX, lspA, secY, serS, murG, dnaA, adk, nadE, ribA, and gmk.
7. The GRO of claim 2 , wherein the gene or genes encoding the endogenous cognate translation machinery corresponding to the at least one reassigned codon is interrupted or deleted.
8. The GRO of claim 1 , wherein the available sense codon is only present in the essential gene of interest.
9. The GRO of claim 7 , further comprising a nucleic acid encoding an expression control sequence operably linked to a sequence encoding the recombinant aminoacyl-tRNA synthetase (aaRS), the recombinant tRNA.
10. The GRO of claim 9 , wherein the nucleic acid is episomal, extrachromosomal, or integrated into a chromosome of the GRO.
11. The GRO of claim 10 , wherein the genomic sequence of the available sense codon is TAG, the recombinant tRNA comprises the anticodon for UAG, and the corresponding release factor or factors is deleted or interrupted.
12. The GRO of claim 9 , wherein culturing the GRO with permissive media including the synthetic amino acid (sAA) or non-standard amino acid (nsAA) results in translation of the full-length protein encoded by the essential gene.
13. The GRO of claim 12 , wherein culturing the GRO with non-permissive media that does not include the synthetic amino acid (sAA) or non-standard amino acid (nsAA) results in truncation of the full-length protein encoded by the essential gene.
14. The GRO of claim 12 , wherein the GRO has reduced viability when cultured with non-permissive media that does not include the synthetic amino acid (sAA) or non-standard amino acid (nsAA) compared to permissive media including the synthetic amino acid (sAA) or non-standard amino acid (nsAA) that results in translation of the full-length protein encoded by the essential gene.
15. The GRO of claim 14 , wherein the escape frequency of the GRO when cultured with non-permissive media is 10 −6 or lower and the fitness of the GRO when cultured with permissive media is at least 70% of its parental strain grown under the same or similar conditions.
16. The GRO of claim 1 , wherein two or more instances of the available sense codon are present as sense codons in at least one of the essential gene of interest.
17. The GRO of claim 1 , wherein at least one instance of the available sense codon is present as a sense codon in at least a second endogenous essential gene of interest.
18. The GRO of claim 1 , wherein the essential gene is one that cannot be complemented by cross-feeding of metabolites to the GRO.
19. The GRO of claim 1 , where the at least one endogenous essential gene of interest is present only at its genomic locus.
20. The GRO of claim 1 , wherein the protein is functional when the synthetic amino acid (sAA) or non-standard amino acid (nsAA) is substituted for the endogenously encoded cognate amino acid.
21. The GRO of claim 20 , where the conserved residue is a tyrosine, phenylalanine or tryptophan.
22. The GRO of claim 1 , wherein the at least one instance of the available sense codon is present at the N-terminal end of the protein.
23. The GRO of claim 21 , wherein the synthetic amino acid or non-standard amino acid is pAcF (p-acetylphenylalanine), pIF (p-iodo-L-phenylalanine), or pAzF (p-azido-L-phenyalanine).
24. A genomically recoded organism (GRO) comprising a nucleic acid encoding a recombinant aminoacyl-tRNA synthetase (aaRS), a nucleic acid encoding a recombinant tRNA, and a genome wherein at least one codon is reassigned creating an available sense codon for a recombinant tRNA and the gene or genes encoding the endogenous cognate translation machinery corresponding to the at least one reassigned codon is interrupted or deleted;
at least one instance of the available sense codon is present as a sense codon in the coding region of three or more endogenous essential genes of interest that encode proteins whose expression is needed for the GRO's viability; and
wherein the recombinant tRNA can be charged by a paired recombinant aminoacyl-tRNA synthetase (aaRS) to permit site-specific incorporation of a synthetic amino acid (sAA) or non-standard amino acid (nsAA) into a nascent peptide chain of the proteins during translation of the transcribed essential genes in the GRO.
25. The GRO of claim 24 , wherein the available sense codons are present as sense codons at conserved amino acid residues at functional sites of the endogenous essential genes having at least one instance of the available sense codon.
26. The GRO of claim 25 , wherein one or more of the essential genes having at least one instance of the available sense codon encodes a protein whose function cannot be complemented by cross-feeding of metabolites to the GRO.
27. The GRO of claim 26 , wherein the escape frequency of the GRO cultured with non-permissive media is 10 −8 or lower and the fitness of the GRO when cultured with permissive media is at least 70% of its parental strain grown under the same conditions.