The technology relates to nucleic acids and methods for producing recombinant cells such as cyanobacteria suitable for standardised strain-engineering. The technology also relates to methods of strain engineering.
This application claims the benefit of Australian Provisional Application No. 2020903460 filed 25 Sep. 2020, the entire content of which is incorporated by reference herein.
Many cyanobacteria are naturally-competent or can be transformed using well known methods. For many years, researchers have routinely exploited this natural cellular DNA-uptake phenomenon or artificially induced competence to chromosomally-integrate new genes via homologous recombination.
Despite many years of genetic modification, DNA insertions in cyanobacteria have typically been limited to ad hoc single or double-insertions into a small number of strain-specific ‘Neutral Sites’ which are intergenic locations within a strain's chromosome that show no observable phenotypic consequence of foreign DNA insertion.
Using constructs containing flanking homologous DNA regions of the Neutral Sites, typically of 400-800 bp, researchers are routinely able to insert genetic cassettes and modify the strain's chromosomal DNA. However, most cyanobacteria research is conducted in a single species, there is little incentive or benefit to move beyond the small set of naturally-occurring ‘Neutral Sites’ and attempt to standardise or engineer a broadly-applicable solution. In addition, Neutral Sites are species or strain-specific and little or no work has been completed to identify regions that are cross-species compatible.
Cyanobacteria produce a large number of secondary metabolites and have the potential to be used in the production of pharmaceuticals, high value chemicals and as tools for bioremediation. The diverse array of biochemical pathways of cyanobacteria are apparent in the more than 400 cyanobacterial genomes available in public databases (Alvarenga et al, Front. Microbiol., volume 8, 2017, page 809). Consequently, the potential to improve and/or modify metabolite production by employing genetically manipulated cyanobacteria is being explored but is limited by the need to re-engineer constructs to be specific for each strain.
Accordingly, there is a need to develop new interspecies ‘landing-zones’, and cells containing the interspecies ‘landing-zones’ for standardised strain engineering of cyanobacteria.
In a first aspect, there is provided a nucleic acid cassette comprising;
The neutral site may be substantially homologous to at least a part of a non-essential region of a microorganism genome.
The non-essential region may be selected from the NSC1 region of Synechocystis sp. strain PCC 6803, the slr0168 region of Synechocystis sp. strain PCC 6803, the A0159 region of Synechocystis sp. strain PCC 7002, the A2842 region of Synechocystis sp. strain PCC 7002, or a non-essential region of Synechocystis sp. strain PCC 7942.
The length of each neutral site sequence portion may be independently selected from about 500 bp, about 550 bp, about 600 bp, about 650 bp, about 700 bp, about 750 bp, about 800 bp, about 850 bp, about 900 bp, about 950 bp, or at least about 1000 bp.
In one embodiment the landing zone comprises a core sequence consisting of a randomly generated nucleic acid sequence with a GC content of approximately 50% and lacking a bacterial promoter sequence.
The landing zone may further comprise at least one transcriptional terminator and at least one translational insulator, preferably the landing zone comprises a transcriptional terminator and a translational insulator at either end of the core sequence.
In some embodiments the landing zone comprises or consists of SEQ ID NO: 1 or SEQ ID NO: 2.
In some embodiments the neutral site may be selected from any one of SEQ ID NOs: 8-17, that is the neutral site portions are selected from within each sequence
The neutral site portions may be SEQ ID NO: 3 and SEQ ID NO: 4.
In cassettes having multiple landing zones, each landing zone may be the same of different same or different.
The selectable marker gene may be selected from genes that confer resistance to bleomycin, chloramphenicol, erythromycin, kanamycin, spectinomycin, neomycin, streptomycin, zeocin or gentamicin.
In a second aspect there is provided a cell comprising the nucleic acid cassette of the first aspect, preferably the nucleic acid cassette is integrated into the genome of the cell.
In a third aspect the heterologous nucleic acid comprises, in a 5′ to 3′ direction a first landing zone, a second landing zone, a first selectable marker, a third landing zone, and a fourth landing zone.
