Name: phage-mediated genetic manipulation of the lyme disease spirochete borrelia burgdorferi
Uploaded: 2022-09-28T14:10:00
Description: Watch this Scientific Journal Video about Phage-Mediated Genetic Manipulation of the Lyme Disease Spirochete Borrelia burgdorferi at JoVE.com

The author wishes to thank Shawna Reed, D. Scott Samuels, and Patrick Secor for their useful discussion and Vareeon (Pam) Chonweerawong for their technical assistance. This work was supported by the Department of Biomedical Sciences and faculty research grants to Christian H. Eggers from the School of Health Sciences at Quinnipiac University.

All experiments using recombinant DNA and BSL-2 organisms were reviewed and approved by the Quinnipiac University Institutional Biosafety Committee.
1. Preparation of B. burgdorferi culture for the production of &#966;BB-1
<ol>
	<li>Prepare Barbour-Stoenner-Kelly medium supplemented with 6.6% heat-inactivated normal rabbit serum (BSK)15. For 1 L of 1x BSK, combine the components listed in Table 1 in 900 mL of water, adjust th...

The use of transduction could represent one method of overcoming at least some of the biological and technical barriers associated with the electrotransformation of B. burgdorferi1,4,13,37. In many systems, bacteriophage can move host (non-prophage) DNA between bacterial cells by either generalized or specialized transduction22,23</s...

