We are grateful to the Environmental Services Association Education Trust, the Synthetic Biology in Cambridge SynBio fund and the Ministry of Social Justice and Empowerment, Government of India, for financial support.

1. Preparation of Culture Media
<ol>
	<li>Prepare BG11 medium according to Castenholz, 198817.
	<ol>
		<li>Prepare stock solutions of 100x BG11, trace elements and iron stock (Table 1).</li>
		<li>Prepare separate solutions of phosphate stock, Na2CO3 stock, N-[Tris(hydroxymethyl)methyl]-2-aminoethanesulfonic acid (TES) buffer and NaHCO3 (Table 1).</li>
		<li>Autoclave the phosphate and Na2CO3 stocks. Filter-ster...

<ol>
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J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Contribution+of+cyanobacterial+alkane+production+to+the+ocean+hydrocarbon+cycle.">Contribution of cyanobacterial alkane production to the ocean hydrocarbon cycle.</a> Proc Natl Acad Sci U S A. , (2015).</li><li>Howe, C. J., Barbrook, A. C., Nisbet, R. E. R., Lockhart, P. J., Larkum, A. W. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+origin+of+plastids.">The origin of plastids.</a> Philos Trans R Soc Lond B Biol Sci. 363, 2675-2685 (2008).</li><li>Lea-Smith, D. J., Bombelli, P., Vasudevan, R., Howe, C. 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J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Terminal+oxidase+mutants+of+the+cyanobacterium+Synechocystis+sp.+PCC+6803+show+increased+electrogenic+activity+in+biological+photo-voltaic+systems.">Terminal oxidase mutants of the cyanobacterium Synechocystis sp. PCC 6803 show increased electrogenic activity in biological photo-voltaic systems.</a> Phys Chem Chem Phys. 15, 13611-13618 (2013).</li><li>Ducat, D. C., Way, J. C., Silver, P. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Engineering+cyanobacteria+to+generate+high-value+products.">Engineering cyanobacteria to generate high-value products.</a> Trends Biotechnol. 29, 95-103 (2011).</li><li>Dismukes, G. C., Carrieri, D., Bennette, N., Ananyev, G. M., Posewitz, M. 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H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antialgal,+antibacterial+and+antifungal+activity+of+two+metabolites+produced+and+excreted+by+cyanobacteria+during+growth.">Antialgal, antibacterial and antifungal activity of two metabolites produced and excreted by cyanobacteria during growth.</a> Microbiol Res. 161, 180-186 (2006).</li><li>Scott, S. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biodiesel+from+algae:+challenges+and+prospects.">Biodiesel from algae: challenges and prospects.</a> Curr Opin Biotechnol. 21, 277-286 (2010).</li><li>Lea-Smith, D. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phycobilisome-deficient+strains+of+Synechocystis+sp.+PCC+6803+have+reduced+size+and+require+carbon-limiting+conditions+to+exhibit+enhanced+productivity.">Phycobilisome-deficient strains of Synechocystis sp. PCC 6803 have reduced size and require carbon-limiting conditions to exhibit enhanced productivity.</a> Plant Physiol. 165, 705-714 (2014).</li><li>Lea-Smith, D. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thylakoid+terminal+oxidases+are+essential+for+the+cyanobacterium+Synechocystis+sp.+PCC+6803+to+survive+rapidly+changing+light+intensities.">Thylakoid terminal oxidases are essential for the cyanobacterium Synechocystis sp. PCC 6803 to survive rapidly changing light intensities.</a> Plant Physiol. 162, 484-495 (2013).</li><li>Liu, X., Sheng, J., Curtiss, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fatty+acid+production+in+genetically+modified+cyanobacteria.">Fatty acid production in genetically modified cyanobacteria.</a> Proc Natl Acad Sci U S A. 108, 6899-6904 (2011).</li><li>Xu, H., Vavilin, D., Funk, C., Vermaas, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiple+deletions+of+small+cab-like+proteins+in+the+cyanobacterium+Synechocystis+sp+PCC+6803+-+Consequences+for+pigment+biosynthesis+and+accumulation.">Multiple deletions of small cab-like proteins in the cyanobacterium Synechocystis sp PCC 6803 - Consequences for pigment biosynthesis and accumulation.