In a fourth aspect there is provided a cell comprising the nucleic acid cassette of the third aspect, preferably the nucleic acid cassette is integrated into the genome of the cell.
In a fifth aspect there is provided a method for generating a recombinant cell comprising a nucleic acid of interest, the method comprising:
The method may further comprise culturing the cell in the presence of a selection agent for the second selectable marker, thereby selecting a recombinant cell comprising the second selectable marker and the nucleic acid of interest.
In a sixth aspect there is provided a method for generating a recombinant cell comprising a first nucleic acid of interest, the method comprising:
The method may further comprise (c) contacting a cell from step (b) with a second nucleic acid insert under conditions that allow recombination of a second nucleic acid insert with the nucleic acid construct in the genome of the cell; wherein
In a seventh aspect there is provided a method for generating a recombinant cell comprising a first nucleic acid of interest, the method comprising:
The method of claim may further comprise (c) contacting a cell from step (b) with a second nucleic acid insert under conditions that allow recombination of the second nucleic acid insert with the nucleic acid construct in the genome of the cell; wherein the second nucleic acid insert comprises, in a 5′ to 3′ direction, the first landing zone, a second nucleic acid of interest, the fifth landing zone, a further selectable marker, and the sixth landing zone, or wherein the first and/or sixth landing zones have at least 90% sequence identity to the first and/or sixth landing zones in the cell, respectively; and
The nucleic acid of interest, first nucleic acid of interest, or second nucleic acid of interest may be operatively coupled to a constitutive or inducible promoter.
The cell may be a Cyanobacteria, for example a Cyanobacteria is selected from the group consisting of Synechocystis sp. PCC 6803, Synechococcus elongatus PCC 7942, Synechococcus sp. PCC 7002, Synechococcus sp.PCC 11901, Synechococcus sp. UTEX 2434, Synechococcus sp. UTEX 2973, Synechococcus sp. UTEX 3153, Synechococcus sp. UTEX 3154, Anabaena variabilis PCC 7120, and Leptolyngbya sp. BL0902.
Throughout this specification, unless the context clearly requires otherwise, the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
Throughout this specification, the term ‘consisting of’ means consisting only of.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present technology. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present technology as it existed before the priority date of each claim of this specification.
Unless the context requires otherwise or specifically stated to the contrary, integers, steps, or elements of the technology recited herein as singular integers, steps or elements clearly encompass both singular and plural forms of the recited integers, steps or elements.
In the context of the present specification the terms ‘a’ and ‘an’ are used to refer to one or more than one (i.e., at least one) of the grammatical object of the article. By way of example, reference to ‘an element’ means one element, or more than one element.
In the context of the present specification the term ‘about’ means that reference to a figure or value is not to be taken as an absolute figure or value, but includes margins of variation above or below the figure or value in line with what a skilled person would understand according to the art, including within typical margins of error or instrument limitation. In other words, use of the term ‘about’ is understood to refer to a range or approximation that a person or skilled in the art would consider to be equivalent to a recited value in the context of achieving the same function or result.
Those skilled in the art will appreciate that the technology described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the technology includes all such variations and modifications. For the avoidance of doubt, the technology also includes all of the steps, features, and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more of said steps, features and compounds.
In order that the present technology may be more clearly understood, preferred embodiments will be described with reference to the following drawings and examples.
The present inventors have developed nucleic acids and methods of using the nucleic acids to facilitate the rapid and simple engineering of multiple species of microorganisms, particularly cyanobacteria, using standardised interspecies DNA cassettes in combination with universal ‘Landing Zones’. By first manipulating wild-type strains and integrating standardised sections of DNA within existing Neutral Sites to create a ‘Landing Zone’, interspecies-compatible DNA ‘Insertion Cassettes’ can be constructed and introduced across multiple strains, without the need to rebuild or transfer the insertion to an appropriate strain-specific integration vector.
