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A new piece of the Shigella Pathogenicity puzzle: spermidine accumulation by silencing of the speG gene [corrected].
PUBLISHED: 06-28-2011
The genome of Shigella, a gram negative bacterium which is the causative agent of bacillary dysentery, shares strong homologies with that of its commensal ancestor, Escherichia coli. The acquisition, by lateral gene transfer, of a large plasmid carrying virulence determinants has been a crucial event in the evolution towards the pathogenic lifestyle and has been paralleled by the occurrence of mutations affecting genes, which negatively interfere with the expression of virulence factors. In this context, we have analysed to what extent the presence of the plasmid-encoded virF gene, the major activator of the Shigella regulon for invasive phenotype, has modified the transcriptional profile of E. coli. Combining results from transcriptome assays and comparative genome analyses we show that in E. coli VirF, besides being able to up-regulate several chromosomal genes, which potentially influence bacterial fitness within the host, also activates genes which have been lost by Shigella. We have focused our attention on the speG gene, which encodes spermidine acetyltransferase, an enzyme catalysing the conversion of spermidine into the physiologically inert acetylspermidine, since recent evidence stresses the involvement of polyamines in microbial pathogenesis. Through identification of diverse mutations, which prevent expression of a functional SpeG protein, we show that the speG gene has been silenced by convergent evolution and that its inactivation causes the marked increase of intracellular spermidine in all Shigella spp. This enhances the survival of Shigella under oxidative stress and allows it to better face the adverse conditions it encounters inside macrophage. This is supported by the outcome of infection assays performed in mouse peritoneal macrophages and of a competitive-infection assay on J774 macrophage cell culture. Our observations fully support the pathoadaptive nature of speG inactivation in Shigella and reveal that the accumulation of spermidine is a key determinant in the pathogenicity strategy adopted by this microrganism.
Authors: Maria J. Mazon Moya, Emma Colucci-Guyon, Serge Mostowy.
Published: 09-09-2014
Shigella flexneri is an intracellular pathogen that can escape from phagosomes to reach the cytosol, and polymerize the host actin cytoskeleton to promote its motility and dissemination. New work has shown that proteins involved in actin-based motility are also linked to autophagy, an intracellular degradation process crucial for cell autonomous immunity. Strikingly, host cells may prevent actin-based motility of S. flexneri by compartmentalizing bacteria inside ‘septin cages’ and targeting them to autophagy. These observations indicate that a more complete understanding of septins, a family of filamentous GTP-binding proteins, will provide new insights into the process of autophagy. This report describes protocols to monitor autophagy-cytoskeleton interactions caused by S. flexneri in vitro using tissue culture cells and in vivo using zebrafish larvae. These protocols enable investigation of intracellular mechanisms that control bacterial dissemination at the molecular, cellular, and whole organism level.
22 Related JoVE Articles!
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Single Cell Measurements of Vacuolar Rupture Caused by Intracellular Pathogens
Authors: Charlotte Keller, Nora Mellouk, Anne Danckaert, Roxane Simeone, Roland Brosch, Jost Enninga, Alexandre Bobard.
Institutions: Institut Pasteur, Paris, France, Institut Pasteur, Paris, France, Institut Pasteur, Paris, France.
Shigella flexneri are pathogenic bacteria that invade host cells entering into an endocytic vacuole. Subsequently, the rupture of this membrane-enclosed compartment allows bacteria to move within the cytosol, proliferate and further invade neighboring cells. Mycobacterium tuberculosis is phagocytosed by immune cells, and has recently been shown to rupture phagosomal membrane in macrophages. We developed a robust assay for tracking phagosomal membrane disruption after host cell entry of Shigella flexneri or Mycobacterium tuberculosis. The approach makes use of CCF4, a FRET reporter sensitive to β-lactamase that equilibrates in the cytosol of host cells. Upon invasion of host cells by bacterial pathogens, the probe remains intact as long as the bacteria reside in membrane-enclosed compartments. After disruption of the vacuole, β-lactamase activity on the surface of the intracellular pathogen cleaves CCF4 instantly leading to a loss of FRET signal and switching its emission spectrum. This robust ratiometric assay yields accurate information about the timing of vacuolar rupture induced by the invading bacteria, and it can be coupled to automated microscopy and image processing by specialized algorithms for the detection of the emission signals of the FRET donor and acceptor. Further, it allows investigating the dynamics of vacuolar disruption elicited by intracellular bacteria in real time in single cells. Finally, it is perfectly suited for high-throughput analysis with a spatio-temporal resolution exceeding previous methods. Here, we provide the experimental details of exemplary protocols for the CCF4 vacuolar rupture assay on HeLa cells and THP-1 macrophages for time-lapse experiments or end points experiments using Shigella flexneri as well as multiple mycobacterial strains such as Mycobacterium marinum, Mycobacterium bovis, and Mycobacterium tuberculosis.
Infection, Issue 76, Infectious Diseases, Immunology, Medicine, Microbiology, Biochemistry, Cellular Biology, Molecular Biology, Pathology, Bacteria, biology (general), life sciences, CCF4-AM, Shigella flexneri, Mycobacterium tuberculosis, vacuolar rupture, fluorescence microscopy, confocal microscopy, pathogens, cell culture
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High-throughput Assay to Phenotype Salmonella enterica Typhimurium Association, Invasion, and Replication in Macrophages
Authors: Jing Wu, Roberta Pugh, Richard C. Laughlin, Helene Andrews-Polymenis, Michael McClelland, Andreas J. Bäumler, L. Garry Adams.
Institutions: Texas A&M University, Texas A&M University System Health Science Center, University of California, Irvine, University of California, Davis.
