We would like to thank the Meningitis Trust and the MRC for providing funding for this work.

1. Generation of the mutating amplicon by SOE-PCR23 and amplification of the spectinomycin cassette
<ol>
	<li>Start by performing PCR for the amplification of the homology arms (ply 5&#8217; (488 bp) and ply3&#8217; (715 bp) respectively) of the flanking regions of the ply gene from strain 519/43. Use primers plyFw1_NOTI (TTT GCGGCCGCCAGTAAATGACTTTATACTAGCTATG), ply5&#8217;R1_BamHI (CGAAATATAGACCAAAGGACGCGGATCC AGAACCAAACTTGACCTTGA), ply3&#8217;F1_BamHI (TCAAGGTCAAGTTTGGTTCT<em...

<ol>
	<li>Bentley, S. D., 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=Genetic+Analysis+of+the+Capsular+Biosynthetic+Locus+from+All+90+Pneumococcal+Serotypes.">Genetic Analysis of the Capsular Biosynthetic Locus from All 90 Pneumococcal Serotypes.</a> PLoS Genetics. 2 (3), 31 (2006).</li><li>Calix, J. J., Nahm, M. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+pneumococcal+serotype,+11E,+has+a+variably+inactivated+wcjE+gene.">A new pneumococcal serotype, 11E, has a variably inactivated wcjE gene.</a> The Journal of Infectious Diseases. 202 (1), 29-38 (2010).</li><li>Park, I. H., Pritchard, D. G., Cartee, R., Brandao, A., Brandileone, M. C. C., Nahm, M. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Discovery+of+a+New+Capsular+Serotype+(6C)+within+Serogroup+6+of+Streptococcus+pneumoniae.">Discovery of a New Capsular Serotype (6C) within Serogroup 6 of Streptococcus pneumoniae.</a> Journal of Clinical Microbiology. 45 (4), 1225-1233 (2007).</li><li>Jin, P., 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=First+Report+of+Putative+Streptococcus+pneumoniae+Serotype+6D+among+Nasopharyngeal+Isolates+from+Fijian+Children.">First Report of Putative Streptococcus pneumoniae Serotype 6D among Nasopharyngeal Isolates from Fijian Children.</a> The Journal of Infectious Diseases. 200 (9), 1375-1380 (2009).</li><li>Oliver, M. B., vander Linden, M. P. G., K&#252;ntzel, S. A., Saad, J. S., Nahm, M. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Discovery+of+Streptococcus+pneumoniae+Serotype+6+Variants+with+Glycosyltransferases+Synthesizing+Two+Differing+Repeating+Units.">Discovery of Streptococcus pneumoniae Serotype 6 Variants with Glycosyltransferases Synthesizing Two Differing Repeating Units.</a> Journal of Biological Chemistry. 288 (36), 25976-25985 (2013).</li><li>Calix, J. 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=Serological+Characterization+of+Two+Capsule+Subtypes+among+Streptococcus+pneumoniae+Serotype+20+Strains.">Serological Characterization of Two Capsule Subtypes among Streptococcus pneumoniae Serotype 20 Strains.</a> Journal of Biological Chemistry. 287 (33), 27885-27894 (2012).</li><li>Park, I. H., 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=and+Serological+Characterization+of+a+New+Pneumococcal+Serotype,+6H,+and+Generation+of+a+Pneumococcal+Strain+Producing+Three+Different+Capsular+Repeat+Units.">and Serological Characterization of a New Pneumococcal Serotype, 6H, and Generation of a Pneumococcal Strain Producing Three Different Capsular Repeat Units.</a> Clinical and Vaccine Immunology. 22 (3), 313-318 (2015).</li><li>O'Brien, K. L., 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=Burden+of+disease+caused+by+Streptococcus+pneumoniae+in+children+younger+than+5+years:+global+estimates.">Burden of disease caused by Streptococcus pneumoniae in children younger than 5 years: global estimates.</a> The Lancet. 374 (9693), 893-902 (2009).</li><li>Henriques-Normark, B., Tuomanen, E. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Pneumococcus:+Epidemiology,+Microbiology,+and+Pathogenesis.">The Pneumococcus: Epidemiology, Microbiology, and Pathogenesis.</a> Cold Spring Harbor Perspectives in Medicine. 3 (7), 010215 (2013).</li><li>Leimkugel, 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+Outbreak+of+Serotype+1+Streptococcus+pneumoniae+Meningitis+in+Northern+Ghana+with+Features+That+Are+Characteristic+of+Neisseria+meningitidis+Meningitis+Epidemics.">An Outbreak of Serotype 1 Streptococcus pneumoniae Meningitis in Northern Ghana with Features That Are Characteristic of Neisseria meningitidis Meningitis Epidemics.</a> The Journal of Infectious Diseases. 192 (2), 192-199 (2005).</li><li>Yaro, S., 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=Epidemiological+and+Molecular+Characteristics+of+a+Highly+Lethal+Pneumococcal+Meningitis+Epidemic+in+Burkina+Faso.">Epidemiological and Molecular Characteristics of a Highly Lethal Pneumococcal Meningitis Epidemic in Burkina Faso.</a> Clinical Infectious Diseases. 43 (6), 693-700 (2006).</li><li>Antonio, M., 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=Molecular+epidemiology+of+pneumococci+obtained+from+Gambian+children+aged+2-29+months+with+invasive+pneumococcal+disease+during+a+trial+of+a+9-valent+pneumococcal+conjugate+vaccine.">Molecular epidemiology of pneumococci obtained from Gambian children aged 2-29 months with invasive pneumococcal disease during a trial of a 9-valent pneumococcal conjugate vaccine.</a> BMC Infectious Diseases. 8 (1), 81 (2008).</li><li>Kwambana-Adams, B. 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=An+outbreak+of+pneumococcal+meningitis+among+older+children+(&#8805;5+years)+and+adults+after+the+implementation+of+an+infant+vaccination+programme+with+the+13-valent+pneumococcal+conjugate+vaccine+in+Ghana.">An outbreak of pneumococcal meningitis among older children (&#8805;5 years) and adults after the implementation of an infant vaccination programme with the 13-valent pneumococcal conjugate vaccine in Ghana.</a> BMC Infectious Diseases. 16 (1), 575 (2016).</li><li>Antonio, M., 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=Seasonality+and+outbreak+of+a+predominant+Streptococcus+pneumoniae+serotype+1+clone+from+The+Gambia:+Expansion+of+ST217+hypervirulent+clonal+complex+in+West+Africa.">Seasonality and outbreak of a predominant Streptococcus pneumoniae serotype 1 clone from The Gambia: Expansion of ST217 hypervirulent clonal complex in West Africa.