The development of tools for the genetic manipulation of the spirochetal bacterium Borrelia burgdorferi has added immeasurable value to the understanding of the nature of Lyme disease1,2,3,4. B. burgdorferi has an unusually complex genome comprised of a small linear chromosome and both linear and circular plasmids5,6. Spontaneous plasmid loss, intragenic rearrangement (movement of genes from one plasmid to another within the same organism), and horizontal gene transfer (HGT, the movement of DNA between two organisms) have given rise to a dizzying amount of genetic heterogeneity among B. burgdorferi (for an example, see Schutzer et al.7). The resulting genotypes (or &#34;strains&#34;) are all members of the same species but have genetic differences that influence their ability to transmit to and infect different mammalian hosts8,9,10,11. In this report, the term &#34;strain&#34; will be used to refer to B. burgdorferi with a particular naturally derived genetic background; the term &#34;clone&#34; will be used to refer to a strain that has been genetically modified for a particular purpose or as a result of experimental manipulation.
The molecular toolbox available for use in B. burgdorferi includes selectable markers, gene reporters, shuttle vectors, transposon mutagenesis, inducible promoters, and counter-selectable markers (for a review, see Drektrah and Samuels12). The effective use of these methodologies requires the artificial introduction of heterologous (foreign) DNA into a B. burgdorferi strain of interest. In B. burgdorferi, the introduction of heterologous DNA is achieved almost exclusively via electroporation, a method that utilizes a pulse of electricity to make a bacterial membrane transiently permeable to small pieces of DNA introduced into the media1. The majority of the cells (estimated to be &#8805;99.5%) are killed by the pulse, but the remaining cells have a high frequency of retaining the heterologous DNA13. Although considered to be among the most highly efficient methods of introducing DNA into bacteria, the frequency of electroporation into B. burgdorferi is very low (ranging from 1 transformant in 5 &#215; 104 to 5 &#215; 106 cells)13. The barriers to achieving higher frequencies of transformation seem to be both technical and biological. Technical barriers to the successful electroporation of B. burgdorferi include both the amount of DNA (&#62;10 &#956;g) that is necessary and the requirement of the spirochetes to be in exactly the correct growth phase (mid-log, between 2 &#215; 107 cells&#183;mL&#8722;1 and 7 &#215; 107 cells&#183;mL&#8722;1) when preparing electrocompetent cells12,13. These technical barriers, however, may be easier to overcome than the biological barriers.
Lyme disease researchers recognize that B. burgdorferi clones can be divided into two broad categories with respect to their ability to be manipulated genetically13,14. High passage, lab-adapted isolates are often readily transformed but usually have lost the plasmids essential for infectivity, behave in a physiologically aberrant fashion, and are not able to infect a mammalian host or persist within a tick vector12,13. While these clones have been useful for dissecting the molecular biology of the spirochete within the lab, they are of little value for studying the spirochete within the biological context of the enzootic cycle. Low-passage infectious isolates, on the other hand, behave in a physiologic manner reflective of an infectious state and can complete the infectious cycle but usually are recalcitrant to the introduction of heterologous DNA and are, therefore, difficult to manipulate for study12,13. The difficulty in transforming low-passage isolates is related to at least two different factors: (i) low-passage isolates often tightly clump together, particularly under the high-density conditions required for electroporation, thus blocking many cells from either the full application of the electrical charge or access to the DNA in the media13,15; and (ii) B. burgdorferi encodes at least two different plasmid-borne restriction-modification (R-M) systems that may be lost in high-passage isolates14,16. R-M systems have evolved to allow bacteria to recognize and eliminate foreign DNA17. Indeed, several studies in B. burgdorferi have demonstrated that transformation efficiencies increase when the source of the DNA is B. burgdorferi rather than Escherichia coli13,16. Unfortunately, acquiring the requisite high concentration of DNA for electroporation from B. burgdorferi is an expensive and time-consuming prospect. Another potential concern when electroporating and selecting low-passage isolates is that the process seems to favor transformants that have lost the critical virulence-associated plasmid, lp2514,18,19; thus, the very act of genetically manipulating low-passage B. burgdorferi isolates via electroporation may select for clones that are not suitable for biologically relevant analysis within the enzootic cycle20. Given these issues, a system in which heterologous DNA could be electrotransformed into high-passage B. burgdorferi clones and then transferred into low-passage infectious isolates by a method other than electroporation could be a welcome addition to the growing collection of molecular tools available for use in the Lyme disease spirochete.
In addition to transformation (the uptake of naked DNA), there are two other mechanisms by which bacteria regularly take up heterologous DNA: conjugation, which is the exchange of DNA between bacteria in direct physical contact with each other, and transduction, which is the exchange of DNA mediated by a bacteriophage21. Indeed, the ability of bacteriophage to mediate HGT has been used as an experimental tool for dissecting the molecular processes within a number of bacterial systems22,23,24. B. burgdorferi is not naturally competent for the uptake of naked DNA, and there is little evidence that B. burgdorferi encodes the apparatus necessary to promote successful conjugation. Previous reports have described, however, the identification and preliminary characterization of &#966;BB-1, a temperate bacteriophage of B. burgdorferi25,26,27,28. &#966;BB-1 packages a family of 30 kb plasmids found within B. burgdorferi25; the members of this family have been designated cp32s. Consistent with a role for &#966;BB-1 in participating in HGT among B. burgdorferi strains, Stevenson et al. reported an identical cp32 found in two strains with otherwise disparate cp32s, suggesting a recent sharing of this cp32 between these two strains, likely via transduction29. There also is evidence of significant recombination via HGT among the cp32s in an otherwise relatively stable genome30,31,32,33. Finally, the ability of &#966;BB-1 to transduce both cp32s and heterologous shuttle vector DNA between cells of the same strain and between cells of two different strains has been demonstrated previously27,28. Given these findings, &#966;BB-1 has been proposed as another tool to be developed for the dissection of the molecular biology of B. burgdorferi.
The goal of this report is to detail a method for inducing and purifying phage &#966;BB-1 from B. burgdorferi, as well as provide a protocol for performing a transduction assay between B. burgdorferi clones and selecting and screening potential transductants.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>1 L filter units (PES, 0.22 &#181;m pore size)</td>
			<td>Millipore Sigma</td>
			<td>S2GPU10RE</td>
			<td></td>
		</tr>
		<tr>
			<td>12 mm x 75 mm tube (dual position cap) (polypropylene)</td>
			<td>USA Scientific</td>
			<td>1450-0810</td>
			<td>holds 4 mL with low void volume (for induction)</td>
		</tr>
		<tr>
			<td>15 mL conical centrifuge tubes (polypropylene)</td>
			<td>USA Scientific</td>
			<td>5618-8271</td>
			<td></td>
		</tr>
		<tr>
			<td>1-methyl-3-nitroso-nitroguanidine (MNNG)</td>
			<td>Millipore Sigma</td>
			<td></td>
			<td>CAUTION: potential carcinogen; no longer readily available, have not tested offered substitute</td>
		</tr>
		<tr>
			<td>5.75&#34; Pasteur Pipettes (cotton-plugged/borosilicate glass/non-sterile)</td>
			<td>Thermo Fisher Scientific</td>
			<td>13-678-8A</td>
			<td>autoclave prior to use</td>
		</tr>
		<tr>
			<td>50 mL conical centrifuge tubes (polypropylene)</td>
			<td>USA Scientific</td>
			<td>1500-1211</td>
			<td></td>
		</tr>
		<tr>
			<td>Absolute ethanol</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Agarose LE</td>
			<td>Dot Scientific inc.</td>
			<td>AGLE-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Bacto Neopeptone</td>
			<td>Gibco</td>
			<td>DF0119-17-9</td>
			<td></td>
		</tr>
		<tr>
			<td>Bacto TC Yeastolate</td>
			<td>Gibco</td>
			<td>255772</td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine serum albumin (serum replacement grade)</td>
			<td>Gemini Bio-Products</td>
			<td>700-104P</td>
			<td></td>
		</tr>
		<tr>
			<td>Chloroform (for molecular biology)</td>
			<td>Thermo Fisher Scientific</td>
			<td>BP1145-1</td>
			<td>CAUTION: volatile organic; use only in a chemical fume hood</td>
		</tr>
		<tr>
			<td>CMRL-1066 w/o L-Glutamine (powder)</td>
			<td>US Biological</td>
			<td>C5900-01</td>
			<td>cell culture grade</td>
		</tr>
		<tr>
			<td>Erythromycin</td>
			<td>Research Products International Corp</td>
			<td>E57000-25.0</td>
			<td></td>
		</tr>
		<tr>
			<td>Gentamicin reagent solution</td>
			<td>Gibco</td>
			<td>15750-060</td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose (Dextrose Anhydrous)</td>
			<td>Thermo Fisher Scientific</td>
			<td>BP350-500</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>Thermo Fisher Scientific</td>
			<td>BP310-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Kanamycin sulfate</td>
			<td>Thermo Fisher Scientific</td>
			<td>25389-94-0</td>
			<td></td>
		</tr>
		<tr>
			<td>Millex-GS (0.22 &#181;M pore size)</td>
			<td>Millipore Sigma</td>
			<td>SLGSM33SS</td>
			<td>to filter sterilize antibiotics and other small volume solutions</td>
		</tr>
		<tr>
			<td>Mitomycin C</td>
			<td>Thermo Fisher Scientific</td>
			<td>BP25312</td>
			<td>CAUTION: potential carcinogen; use only in a chemical fume hood</td>
		</tr>
		<tr>
			<td>N-acetyl-D-glucosamine</td>
			<td>MP Biomedicals, LLC</td>
			<td>100068</td>
			<td></td>
		</tr>
		<tr>
			<td>Oligonucleotides (primers for PCR)</td>
			<td>IDT DNA</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>OmniPrep (total genomic extraction kit)</td>
			<td>G Biosciences</td>
			<td>786-136</td>
			<td></td>
		</tr>
		<tr>
			<td>Petri Dish (100 mm &#215; 15 mm)</td>
			<td>Thermo Fisher Scientific</td>
			<td>FB0875712</td>
			<td></td>
		</tr>
		<tr>
			<td>Petroff-Hausser counting chamber</td>
			<td>Hausser scientific</td>
			<td>HS-3900</td>
			<td></td>
		</tr>
		<tr>
			<td>Petroff-Hausser counting chamber cover glass</td>
			<td>Hausser scientific</td>
			<td>HS-5051</td>
			<td></td>
		</tr>
		<tr>
			<td>Polyethylene glycol 8000 (PEG)</td>
			<td>Thermo Fisher Scientific</td>
			<td>BP233-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Rabbit serum non-sterile trace-hemolyzed young (NRS)</td>
			<td>Pel-Freez Biologicals</td>
			<td>31119-3</td>
			<td>heat inactivate as per manufacturer&#39;s instructions</td>
		</tr>
		<tr>
			<td>Semi-micro UV transparent cuvettes</td>
			<td>USA Scientific</td>
			<td>9750-9150</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium bicarbonate</td>
			<td>Thermo Fisher Scientific</td>
			<td>BP328-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium chloride</td>
			<td>Thermo Fisher Scientific</td>
			<td>BP358-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium pyruvate</td>
			<td>Millipore Sigma</td>
			<td>P8674-25G</td>
			<td></td>
		</tr>
		<tr>
			<td>Spectronic Genesys 5</td>
			<td>Thermo Fisher Scientific</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Streptomycin sulfate solution</td>
			<td>Millipore Sigma</td>
			<td>S6501-50G</td>
			<td></td>
		</tr>
		<tr>
			<td>Trisodium citrate dihydrate</td>
			<td>Millipore Sigma</td>
			<td>S1804-500G</td>
			<td>sodium citrate for BSK</td>
		</tr>
	</tbody>
</table>