Salmonella species are zoonotic pathogens and leading causes of food borne illnesses in humans and livestock1. Understanding the mechanisms underlying Salmonella-host interactions are important to elucidate the molecular pathogenesis of Salmonella infection. The Gentamicin protection assay to phenotype Salmonella association, invasion and replication in phagocytic cells was adapted to allow high-throughput screening to define the roles of deletion mutants of Salmonella enterica serotype Typhimurium in host interactions using RAW 264.7 murine macrophages. Under this protocol, the variance in measurements is significantly reduced compared to the standard protocol, because wild-type and multiple mutant strains can be tested in the same culture dish and at the same time. The use of multichannel pipettes increases the throughput and enhances precision. Furthermore, concerns related to using less host cells per well in 96-well culture dish were addressed. Here, the protocol of the modified in vitro Salmonella invasion assay using phagocytic cells was successfully employed to phenotype 38 individual Salmonella deletion mutants for association, invasion and intracellular replication. The in vitro phenotypes are presented, some of which were subsequently confirmed to have in vivo phenotypes in an animal model. Thus, the modified, standardized assay to phenotype Salmonella association, invasion and replication in macrophages with high-throughput capacity could be utilized more broadly to study bacterial-host interactions.
Infectious Diseases, Issue 90, Salmonella enterica Typhimurium, association, invasion, replication, phenotype, intracellular pathogens, macrophages
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TransFLP — A Method to Genetically Modify Vibrio cholerae Based on Natural Transformation and FLP-recombination
Authors: Melanie Blokesch.
Institutions: Ecole Polytechnique Fédérale de Lausanne (EPFL).
Several methods are available to manipulate bacterial chromosomes1-3. Most of these protocols rely on the insertion of conditionally replicative plasmids (e.g. harboring pir-dependent or temperature-sensitive replicons1,2). These plasmids are integrated into bacterial chromosomes based on homology-mediated recombination. Such insertional mutants are often directly used in experimental settings. Alternatively, selection for plasmid excision followed by its loss can be performed, which for Gram-negative bacteria often relies on the counter-selectable levan sucrase enzyme encoded by the sacB gene4. The excision can either restore the pre-insertion genotype or result in an exchange between the chromosome and the plasmid-encoded copy of the modified gene. A disadvantage of this technique is that it is time-consuming. The plasmid has to be cloned first; it requires horizontal transfer into V. cholerae (most notably by mating with an E. coli donor strain) or artificial transformation of the latter; and the excision of the plasmid is random and can either restore the initial genotype or create the desired modification if no positive selection is exerted. Here, we present a method for rapid manipulation of the V. cholerae chromosome(s)5 (Figure 1). This TransFLP method is based on the recently discovered chitin-mediated induction of natural competence in this organism6 and other representative of the genus Vibrio such as V. fischeri7. Natural competence allows the uptake of free DNA including PCR-generated DNA fragments. Once taken up, the DNA recombines with the chromosome given the presence of a minimum of 250-500 bp of flanking homologous region8. Including a selection marker in-between these flanking regions allows easy detection of frequently occurring transformants. This method can be used for different genetic manipulations of V. cholerae and potentially also other naturally competent bacteria. We provide three novel examples on what can be accomplished by this method in addition to our previously published study on single gene deletions and the addition of affinity-tag sequences5. Several optimization steps concerning the initial protocol of chitin-induced natural transformation6 are incorporated in this TransFLP protocol. These include among others the replacement of crab shell fragments by commercially available chitin flakes8, the donation of PCR-derived DNA as transforming material9, and the addition of FLP-recombination target sites (FRT)5. FRT sites allow site-directed excision of the selection marker mediated by the Flp recombinase10.
Immunology, Issue 68, Microbiology, Genetics, natural transformation, DNA uptake, FLP recombination, chitin, Vibrio cholerae
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Electricity-Free, Sequential Nucleic Acid and Protein Isolation
Authors: David R. Pawlowski, Richard J. Karalus.
Institutions: CUBRC, Inc., State University of New York at Buffalo, School of Medicine and Biomedical Sciences.
Traditional and emerging pathogens such as Enterohemorrhagic Escherichia coli (EHEC), Yersinia pestis, or prion-based diseases are of significant concern for governments, industries and medical professionals worldwide. For example, EHECs, combined with Shigella, are responsible for the deaths of approximately 325,000 children each year and are particularly prevalent in the developing world where laboratory-based identification, common in the United States, is unavailable 1. The development and distribution of low cost, field-based, point-of-care tools to aid in the rapid identification and/or diagnosis of pathogens or disease markers could dramatically alter disease progression and patient prognosis. We have developed a tool to isolate nucleic acids and proteins from a sample by solid-phase extraction (SPE) without electricity or associated laboratory equipment 2. The isolated macromolecules can be used for diagnosis either in a forward lab or using field-based point-of-care platforms. Importantly, this method provides for the direct comparison of nucleic acid and protein data from an un-split sample, offering a confidence through corroboration of genomic and proteomic analysis. Our isolation tool utilizes the industry standard for solid-phase nucleic acid isolation, the BOOM technology, which isolates nucleic acids from a chaotropic salt solution, usually guanidine isothiocyanate, through binding to silica-based particles or filters 3. CUBRC's proprietary solid-phase extraction chemistry is used to purify protein from chaotropic salt solutions, in this case, from the waste or flow-thru following nucleic acid isolation4. By packaging well-characterized chemistries into a small, inexpensive and simple platform, we have generated a portable system for nucleic acid and protein extraction that can be performed under a variety of conditions. The isolated nucleic acids are stable and can be transported to a position where power is available for PCR amplification while the protein content can immediately be analyzed by hand held or other immunological-based assays. The rapid identification of disease markers in the field could significantly alter the patient's outcome by directing the proper course of treatment at an earlier stage of disease progression. The tool and method described are suitable for use with virtually any infectious agent and offer the user the redundancy of multi-macromolecule type analyses while simultaneously reducing their logistical burden.
Chemistry, Issue 63, Solid phase extraction, nucleic acid, protein, isolation, silica, Guanidine thiocyanate, isopropanol, remote, DTRA
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Optimization and Utilization of Agrobacterium-mediated Transient Protein Production in Nicotiana
Authors: Moneim Shamloul, Jason Trusa, Vadim Mett, Vidadi Yusibov.
Institutions: Fraunhofer USA Center for Molecular Biotechnology.
