Targeted mutations
The present invention relates to a process for producing and selecting for targeted mutations in bacterial genomes. In particular, the process relates to the transformation of bacteria with a Recombination Element which comprises the desired mutation followed by homologous recombination of the Recombination Element into the bacterial genome; the CRISPR/Cas system is then used to eliminate bacteria which do not have the desired mutation.
1. A process for producing a mutation in an Intended Mutagenesis Region (IMR) within a bacterial genome, wherein the bacteria are of the class Clostridia, wherein the bacteria comprise a CRISPR/Cas system, and wherein the IMR comprises a CRISPR PAM/Protospacer which is capable of being recognised by the bacteria's CRISPR/Cas systems, the process comprising the steps:
(a) transforming a population of said bacteria with a Recombination Vector, wherein the Recombination Vector comprises a Recombination Element, wherein the Recombination Element comprises:
(i) a Substitution Element, wherein the Substitution Element comprises the mutation, and
(ii) Homology Arms which flank the Substitution Element, wherein the Homology Arms are capable of promoting the replacement of all or part of the IMR in the bacterial genome with an element which comprises the Substitution Element,
wherein the Recombination Element does not comprise a CRISPR PAM/Protospacer which is capable of being recognised by a crRNA which recognises the CRISPR/PAM Protospacer in the IMR;
(b) culturing the population of bacteria under conditions wherein, in one or more bacteria within the population, all or part of the IMR in the genomes of those bacteria is replaced by an element which comprises the Substitution Element and whereby the CRISPR PAM/Protospacer is removed from the IMR in the genomes of those bacteria or is rendered incapable of being recognised by a crRNA which recognises the CRISPR/PAM Protospacer in the IMR;
(c) transforming the population of bacteria with a Killing Vector which is capable of directing production of a crRNA which targets the CRISPR PAM/Protospacer in the IMR of any bacteria in the population from which the CRISPR PAM/Protospacer has not been removed or rendered incapable of being recognised by the crRNA, thereby promoting the CAS endonuclease-induced cleavage of those CRISPR PAM/Protospacers in the genomic DNA which are recognised by the crRNA and the subsequent death of those bacteria; and
(d) selecting or isolating one or more bacteria from the population whose genomes comprise the Substitution Element comprising the mutation.
2. A process as claimed in claim 1 , wherein prior to step (c), one or more transformed bacteria are isolated and sub-cultured further to produce one or more further populations of bacteria which are then transformed with the Killing Vector.
3. A process as claimed in claim 1 , wherein the PAM/Protospacer in the IMR is present within a region of DNA which corresponds in the Recombination Element to:
(i) the Substitution Element;
(ii) the overlap between the upstream Homology Arm and the Substitution Element;
(iii) the overlap between the downstream Homology Arm and the Substitution Element;
(iv) the upstream Homology Arm; or
(v) the downstream Homology Arm.
4. A process as claimed in claim 3 , wherein the PAM/Protospacer in the IMR is present within a region of DNA which corresponds in the Recombination Element to:
(i) the Substitution Element;
(ii) the overlap between the upstream Homology Arm and the Substitution Element; or
(iii) the overlap between the downstream Homology Arm and the Substitution Element.
5. A process as claimed in claim 4 , wherein the PAM/Protospacer in the IMR is present within a region of DNA which corresponds to the Substitution Element.
6. A process as claimed in claim 1 , wherein the Killing Vector comprises:
(i) a Cas Leader Element
(ii) a first Cas Direct Repeat Element
(iii) a Cas Spacer Element which encodes a crRNA which targets the CRISPR PAM/Protospacer in the IMR; and
(iv) a second Cas Direct Repeat Element.
7. A process as claimed in claim 1 , wherein the mutation is a substitution, deletion or insertion of one or more nucleotides, or a combination of one or more substitution, deletion or insertion.
8. A process as claimed in claim 7 , wherein the mutation is in the PAM/Protospacer.
9. A process as claimed in claim 7 , wherein the mutation is a SNP.
10. A process as claimed in claim 1 , wherein the bacteria have an endogenous CRISPR/Cas system.
11. A process as claimed in claim 1 , wherein the bacteria have a Type I CRISPR/Cas system.
12. A process as claimed in claim 1 , wherein the bacteria are of the genus Clostridium.
13. A process as claimed in claim 12 , wherein the bacteria are selected from the group consisting of C. acetobutylicum, C. arbusti, C. aurantibutyricum, C. beijerinckii, C. cellulovorans, C. cellulolyticum, C. thermocellum, C. thermobutyricum, C. pasteurianum, C. kluyveri, C. novyi, C. saccharobutylicum, C. thermosuccinogenes, C. thermopalmarium, C. saccharolyticum, C. saccharoperbutylacetonicum, C. tyrobutyricum, C. tetanomorphum, C. magnum, C. ljungdahlii, C. autoethanogenum, C. butyricum, C. puniceum, C. diolis, C. homopropionicum and C. roseum.
14. A process for making a mutated bacterium, which comprises producing a mutation in an Intended Mutagenesis Region (IMR) within a bacterial genome of a bacterium by a process as claimed in claim 1 .