phage-mediated genetic manipulation of the lyme disease spirochete borrelia burgdorferi

Introducing foreign DNA into the spirochete Borrelia burgdorferi has been almost exclusively accomplished by transformation using electroporation. This process has notably lower efficiencies in the Lyme disease spirochete relative to other, better-characterized Gram-negative bacteria. The rate of success of transformation is highly dependent upon having concentrated amounts of high-quality DNA from specific backgrounds and is subject to significant strain-to-strain variability. Alternative means for introducing foreign DNA (i.e., shuttle vectors, fluorescent reporters, and antibiotic-resistance markers) into B. burgdorferi could be an important addition to the armamentarium of useful tools for the genetic manipulation of the Lyme disease spirochete. Bacteriophage have been well-recognized as natural mechanisms for the movement of DNA among bacteria in a process called transduction. In this study, a method has been developed for using the ubiquitous borrelial phage &#966;BB-1 to transduce DNA between B. burgdorferi cells of both the same and different genetic backgrounds. The transduced DNA includes both borrelial DNA and heterologous DNA in the form of small shuttle vectors. This demonstration suggests a potential use of phage-mediated transduction as a complement to electroporation for the genetic manipulation of the Lyme disease spirochete. This report describes methods for the induction and purification of phage &#966;BB-1 from B. burgdorferi, the use of this phage in transduction assays, and the selection and screening of potential transductants.

The use of bacteriophage to move DNA between more readily transformable B. burgdorferi strains or clones that are recalcitrant to electrotransformation represents another tool for the continued molecular investigation of the determinants of Lyme disease. The transduction assay described herein can be modified as needed to facilitate the movement of DNA between any clones of interest using either one or two antibiotics for the selection of potential transductants. The transduction of both prophage DNA and heterol...