</a> BMC Microbiology. 8 (1), 198 (2008).</li><li>Staples, M., 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=Molecular+characterization+of+an+Australian+serotype+1+Streptococcus+pneumoniae+outbreak.">Molecular characterization of an Australian serotype 1 Streptococcus pneumoniae outbreak.</a> Epidemiology and Infection. 143 (2), 325-333 (2015).</li><li>Gessner, B. D., Mueller, J. E., Yaro, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=African+meningitis+belt+pneumococcal+disease+epidemiology+indicates+a+need+for+an+effective+serotype+1+containing+vaccine,+including+for+older+children+and+adults.">African meningitis belt pneumococcal disease epidemiology indicates a need for an effective serotype 1 containing vaccine, including for older children and adults.</a> BMC Infectious Diseases. 10 (1), 22 (2010).</li><li>Hill, P. C., 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=Nasopharyngeal+carriage+of+Streptococcus+pneumoniae+in+Gambian+infants:+a+longitudinal+study.">Nasopharyngeal carriage of Streptococcus pneumoniae in Gambian infants: a longitudinal study.</a> Clinical Infectious Diseases. 46 (6), 807-814 (2008).</li><li>Ebruke, C., 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=Temporal+changes+in+nasopharyngeal+carriage+of+Streptococcus+pneumoniae+serotype+1+genotypes+in+healthy+Gambians+before+and+after+the+7-valent+pneumococcal+conjugate+vaccine.">Temporal changes in nasopharyngeal carriage of Streptococcus pneumoniae serotype 1 genotypes in healthy Gambians before and after the 7-valent pneumococcal conjugate vaccine.</a> PeerJ. 3, 90 (2015).</li><li>Adegbola, R. 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=Serotype+and+antimicrobial+susceptibility+patterns+of+isolates+of+Streptococcus+pneumoniae+causing+invasive+disease+in+The+Gambia+1996-2003.">Serotype and antimicrobial susceptibility patterns of isolates of Streptococcus pneumoniae causing invasive disease in The Gambia 1996-2003.</a> Tropical Medicine and International Health. 11 (7), 1128-1135 (2006).</li><li>Marks, L. R., Reddinger, R. M., Hakansson, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+Levels+of+Genetic+Recombination+during+Nasopharyngeal+Carriage+and+Biofilm+Formation+in+Streptococcus+pneumoniae.">High Levels of Genetic Recombination during Nasopharyngeal Carriage and Biofilm Formation in Streptococcus pneumoniae.</a> mBio. 3 (5), (2012).</li><li>Ritchie, N. D., Mitchell, T. J., Evans, T. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=What+is+different+about+serotype+1+pneumococci.">What is different about serotype 1 pneumococci.</a> Future Microbiology. 7 (1), 33-46 (2012).</li><li>Harvey, R. M., 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=The+variable+region+of+pneumococcal+pathogenicity+island+1+is+responsible+for+unusually+high+virulence+of+a+serotype+1+isolate.">The variable region of pneumococcal pathogenicity island 1 is responsible for unusually high virulence of a serotype 1 isolate.</a> Infection and Immunity. 84 (3), 822-832 (2016).</li><li>Horton, R. M., Cai, Z. L., Ho, S. N., Pease, L. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gene+splicing+by+overlap+extension:+tailor-made+genes+using+the+polymerase+chain+reaction.">Gene splicing by overlap extension: tailor-made genes using the polymerase chain reaction.</a> BioTechniques. 8 (5), 528-535 (1990).</li><li>Alioing, G., Granadel, C., Morrison, D. A., Claverys, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Competence+pheromone,+oligopeptide+permease,+and+induction+of+competence+in+Streptococcus+pneumoniae.">Competence pheromone, oligopeptide permease, and induction of competence in Streptococcus pneumoniae.</a> Molecular Microbiology. 21 (3), 471-478 (1996).</li><li>Lund, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Enumeration and description of the strains belonging to the State Serum Institute, Copenhagen Denmark. , (1951).</li><li>Barany, F., Tomasz, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genetic+transformation+of+Streptococcus+pneumoniae+by+heterologous+plasmid+deoxyribonucleic+acid.">Genetic transformation of Streptococcus pneumoniae by heterologous plasmid deoxyribonucleic acid.</a> Journal of Bacteriology. 144 (2), 698-709 (1980).</li><li>Terra, V. S., Homer, K. A., Rao, S. G., Andrew, P. W., Yesilkaya, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+novel+&#946;-galactosidase+activity+that+contributes+to+glycoprotein+degradation+and+virulence+in+Streptococcus+pneumoniae.">Characterization of novel &#946;-galactosidase activity that contributes to glycoprotein degradation and virulence in Streptococcus pneumoniae.</a> Infection and Immunity. 78 (1), (2010).</li><li>Terra, V. S., Zhi, X., Kahya, H. F., Andrew, P. W., Yesilkaya, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pneumococcal+6-phospho-&#946;-glucosidase+(BglA3)+is+involved+in+virulence+and+nutrient+metabolism.">Pneumococcal 6-phospho-&#946;-glucosidase (BglA3) is involved in virulence and nutrient metabolism.</a> Infection and Immunity. 84 (1), (2015).</li><li>Harvey, R. M., Ogunniyi, A. D., Chen, A. Y., Paton, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pneumolysin+with+Low+Hemolytic+Activity+Confers+an+Early+Growth+Advantage+to+Streptococcus+pneumoniae+in+the+Blood.">Pneumolysin with Low Hemolytic Activity Confers an Early Growth Advantage to Streptococcus pneumoniae in the Blood.</a> Infection and Immunity. 79 (10), 4122 (2011).</li><li>Terra, V. S., Plumptre, C. D., Wall, E. C., Brown, J. S., Wren, B. 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Streptococcus pneumoniae, in particular serotype 1, continues to be a global threat causing invasive pneumococcal disease and meningitis. Despite the introduction of various vaccines that should be protective against serotype 1, in Africa, this serotype is still capable of causing outbreaks that lead to high morbidity and mortality13. The ability to genetically manipulate this serotype is of critical importance because of its clinical relevance. The method described in this study allows t...

