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Sykes EME, Deo S, Kumar A. Recent Advances in Genetic Tools for Acinetobacter baumannii. Front Genet 2020; 11:601380. [PMID: 33414809 PMCID: PMC7783400 DOI: 10.3389/fgene.2020.601380] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2020] [Accepted: 11/30/2020] [Indexed: 12/26/2022] Open
Abstract
Acinetobacter baumannii is classified as a top priority pathogen by the World Health Organization (WHO) because of its widespread resistance to all classes of antibiotics. This makes the need for understanding the mechanisms of resistance and virulence critical. Therefore, tools that allow genetic manipulations are vital to unravel the mechanisms of multidrug resistance (MDR) and virulence in A. baumannii. A host of current strategies are available for genetic manipulations of A. baumannii laboratory-strains, including ATCC® 17978TM and ATCC® 19606T, but depending on susceptibility profiles, these strategies may not be sufficient when targeting strains newly obtained from clinic, primarily due to the latter's high resistance to antibiotics that are commonly used for selection during genetic manipulations. This review highlights the most recent methods for genetic manipulation of A. baumannii including CRISPR based approaches, transposon mutagenesis, homologous recombination strategies, reporter systems and complementation techniques with the spotlight on those that can be applied to MDR clinical isolates.
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Affiliation(s)
| | | | - Ayush Kumar
- Department of Microbiology, University of Manitoba, Winnipeg, MB, Canada
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2
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Abstract
Genetic studies in Borrelia require special consideration of the highly segmented genome, complex growth requirements and evolutionary distance of spirochetes from other genetically tractable bacteria. Despite these challenges, a robust molecular genetic toolbox has been constructed to investigate the biology and pathogenic potential of these important human pathogens. In this review we summarize the tools and techniques that are currently available for the genetic manipulation of Borrelia, including the relapsing fever spirochetes, viewing them in the context of their utility and shortcomings. Our primary objective is to help researchers discern what is feasible and what is not practical when thinking about potential genetic experiments in Borrelia. We have summarized published methods and highlighted their critical elements, but we are not providing detailed protocols. Although many advances have been made since B. burgdorferi was first transformed over 25 years ago, some standard genetic tools remain elusive for Borrelia. We mention these limitations and why they persist, if known. We hope to encourage investigators to explore what might be possible, in addition to optimizing what currently can be achieved, through genetic manipulation of Borrelia.
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Affiliation(s)
- Patricia A. Rosa
- Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 903 S 4th St. Hamilton, MT 59840 USA
| | - Mollie W. Jewett
- Division of Immunity and Pathogenesis, Burnett School of Biomedical Sciences, University of Central Florida College of Medicine, 6900 Lake Nona Blvd, Orlando, FL 32827 USA
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3
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Abstract
The spirochetes Borrelia (Borreliella) burgdorferi and Borrelia hermsii, the etiologic agents of Lyme disease and relapsing fever, respectively, cycle in nature between an arthropod vector and a vertebrate host. They have extraordinarily unusual genomes that are highly segmented and predominantly linear. The genetic analyses of Lyme disease spirochetes have become increasingly more sophisticated, while the age of genetic investigation in the relapsing fever spirochetes is just dawning. Molecular tools available for B. burgdorferi and related species range from simple selectable markers and gene reporters to state-of-the-art inducible gene expression systems that function in the animal model and high-throughput mutagenesis methodologies, despite nearly overwhelming experimental obstacles. This armamentarium has empowered borreliologists to build a formidable genetic understanding of the cellular physiology of the spirochete and the molecular pathogenesis of Lyme disease.
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Affiliation(s)
- Dan Drecktrah
- Division of Biological Sciences, University of Montana, Missoula, MT, 59812, USA.
| | - D Scott Samuels
- Division of Biological Sciences, University of Montana, Missoula, MT, 59812, USA.