Watch this Scientific Journal Video about Phage-Mediated Genetic Manipulation of the Lyme Disease Spirochete Borrelia burgdorferi at JoVE.com

Phage-Mediated Genetic Manipulation of the Lyme Disease Spirochete Borrelia burgdorferi

The ability of bacteriophage to move DNA between bacterial cells makes them effective tools for the genetic manipulation of their bacterial hosts. Presented here is a methodology for inducing, recovering, and using &#966;BB-1, a bacteriophage of Borrelia burgdorferi, to transduce heterologous DNA between different strains of the Lyme disease spirochete.

Phage-Mediated Genetic Manipulation of the Lyme Disease Spirochete Borrelia burgdorferi

Introducing foreign DNA into the spirochete Borrelia burgdorferi has been almost exclusively accomplished by transformation using electroporation. This ...

This protocol is significant because it describes another important tool for dissecting the molecular biology of the Lyme disease agent Borrelia burgdorferi. The main advantage of this technique is that by using phage transduction, it provides an alternative method for introducing DNA in the Borrelia burgdorferi without requiring the application of an electric pulse, as in electroporation. This method could be used to provide further insight into the molecular mechanisms used by Borrelia burgdorferi to persist in its enzootic cycle and ultimately cause Lyme disease in humans.To begin, inoculate 150 microliters of the appropriate Borrelia burgdorferi clone into 15 milliliters of BSK in tightly-capped sterile conical centrifuge tubes for the transduction protocol. Then, supplement the medium with the appropriate concentration of antibiotics or a combination of antibiotics for the selection and maintenance of heterologous DNA within the Borrelia burgdorferi clone and incubate the sample at 33 degrees Celsius. After the culture has grown up, centrifuge the appropriate volume of culture at 6, 000 G for 10 minutes.After decanting the supernatant, resuspend the pellet in four milliliters at fresh BSK and transfer the sample to the smallest sterile tube available to hold the sample with minimal head space. Then, add the appropriate amount of inducing agent to the recommended concentration based on a culture volume of four milliliters to induce phage production, cap the tube tightly, and mix thoroughly. Incubate the sample at 33 degrees Celsius for two to four hours.Then, transfer the sample to a 15-milliliter centrifuge tube. Centrifuge the sample at 6, 000 G for 10 minutes. After decanting the supernatant, resuspend the cell pellet in 15 milliliters of BSK.Supplement the prepared culture with the appropriate antibiotic concentration described in the manuscript, while incubating the sample at 33 degrees Celsius for 72 to 96 hours. To prepare solutions for PEG precipitation, prepare 500 milliliters of five-molar sodium chloride, 500 milliliters of 40%PEG, and 100 milliliters of suspension medium as described in the manuscript. To sterilize, autoclave the solution, cool prior to use, and store room temperature or four degrees Celsius.For PEG precipitation of phage from the donor Borrelia burgdorferi clone, after 72 to 96 hours of incubation, centrifuge the samples at 8, 000 G for 20 minutes at four degrees Celsius. Decant the supernatant into a clean, 50-milliliter conical tube and dispose of the cell pellet. Add five-molar sodium chloride to a final concentration of one molar.After mixing well, rock gently at room temperature for one hour. Centrifuge the samples at 8, 000 G for 10 minutes at four degrees Celsius. After decanting the supernatant into a clean 50-milliliter conical tube as demonstrated previously, add 40%PEG-8000 solution to the supernatant to a final concentration of 10%Mix well and set on ice for more than one hour, up to overnight.Centrifuge to the samples at 8, 000 G for 20 minutes at four degrees Celsius as demonstrated previously. Discard the supernatant and remove as much excess liquid as possible without losing any pellet, which contains the phage particles. Resuspend the pellet in a minimal volume of suspension medium using the suspension medium to wash down the side of the bottle and collect any potential phage particles.Treat the recovered phage sample with an equal volume of chloroform based on the volume of resuspension. Mix the sample well and centrifuge at 8, 000 G for 10 minutes. Then, remove the aqueous layer to a clean tube, avoiding any of the thick interface layers.After determining the volume recovered, following the first chloroform treatment, again treat the sample with an amount of chloroform equal to 10%of that volume. Transfer the aqueous layer to a clean tube while being careful to avoid any of the interface or organic layers. Use the phage immediately or store it at four degrees Celsius.After preparing Borrelia burgdorferi cultures to be used as the recipient in transduction assays as demonstrated previously, centrifuge the volume of culture at 6, 000 G for 10 minutes. Decant the supernatant and resuspend the pellet in 14.5 milliliters of fresh BSK. Add less than or equal to 500 microliters of PEG-precipitated phage sample to the culture of the recipient clone.After mixing well, incubate at 33 degrees Celsius for 72 to 96 hours. Perform the selection of transductants by solid-phase plating after mixing with PEG-precipitated phage as described in the manuscript. Depending on the background of the recipient clone, check that the colonies appear within the agarose on the selection plates after 10 to 21 days of incubation.Pick at least 5 to 10 colonies that grow on the plate in the presence of both antibiotics using sterilized cotton-plugged 5.75-inches borosilicate pipette and inoculate them into 1.5 milliliters of BSK with the appropriate antibiotic. The PCR amplification of the genes was performed on 10 of the clones encoding kanamycin and gentamycin resistance. The kanamycin resistance gene could be amplified from the donor c1673 and the potential transductants but not the recipient c1706.Similarly, the gentamycin resistance gene could be amplified from the recipient c1706 and the potential transductants but not the donor, representing transduction events. To demonstrate that the kanamycin resistance cassette was transduced by 5BB1 from the donor into the recipient. The background of the transductants was determined using strain-specific markers.The c1673 clone and the CA-112A background encodes specific amplicons four, five, and six, whereas c1706, which has a high-passage B31 background, does not. Similarly, the transductants one and two were missing amplicons four, five and six, demonstrating that the clones have the c1706 background and have acquired the kanamycin resistance gene from c1673. For the PEG precipitation of phage, perform all steps carefully to maximize the yield of phage and treat the resuspended phage thoroughly with chloroform to remove as much PEG and culture media contaminants as possible prior to phage use and storage.Once the transduction assay has been successfully performed and the transductant verified, these clones are then available to answer the questions that require genetically-modified Borrelia burgdorferi. The development of this technique will hopefully allow researchers to genetically manipulate Borrelia burgdorferi strains for which the introduction of DNA via electroporation is currently difficult.