Streptococcus pneumoniae (S. pneumoniae, the pneumococcus) is one of the principal causes of morbidity and mortality globally. Up until recently, close to 100 serotypes of S. pneumoniae have been discovered1,2,3,4,5,6,7. Yearly, invasive pneumococcal disease (IPD) claims around 700,000 deaths, of children younger than 5 years old8. S. pneumoniae is the major cause of bacterial pneumonia, otitis media, meningitis and septicaemia worldwide9.
In the African meningitis belt, serotype 1 is responsible for meningitis outbreaks, where sequence type (ST) ST217, an extremely virulent sequence type, is dominant10,11,12,13,14,15. Its importance in meningitis pathology has been likened to that of Neisseria meningitidis in the African meningitis belt16. Serotype 1 is often the main cause of IPD; however, it is very rarely found in carriage. In fact, in the Gambia, this serotype is accountable for 20% of all invasive disease, but it was only found in 0.5% of healthy carriers14,17,18,19. Genetic exchange and recombination in competent pneumococci occurs generally in carriage rather than in invasive disease20. Furthermore, serotype 1 has been shown to have one of the shortest carriage rates described amongst pneumococci (only 9 days). Therefore, it has been proposed that this serotype might have a much lower recombination rate than others21.
In depth studies are necessary to understand the reason behind serotype 1 strains&#8217; low rate of carriage and its importance in invasive disease in sub-Saharan Africa.
Here we report a protocol that allows genome-wide mutagenesis of a particular serotype 1 strain, 519/43. This strain can easily acquire and recombine new DNA into its genome. This method is not yet inter-strain, but it is very efficient when done in 519/43 background (other targets have been mutated, manuscripts in preparation). By simply using 519/43 strain, and exploit its natural competence, as well as substituting the way that the exogenous DNA is provided, we were able to mutate the pneumolysin gene (ply) in this serotype 1 strain. This method represents an improvement on the one presented by Harvey et al.22 as it is done in one-step without the need to passage the DNA through a different serotype. Nevertheless, and due to inter-strain variability, no method has been standardized to all strains. The ability to mutate specific genes and observe its effects will allow a profound understanding of serotype 1 S. pneumoniae strains and it will provide answers for the role of these strains in meningitis in sub-Saharan Africa.