Agrobacterium-mediated transient protein production in plants is a promising approach to produce vaccine antigens and therapeutic proteins within a short period of time. However, this technology is only just beginning to be applied to large-scale production as many technological obstacles to scale up are now being overcome. Here, we demonstrate a simple and reproducible method for industrial-scale transient protein production based on vacuum infiltration of Nicotiana plants with Agrobacteria carrying launch vectors. Optimization of Agrobacterium cultivation in AB medium allows direct dilution of the bacterial culture in Milli-Q water, simplifying the infiltration process. Among three tested species of Nicotiana, N. excelsiana (N. benthamiana × N. excelsior) was selected as the most promising host due to the ease of infiltration, high level of reporter protein production, and about two-fold higher biomass production under controlled environmental conditions. Induction of Agrobacterium harboring pBID4-GFP (Tobacco mosaic virus-based) using chemicals such as acetosyringone and monosaccharide had no effect on the protein production level. Infiltrating plant under 50 to 100 mbar for 30 or 60 sec resulted in about 95% infiltration of plant leaf tissues. Infiltration with Agrobacterium laboratory strain GV3101 showed the highest protein production compared to Agrobacteria laboratory strains LBA4404 and C58C1 and wild-type Agrobacteria strains at6, at10, at77 and A4. Co-expression of a viral RNA silencing suppressor, p23 or p19, in N. benthamiana resulted in earlier accumulation and increased production (15-25%) of target protein (influenza virus hemagglutinin).
Plant Biology, Issue 86, Agroinfiltration, Nicotiana benthamiana, transient protein production, plant-based expression, viral vector, Agrobacteria
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Lignin Down-regulation of Zea mays via dsRNAi and Klason Lignin Analysis
Authors: Sang-Hyuck Park, Rebecca Garlock Ong, Chuansheng Mei, Mariam Sticklen.
Institutions: University of Arizona, Michigan State University, The Institute for Advanced Learning and Research, Michigan State University.
To facilitate the use of lignocellulosic biomass as an alternative bioenergy resource, during biological conversion processes, a pretreatment step is needed to open up the structure of the plant cell wall, increasing the accessibility of the cell wall carbohydrates. Lignin, a polyphenolic material present in many cell wall types, is known to be a significant hindrance to enzyme access. Reduction in lignin content to a level that does not interfere with the structural integrity and defense system of the plant might be a valuable step to reduce the costs of bioethanol production. In this study, we have genetically down-regulated one of the lignin biosynthesis-related genes, cinnamoyl-CoA reductase (ZmCCR1) via a double stranded RNA interference technique. The ZmCCR1_RNAi construct was integrated into the maize genome using the particle bombardment method. Transgenic maize plants grew normally as compared to the wild-type control plants without interfering with biomass growth or defense mechanisms, with the exception of displaying of brown-coloration in transgenic plants leaf mid-ribs, husks, and stems. The microscopic analyses, in conjunction with the histological assay, revealed that the leaf sclerenchyma fibers were thinned but the structure and size of other major vascular system components was not altered. The lignin content in the transgenic maize was reduced by 7-8.7%, the crystalline cellulose content was increased in response to lignin reduction, and hemicelluloses remained unchanged. The analyses may indicate that carbon flow might have been shifted from lignin biosynthesis to cellulose biosynthesis. This article delineates the procedures used to down-regulate the lignin content in maize via RNAi technology, and the cell wall compositional analyses used to verify the effect of the modifications on the cell wall structure.
Bioengineering, Issue 89, Zea mays, cinnamoyl-CoA reductase (CCR), dsRNAi, Klason lignin measurement, cell wall carbohydrate analysis, gas chromatography (GC)
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Biosensor for Detection of Antibiotic Resistant Staphylococcus Bacteria
Authors: Rajesh Guntupalli, Iryna Sorokulova, Eric Olsen, Ludmila Globa, Oleg Pustovyy, Vitaly Vodyanoy.
Institutions: Auburn University , Keesler Air Force Base.
A structurally transformed lytic bacteriophage having a broad host range of Staphylococcus aureus strains and a penicillin-binding protein (PBP 2a) antibody conjugated latex beads have been utilized to create a biosensor designed for discrimination of methicillin resistant (MRSA) and sensitive (MSSA) S. aureus species 1,2. The lytic phages have been converted into phage spheroids by contact with water-chloroform interface. Phage spheroid monolayers have been moved onto a biosensor surface by Langmuir-Blodgett (LB) technique 3. The created biosensors have been examined by a quartz crystal microbalance with dissipation tracking (QCM-D) to evaluate bacteria-phage interactions. Bacteria-spheroid interactions led to reduced resonance frequency and a rise in dissipation energy for both MRSA and MSSA strains. After the bacterial binding, these sensors have been further exposed to the penicillin-binding protein antibody latex beads. Sensors analyzed with MRSA responded to PBP 2a antibody beads; although sensors inspected with MSSA gave no response. This experimental distinction determines an unambiguous discrimination between methicillin resistant and sensitive S. aureus strains. Equally bound and unbound bacteriophages suppress bacterial growth on surfaces and in water suspensions. Once lytic phages are changed into spheroids, they retain their strong lytic activity and show high bacterial capture capability. The phage and phage spheroids can be utilized for testing and sterilization of antibiotic resistant microorganisms. Other applications may include use in bacteriophage therapy and antimicrobial surfaces.
Bioengineering, Issue 75, Microbiology, Infectious Diseases, Infection, Medicine, Immunology, Cellular Biology, Molecular Biology, Genetics, Anatomy, Physiology, Bacteria, Pharmacology, Staphylococcus, Bacteriophages, phage, Binding, Competitive, Biophysics, surface properties (nonmetallic materials), surface wave acoustic devices (electronic design), sensors, Lytic phage spheroids, QCM-D, Langmuir-Blodgett (LB) monolayers, MRSA, Staphylococcus aureus, assay
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Combining Magnetic Sorting of Mother Cells and Fluctuation Tests to Analyze Genome Instability During Mitotic Cell Aging in Saccharomyces cerevisiae
Authors: Melissa N. Patterson, Patrick H. Maxwell.