</a> J Biol Chem. 279, 27971-27979 (2004).</li><li>Castenholz, R. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Culturing+methods+for+Cyanobacteria.">Culturing methods for Cyanobacteria.</a> Method Enzymol. 167, 68-93 (1988).</li><li>Mitschke, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+experimentally+anchored+map+of+transcriptional+start+sites+in+the+model+cyanobacterium+Synechocystis+sp+PCC6803.">An experimentally anchored map of transcriptional start sites in the model cyanobacterium Synechocystis sp PCC6803.</a> Proc Natl Acad Sci U S A. 108, 2124-2129 (2011).</li><li>Ried, J. L., Collmer, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+nptI-sacB-sacR+cartridge+for+constructing+directed,+unmarked+mutations+in+gram-negative+bacteria+by+marker+exchange-eviction+mutagenesis.">An nptI-sacB-sacR cartridge for constructing directed, unmarked mutations in gram-negative bacteria by marker exchange-eviction mutagenesis.</a> Gene. 57, 239-246 (1987).</li><li>Vieira, J., Messing, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+pUC+plasmids,+an+M13mp7-derived+system+for+insertion+mutagenesis+and+sequencing+with+synthetic+universal+primers.">The pUC plasmids, an M13mp7-derived system for insertion mutagenesis and sequencing with synthetic universal primers.</a> Gene. 19, 259-268 (1982).</li><li>Vermaas, W. F. J., Williams, J. G. K., Rutherford, A. W., Mathis, P., Arntzen, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genetically+Engineered+Mutant+of+the+Cyanobacterium+Synechocystis+6803+Lacks+the+Photosystem-Ii+Chlorophyll-Binding+Protein+Cp-47.">Genetically Engineered Mutant of the Cyanobacterium Synechocystis 6803 Lacks the Photosystem-Ii Chlorophyll-Binding Protein Cp-47.</a> Proc Natl Acad Sci U S A. 83, 9474-9477 (1986).</li><li>Westphal, S., Heins, L., Soll, J., Vothknecht, U. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vipp1+deletion+mutant+of+Synechocystis:+A+connection+between+bacterial+phage+shock+and+thylakoid+biogenesis?.">Vipp1 deletion mutant of Synechocystis: A connection between bacterial phage shock and thylakoid biogenesis?.</a> Proc Natl Acad Sci U S A. 98, 4243-4248 (2001).</li><li>Zhang, S. Y., Shen, G. Z., Li, Z. K., Golbeck, J. H., Bryant, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vipp1+Is+Essential+for+the+Biogenesis+of+Photosystem+I+but+Not+Thylakoid+Membranes+in+Synechococcus+sp+PCC+7002.">Vipp1 Is Essential for the Biogenesis of Photosystem I but Not Thylakoid Membranes in Synechococcus sp PCC 7002.</a> J Biol Chem. 289, 15904-15914 (2014).</li><li>Taroncher-Oldenberg, G., Nishina, K., Stephanopoulos, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+and+analysis+of+the+polyhydroxyalkanoate-specific+beta-ketothiolase+and+acetoacetyl+coenzyme+A+reductase+genes+in+the+cyanobacterium+Synechocystis+sp+strain+PCC6803.">Identification and analysis of the polyhydroxyalkanoate-specific beta-ketothiolase and acetoacetyl coenzyme A reductase genes in the cyanobacterium Synechocystis sp strain PCC6803.</a> Appl Environ Microbiol. 66, 4440-4448 (2000).</li><li>Hein, S., Tran, H., Steinbuchel, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synechocystis+sp.+PCC6803+possesses+a+two-component+polyhydroxyalkanoic+acid+synthase+similar+to+that+of+anoxygenic+purple+sulfur+bacteria.">Synechocystis sp. PCC6803 possesses a two-component polyhydroxyalkanoic acid synthase similar to that of anoxygenic purple sulfur bacteria.</a> Arch Microbiol. 170, 162-170 (1998).</li><li>Ng, A. H., Berla, B. M., Pakrasi, H. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fine+tuning+of+photoautotrophic+protein+production+by+combining+promoters+and+neutral+sites+in+Synechocystis+6803,+a+cyanobacterium.">Fine tuning of photoautotrophic protein production by combining promoters and neutral sites in Synechocystis 6803, a cyanobacterium.</a> Appl Environ Microbiol. , (2015).</li></ol>

The authors declare that they have no competing financial interests.