Wild-type strains of naturally-competent cyanobacteria are initially engineered to include a set of universal ‘Landing Zones’ as follows:
Strain development often takes an iterative approach, whereby further modifications are incorporated by the insertion of additional genetic cassettes. Previously this required use of a separate neutral site (NS) for each modification. Given that there are typically only 2 or 3 known neutral sites in each strain this limits the number of modifications that can be made.
The inventors have developed the use of universal Landing Zones (LZs) to design a nucleic acid construct comprising a nucleic acid of interest, strain-independent Landing Zones, and a Selection Marker (SM).
In one embodiment four LZs are used (see
Critically, with reference to
In one aspect the invention provides a nucleic acid construct comprising two portions of a neutral site. A heterologous nucleic acid is inserted between the neutral site portions. The heterologous nucleic acid can comprise two landing zones separated by a selectable marker. This nucleic acid construct can be transformed into a microorganism and combine with the genome of the microorganism, which contains a neutral site having a corresponding sequence to the portions of the neutral site of the nucleic acid construct. This occurs via homologous recombination.
Accordingly, there is provided a microorganism or ‘chassis strain’ comprising the nucleic acid construct integrated into the genome of the microorganism such that the genome of the ‘chassis-strain’ comprises the neutral site portions, landing zones and selectable marker of the nucleic acid construct.
The term ‘homologous recombination’ refers to the introduction of a nucleic acid fragment of interest into a genome by the process of strand exchange that can occur spontaneously with the alignment of homologous nucleic acid sequences (i.e. sets of complementary strands). As is known in the art, microorganisms are efficient at homologous recombination. Methods and conditions allowing homologous recombination are well known in the art. Thus, in general, the neutral site portions (and landing zones) in the nucleic acid constructs disclosed herein function in pairs (for example the neutral site portions). The first member of the pair is located 5′ to an intervening nucleic acid sequence typically comprising a nucleic acid of interest and a selectable marker. The second member of the pair is located 3′ to the intervening nucleic acid sequence.
The neutral sites can be designed to be homologous to any region of the cyanobacterial genome and a skilled person can design the neutral sites using methods known in the art.
In some embodiments the length of the neutral site portions are at least 500 bp. For example, the length of each neutral site portion may be independently selected from about 500 bp, 550 bp, 600 bp, 650 bp, 700 bp, 750 bp, 800 bp, 850 bp, 900 bp, 950 bp, or at least about 1000 bp.
In some embodiments the neutral site may be selected from any one of SEQ ID NOs: 8-17, that is the neutral site portions are selected from within each sequence.
In one embodiment the neutral site portions may be SEQ ID NO: 3 and SEQ ID NO: 4. SEQ ID NO: 3 is a portion of a PCC 7002 non-essential region, found in GenBank accession ACA99827). SEQ ID NO: 4 is also a portion of a PCC 7002 non-essential region, found in GenBank accession ACA99827
The neutral sites can be homologous to any region of the microbial genome is not required for viability and can therefore be tailored using methods known in the art. In some embodiments the neutral sites are homologous to non-essential regions. Non-essential regions are known in the art.
Suitable non-essential regions include the following:
Suitable non-essential regions for PCC 6803 are described as the NSC1 site by Ng, A. H., Berla, B. M. and Pakrasi, H. B., 2015. Fine-tuning of photoautotrophic protein production by combining promoters and neutral sites in the Cyanobacterium Synechocystis sp. strain PCC 6803. Appl. Environ. Microbiol., 81(19), pp. 6857-6863.
In another embodiment the non-essential site may for PCC 6803 may be slr0168 as described by the Xiao, Y., Wang, S., Rommelfanger, S., Balassy, A., Barba-Ostria, C., Gu, P., Galazka, J. M. and Zhang, F., 2018. Developing a Cas9-based tool to engineer native plasmids in Synechocystis sp. PCC 6803. Biotechnology and bioengineering, 115(9), pp. 2305-2314.