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Research

JoVE Journal

Immunology and Infection

Protocol for Production of a Genetic Cross of the Rodent Malaria Parasites

Variation in response to antimalarial drugs and in pathogenicity of malaria parasites is of biologic and medical importance. Linkage mapping has led to successful identification of genes or loci underlying various traits in malaria parasites of rodents1-3 and humans4-6. The malaria parasite Plasmodium yoelii is one of many malaria species isolated from wild African rodents and has been adapted to grow in laboratories. This species reproduces many of the biologic characteristics of the human malaria parasites; genetic markers such as microsatellite and amplified fragment length polymorphism (AFLP) markers have also been developed for the parasite7-9. Thus, genetic studies in rodent malaria parasites can be performed to complement research on Plasmodium falciparum. Here, we demonstrate the techniques for producing a genetic cross in P. yoelii that were first pioneered by Drs. David Walliker, Richard Carter, and colleagues at the University of Edinburgh10.

Genetic crosses in P. yoelii and other rodent malaria parasites are conducted by infecting mice Mus musculus with an inoculum containing gametocytes of two genetically distinct clones that differ in phenotypes of interest and by allowing mosquitoes to feed on the infected mice 4 days after infection. The presence of male and female gametocytes in the mouse blood is microscopically confirmed before feeding. Within 48 hrs after feeding, in the midgut of the mosquito, the haploid gametocytes differentiate into male and female gametes, fertilize, and form a diploid zygote (Fig. 1). During development of a zygote into an ookinete, meiosis appears to occur11. If the zygote is derived through cross-fertilization between gametes of the two genetically distinct parasites, genetic exchanges (chromosomal reassortment and cross-overs between the non-sister chromatids of a pair of homologous chromosomes; Fig. 2) may occur, resulting in recombination of genetic material at homologous loci. Each zygote undergoes two successive nuclear divisions, leading to four haploid nuclei. An ookinete further develops into an oocyst. Once the oocyst matures, thousands of sporozoites (the progeny of the cross) are formed and released into mosquito hemoceal. Sporozoites are harvested from the salivary glands and injected into a new murine host, where pre-erythrocytic and erythrocytic stage development takes place. Erythrocytic forms are cloned and classified with regard to the characters distinguishing the parental lines prior to genetic linkage mapping. Control infections of individual parental clones are performed in the same way as the production of a genetic cross.

Genetic crosses of rodent malaria parasites are performed by feeding two genetically distinct parasites to mosquitoes. Recombinant progeny are cloned from mouse blood after allowing mosquitoes to bite infected mice. This video shows how to produce genetic crosses of Plasmodium yoelii and is applicable to other rodent malaria parasites.

Variation in response to antimalarial drugs and in pathogenicity of malaria parasites is of biologic and medical importance. Linkage mapping has led to ...

Methods for Rapid Transfer and Localization of Lyme Disease Pathogens Within the Tick Gut

Lyme disease is caused by infection with the spirochete pathogen Borrelia burgdorferi, which is maintained in nature by a tick-rodent infection cycle 1. A tick-borne murine model 2 has been developed to study Lyme disease in the laboratory. While na&iacute;ve ticks can be infected with B. burgdorferi by feeding them on infected mice, the molting process takes several weeks to months to complete. Therefore, development of more rapid and efficient tick infection techniques, such as a microinjection-based procedure, is an important tool for the study of Lyme disease 3,4. The procedure requires only hours to generate infected ticks and allows control over the delivery of equal quantities of spirochetes in a cohort of ticks. This is particularly important as the generation of B. burgdorferi infected ticks by the natural feeding process using mice fails to ensure 100% infection rate and potentially results in variation of pathogen burden amongst fed ticks. Furthermore, microinjection can be used to infect ticks with B. burgdorferi isolates in cases where an attenuated strain is unable to establish infection in mice and thus can not be naturally acquired by ticks 5. This technique can also be used to deliver a variety of other biological materials into ticks, for example, specific antibodies or double stranded RNA 6. In this article, we will demonstrate the microinjection of nymphal ticks with in vitro-grown B. burgdorferi. We will also describe a method for localization of Lyme disease pathogens in the tick gut using confocal immunofluorescence microscopy.