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Takacs CN, Kloos ZA, Scott M, Rosa PA, Jacobs-Wagner C. Fluorescent Proteins, Promoters, and Selectable Markers for Applications in the Lyme Disease Spirochete Borrelia burgdorferi. Appl Environ Microbiol 2018; 84:e01824-18. [PMID: 30315081 PMCID: PMC6275353 DOI: 10.1128/aem.01824-18] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2018] [Accepted: 10/08/2018] [Indexed: 11/30/2022] Open
Abstract
Lyme disease is the most widely reported vector-borne disease in the United States. Its incidence is rapidly increasing, and disease symptoms can be debilitating. The need to understand the biology of the disease agent, the spirochete Borrelia burgdorferi, is thus evermore pressing. Despite important advances in B. burgdorferi genetics, the array of molecular tools available for use in this organism remains limited, especially for cell biological studies. Here, we adapt a palette of bright and mostly monomeric fluorescent proteins for versatile use and multicolor imaging in B. burgdorferi We also characterize two novel antibiotic selection markers and establish the feasibility of their use in conjunction with extant markers. Last, we describe a set of promoters of low and intermediate strengths that allow fine-tuning of gene expression levels. These molecular tools complement and expand current experimental capabilities in B. burgdorferi, which will facilitate future investigation of this important human pathogen. To showcase the usefulness of these reagents, we used them to investigate the subcellular localization of BB0323, a B. burgdorferi lipoprotein essential for survival in the host and vector environments. We show that BB0323 accumulates at the cell poles and future division sites of B. burgdorferi cells, highlighting the complex subcellular organization of this spirochete.IMPORTANCE Genetic manipulation of the Lyme disease spirochete B. burgdorferi remains cumbersome, despite significant progress in the field. The scarcity of molecular reagents available for use in this pathogen has slowed research efforts to study its unusual biology. Of interest, B. burgdorferi displays complex cellular organization features that have yet to be understood. These include an unusual morphology and a highly fragmented genome, both of which are likely to play important roles in the bacterium's transmission, infectivity, and persistence. Here, we complement and expand the array of molecular tools available for use in B. burgdorferi by generating and characterizing multiple fluorescent proteins, antibiotic selection markers, and promoters of varied strengths. These tools will facilitate investigations in this important human pathogen, as exemplified by the polar and midcell localization of the cell envelope regulator BB0323, which we uncovered using these reagents.
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Affiliation(s)
- Constantin N Takacs
- Microbial Sciences Institute, Yale West Campus, West Haven, Connecticut, USA
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut, USA
- Howard Hughes Medical Institute, Yale West Campus, West Haven, Connecticut, USA
| | - Zachary A Kloos
- Microbial Sciences Institute, Yale West Campus, West Haven, Connecticut, USA
- Microbiology Program, Yale University, New Haven, Connecticut, USA
| | - Molly Scott
- Microbial Sciences Institute, Yale West Campus, West Haven, Connecticut, USA
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut, USA
- Howard Hughes Medical Institute, Yale West Campus, West Haven, Connecticut, USA
| | - Patricia A Rosa
- Laboratory of Bacteriology, Rocky Mountain Laboratories, Division of Intramural Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, USA
| | - Christine Jacobs-Wagner
- Microbial Sciences Institute, Yale West Campus, West Haven, Connecticut, USA
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut, USA
- Howard Hughes Medical Institute, Yale West Campus, West Haven, Connecticut, USA
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, Connecticut, USA
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5
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Abstract
The disciplines of Borrelia (Borreliella) burgdorferi microbiology and Lyme disease pathogenesis have come to depend on the genetic manipulation of the spirochete. Generating mutants in these recalcitrant bacteria, while not straightforward, is routinely accomplished in numerous laboratories, although there are several crucial caveats to consider. This chapter describes the design of basic molecular genetic experiments as well as the detailed methodologies to prepare and transform competent cells, select for and isolate transformants, and complement or genetically restore mutants.
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Affiliation(s)
- D Scott Samuels
- Division of Biological Sciences, University of Montana, Missoula, MT, USA.