Institutions: Rensselaer Polytechnic Institute.
Saccharomyces cerevisiae has been an excellent model system for examining mechanisms and consequences of genome instability. Information gained from this yeast model is relevant to many organisms, including humans, since DNA repair and DNA damage response factors are well conserved across diverse species. However, S. cerevisiae has not yet been used to fully address whether the rate of accumulating mutations changes with increasing replicative (mitotic) age due to technical constraints. For instance, measurements of yeast replicative lifespan through micromanipulation involve very small populations of cells, which prohibit detection of rare mutations. Genetic methods to enrich for mother cells in populations by inducing death of daughter cells have been developed, but population sizes are still limited by the frequency with which random mutations that compromise the selection systems occur. The current protocol takes advantage of magnetic sorting of surface-labeled yeast mother cells to obtain large enough populations of aging mother cells to quantify rare mutations through phenotypic selections. Mutation rates, measured through fluctuation tests, and mutation frequencies are first established for young cells and used to predict the frequency of mutations in mother cells of various replicative ages. Mutation frequencies are then determined for sorted mother cells, and the age of the mother cells is determined using flow cytometry by staining with a fluorescent reagent that detects bud scars formed on their cell surfaces during cell division. Comparison of predicted mutation frequencies based on the number of cell divisions to the frequencies experimentally observed for mother cells of a given replicative age can then identify whether there are age-related changes in the rate of accumulating mutations. Variations of this basic protocol provide the means to investigate the influence of alterations in specific gene functions or specific environmental conditions on mutation accumulation to address mechanisms underlying genome instability during replicative aging.
Microbiology, Issue 92, Aging, mutations, genome instability, Saccharomyces cerevisiae, fluctuation test, magnetic sorting, mother cell, replicative aging
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VIGS-Mediated Forward Genetics Screening for Identification of Genes Involved in Nonhost Resistance
Authors: Muthappa Senthil-Kumar, Hee-Kyung Lee, Kirankumar S. Mysore.
Institutions: The Samuel Roberts Noble Foundation.
Nonhost disease resistance of plants against bacterial pathogens is controlled by complex defense pathways. Understanding this mechanism is important for developing durable disease-resistant plants against wide range of pathogens. Virus-induced gene silencing (VIGS)-based forward genetics screening is a useful approach for identification of plant defense genes imparting nonhost resistance. Tobacco rattle virus (TRV)-based VIGS vector is the most efficient VIGS vector to date and has been efficiently used to silence endogenous target genes in Nicotiana benthamiana. In this manuscript, we demonstrate a forward genetics screening approach for silencing of individual clones from a cDNA library in N. benthamiana and assessing the response of gene silenced plants for compromised nonhost resistance against nonhost pathogens, Pseudomonas syringae pv. tomato T1, P. syringae pv. glycinea, and X. campestris pv. vesicatoria. These bacterial pathogens are engineered to express GFPuv protein and their green fluorescing colonies can be seen by naked eye under UV light in the nonhost pathogen inoculated plants if the silenced target gene is involved in imparting nonhost resistance. This facilitates reliable and faster identification of gene silenced plants susceptible to nonhost pathogens. Further, promising candidate gene information can be known by sequencing the plant gene insert in TRV vector. Here we demonstrate the high throughput capability of VIGS-mediated forward genetics to identify genes involved in nonhost resistance. Approximately, 100 cDNAs can be individually silenced in about two to three weeks and their relevance in nonhost resistance against several nonhost bacterial pathogens can be studied in a week thereafter. In this manuscript, we enumerate the detailed steps involved in this screening. VIGS-mediated forward genetics screening approach can be extended not only to identifying genes involved in nonhost resistance but also to studying genes imparting several biotic and abiotic stress tolerances in various plant species.
Virology, Issue 78, Plant Biology, Infection, Genetics, Molecular Biology, Cellular Biology, Physiology, Genomics, Pathology, plants, Nonhost Resistance, Virus-induced gene silencing, VIGS, disease resistance, gene silencing, Pseudomonas, GFPuv, sequencing, virus, Nicotiana benthamiana, plant model
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Application of a Mouse Ligated Peyer’s Patch Intestinal Loop Assay to Evaluate Bacterial Uptake by M cells
Authors: Shinji Fukuda, Koji Hase, Hiroshi Ohno.
Institutions: RIKEN Research Center for Allergy and Immunology.
The inside of our gut is inhabited with enormous number of commensal bacteria. The mucosal surface of the gastrointestinal tract is continuously exposed to them and occasionally to pathogens. The gut-associated lymphoid tissue (GALT) play a key role for induction of the mucosal immune response to these microbes1, 2. To initiate the mucosal immune response, the mucosal antigens must be transported from the gut lumen across the epithelial barrier into organized lymphoid follicles such as Peyer's patches. This antigen transcytosis is mediated by specialized epithelial M cells3, 4. M cells are atypical epithelial cells that actively phagocytose macromolecules and microbes. Unlike dendritic cells (DCs) and macrophages, which target antigens to lysosomes for degradation, M cells mainly transcytose the internalized antigens. This vigorous macromolecular transcytosis through M cells delivers antigen to the underlying organized lymphoid follicles and is believed to be essential for initiating antigen-specific mucosal immune responses. However, the molecular mechanisms promoting this antigen uptake by M cells are largely unknown. We have previously reported that glycoprotein 2 (Gp2), specifically expressed on the apical plasma membrane of M cells among enterocytes, serves as a transcytotic receptor for a subset of commensal and pathogenic enterobacteria, including Escherichia coli and Salmonella enterica serovar Typhimurium (S. Typhimurium), by recognizing FimH, a component of type I pili on the bacterial outer membrane 5. Here, we present a method for the application of a mouse Peyer's patch intestinal loop assay to evaluate bacterial uptake by M cells. This method is an improved version of the mouse intestinal loop assay previously described 6, 7. The improved points are as follows: 1. Isoflurane was used as an anesthetic agent. 2. Approximately 1 cm ligated intestinal loop including Peyer's patch was set up. 3. Bacteria taken up by M cells were fluorescently labeled by fluorescence labeling reagent or by overexpressing fluorescent protein such as green fluorescent protein (GFP). 4. M cells in the follicle-associated epithelium covering Peyer's patch were detected by whole-mount immunostainig with anti Gp2 antibody. 5. Fluorescent bacterial transcytosis by M cells were observed by confocal microscopic analysis. The mouse Peyer's patch intestinal loop assay could supply the answer what kind of commensal or pathogenic bacteria transcytosed by M cells, and may lead us to understand the molecular mechanism of how to stimulate mucosal immune system through M cells.