The most critical steps in generation of unmarked mutants are: 1) careful plasmid design to ensure only the targeted region is altered; 2) ensuring that samples remain axenic, especially when cultured on sucrose; 3) plating transformed cells for marked mutant generation initially on BG11 agar plates lacking antibiotics, followed by addition of agar plus antibiotics 24 hr later; 4) culturing marked mutants for 4 full days prior to plating on BG11 plus sucrose agar plates: 5) ensuring that marked mutants are fully segregat...

Cyanobacteria are an evolutionarily ancient and diverse phylum of bacteria found in nearly every natural environment on Earth. In marine ecosystems they are particularly abundant and play a key role in many nutrient cycles, accounting for approximately half of carbon fixation1, the majority of nitrogen fixation2 and hundreds of millions of tons of hydrocarbon production3 in the oceans annually. Chloroplasts, the organelle responsible for photosynthesis in eukaryotic algae and plants, are likely to have evolved from a cyanobacterium that was engulfed by a host organism4. Cyanobacteria have proved useful model organisms for the study of photosynthesis, electron transport5 and biochemical pathways, many of which are conserved in plants. In addition cyanobacteria are increasingly being used for production of food, biofuels6, electricity7 and industrial compounds8, due to their highly efficient conversion of water and CO2 to biomass using solar energy9. Many species can be cultivated on non-arable land with minimal nutrients and seawater, suggesting that cyanobacteria could potentially be grown at large scale without affecting agricultural production. Certain species are also sources of natural products, including antifungal, antibacterial and anti-cancer compounds10,11.
The ability to generate mutants is key to understanding cyanobacterial photosynthesis, biochemistry and physiology, and essential for development of strains for industrial purposes. The majority of published studies generate genetically modified strains by insertion of an antibiotic resistance cassette into the site of interest. This limits the number of mutations that can be introduced into a strain, as only a few antibiotic resistance cassettes are available for use in cyanobacteria. Strains containing genes conferring antibiotic resistance cannot be used for industrial production in open ponds, which is likely to be the only cost-effective means to produce biofuels and other low value products12. The generation of unmarked mutants overcomes these limitations. Unmarked mutants contain no foreign DNA, unless intentionally included, and can be manipulated multiple times. Therefore it is possible to generate as many alterations in a strain as desired. In addition, polar effects on genes downstream of the modification site can be minimized, allowing more precise modification of the organism13.
To generate mutant strains, suicide plasmids containing two DNA fragments identical to regions in the cyanobacterial chromosome flanking the gene to be deleted (termed the 5&#39; and 3&#39; flanking regions) are first constructed. Two genes are then inserted between these flanking regions. One of these encodes an antibiotic resistance protein; the second encodes SacB, which produces levansucrase, a compound conferring sensitivity to sucrose. In the first stage of the process, marked mutants, i.e. strains containing some foreign DNA, are generated. The plasmid construct is mixed with the cyanobacterial cells and the DNA is taken up naturally by the organism. Transformants are selected by growth on agar plates containing the appropriate antibiotic and the mutant genotype verified by PCR. Suicide plasmids cannot replicate within the strain of interest. Therefore any antibiotic resistant colonies will result from a recombination event whereby the gene of interest in inserted into the chromosome. To generate unmarked mutants, the marked mutant is then mixed with a second suicide plasmid containing just the 5&#39; and 3&#39; flanking regions. However, if insertion of foreign DNA is required, a plasmid consisting of the 5&#39; and 3&#39; flanking regions with a cassette containing the genes of interest inserted between these DNA fragments, can be used. Selection is via growth on agar plates containing sucrose. As sucrose is lethal to cells when the sacB gene product is expressed, the only cells that survive are those in which a second recombination event has occurred, whereby the sucrose sensitivity gene, in addition to the antibiotic resistance gene, has been recombined out of the chromosome and onto the plasmid. As a consequence of the recombinational exchange, the flanking regions and any DNA between them are inserted into the chromosome.
We have successfully used these methods to generate multiple chromosomal mutations in the same strain of Synechocystis sp. PCC6803 (hereafter referred to as Synechocystis)13,14, to introduce single point mutations into a gene of interest13 and for expression of gene cassettes. While generation of unmarked knockouts has been demonstrated prior to our work in Synechocystis15,16, a detailed method, aided by a visual presentation of the critical steps, is not publicly available. We have also applied the same method for generation of marked knockouts in another model cyanobacterium, Synechococcus sp. PCC7002 (hereafter referred to as Synechococcus). This protocol provides a clear, simple method for generating mutants and a rapid protocol for validating and storing these strains.