Lyme disease research studies often require generation of ticks infected with the pathogen Borrelia burgdorferi, a process that typically takes several weeks. Here we demonstrate a microinjection-based tick infection procedure that can be accomplished within hours. We also demonstrate an immunofluorescence method for in situ localization of B. burgdorferi within ticks.

Lyme disease is caused by infection with the spirochete pathogen Borrelia burgdorferi, which is maintained in nature by a tick-rodent infection cycle 1.  ...

Genetic Manipulation in &Delta;ku80 Strains for Functional Genomic Analysis of Toxoplasma gondii

Targeted genetic manipulation using homologous recombination is the method of choice for functional genomic analysis to obtain a detailed view of gene function and phenotype(s). The development of mutant strains with targeted gene deletions, targeted mutations, complemented gene function, and/or tagged genes provides powerful strategies to address gene function, particularly if these genetic manipulations can be efficiently targeted to the gene locus of interest using integration mediated by double cross over homologous recombination.
Due to very high rates of nonhomologous recombination, functional genomic analysis of Toxoplasma gondii has been previously limited by the absence of efficient methods for targeting gene deletions and gene replacements to specific genetic loci. Recently, we abolished the major pathway of nonhomologous recombination in type I and type II strains of T. gondii by deleting the gene encoding the KU80 protein1,2. The &Delta;ku80 strains behave normally during tachyzoite (acute) and bradyzoite (chronic) stages in vitro and in vivo and exhibit essentially a 100% frequency of homologous recombination. The &Delta;ku80 strains make functional genomic studies feasible on the single gene as well as on the genome scale1-4.
Here, we report methods for using type I and type II &Delta;ku80&Delta;hxgprt strains to advance gene targeting approaches in T. gondii. We outline efficient methods for generating gene deletions, gene replacements, and tagged genes by targeted insertion or deletion of the hypoxanthine-xanthine-guanine phosphoribosyltransferase (HXGPRT) selectable marker. The described gene targeting protocol can be used in a variety of ways in &Delta;ku80 strains to advance functional analysis of the parasite genome and to develop single strains that carry multiple targeted genetic manipulations. The application of this genetic method and subsequent phenotypic assays will reveal fundamental and unique aspects of the biology of T. gondii and related significant human pathogens that cause malaria (Plasmodium sp.) and cryptosporidiosis (Cryptosporidium).

Genetic Manipulation in &lt;em&gt;&amp;Delta;ku80&lt;/em&gt; Strains for Functional Genomic Analysis of &lt;em&gt;Toxoplasma gondii&lt;/em&gt;

Here we report a method for using type I and type II &Delta;ku80 strains of Toxoplasma gondii to efficiently generate targeted gene deletions and gene replacements for functional genomic analysis.

Targeted genetic manipulation using homologous recombination is the method of choice for functional genomic analysis to obtain a detailed view of gene ...

Feeding of Ticks on Animals for Transmission and Xenodiagnosis in Lyme Disease Research

Transmission of the etiologic agent of Lyme disease, Borrelia burgdorferi, occurs by the attachment and blood feeding of Ixodes species ticks on mammalian hosts. In nature, this zoonotic bacterial pathogen may use a variety of reservoir hosts, but the white-footed mouse (Peromyscus leucopus) is the primary reservoir for larval and nymphal ticks in North America. Humans are incidental hosts most frequently infected with B. burgdorferi by the bite of ticks in the nymphal stage. B. burgdorferi adapts to its hosts throughout the enzootic cycle, so the ability to explore the functions of these spirochetes and their effects on mammalian hosts requires the use of tick feeding. In addition, the technique of xenodiagnosis (using the natural vector for detection and recovery of an infectious agent) has been useful in studies of cryptic infection. In order to obtain nymphal ticks that harbor B. burgdorferi, ticks are fed live spirochetes in culture through capillary tubes. Two animal models, mice and nonhuman primates, are most commonly used for Lyme disease studies involving tick feeding. We demonstrate the methods by which these ticks can be fed upon, and recovered from animals for either infection or xenodiagnosis.

Lyme disease is the most commonly-reported vector-borne disease in North America. The causative agent, Borrelia burgdorferi is a spirochete bacterium transmitted by Ixodid ticks. Transmission and detection of infection in animal models is optimized by the use of tick feeding, which we describe here.

Transmission of the etiologic agent of Lyme disease, Borrelia burgdorferi, occurs by the  attachment and blood feeding of Ixodes species ticks on ...