For PCC 7002 non-essential sites such as A0159 and A2842 may be used, these sites are described in Vogel, A. I. M., Lale, R. and Hohmann-Marriott, M. F., 2017. Streamlining recombination-mediated genetic engineering by validating three neutral integration sites in Synechococcus sp. PCC 7002. Journal of biological engineering, 11(1), p. 19.
Non-essential sites suitable for PCC 7942 are described in Kulkarni, R. D. and Golden, S. S., 1997. mRNA stability is regulated by a coding-region element and the unique 5′ untranslated leader sequences of the three Synechococcus psbA transcripts. Molecular microbiology, 24(6), pp. 1131-1142; and Andersson, C. R., 2000. Application of bioluminescence to the study of circadian rhythms in cyanobacteria. Methods Enzymol., 305, pp. 527-542
The landing zones are artificial sequences designed to be amenable to homologous recombination. Landing zones comprise a core sequence (LZ core) that mirrors the GC content of native cyanobacterial DNA which has a GC content of about 50%. Accordingly, the GC content of the LZ core is from about 40% to about 60%. Ideally the landing zone sequences are not transcribed and therefore contain at least one transcriptional terminator sequence (TER), at least one translational insulator sequence (TLT), or both.
In a preferred embodiment the landing zone comprises a TER and a TLT at either side of the LZ core.
LZ cores can be produced by randomly generating DNA sequences of approximately 50% GC content. Any sequences containing bacterial promoters can be altered or discarded. The LZ core may be about 50 bp to about 150 bp, for example the LZ core may be 50 bp, 60 bp, 70 bp, 80 bp, 90 bp, 100 bp, 110 bp, 120 bp, 130 bp, 140 bp, or 150 bp. In some embodiments the LZ core is about 100 bp.
Any known transcriptional terminators (TER) sequences can be used in the landing zones.
Suitable translational insulators (TLT), include stop-codons in all six reading frames, were created and screened, removing repetitive parts.
The TLT and/or TER sequences can be added to the 5′ and/or 3′ ends of the LZ core to generate a landing zone.
Each landing zone is a nucleic acid sequence which is unique to the nucleic acid construct in that the nucleic acid construct does not comprise another landing zone of the same sequence, and the landing zone sequence is not found in the wild type organism used in the methods.
Preferably, the landing zones are each about 150 bp, about 200 bp, about 250 bp, about 300 bp, about 350 bp, about 400 bp, about 450 bp, about 500 bp, about 550 bp, about 600 bp, about 650 bp, about 700 bp, about 750 bp, about 800 bp, about 850 bp, about 900 bp, about 950 bp, or at least about 1000 bp.
In some embodiment the landing zone may consist, consist essentially of or comprise SEQ ID NO; 1 or SEQ ID NO: 2.
There are also provided methods for generating a recombinant microorganism containing a nucleic acid of interest from the chassis-strain. In general the methods comprise transforming the chassis-strain with a nucleic acid insert comprising the nucleic acid of interest under conditions that allow recombination of the gene cassette with the nucleic acid construct in the genome of the microorganism.
The nucleic acid insert comprises a nucleic acid of interest (either alone or operably linked to a promoter) and a selectable marker that is different to the selectable marker in the chassis strain, these elements are flanked by two landing zones, each landing zone comprising a sequence at least 90% identical to the landing zones in the chassis strain.
It is noted that absolute homology between the landing zones in the chassis strain and the corresponding landing zones in the gene cassette is not required as homologous recombination can occur between sequences that do not exactly match. For example the landing zones in the nucleic acid insert may be about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the landing zones in the chassis-strain.
Previously, the insertion of the same nucleic acid of interest into multiple strains would require the preparation of different constructs for each strain, each having the nucleic acid of interest and neutral-site portions unique to each strain. The present invention provides chassis strains containing universal landing zones that allow, in this example, the preparation of a single nucleic acid insert that can be transformed into multiple chassis-strains.