Neuroscience, Issue 58, M cell, Peyer's patch, bacteria, immunosurveillance, confocal microscopy, Glycoprotein 2
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Enteric Bacterial Invasion Of Intestinal Epithelial Cells In Vitro Is Dramatically Enhanced Using a Vertical Diffusion Chamber Model
Authors: Neveda Naz, Dominic C. Mills, Brendan W. Wren, Nick Dorrell.
Institutions: London School of Hygiene & Tropical Medicine.
The interactions of bacterial pathogens with host cells have been investigated extensively using in vitro cell culture methods. However as such cell culture assays are performed under aerobic conditions, these in vitro models may not accurately represent the in vivo environment in which the host-pathogen interactions take place. We have developed an in vitro model of infection that permits the coculture of bacteria and host cells under different medium and gas conditions. The Vertical Diffusion Chamber (VDC) model mimics the conditions in the human intestine where bacteria will be under conditions of very low oxygen whilst tissue will be supplied with oxygen from the blood stream. Placing polarized intestinal epithelial cell (IEC) monolayers grown in Snapwell inserts into a VDC creates separate apical and basolateral compartments. The basolateral compartment is filled with cell culture medium, sealed and perfused with oxygen whilst the apical compartment is filled with broth, kept open and incubated under microaerobic conditions. Both Caco-2 and T84 IECs can be maintained in the VDC under these conditions without any apparent detrimental effects on cell survival or monolayer integrity. Coculturing experiments performed with different C. jejuni wild-type strains and different IEC lines in the VDC model with microaerobic conditions in the apical compartment reproducibly result in an increase in the number of interacting (almost 10-fold) and intracellular (almost 100-fold) bacteria compared to aerobic culture conditions1. The environment created in the VDC model more closely mimics the environment encountered by C. jejuni in the human intestine and highlights the importance of performing in vitro infection assays under conditions that more closely mimic the in vivo reality. We propose that use of the VDC model will allow new interpretations of the interactions between bacterial pathogens and host cells.
Infection, Issue 80, Gram-Negative Bacteria, Bacterial Infections, Gastrointestinal Diseases, Campylobacter jejuni, bacterial invasion, intestinal epithelial cells, models of infection
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Aseptic Laboratory Techniques: Plating Methods
Authors: Erin R. Sanders.
Institutions: University of California, Los Angeles .
Microorganisms are present on all inanimate surfaces creating ubiquitous sources of possible contamination in the laboratory. Experimental success relies on the ability of a scientist to sterilize work surfaces and equipment as well as prevent contact of sterile instruments and solutions with non-sterile surfaces. Here we present the steps for several plating methods routinely used in the laboratory to isolate, propagate, or enumerate microorganisms such as bacteria and phage. All five methods incorporate aseptic technique, or procedures that maintain the sterility of experimental materials. Procedures described include (1) streak-plating bacterial cultures to isolate single colonies, (2) pour-plating and (3) spread-plating to enumerate viable bacterial colonies, (4) soft agar overlays to isolate phage and enumerate plaques, and (5) replica-plating to transfer cells from one plate to another in an identical spatial pattern. These procedures can be performed at the laboratory bench, provided they involve non-pathogenic strains of microorganisms (Biosafety Level 1, BSL-1). If working with BSL-2 organisms, then these manipulations must take place in a biosafety cabinet. Consult the most current edition of the Biosafety in Microbiological and Biomedical Laboratories (BMBL) as well as Material Safety Data Sheets (MSDS) for Infectious Substances to determine the biohazard classification as well as the safety precautions and containment facilities required for the microorganism in question. Bacterial strains and phage stocks can be obtained from research investigators, companies, and collections maintained by particular organizations such as the American Type Culture Collection (ATCC). It is recommended that non-pathogenic strains be used when learning the various plating methods. By following the procedures described in this protocol, students should be able to: ● Perform plating procedures without contaminating media. ● Isolate single bacterial colonies by the streak-plating method. ● Use pour-plating and spread-plating methods to determine the concentration of bacteria. ● Perform soft agar overlays when working with phage. ● Transfer bacterial cells from one plate to another using the replica-plating procedure. ● Given an experimental task, select the appropriate plating method.
Basic Protocols, Issue 63, Streak plates, pour plates, soft agar overlays, spread plates, replica plates, bacteria, colonies, phage, plaques, dilutions
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Tractable Mammalian Cell Infections with Protozoan-primed Bacteria
Authors: Samuel L. Drennan, Amrita Lama, Ben Doron, Eric D. Cambronne.
Institutions: Oregon Health & Science University.
Many intracellular bacterial pathogens use freshwater protozoans as a natural reservoir for proliferation in the environment. Legionella pneumophila, the causative agent of Legionnaires' pneumonia, gains a pathogenic advantage over in vitro cultured bacteria when first harvested from protozoan cells prior to infection of mammalian macrophages. This suggests that important virulence factors may not be properly expressed in vitro. We have developed a tractable system for priming L. pneumophila through its natural protozoan host Acanthamoeba castellanii prior to mammalian cell infection. The contribution of any virulence factor can be examined by comparing intracellular growth of a mutant strain to wild-type bacteria after protozoan priming. GFP-expressing wild-type and mutant L. pneumophila strains are used to infect protozoan monolayers in a priming step and allowed to reach late stages of intracellular growth. Fluorescent bacteria are then harvested from these infected cells and normalized by spectrophotometry to generate comparable numbers of bacteria for a subsequent infection into mammalian macrophages. For quantification, live bacteria are monitored after infection using fluorescence microscopy, flow cytometry, and by colony plating. This technique highlights and relies on the contribution of host cell-dependent gene expression by mimicking the environment that would be encountered in a natural acquisition route. This approach can be modified to accommodate any bacterium that uses an intermediary host as a means for gaining a pathogenic advantage.