| | - Dan Drecktrah
- Division of Biological Sciences, University of Montana, Missoula, MT, USA
| | - Laura S Hall
- Division of Biological Sciences, University of Montana, Missoula, MT, USA
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pyrF as a Counterselectable Marker for Unmarked Genetic Manipulations in Treponema denticola. Appl Environ Microbiol 2015; 82:1346-52. [PMID: 26682856 DOI: 10.1128/aem.03704-15] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2015] [Accepted: 12/14/2015] [Indexed: 12/11/2022] Open
Abstract
The pathophysiology of Treponema denticola, an oral pathogen associated with both periodontal and endodontic infections, is poorly understood due to its fastidious growth and recalcitrance to genetic manipulations. Counterselectable markers are instrumental in constructing clean and unmarked mutations in bacteria. Here, we demonstrate that pyrF, a gene encoding orotidine-5'-monophosphate decarboxylase, can be used as a counterselectable marker in T. denticola to construct marker-free mutants. T. denticola is susceptible to 5-fluoroorotic acid (5-FOA). To establish a pyrF-based counterselectable knockout system in T. denticola, the pyrF gene was deleted. The deletion conferred resistance to 5-FOA in T. denticola. Next, a single-crossover mutant was constructed by reintroducing pyrF along with a gentamicin resistance gene (aacC1) back into the chromosome of the pyrF mutant at the locus of choice. In this study, we chose flgE, a flagellar hook gene that is located within a large polycistronic motility gene operon, as our target gene. The obtained single-crossover mutant (named FlgE(in)) regained the susceptibility to 5-FOA. Finally, FlgE(in) was plated on solid agar containing 5-FOA. Numerous colonies of the 5-FOA-resistant mutant (named FlgE(out)) were obtained and characterized by PCR and Southern blotting analyses. The results showed that the flgE gene was deleted and FlgE(out) was free of selection markers (i.e., pyrF and aacC1). Compared to previously constructed flgE mutants that contain an antibiotic selection marker, the deletion of flgE in FlgE(out) has no polar effect on its downstream gene expression. The system developed here will provide us with a new tool for investigating the genetics and pathogenicity of T. denticola.
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Su C, Zhao XQ, Wang HN, Qiu RG, Tang L. Seamless stitching of biosynthetic gene cluster containing type I polyketide synthases using Red/ET mediated recombination for construction of stably co-existing plasmids. Gene 2014; 554:233-40. [PMID: 25311549 DOI: 10.1016/j.gene.2014.10.022] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Revised: 09/23/2014] [Accepted: 10/09/2014] [Indexed: 01/27/2023]
Abstract
Type I polyketides are natural products with diverse functions that are important for medical and agricultural applications. Manipulation of large biosynthetic gene clusters containing type I polyketide synthases (PKS) for heterologous expression is difficult due to the existence of conservative sequences of PKS in multiple modules. Red/ET mediated recombination has permitted rapid manipulation of large fragments; however, it requires insertion of antibiotic selection marker in the cassette, raising the problem of interference of expression by leaving "scar" sequence. Here, we report a method for precise seamless stitching of large polyketide biosynthetic gene cluster using a 48.4kb fragment containing type I PKS involved in fostriecin biosynthesis as an example. rpsL counter-selection was used to assist seamless stitching of large fragments, where we have overcome both the size limitations and the restriction on endonuclease sites during the Red/ET recombination. The compatibility and stability of the co-existing vectors (p184 and pMT) which respectively accommodate 16kb and 32.4kb inserted fragments were demonstrated. The procedure described here is efficient for manipulation of large DNA fragments for heterologous expression.
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Affiliation(s)
- Chun Su
- Research Center for Molecular Medicine, Faculty of Chemical, Environmental and Biological Science and Technology, Dalian University of Technology, Dalian 116024, China
| | - Xin-Qing Zhao
- Research Center for Molecular Medicine, Faculty of Chemical, Environmental and Biological Science and Technology, Dalian University of Technology, Dalian 116024, China; School of Life Science and Biotechnology, Dalian University of Technology, Dalian 116024, China
| | - Hai-Na Wang
- School of Life Science and Biotechnology, Dalian University of Technology, Dalian 116024, China
| | - Rong-Guo Qiu
- Research Center for Molecular Medicine, Faculty of Chemical, Environmental and Biological Science and Technology, Dalian University of Technology, Dalian 116024, China; Beijing Biostar Technologies, Ltd., Beijing 101111, China
| | - Li Tang
- Research Center for Molecular Medicine, Faculty of Chemical, Environmental and Biological Science and Technology, Dalian University of Technology, Dalian 116024, China; Beijing Biostar Technologies, Ltd., Beijing 101111, China.