In some aspects the nucleic acid construct comprises two portions of a neutral site with an intervening heterologous nucleic acid comprising, in a 5′ to 3′ direction, a first (eg LZA in
Similar to the above this nucleic acid construct can be integrated into the genome of a microorganism to generate a ‘resistance-pivot chassis-strain’ wherein the genome of the chassis-strain comprises the neutral site portions, multiple landing zones and selectable marker of the nucleic acid construct.
There are also provided methods for generating a recombinant microorganism containing multiple nucleic acids of interest from the resistance-pivot chassis-strain. In general the methods comprise transforming the resistance-pivot chassis-strain with a first nucleic acid insert comprising the nucleic acid of interest under conditions that allow recombination of the first nucleic acid insert with a first portion of nucleic acid construct in the genome of the microorganism. The methods then require a second transformation with a second nucleic acid insert under conditions that allow recombination of the second nucleic acid insert with a second portion of nucleic acid construct in the genome of the microorganism.
In one embodiment the first nucleic acid insert comprises a nucleic acid of interest (either alone or operably linked to a promoter) and a selectable marker that is different to the selectable marker in the resistance-pivot chassis strain. In this embodiment the first nucleic acid insert comprises, in a 5′ to 3′ direction the flanked by the first landing zone (e.g. LZA in
Once the first nucleic acid insert is recombined into the genome of the resistance-pivot chassis strain, the strain comprises the first, fifth, third and fourth landing zones. That is the second landing zone is lost during recombination. In addition, the selectable marker is flanked by fifth and sixth landing zones.
The second nucleic acid insert comprises a second nucleic acid of interest (either alone or operably linked to a promoter) and a selectable marker that is different to the selectable marker in the resistance-pivot chassis (i.e. different to the selectable marker in the first nucleic acid insert. In this embodiment the second nucleic acid insert comprises, in a 5′ to 3′ direction the fifth landing zone (e.g. LZB2 in
Once the first and second nucleic acid inserts are recombined into the genome of the resistance-pivot chassis strain, the strain comprises the first, fifth, sixth and fourth landing zones in addition to a selectable marker and both the first and seconds nucleic acids of interest. The third landing zone is lost during recombination
In an alternate embodiment the first nucleic acid insert comprises a nucleic acid of interest (either alone or operably linked to a promoter) and a selectable marker that is different to the selectable marker in the resistance-pivot chassis strain. In this embodiment the first nucleic acid insert comprises, in a 5′ to 3′ direction the second landing zone (e.g. LZB1 in
Once the first nucleic acid insert is recombined into the genome of the resistance-pivot chassis strain, the strain comprises the first, second, sixth, and fourth landing zones. That is the third landing zone is lost during recombination.
The second nucleic acid insert comprises a second nucleic acid of interest (either alone or operably linked to a promoter) and a selectable marker that is different to the selectable marker in the resistance-pivot chassis (i.e. different to the selectable marker in the first nucleic acid insert. In this embodiment the second nucleic acid insert comprises, in a 5′ to 3′ direction the first landing zone (e.g. LZA in
Once the first and second nucleic acid inserts are recombined into the genome of the resistance-pivot chassis strain, the strain comprises the first, sixth, fifth, and fourth landing zones in addition to a selectable marker and both the first and second nucleic acids of interest. The second landing zone is lost during recombination. In addition, the selectable marker is flanked by fifth and sixth landing zones.
In both of the preceding embodiments the recombinant microorganism comprises a selectable marker flanked by landing zones. Accordingly, further nucleic acid inserts can be designed and prepared to contain a different selectable marker, a further nucleic acid of interest and additional landing zones to facilitate yet further recombination events to include yet further nucleic acids of interest. Based on the teaching of this specification it is within the ability of a skilled person to design and prepare such further nucleic acid inserts using methods known in the art.
After each transformation step the methods require culturing the microorganism in the presence of a selection agent for the selectable marker in the nucleic acid insert to select for a recombinant microorganism comprising the nucleic acid of interest.