Infection, Issue 74, Immunology, Microbiology, Infectious Diseases, Medicine, Cellular Biology, Bacteria, Bacterial Infections, Mycoses, Legionella, amoeba, macrophage, priming, intracellular pathogen, fluorescence microscopy, flow cytometry, cell
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Protocols for Implementing an Escherichia coli Based TX-TL Cell-Free Expression System for Synthetic Biology
Authors: Zachary Z. Sun, Clarmyra A. Hayes, Jonghyeon Shin, Filippo Caschera, Richard M. Murray, Vincent Noireaux.
Institutions: California Institute of Technology, California Institute of Technology, Massachusetts Institute of Technology, University of Minnesota.
Ideal cell-free expression systems can theoretically emulate an in vivo cellular environment in a controlled in vitro platform.1 This is useful for expressing proteins and genetic circuits in a controlled manner as well as for providing a prototyping environment for synthetic biology.2,3 To achieve the latter goal, cell-free expression systems that preserve endogenous Escherichia coli transcription-translation mechanisms are able to more accurately reflect in vivo cellular dynamics than those based on T7 RNA polymerase transcription. We describe the preparation and execution of an efficient endogenous E. coli based transcription-translation (TX-TL) cell-free expression system that can produce equivalent amounts of protein as T7-based systems at a 98% cost reduction to similar commercial systems.4,5 The preparation of buffers and crude cell extract are described, as well as the execution of a three tube TX-TL reaction. The entire protocol takes five days to prepare and yields enough material for up to 3000 single reactions in one preparation. Once prepared, each reaction takes under 8 hr from setup to data collection and analysis. Mechanisms of regulation and transcription exogenous to E. coli, such as lac/tet repressors and T7 RNA polymerase, can be supplemented.6 Endogenous properties, such as mRNA and DNA degradation rates, can also be adjusted.7 The TX-TL cell-free expression system has been demonstrated for large-scale circuit assembly, exploring biological phenomena, and expression of proteins under both T7- and endogenous promoters.6,8 Accompanying mathematical models are available.9,10 The resulting system has unique applications in synthetic biology as a prototyping environment, or "TX-TL biomolecular breadboard."
Cellular Biology, Issue 79, Bioengineering, Synthetic Biology, Chemistry Techniques, Synthetic, Molecular Biology, control theory, TX-TL, cell-free expression, in vitro, transcription-translation, cell-free protein synthesis, synthetic biology, systems biology, Escherichia coli cell extract, biological circuits, biomolecular breadboard
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Detection of Live Escherichia coli O157:H7 Cells by PMA-qPCR
Authors: Baoguang Li, Zonglin Hu, Christopher A. Elkins.
Institutions: Food and Drug Administration.
A unique open reading frame (ORF) Z3276 was identified as a specific genetic marker for E. coli O157:H7. A qPCR assay was developed for detection of E. coli O157:H7 by targeting ORF Z3276. With this assay, we can detect as low as a few copies of the genome of DNA of E. coli O157:H7. The sensitivity and specificity of the assay were confirmed by intensive validation tests with a large number of E. coli O157:H7 strains (n = 369) and non-O157 strains (n = 112). Furthermore, we have combined propidium monoazide (PMA) procedure with the newly developed qPCR protocol for selective detection of live cells from dead cells. Amplification of DNA from PMA-treated dead cells was almost completely inhibited in contrast to virtually unaffected amplification of DNA from PMA-treated live cells. Additionally, the protocol has been modified and adapted to a 96-well plate format for an easy and consistent handling of a large number of samples. This method is expected to have an impact on accurate microbiological and epidemiological monitoring of food safety and environmental source.
Microbiology, Issue 84, Propidium monoazide (PMA), real-time PCR, E. coli O157:H7, pathogen, selective detection, live cells
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A Restriction Enzyme Based Cloning Method to Assess the In vitro Replication Capacity of HIV-1 Subtype C Gag-MJ4 Chimeric Viruses
Authors: Daniel T. Claiborne, Jessica L. Prince, Eric Hunter.
Institutions: Emory University, Emory University.
The protective effect of many HLA class I alleles on HIV-1 pathogenesis and disease progression is, in part, attributed to their ability to target conserved portions of the HIV-1 genome that escape with difficulty. Sequence changes attributed to cellular immune pressure arise across the genome during infection, and if found within conserved regions of the genome such as Gag, can affect the ability of the virus to replicate in vitro. Transmission of HLA-linked polymorphisms in Gag to HLA-mismatched recipients has been associated with reduced set point viral loads. We hypothesized this may be due to a reduced replication capacity of the virus. Here we present a novel method for assessing the in vitro replication of HIV-1 as influenced by the gag gene isolated from acute time points from subtype C infected Zambians. This method uses restriction enzyme based cloning to insert the gag gene into a common subtype C HIV-1 proviral backbone, MJ4. This makes it more appropriate to the study of subtype C sequences than previous recombination based methods that have assessed the in vitro replication of chronically derived gag-pro sequences. Nevertheless, the protocol could be readily modified for studies of viruses from other subtypes. Moreover, this protocol details a robust and reproducible method for assessing the replication capacity of the Gag-MJ4 chimeric viruses on a CEM-based T cell line. This method was utilized for the study of Gag-MJ4 chimeric viruses derived from 149 subtype C acutely infected Zambians, and has allowed for the identification of residues in Gag that affect replication. More importantly, the implementation of this technique has facilitated a deeper understanding of how viral replication defines parameters of early HIV-1 pathogenesis such as set point viral load and longitudinal CD4+ T cell decline.