<table border="0" cellpadding="0" cellspacing="0" width="645">
	<tbody>
		<tr height="25">
			<td height="25" style="height:25px;width:237px;">NaNO3</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">S5506</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">MgSO4.7H2O</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">230391</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">CaCl2</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">C1016</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">citric acid</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">C0759</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Na2EDTA</td>
			<td style="width:123px;">Fisher</td>
			<td style="width:119px;">EDT002</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">H3BO3</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">339067</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">MnCl2.4H2O</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">M3634</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">ZnSO4.7H2O</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">Z4750</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Na2MoO4.2H2O</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">331058</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">CuSO4.5H2O</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">209198</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Co(NO3)2.6H2O</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">239267</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ferric ammonium citrate</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">F5879</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">K2HPO4</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">P3786</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Na2CO3</td>
			<td style="width:123px;">Fisher</td>
			<td style="width:119px;">SODC001</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">TES</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">T1375</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">NaHCO3</td>
			<td style="width:123px;">Fisher</td>
			<td style="width:119px;">SODH001</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">HEPES</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">H3375</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">cyanocobalamin</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">47869</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Na2S2O3</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">72049</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Bacto agar</td>
			<td style="width:123px;">BD</td>
			<td style="width:119px;">214010</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Sucrose</td>
			<td style="width:123px;">Fisher</td>
			<td style="width:119px;">SUC001</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Petri dish 90 mm triple vented</td>
			<td style="width:123px;">Greiner</td>
			<td style="width:119px;">633185</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">0.2 &#181;m filters</td>
			<td style="width:123px;">Sartorius</td>
			<td style="width:119px;">16534</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">100 mL conical flasks</td>
			<td style="width:123px;">Pyrex</td>
			<td style="width:119px;">CON004</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Parafilm M 100 mm x38 m</td>
			<td style="width:123px;">Bemis</td>
			<td style="width:119px;">FIL003</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Phusion high fidelity DNA polymerase&#160;</td>
			<td style="width:123px;">Phusion</td>
			<td style="width:119px;">F-530</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Agarose</td>
			<td style="width:123px;">Melford</td>
			<td style="width:119px;">MB1200</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">DNA purification kit&#160;</td>
			<td style="width:123px;">MoBio</td>
			<td style="width:119px;">12100-300</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Restriction endonucleases</td>
			<td style="width:123px;">NEB</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">T4 ligase</td>
			<td style="width:123px;">Thermo Scientific</td>
			<td style="width:119px;">EL0011</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Luria Bertani broth</td>
			<td style="width:123px;">Invitrogen</td>
			<td style="width:119px;">12795-027</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">MES</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">M8250</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Kanamycin sulfate</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">60615</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Ampicillin</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">A9518</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">GeneJET plasmid miniprep kit</td>
			<td style="width:123px;">Thermo Scientific</td>
			<td style="width:119px;">K0503</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">14 mL round-bottom tube</td>
			<td style="width:123px;">BD falcon</td>
			<td style="width:119px;">352059</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">GoTaq G2 Flexi DNA polymerase</td>
			<td style="width:123px;">Promega</td>
			<td style="width:119px;">M7805</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">425-600 &#181;m glass beads</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">G8772</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Glycerol</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">G5516</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">DMSO</td>
			<td style="width:123px;">Sigma</td>
			<td style="width:119px;">D8418</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Fluorescent bulbs</td>
			<td style="width:123px;">Gro-Lux</td>
			<td style="width:119px;">69</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">HT multitron photobioreactor</td>
			<td style="width:123px;">Infors</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

generation of marked and markerless mutants in model cyanobacterial species

Cyanobacteria are ecologically important organisms and potential platforms for production of biofuels and useful industrial products. Genetic manipulation of cyanobacteria, especially model organisms such as Synechocystis sp. PCC6803 and Synechococcus sp. PCC7002, is a key tool for both basic and applied research. Generation of unmarked mutants, whereby chromosomal alterations are introduced into a strain via insertion of an antibiotic resistance cassette (a manipulatable fragment of DNA containing one or more genes), followed by subsequent removal of this cassette using a negative selectable marker, is a particularly powerful technique. Unmarked mutants can be repeatedly genetically manipulated, allowing as many alterations to be introduced into a strain as desired. In addition, the absence of genes encoding antibiotic resistance proteins in the mutated strain is desirable, as it avoids the possibility of 'escape' of antibiotic resistant organisms into the environment. However, detailed methods for repeated rounds of genetic manipulation of cyanobacteria are not well described in the scientific literature. Here we provide a comprehensive description of this technique, which we have successfully used to generate mutants with multiple deletions, single point mutations within a gene of interest and insertion of novel gene cassettes.