Additional confirmation that the nucleic acid insert or nucleic acid construct has been incorporated into the genome of the microorganism may be required in some instances. This may be achieved by any method known in the art, for example PCR, nucleic acid sequencing, southern blotting, RFLP analysis, and the like.
Any selectable marker known in the art may be used in the nucleic acids and methods described herein.
The choice of selectable marker may vary depending on the cell or microorganism used. For example in embodiments where the cell is a microorganism a selectable marker may be a gene encoding antibiotic resistance.
Suitable selectable markers for use in cyanobacteria include genes that confer resistance to bleomycin, chloramphenicol, erythromycin, kanamycin, spectinomycin, neomycin, streptomycin, zeocin or gentamicin.
Any type of nucleic acid may be used as a nucleic acid insert, for example linear or circular DNA. The nucleic acid insert will contain a nucleic acid of interest, a number of landing zones and a selectable marker.
The nucleic acid of interest may be for example a sequence encoding a modified version of one or more cyanobacterial genes or may be one or more heterologous genes to be expressed in the cell.
The nucleic acid insert may be synthesised as a linear nucleic acid or may be constructed in a plasmid using molecular biology techniques known in the art. The plasmids may also contain replication origins for commonly used bacteria such as E. coli to facilitate modification of the nucleic acid insert sequences, and preparation of the plasmid containing the nucleic acid insert in an amendable species before transformation into a cell.
The nucleic acid insert can be isolated from a plasmid prior to use in the methods, for example the nucleic acid insert may be excised from a plasmid using restriction enzymes, or amplified by PCR, before use in the methods.
In some embodiments the nucleic acid insert comprises a promoter operatively coupled to the nucleic acid of interest.
A “promoter” refers to the DNA sequence(s) that control or otherwise modify transcription of a gene and can include binding sites for transcription factors, RNA polymerases, and other biomolecules and substances (e.g. inorganic compounds) that can influence transcription of a gene by interaction with the promoter. Typically these sequences are located at the 5′ end of the sense strand of the gene, but can be located anywhere in the genome.
As used herein, “operatively coupled” indicates that the regulatory sequences (e.g. the promoter) useful for expression of the coding sequences of a nucleic acid are placed in the nucleic acid molecule in the appropriate positions relative to the coding sequence so as to effect or enhance expression of the coding sequence. This same definition is sometimes applied to the arrangement of coding sequences and transcription control elements (e.g. promoters, enhancers, and termination elements), and/or selectable markers in an expression vector.
The promoter may be a constitutively active promoter or an inducible promoter. An inducible promoter is one that responds to a specific signal. In some embodiments an inducible promoter will not be activated in the absence of inducer, it will produce a predictable response to a given concentration of inducer or repressor. This response may be binary (i.e., on/off) or graded change with different concentrations of inducer/repressor. Ideally, saturating concentrations of the inducer is not harmful to the cyanobacteria host organism.
The inducible promoter may be a metal inducible promoter, a metabolite inducible promoter, a macronutrient inducible promoter.
The metal inducible promoter may be selected from the group comprising ArsB (induced by AsO2−), ziaA (induced by Cd2+ or Zn2+), coat (induced by Co2+ or Zn2+), nrsB (induced by Co2+ or Ni2+), petE (induced by Cu+2), isiAB (repressed by Fe3+), idiA (repressed by Fe2+), Smt (induced by Zn2+).
The metabolite inducible promoter may be selected from the group comprising the tetracycline inducible and the IPTG (Isopropyl β-D-1-thiogalactopyranoside) inducible tetR, trp-lac, Trc, A1lacO-1, trc10, trc20, LlacO1, clac143, and Trc. In one embodiment the inducible promoter is clac143.
The macronutrient inducible promoter may be selected from psbA2 (induced by light), psbA1 (induced by light), nirA (induced by NO3−, repressed by NH4+), and Nir (induced by NO3−, repressed by NH4−).