<table>
	<tbody>
		<tr>
			<td>AccuPrime Pfx DNA polymerase</td>
			<td>Invitrogen</td>
			<td>12344024</td>
			<td>Used for amplification of the fragments</td>
		</tr>
		<tr>
			<td>Ampicillin sodium salt</td>
			<td>Sigma Aldrich</td>
			<td>A9518</td>
			<td>Used for bacterial selection on stage 1(pSD1)</td>
		</tr>
		<tr>
			<td>Blood Agar Base</td>
			<td>Oxoid</td>
			<td>CM0055</td>
			<td>Used to plate S. pneumoniae transformants</td>
		</tr>
		<tr>
			<td>Bovine Serum Albumine</td>
			<td>sigma</td>
			<td>55470</td>
			<td>used for S. pneumoniae Transformation</td>
		</tr>
		<tr>
			<td>Brain Heart Infusion</td>
			<td>Oxoid</td>
			<td>CM1135</td>
			<td>used to grow S. pneumoniae cells</td>
		</tr>
		<tr>
			<td>Calcium Chloride Cacl2</td>
			<td>Sigma</td>
			<td>449709</td>
			<td>used for S. pneumoniae Transformation</td>
		</tr>
		<tr>
			<td>Competence stimulating peptide 1</td>
			<td>AnaSpec</td>
			<td>AS-63779</td>
			<td>used for S. pneumoniae Transformation</td>
		</tr>
		<tr>
			<td>Luria Broth Agar</td>
			<td>Gibco</td>
			<td>22700025</td>
			<td>used for plating and selection of pSD1 and pSD2</td>
		</tr>
		<tr>
			<td>Luria Broth Base (Miller&#39;s formulation)</td>
			<td>Gibco</td>
			<td>12795027</td>
			<td>used for plating and selection of pSD1 and pSD2</td>
		</tr>
		<tr>
			<td>Monarch Gel Extraction Kit</td>
			<td>NEB</td>
			<td>T1020S</td>
			<td>Used to extract the bands from the DNA gel</td>
		</tr>
		<tr>
			<td>Monarch Plasmid Miniprep Kit</td>
			<td>NEB</td>
			<td>T1010S</td>
			<td>Used to extract plasmid from the cells</td>
		</tr>
		<tr>
			<td>pGEM T-easy</td>
			<td>Promega</td>
			<td>A1360</td>
			<td>used as suicide plasmid</td>
		</tr>
		<tr>
			<td>S.O.C.</td>
			<td>Invitrogen</td>
			<td>15544034</td>
			<td>used for recovery of cells after transformation</td>
		</tr>
		<tr>
			<td>Sodium Hydroxide (NaOH)</td>
			<td>Sigma</td>
			<td>S0899</td>
			<td>used for S.pneumoniae Transformation</td>
		</tr>
		<tr>
			<td>Spectinomycin Hydrochloride</td>
			<td>SigmaAldrich</td>
			<td>PHR1426</td>
			<td>Used for bacterial selection</td>
		</tr>
		<tr>
			<td>Subcloning Efficiency DH5&#945; Competent Cells</td>
			<td>Invitrogen</td>
			<td>18265017</td>
			<td>used for the creation of pSD1 and pSD2</td>
		</tr>
	</tbody>
</table>