Retroviral Transduction of Helper T Cells as a Genetic Approach to Study Mechanisms Controlling their Differentiation and Function

Helper T cell development and function must be tightly regulated to induce an appropriate immune response that eliminates specific pathogens yet prevents autoimmunity. Many approaches involving different model organisms have been utilized to understand the mechanisms controlling helper T cell development and function. However, studies using mouse models have proven to be highly informative due to the availability of genetic, cellular, and biochemical systems. One genetic approach in mice used by many labs involves retroviral transduction of primary helper T cells. This is a powerful approach due to its relative ease, making it accessible to almost any laboratory with basic skills in molecular biology and immunology. Therefore, multiple genes in wild type or mutant forms can readily be tested for function in helper T cells to understand their importance and mechanisms of action. We have optimized this approach and describe here the protocols for production of high titer retroviruses, isolation of primary murine helper T cells, and their transduction by retroviruses and differentiation toward the different helper subsets. Finally, the use of this approach is described in uncovering mechanisms utilized by microRNAs (miRNAs) to regulate pathways controlling helper T cell development and function.

Many experimental systems have been utilized to understand the mechanisms regulating T cell development and function in an immune response. Here a genetic approach using retroviral transduction is described, which is economic, time efficient, and most importantly, highly informative in identifying regulatory pathways.

Helper T cell development and function must be tightly regulated to induce an appropriate immune response that eliminates specific pathogens yet prevents ...

A Simple Red Blood Cell Lysis Method for the Establishment of B Lymphoblastoid Cell Lines

A number of methods exist for the transformation of B lymphocytes by the Epstein Barr virus in vitro into immortalized cell lines. We have developed a new method with a powerful and simple strategy for the establishment of B-LCLs, the red blood cell lysis method. This method simplified the PBMC separation procedure with red blood cell removal, and used as little as 0.5 mL of whole blood for establishing EBV-immortalized cell lines, which can proliferate to large cell numbers in a relatively short amount time with a 100% success rate. The method is simple, reliable, time saving, and applicable to treating a large number of the clinical samples.

A simple red blood cell lysis method for establishing B-LCLs was developed with high immortalization efficiency, requiring a small amount of blood and saving time from initiation to cryopreservation.

A number of methods exist for the transformation of B lymphocytes by the Epstein Barr virus in vitro into immortalized cell lines. We have developed a new ...

Swab Sampling Method for the Detection of Human Norovirus on Surfaces

Human noroviruses are a leading cause of epidemic and sporadic gastroenteritis worldwide. Because most infections are either spread directly via the person-to-person route or indirectly through environmental surfaces or food, contaminated fomites and inanimate surfaces are important vehicles for the spread of the virus during norovirus outbreaks.
We developed and evaluated a protocol using macrofoam swabs for the detection and typing of human noroviruses from hard surfaces. Compared with fiber-tipped swabs or antistatic wipes, macrofoam swabs allow virus recovery (range 1.2-33.6%) from toilet seat surfaces of up to 700 cm2. The protocol includes steps for the extraction of the virus from the swabs and further concentration of the viral RNA using spin columns. In total, 127 (58.5%) of 217 swab samples that had been collected from surfaces in cruise ships and long-term care facilities where norovirus gastroenteritis had been reported tested positive for GII norovirus by RT-qPCR. Of these 29 (22.8%) could be successfully genotyped. In conclusion, detection of norovirus on environmental surfaces using the protocol we developed may assist in determining the level of environmental contamination during outbreaks as well as detection of virus when clinical samples are not available; it may also facilitate monitoring of effectiveness of remediation strategies.

A macrofoam based sampling methodology was developed and evaluated for the detection and quantification of norovirus on environmental hard surfaces.

Human noroviruses are a leading cause of epidemic and sporadic gastroenteritis worldwide. Because most infections are either spread directly via the ...

Gene Knock-in by CRISPR/Cas9 and Cell Sorting in Macrophage and T Cell Lines

Functional genomics studies of the immune system require genetic manipulations that involve both deletion of target genes and addition of elements to proteins of interest. Identification of gene functions in cell line models is important for gene discovery and exploration of cell-intrinsic mechanisms. However, genetic manipulations of immune cells such as T cells and macrophage cell lines using CRISPR/Cas9-mediated knock-in are difficult because of the low transfection efficiency of these cells, especially in a quiescent state. To modify genes in immune cells, drug-resistance selection and viral vectors are typically used to enrich for cells expressing the CRIPSR/Cas9 system, which inevitably results in undesirable intervention of the cells. In a previous study, we designed dual fluorescent reporters coupled to CRISPR/Cas9 that were transiently expressed after electroporation. This technical solution leads to rapid gene deletion in immune cells; however, gene knock-in in immune cells such as T cells and macrophages without the use of drug-resistance selection or viral vectors is even more challenging. In this article, we show that by using cell sorting to aid selection of cells transiently expressing CRISPR/Cas9 constructs targeting the Rosa26 locus in combination with a donor plasmid, gene knock-in can be achieved in both T cells and macrophages without drug-resistance enrichment. As an example, we show how to express human ACE2, a receptor of SARS-Cov-2, which is responsible for the current Covid-19 pandemic, in RAW264.7 macrophages by performing knock-in experiments. Such gene knock-in cells can be widely used for mechanistic studies.