Infectious Diseases, Issue 90, HIV-1, Gag, viral replication, replication capacity, viral fitness, MJ4, CEM, GXR25
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Mapping Bacterial Functional Networks and Pathways in Escherichia Coli using Synthetic Genetic Arrays
Authors: Alla Gagarinova, Mohan Babu, Jack Greenblatt, Andrew Emili.
Institutions: University of Toronto, University of Toronto, University of Regina.
Phenotypes are determined by a complex series of physical (e.g. protein-protein) and functional (e.g. gene-gene or genetic) interactions (GI)1. While physical interactions can indicate which bacterial proteins are associated as complexes, they do not necessarily reveal pathway-level functional relationships1. GI screens, in which the growth of double mutants bearing two deleted or inactivated genes is measured and compared to the corresponding single mutants, can illuminate epistatic dependencies between loci and hence provide a means to query and discover novel functional relationships2. Large-scale GI maps have been reported for eukaryotic organisms like yeast3-7, but GI information remains sparse for prokaryotes8, which hinders the functional annotation of bacterial genomes. To this end, we and others have developed high-throughput quantitative bacterial GI screening methods9, 10. Here, we present the key steps required to perform quantitative E. coli Synthetic Genetic Array (eSGA) screening procedure on a genome-scale9, using natural bacterial conjugation and homologous recombination to systemically generate and measure the fitness of large numbers of double mutants in a colony array format. Briefly, a robot is used to transfer, through conjugation, chloramphenicol (Cm) - marked mutant alleles from engineered Hfr (High frequency of recombination) 'donor strains' into an ordered array of kanamycin (Kan) - marked F- recipient strains. Typically, we use loss-of-function single mutants bearing non-essential gene deletions (e.g. the 'Keio' collection11) and essential gene hypomorphic mutations (i.e. alleles conferring reduced protein expression, stability, or activity9, 12, 13) to query the functional associations of non-essential and essential genes, respectively. After conjugation and ensuing genetic exchange mediated by homologous recombination, the resulting double mutants are selected on solid medium containing both antibiotics. After outgrowth, the plates are digitally imaged and colony sizes are quantitatively scored using an in-house automated image processing system14. GIs are revealed when the growth rate of a double mutant is either significantly better or worse than expected9. Aggravating (or negative) GIs often result between loss-of-function mutations in pairs of genes from compensatory pathways that impinge on the same essential process2. Here, the loss of a single gene is buffered, such that either single mutant is viable. However, the loss of both pathways is deleterious and results in synthetic lethality or sickness (i.e. slow growth). Conversely, alleviating (or positive) interactions can occur between genes in the same pathway or protein complex2 as the deletion of either gene alone is often sufficient to perturb the normal function of the pathway or complex such that additional perturbations do not reduce activity, and hence growth, further. Overall, systematically identifying and analyzing GI networks can provide unbiased, global maps of the functional relationships between large numbers of genes, from which pathway-level information missed by other approaches can be inferred9.
Genetics, Issue 69, Molecular Biology, Medicine, Biochemistry, Microbiology, Aggravating, alleviating, conjugation, double mutant, Escherichia coli, genetic interaction, Gram-negative bacteria, homologous recombination, network, synthetic lethality or sickness, suppression
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A Toolkit to Enable Hydrocarbon Conversion in Aqueous Environments
Authors: Eva K. Brinkman, Kira Schipper, Nadine Bongaerts, Mathias J. Voges, Alessandro Abate, S. Aljoscha Wahl.
Institutions: Delft University of Technology, Delft University of Technology.
This work puts forward a toolkit that enables the conversion of alkanes by Escherichia coli and presents a proof of principle of its applicability. The toolkit consists of multiple standard interchangeable parts (BioBricks)9 addressing the conversion of alkanes, regulation of gene expression and survival in toxic hydrocarbon-rich environments. A three-step pathway for alkane degradation was implemented in E. coli to enable the conversion of medium- and long-chain alkanes to their respective alkanols, alkanals and ultimately alkanoic-acids. The latter were metabolized via the native β-oxidation pathway. To facilitate the oxidation of medium-chain alkanes (C5-C13) and cycloalkanes (C5-C8), four genes (alkB2, rubA3, rubA4and rubB) of the alkane hydroxylase system from Gordonia sp. TF68,21 were transformed into E. coli. For the conversion of long-chain alkanes (C15-C36), theladA gene from Geobacillus thermodenitrificans was implemented. For the required further steps of the degradation process, ADH and ALDH (originating from G. thermodenitrificans) were introduced10,11. The activity was measured by resting cell assays. For each oxidative step, enzyme activity was observed. To optimize the process efficiency, the expression was only induced under low glucose conditions: a substrate-regulated promoter, pCaiF, was used. pCaiF is present in E. coli K12 and regulates the expression of the genes involved in the degradation of non-glucose carbon sources. The last part of the toolkit - targeting survival - was implemented using solvent tolerance genes, PhPFDα and β, both from Pyrococcus horikoshii OT3. Organic solvents can induce cell stress and decreased survivability by negatively affecting protein folding. As chaperones, PhPFDα and β improve the protein folding process e.g. under the presence of alkanes. The expression of these genes led to an improved hydrocarbon tolerance shown by an increased growth rate (up to 50%) in the presences of 10% n-hexane in the culture medium were observed. Summarizing, the results indicate that the toolkit enables E. coli to convert and tolerate hydrocarbons in aqueous environments. As such, it represents an initial step towards a sustainable solution for oil-remediation using a synthetic biology approach.
Bioengineering, Issue 68, Microbiology, Biochemistry, Chemistry, Chemical Engineering, Oil remediation, alkane metabolism, alkane hydroxylase system, resting cell assay, prefoldin, Escherichia coli, synthetic biology, homologous interaction mapping, mathematical model, BioBrick, iGEM
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Genetic Manipulation in Δku80 Strains for Functional Genomic Analysis of Toxoplasma gondii
Authors: Leah M. Rommereim, Miryam A. Hortua Triana, Alejandra Falla, Kiah L. Sanders, Rebekah B. Guevara, David J. Bzik, Barbara A. Fox.