constructing mutants in serotype 1 streptococcus pneumoniae strain 519/43

Streptococcus pneumoniae serotype 1 remains a huge problem in low-and-middle income countries, particularly in sub-Saharan Africa. Despite its importance, studies in this serotype have been hindered by the lack of genetic tools to modify it. In this study, we describe a method to genetically modify a serotype 1 clinical isolate (strain 519/43). Interestingly, this was achieved by exploiting the Pneumococcus&#8217; ability to naturally acquire DNA. However, unlike most pneumococci, the use of linear DNA was not successful; to mutate this important strain, a suicide plasmid had to be used. This methodology has provided the means for a deeper understanding of this elusive serotype, both in terms of its biology and pathogenicity. To validate the method, the major known pneumococcal toxin, pneumolysin, was mutated because it has a well-known and easy to follow phenotype. We showed that the mutant, as expected, lost its ability to lyse red blood cells. By being able to mutate an important gene in the serotype of interest, we were able to observe different phenotypes for loss of function mutants upon intraperitoneal and intranasal infections from the ones observed for other serotypes. In summary, this study proves that strain 519/43 (serotype 1) can be genetically modified.

The protocol described here starts by using PCR to amplify the left and right homology arms, whilst simultaneously deleting 191 bp from the middle region of the ply gene. While performing the PCR a BamHI site is introduced at the 3&#8217; of the left homology arm and at the 5&#8217; end of the right homology arm (Figure 1A). This is followed by PCR-SOE where left and right homology arms are fused into one amplicon (Figure 1B). This SOE-PCR amplicon is t...

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Constructing Mutants in Serotype 1 Streptococcus pneumoniae strain 519/43

Here, we describe a S. pneumoniae serotype 1 strain 519/43 that can be genetically modified by using its ability to naturally acquire DNA and a suicide-plasmid. As proof of principle, an isogenic mutant in the pneumolysin (ply) gene was made.

Constructing Mutants in Serotype 1 Streptococcus pneumoniae strain 519/43

Streptococcus pneumoniae serotype 1 remains a huge problem in low-and-middle income countries, particularly in sub-Saharan Africa. Despite its importance, ...