The promoter may be a Type I, Type II or Type III promoters. A type I promoter comprises transcriptional start site at +1 (by definition), a −10 element (consensus sequence 5′-TATAAT-3′), and a −35 element (consensus sequence 5′-TTGACA-3′). A type II promoter is usually used when expression of a gene is to be induced by stress or adaptation responses and thus are normally transcribed by group 2 sigma factors. Type II promoters have a −10 element but typically lack the −35 element. Type III promoters do not have regular −10 and −35 elements. Accordingly, the choice of promoter can be tailored to the desired growth conditions.
In some embodiments constitutive promoter may be used. Examples of suitable constitutive promoters include cpc560, psbA, plastocyanin promoter, BBaJ23101, and J23.
Any transformation method known in the art may be used in the methods described herein. The choice or Transformation method will vary depending on the cell used in the methods and will be within the knowledge of the skilled person.
As used herein, the term “transformation” is used in the context of nucleic acid entering a cyanobacterial cell, to refer to the introduction of an exogenous and/or recombinant nucleic acid sequence into the interior of a living cyanobacteria. The nucleic acid may be in the form of naked DNA or RNA, it may be associated with various proteins or other elements such as lipids, or surfactants.
The nucleic acids and methods described herein are broadly applicable to any cyanobacteria capable of being transformed with a heterologous genetic element.
The cyanobacterial cells may be naturally competent. Alternatively, competence may be induced in the cell, for example using chemical, electrical or mechanical means or any other means known in the art.
Typically cyanobacterial cells are used in the methods when they are in an active growth phase. For example actively growing cyanobacteria are used in methods. The cyanobacteria may be in early, mid or late exponential phase. This can be determined using an OD measurement, for example at 750 nm. Cyanobacteria from a culture with an OD of 0.1 to 3.0 can be used. For example suitable ODs are 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, or 3.0.
Cyanobacteria cultured under any growth conditions known in the art can be used. In some embodiments the cyanobacteria are grown under low-light conditions, constant light or using periods of light and dark, for example light and dark periods that mimic a normal day/night cycle.
In embodiments where a light/dark cycle is used to prepare the cyanobacteria for transformation, the cyanobacteria may be harvested at any point in the light/dark cycle. However, it is known that in some (but not necessarily all) strains pilus biogenesis occurs daily in the morning, but natural competence is at is peak with the onset of darkness, that is natural cyanobacterial competence is conditional and tied to the cells' circadian rhythm. Accordingly, in some embodiments the cells are harvested at or near the transition from light to dark, or near the end of the light cycle.
The cyanobacteria cultured for transformation may be cultured in low-light conditions (i.e. less than 100 μmol photons·m−2·s−1), for example 50 μmol photons·m−2·s−1, normal light conditions (from 100-750 μmol photons·m−2·s−1), for example 100-150 μmol photons·m−2·s−1or light saturated conditions (greater than 750 μmol photons·m−2·s−1). In embodiments where light/dark cycles are used the level of light in each light cycle may be independently selected from low-light, normal light or light saturated.
In some embodiments the cells are grown without controlling CO2 levels. In other embodiments the cells are cultured in an atmosphere comprising about 0.05% to about 10% CO2, for example the CO2 level is about 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or about 10%.
Most cyanobacteria harbor genes encoding proteins for type IV pili apparatus which are known to be involved in natural competence. Accordingly, it is envisaged that in some embodiments the methods disclosed herein can be used with any genus of cyanobacteria having type IV pili.
Cyanobacterial genera that can be used in the methods disclosed herein include those selected from the group comprising Collenia, Girvanella, Gunflintia, Morania, Sphaerocodium, Acaryochloris, Anabaena, Anabaenopsis, Aphanizomenon, Arthrospira, Aulosira, Borzia, Calothrix, Chlorogloeopsis, Chroococcidiopsis, Cyanobacterium, Cyanonephron, Cyanothece, Cylindrospermopsis, Cylindrospermum, Gloeobacter, Gloeocapsa, Gloeotrichia, Homoeothrix, Jakutophyton, Johannesbaptistia, Loefgrenia, Lyngbya, Merismopedia, Microcystis, Nodularia, Nostoc, Oscillatoria, Ozarkcollenia, Palaeolyngbya, Petalonema, Planktothrix, Prochlorococcus, Prochloron, Radaisia, Rivularia, Rothpletzella, Scytonema, Spirulina, Synechococcus, Synechocystis, Trichodesmium, and Wollea.