This protocol uses fluorescent reporters and cell sorting to simplify knock-in experiments in macrophage and T cell lines. Two plasmids are used for these simplified knock-in experiments, namely a CRISPR/Cas9- and DsRed2-expressing plasmid and a homologous recombination donor plasmid expressing EBFP2, which is permanently integrated at the Rosa26 locus in immune cells.

Functional genomics studies of the immune system require genetic manipulations that involve both deletion of target genes and addition of elements to ...

A TNBS-Induced Rodent Model to Study the Pathogenic Role of Mechanical Stress in Crohn's Disease

Inflammatory bowel diseases (IBD) such as Crohn&#39;s disease (CD) are chronic inflammatory disorders of the gastrointestinal tract affecting approximately 20 per 1,000,000 in Europe and USA. CD is characterized by transmural inflammation, intestinal fibrosis, and luminal stenosis. Although anti-inflammatory therapies may help control inflammation, they have no efficacy on fibrosis and stenosis in CD. The pathogenesis of CD is not well understood. Current studies focus mainly on delineating dysregulated gut immune response mechanisms. While CD-associated transmural inflammation, intestinal fibrosis, and luminal stenosis all represent mechanical stress to the gut wall, the role of mechanical stress in CD is not well defined. To determine if mechanical stress plays an independent pathogenic role in CD, a protocol of TNBS-induced CD-like colitis model in rodents has been developed. This TNBS-induced transmural inflammation and fibrosis model resembles pathological hallmarks of CD in the colon. It is induced by intracolonic instillation of TNBS into the distal colon of adult Sprague-Dawley rats. In this model, transmural inflammation leads to stenosis at the TNBS instillation site (Site I). Mechanical distention is observed in the portion proximal to the instillation site (Site P), representing mechanical stress but not visible inflammation. Colonic portion distal to inflammation (Site D) presents neither inflammation nor mechanical stress. Distinctive changes of gene expression, immune response, fibrosis, and smooth muscle growth at different sites (P, I, and D) were observed, highlighting a profound impact of mechanical stress. Therefore, this model of CD-like colitis will help us better understand CD&#39;s pathogenic mechanisms, particularly the role of mechanical stress and mechanical stress-induced gene expression in immune dysregulation, intestinal fibrosis, and tissue remodeling in CD.

A TNBS-Induced Rodent Model to Study the Pathogenic Role of Mechanical Stress in Crohn&#039;s Disease

The present protocol describes the development of a Crohn's-like colitis model in rodents. Transmural inflammation leads to stenosis at the TNBS instillation site, and mechanical enlargement is observed in the segment proximal to the stenosis. These changes allow studying mechanical stress in colitis.

Inflammatory bowel diseases (IBD) such as Crohn&#39;s disease (CD) are chronic inflammatory disorders of the gastrointestinal tract affecting ...

Essential Components of Borreliella (Borrelia) burgdorferi In Vitro Transcription Assays

Borreliella burgdorferi is a bacterial pathogen with limited metabolic and genomic repertoires. B. burgdorferi transits extracellularly between vertebrates and ticks and dramatically remodels its transcriptional profile to survive in disparate environments during infection. A focus of B. burgdorferi studies is to clearly understand how the bacteria responds to its environment through transcriptional changes. In vitro transcription assays allow for the basic mechanisms of transcriptional regulation to be biochemically dissected. Here, we present a detailed protocol describing B. burgdorferi RNA polymerase purification and storage, sigma factor purification, DNA template generation, and in vitro transcription assays. The protocol describes the use of RNA polymerase purified from B. burgdorferi 5A4 RpoC-His (5A4-RpoC). 5A4-RpoC is a previously published strain harboring a 10XHis-tag on the rpoC gene encoding the largest subunit of the RNA polymerase. In vitro transcription assays consist of the RNA polymerase purified from strain 5A4-RpoC, a recombinant version of the housekeeping sigma factor RpoD, and a PCR-generated double-stranded DNA template. While the protein purification techniques and approaches to assembling in vitro transcription assays are conceptually well understood and relatively common, handling considerations for RNA polymerases often differ from organism to organism. The protocol presented here is designed for enzymatic studies on the B. burgdorferi RNA polymerase. The method can be adapted to test the role of transcription factors, promoters, and post-translational modifications on the activity of the RNA polymerase.

Essential Components of Borreliella Borrelia burgdorferi In Vitro Transcription Assays

In vitro transcription assays can decipher the mechanisms of transcriptional regulation in Borreliella burgdorferi. This protocol describes the steps to purify B. burgdorferi RNA polymerase and perform in vitro transcription reactions. Experimental approaches using in vitro transcription assays require reliable purification and storage of active RNA polymerase.