This protocol is significant because it allows genetic modification of a previously not-tractable serotype, making it possible to research and gain understanding of the serotype. This opens avenues for biological work such as vaccine development. Demonstrating the procedure will be Vanessa S.Terra, an assistant professor from the London School of Hygiene and Tropical Medicine.To begin generate plasmid pSD1 by performing a ligation following the pGEM-T Easy System I manufacturer instructions. Incubate the reaction overnight at four degree Celsius. On the next day, transform chemically competent E.coli Dh5-alpha with pSD1, incubating 50 microliters of the cells with three microliters of pSD1 ligation reaction for 15 minutes on ice, then expose the cells to thermic shock and place the cells on ice for two minutes.Remove the cells from ice and add 350 microliters of SOC media then incubate the culture for two hours at 37 degrees Celsius and 120 RPM. Plate the transformation on Luria-Bertani agar supplemented with 0.4 millimolar IPTG, 0.24 milligrams per milliliter X-Gal for blue-white selection, and 100 micrograms per milliliter ampicillin to ensure all colonies growing on the plate have the plasmid backbone. Pick three white colonies which contain pSD1 and set up overnight growths in 10 milliliters of L-B supplemented with 100 micrograms per milliliter ampicillin.Incubate the cultures overnight at 37 degrees Celsius with shaking. On the next day, centrifuge the cultures at 3, 082 G and use the pellet for plasmid extraction. After extracting the plasmid DNA, set up a BamH1 restriction digestion for both pSD1 plasmid and the spectinomycin cassette.Incubate the restriction digestion reactions and controls at 37 degree Celsius for three hours. When the restriction is finished, analyze the products by electrophoresis then excise the correct band and purify it using a commercial kit. Next, run a ligation reaction using the BamH1-digested pSD1 and spectinomycin.This will generate the plasmid pSD2. Transform pSD2 into chemically-competent E.coli DH5-alpha as previously described. Then, select the transformants carrying plasmid pSD2 based on their ability to grow in LBA supplemented with 100 micrograms per milliliter of spectinomycin and ampicillin and extract the plasmid DNA.Prepare an overnight culture of S.pneumoniae 519/43 in BHI and allow it to grow statically at 37 degrees Celsius and 5%carbon dioxide. On the next day, dilute the cultures 1:50 and 1:100 in 10 milliliters of fresh BHI broth. Incubate the culture statically at 37 degrees Celsius until the OD at 595 nanometers is between 0.05 and 0.1.Once the appropriate OD is reached, take 860 microliters of culture and transfer it into a microcentrifuge tube. Add 100 microliters of 100-millimolar sodium hydroxide, 10 microliters of 20%BSA, 10 microliters of 100-millimolar calcium chloride, two microliters of 50 nanograms per milliliter CSP1 and 500 nanograms of pSD2. Incubate the reaction statically at 37 degrees Celsius for three hours.Then, plate 330 microliters onto 5%blood agar plates supplemented with 100 micrograms per milliliter spectinomycin every hour over a three-hour incubation period. Then, incubate the plates overnight at 37 degrees Celsius and 5%carbon dioxide. Patch spectinomycin-resistant colonies onto another blood agar plate supplemented with 100 micrograms per milliliter spectinomycin and onto blood agar plates supplemented with 100 micrograms per milliliter of ampicillin, which tests for the presence of the plasmid backbone.Incubate both sets of plates overnight. Correct assembly of pSD2 was confirmed by restriction digestion. pSD2 was then used to transform 519.43 wild-type cells.Colonies growing on spectinomycin after an overnight incubation were considered positive transformants. Phenotypic confirmation of the pneumolysin mutation was performed by assessing hemolytic activity for D39, 519/43 wild-type, and mutant 519/43 delta ply. This was compared to hemolysis of red blood cells by 0.5%saponin, which is considered 100%The mutant lost its ability to lyse red blood cells.All positive colonies were further confirmed by sequencing to assess the location of the insertion. Primers with binding sites outside of the homology region were used. When performing the transformation reaction, it is important to add the reagents in the correct order.

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Research

JoVE Journal

Immunology and Infection

1.5K vistas.  London School of Hygiene and Tropical Medicine. This protocol is significant because it allows genetic modification of a previously not-tractable serotype, making it possible to research and gain understanding of the serotype. This opens avenues for biological work such as vaccine development. Demonstrating the procedure will be Vanessa S.Terra, an assistant professor from the London School of Hygiene and Tropical Medicine.To begin generate plasmid pSD1 by performing a ligation following the pGEM-T Easy System I manufacturer instruc...