Institutions: The Geisel School of Medicine at Dartmouth.
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 Δku80 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 Δku80 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 Δku80Δhxgprt 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 Δku80 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).
Infectious Diseases, Issue 77, Genetics, Microbiology, Infection, Medicine, Immunology, Molecular Biology, Cellular Biology, Biomedical Engineering, Bioengineering, Genomics, Parasitology, Pathology, Apicomplexa, Coccidia, Toxoplasma, Genetic Techniques, Gene Targeting, Eukaryota, Toxoplasma gondii, genetic manipulation, gene targeting, gene deletion, gene replacement, gene tagging, homologous recombination, DNA, sequencing
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In vitro Coculture Assay to Assess Pathogen Induced Neutrophil Trans-epithelial Migration
Authors: Mark E. Kusek, Michael A. Pazos, Waheed Pirzai, Bryan P. Hurley.
Institutions: Harvard Medical School, MGH for Children, Massachusetts General Hospital.
Mucosal surfaces serve as protective barriers against pathogenic organisms. Innate immune responses are activated upon sensing pathogen leading to the infiltration of tissues with migrating inflammatory cells, primarily neutrophils. This process has the potential to be destructive to tissues if excessive or held in an unresolved state.  Cocultured in vitro models can be utilized to study the unique molecular mechanisms involved in pathogen induced neutrophil trans-epithelial migration. This type of model provides versatility in experimental design with opportunity for controlled manipulation of the pathogen, epithelial barrier, or neutrophil. Pathogenic infection of the apical surface of polarized epithelial monolayers grown on permeable transwell filters instigates physiologically relevant basolateral to apical trans-epithelial migration of neutrophils applied to the basolateral surface. The in vitro model described herein demonstrates the multiple steps necessary for demonstrating neutrophil migration across a polarized lung epithelial monolayer that has been infected with pathogenic P. aeruginosa (PAO1). Seeding and culturing of permeable transwells with human derived lung epithelial cells is described, along with isolation of neutrophils from whole human blood and culturing of PAO1 and nonpathogenic K12 E. coli (MC1000).  The emigrational process and quantitative analysis of successfully migrated neutrophils that have been mobilized in response to pathogenic infection is shown with representative data, including positive and negative controls. This in vitro model system can be manipulated and applied to other mucosal surfaces. Inflammatory responses that involve excessive neutrophil infiltration can be destructive to host tissues and can occur in the absence of pathogenic infections. A better understanding of the molecular mechanisms that promote neutrophil trans-epithelial migration through experimental manipulation of the in vitro coculture assay system described herein has significant potential to identify novel therapeutic targets for a range of mucosal infectious as well as inflammatory diseases.
Infection, Issue 83, Cellular Biology, Epithelium, Neutrophils, Pseudomonas aeruginosa, Respiratory Tract Diseases, Neutrophils, epithelial barriers, pathogens, transmigration
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A Method for High Fidelity Optogenetic Control of Individual Pyramidal Neurons In vivo
Authors: Shinya Nakamura, Michael V. Baratta, Donald C. Cooper.
Institutions: University of Colorado Boulder, University of Colorado Boulder.
Optogenetic methods have emerged as a powerful tool for elucidating neural circuit activity underlying a diverse set of behaviors across a broad range of species. Optogenetic tools of microbial origin consist of light-sensitive membrane proteins that are able to activate (e.g., channelrhodopsin-2, ChR2) or silence (e.g., halorhodopsin, NpHR) neural activity ingenetically-defined cell types over behaviorally-relevant timescales. We first demonstrate a simple approach for adeno-associated virus-mediated delivery of ChR2 and NpHR transgenes to the dorsal subiculum and prelimbic region of the prefrontal cortex in rat. Because ChR2 and NpHR are genetically targetable, we describe the use of this technology to control the electrical activity of specific populations of neurons (i.e., pyramidal neurons) embedded in heterogeneous tissue with high temporal precision. We describe herein the hardware, custom software user interface, and procedures that allow for simultaneous light delivery and electrical recording from transduced pyramidal neurons in an anesthetized in vivo preparation. These light-responsive tools provide the opportunity for identifying the causal contributions of different cell types to information processing and behavior.
Neuroscience, Issue 79, Genetic Techniques, Genetics, Behavioral, Biological Science Disciplines, Neurosciences, genetics (animal and plant), Investigative Techniques, Behavior and Behavior Mechanisms, Behavioral Disciplines and Activities, Natural Science Disciplines, Optogenetics, prefrontal cortex, subiculum, virus injection, in vivo recording, Neurophysiology, prelimbic, optrode, molecular neurogenetics, Gene targeting
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Purifying Plasmid DNA from Bacterial Colonies Using the Qiagen Miniprep Kit
Authors: Shenyuan Zhang, Michael D. Cahalan.
Institutions: University of California, Irvine (UCI).
Plasmid DNA purification from E. coli is a core technique for molecular cloning. Small scale purification (miniprep) from less than 5 ml of bacterial culture is a quick way for clone verification or DNA isolation, followed by further enzymatic reactions (polymerase chain reaction and restriction enzyme digestion). Here, we video-recorded the general procedures of miniprep through the QIAGEN's QIAprep 8 Miniprep Kit, aiming to introducing this highly efficient technique to the general beginners for molecular biology techniques. The whole procedure is based on alkaline lysis of E. coli cells followed by adsorption of DNA onto silica in the presence of high salt. It consists of three steps: 1) preparation and clearing of a bacterial lysate, 2) adsorption of DNA onto the QIAprep membrane, 3) washing and elution of plasmid DNA. All steps are performed without the use of phenol, chloroform, CsCl, ethidium bromide, and without alcohol precipitation. It usually takes less than 2 hours to finish the entire procedure.
Issue 6, Basic Protocols, plasmid, DNA, purification, Qiagen
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