In some embodiments suitable strains include Synechocystis sp. PCC 6803, Synechococcus elongatus PCC 7942, Synechococcus sp. PCC 7002, Synechococcus sp.PCC 11901, Synechococcus sp. UTEX 2434, Synechococcus sp. UTEX 2973, Synechococcus sp. UTEX 3153, Synechococcus sp. UTEX 3154, Anabaena variabilis PCC 7120, and Leptolyngbya sp. BL0902
It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.
As exemplified herein, the inventors have demonstrated the use of Landing Zones and the exchange of the Selection Marker. This is detailed in
Synechococcus sp. PCC 7002 Wildtype (WT) cells were transformed with plasmid pBB-SHL5-231 (
Plasmid pBB-SHL5-232 (
Strain SHL5-231 was grown in liquid medium supplemented with 20 ug/mL of Spectinomycin and washed with regular medium before the transformation to remove residual amounts of antibiotic.
Strain SHL5-231 was transformed with DNA LIN-SHL5-001 and transformants selected with gentamicin (10 ug/mL) were designated strain SHL5-232. Additionally, SHLS-232 colonies were screened by colony PCR. Given that SM2 is ˜500 bp shorter than SM1, a identifiable length shift can be observed on an agarose gel (
Step 1: PCC 7002 Wildtype (WT) cells were transformed with plasmid pBB-TMR1-231 (
Step 2: Strain TMR1-231 was grown in liquid medium supplemented with 20 ug/mL of spectinomycin and washed with regular medium before the transformation (step 3) to remove residual amounts of antibiotic.
Step 3: Cyanobacteria strain TMR1-231 (step 1) was transformed with plasmid pBB-TMR1-237 (
In addition to the ability for newly-engineered strains to grow on the alternative antibiotic, TMR1-237 colonies were also screened by colony PCR. Given that SM2+GCA (SEQ ID: 7) is ˜600 bp longer than SM1, an identifiable length shift can be observed on an agarose gel (
The landing zones are artificial sequences designed to be amenable to homologous recombination. Landing zones are designed to mirror the GC content of native cyanobacterial DNA, while also not generating transcriptional output via the unintended incorporation of bacterial promoter sequences. Transcriptional terminators (TER) and translational insulators (TLT) can be included at either end of each Landing Zone cassette to avoid any potential readthrough to/from inserted Genetic Cassettes in engineered strains.
Landing Zones can be produced by randomly generating 1000 bp DNA sequences of approximately 50% GC content (50% is the average GC content in relevant cyanobacterial genomes).
Sequences are screened for potential bacterial promoters; where potential promoters were identified, sequences were altered until no potential promoters were found.
A collection of strong transcriptional terminators (TER) sequences was screened and repetitive parts removed.
A set of randomised translational insulators (TLT), including stop-codons in all x6 reading frames, were created and screened, removing repetitive parts.
A TLT and TER were added to both 5′ and 3′ ends of the 1000 bp DNA ‘core’ sequences. The ‘core’ sequence was then trimmed so that the complete LZ cassette (comprising 2 TLT, 2 TLT and a core) was approximately 1000 bp long.
The LZ cassettes were then screened for homology/interaction with each other and an internal parts database. TER/TLT sequences were interchanged between cassettes to ensure no significant repeats were present within the complete collection.
A schematic of a LZ is provided in
Number | Date | Country | Kind |
---|---|---|---|
2020903460 | Sep 2020 | AU | national |
Filing Document | Filing Date | Country | Kind |
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PCT/AU2021/051121 | 9/24/2021 | WO |