Plasmid design is critical for successful generation of both marked and unmarked mutants. Figure 1 gives an example of plasmid A and B used to generate a deletion mutant in the Synechocystis genes cpcC1 and cpcC213. In each case the 5&#39; and 3&#39; flanking regions are approximately 900-1,000 bp. Reduced flanking regions can be used although the smallest we have successfully trialed has been approximately 500 bp. Plasmid B can also ...

Watch this Scientific Journal Video about Generation of Marked and Markerless Mutants in Model Cyanobacterial Species at JoVE.com

Generation of Marked and Markerless Mutants in Model Cyanobacterial Species

Introducing multiple genomic alterations into cyanobacteria is an essential tool in the development of strains for industrial and basic research purposes. We describe a system for generating unmarked mutants in the model cyanobacterial species Synechocystis sp. PCC6803 and marked mutants in Synechococcus sp. PCC7002.

Cyanobacteria are ecologically important organisms and potential platforms for production of biofuels and useful industrial products. Genetic manipulation ...

The overall goal of this procedure is to demonstrate a system for generating unmarked mutants in the cyanobacterial Synechocystis species PCC6803 and marked mutants in Synechococcus species PCC7002. This method can help answer key questions in the cyanobacterial genetics field. Such as how to introduce chromosomal alterations into a strain.By insertion of an antibiotic resistance gene, followed by a subsequent removal of this cassette, using a negative selectable marker. The main advantage of this technique is that strains can be repeatedly genetically manipulated. Allowing as many alternations to be introduced into a strain as desired.After preparing media, cyanobacterial strains and plasmids, according to the text protocol. Set up a fresh culture by inoculating a loop full of cyanobacterial cells, into 30 to 50 mililiters of BG11 medium. Grow the culture in the light at 30 degrees Celsius for two to three days, to an OD7500, equal to 0.2 to 0.6.Following the incubation, centrifuge one to two milliliters of the culture at 2, 300g's for five minutes. Then after discarding the supernatant, use BG11 medium to wash the pellets once, gently pipetting to resuspend the cells. As vortexing may result in the loss of pili, which are essential for DNA uptake.After pelleting the cells again, and removing the supernatant, add BG11 medium to a final volume of 100 microliters, and transfer the cells to a 14 milliliter round bottom tube. Next, add 1 microgram of previous prepared plasmid A to the cells. And gently tap to mix.Then lay the tubes down horizontally in the incubator at 30 degrees Celsius, and incubate for four to six hours. Following the incubation, spread aliquots of the cell culture plasmid DNA mixture on BG11 agar plates without antibiotics. And incubate at 30 degrees Celsius.Approximately 24 hours later, prepare a 0.6%agar solution, in water containing kanamycin. And allow it to cool to 42 degress Celsius. Then add 2.5 to three milliliters to the edges of the culture plates and tilt the plate, so the solution forms an even top agar layer on the surface.Incubate the plates approximately seven days for colonies to be visible. Then divide a fresh BG11 agar plus kanamycin plate into six sectors. And use a blunt end toothpick to streak out individual colonies.To carry out PCR, to confirm marked knockout, transfer a small amount of cells into a tube containing 50 microliters of water, and approximately 20 425 to 600 micrometer glass beads. Shake the cells and beads at approximately 2, 000 rpm for five minutes, before spinning at 15, 700 g's for five minutes. Then use five microliters of the supernatant to prepare 50 microliter PCR reactions with tack DNA preliminaries.To validate the mutants, after designing primers according to the text protocol, amplified product using the following program, and include a wild-type control. Through gelelektroforeses, verify the genotype of knockout transformants. Showing a band of approximately four kilobase pairs and lacking the wild-type band.Refer to the text protocol for further details. If a wild-type band is still present, re-streak the strain on the fresh plate and repeat the PCR. Repeat the validation process until the mutant is segregated, and no wild-type band is observed in the PCR reaction.For a strain that shows marked mutant profile, re-streak on a fresh plate for use in generating an unmarked knockout. To generate unmarked Synechocystis mutants, set up a fresh culture of the marked knockout by inoculating the loop full of cells into 30 to 50 milliliters of BG11 medium. Grow the culture for two to three days to and OD750, equal to 0.2 to 0.6.Centrifuge 10 milliliters of the culture at 2, 300 g's for five minutes and discard the supernatant. Then us BG11 medium to gently wash the cells. After adding BG11 to a final volume of 200 microliters, and transferring the cells to a 14 milliliter round bottom tube, add 1 microgram of plasmid B DNA to the cells, and gently tap to mix.Then lay the tubes down horizontally in the incubator, and incubate for four to six hours. Following the incubation, add 1.8 milliliters of BG11 medium and incubate the samples for a total of four days with shaking. This is a sufficient time to allow recombination to occur in the multiple chromosomal copies.Plate 50, 10, and 1 microliter aliquots of the transformed culture onto BG11 plus 5%sucrose agar plates and incubate for approximately seven days to generate single colonies. Next, using a blunt end toothpick, hatch 30 to 50 individual colonies on BG11 plus kanamycin plates. Then patch onto BG11 plus 5%sucrose.Colonies that grow on BG11 plus sucrose, but not on plates with kanamycin are potential unmarked knockouts. Colonies that grow on both plates are likely to be sucrose resistant due to a mutation in the sacB gene. Following the PCR method, demonstrated earlier in this video, verify unmarked knockouts, which will produce a gel band corresponding to the wild-type size minus the deleted region.If the strain shows an unmarked mutant profile, then re-streak it on fresh BG11 agar without antibiotics. To store the strains long term, set up a fresh culture of the strain by inoculating a loop full of cells into 30 to 50 milliliters of BG11 medium. Grow the culture for three to four days to and OD750 equal to 0.4 to 0.7.After using BG11 to wash the cells once, resuspend the pellet in approximately two milliliters of BG11. Add 0.8 milliliters of the concentrated cells to one tube. Then add 0.2 milliliters of 80%filter sterilized glycerol.To another tube, add 0.93 milliliters of concentrated cells and 0.07 milliliters of DMSO. Store both tubes at negative 80 degrees Celsius. To revive the strains, remove the tube and use a blunt end toothpick to scrape off some cells onto an agar plate without antibiotics.Then use a sterile loop to streak out as normal. This figure shows examples of plasmids A and B used to generate deletion mutants. In each case, the five prime and three prime planking regions are approximately 900 to 1, 000 base pairs.Plasmid B, can also contain a gene cassette between the five prime and three prime approximately one kilobase pair flanking regions. Or a modified version of the native gene sequence. Upon transformation with plasmid A, several hundred colonies will appear on a plate after seven to 10 days.If genes are non-essential and mutants demonstrate growth, similar to the wild-type strain, then all of the chromosomes should contain a copy npt1/sacB inserted sequence, as determined via PCR. If genes are non-essential, and mutants grow slow, then several rounds of re-streaking with increasing concentrations of kanamycin, are necessary to obtain a segregated marked mutant. If upon re-streaking, a marked mutant is not obtained, the gene is likely essential for survival.The majority of individual colonies, obtained from transformation with plasmid B, will be kanamycin sensitive and sucrose resistant. As demonstrated here, PCR amplification of the target region in these colonies, shows that nearly 100%of the unmarked mutant profile. Once mastered, this technique can be done in hours over a six week period if it is performed properly.While attempting this procedure it's important to remember to use sterile technique. Following this procedure, other methods like measuring oxygen production, or gas chromatography mass spectrometry, can be performed in order to answer additional questions, like measuring photosynthetic rates or metabolite production. After its development, this technique paved the way for researchers in the field of cyanobacterial genetics.To explore key biochemical and physiological processes in this phylum, and developmental strains for industrial purposes. After watching this video, you should have a good understanding of how to generate unmarked knockouts in Synechococcus species PCC6803.

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11.8K Views.  University of Cambridge. The overall goal of this procedure is to demonstrate a system for generating unmarked mutants in the cyanobacterial Synechocystis species PCC6803 and marked mutants in Synechococcus species PCC7002. This method can help answer key questions in the cyanobacterial genetics field. Such as how to introduce chromosomal alterations into a strain.By insertion of an antibiotic resistance gene, followed by a subsequent removal of this cassette, using a negative selectable marker. The main advan...