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Tsai YK, Liou CH, Lin JC, Ma L, Fung CP, Chang FY, Siu LK. A suitable streptomycin-resistant mutant for constructing unmarked in-frame gene deletions using rpsL as a counter-selection marker. PLoS One 2014; 9:e109258. [PMID: 25268958 PMCID: PMC4182516 DOI: 10.1371/journal.pone.0109258] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2014] [Accepted: 09/08/2014] [Indexed: 01/14/2023] Open
Abstract
The streptomycin counter-selection system is a useful tool for constructing unmarked in-frame gene deletions, which is a fundamental approach to study bacteria and their pathogenicity at the molecular level. A prerequisite for this system is acquiring a streptomycin-resistant strain due to rpsL mutations, which encodes the ribosomal protein S12. However, in this study no streptomycin resistance was found to be caused by rpsL mutations in all 127 clinical strains of Klebsiella pneumoniae isolated from liver abscess patients. By screening 107 spontaneous mutants of streptomycin resistance from a clinical strain of K. pneumoniae, nucleotide substitution or insertion located within the rpsL was detected in each of these strains. Thirteen different mutants with varied S12 proteins were obtained, including nine streptomycin-dependent mutants. The virulence of all four streptomycin-resistant mutants was further evaluated. Compared with the parental strain, the K42N, K42T and K87R mutants showed a reduction in growth rate, and the K42N and K42T mutants became susceptible to normal human serum. In the mice LD50 (the bacterial dose that caused 50% death) assay, the K42N and K42T mutants were ∼ 1,000-fold less lethal (∼ 2 × 10(5) CFU) and the K87R mutant was ∼ 50-fold less lethal (∼ 1 × 10(4) CFU) than the parental strain (∼ 2 × 10(2) CFU). A K42R mutant showed non-observable effects on the above assays, while this mutant exhibited a small cost (P < 0.01) in an in vitro growth competition experiment. In summary, most of the K. pneumoniae strains with streptomycin resistance caused by rpsL mutations are less virulent than their parental strain in the absence of streptomycin. The K42R mutant showed similar pathogenicity to its parental strain and should be one of the best choices when using rpsL as a counter-selection marker.
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Affiliation(s)
- Yu-Kuo Tsai
- Institute of Infectious Diseases and Vaccinology, National Health Research Institutes, Miaoli, Taiwan
| | - Ci-Hong Liou
- Division of Infectious Diseases and Tropical Medicine, Department of Internal Medicine, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan
| | - Jung-Chung Lin
- Division of Infectious Diseases and Tropical Medicine, Department of Internal Medicine, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan
| | - Ling Ma
- Institute of Infectious Diseases and Vaccinology, National Health Research Institutes, Miaoli, Taiwan
| | - Chang-Phone Fung
- Section of Infectious Diseases, Department of Medicine, Taipei Veterans General Hospital and National Yang-Ming University, Taipei, Taiwan
| | - Feng-Yee Chang
- Division of Infectious Diseases and Tropical Medicine, Department of Internal Medicine, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan
- Taiwan Centres for Disease Control, Taipei, Taiwan
| | - L. Kristopher Siu
- Institute of Infectious Diseases and Vaccinology, National Health Research Institutes, Miaoli, Taiwan
- Division of Infectious Diseases and Tropical Medicine, Department of Internal Medicine, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan
- Graduate Institute of Basic Medical Science, China Medical University, Taichung, Taiwan
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Hu S, Fu J, Huang F, Ding X, Stewart AF, Xia L, Zhang Y. Genome engineering of Agrobacterium tumefaciens using the lambda Red recombination system. Appl Microbiol Biotechnol 2013; 98:2165-72. [DOI: 10.1007/s00253-013-5412-x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2013] [Revised: 11/01/2013] [Accepted: 11/10/2013] [Indexed: 10/26/2022]
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10
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Deletion of the Cytophaga hutchinsonii type IX secretion system gene sprP results in defects in gliding motility and cellulose utilization. Appl Microbiol Biotechnol 2013; 98:763-75. [PMID: 24257839 DOI: 10.1007/s00253-013-5355-2] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2013] [Revised: 10/16/2013] [Accepted: 10/21/2013] [Indexed: 10/26/2022]
Abstract
Cytophaga hutchinsonii glides rapidly over surfaces and employs a novel collection of cell-associated proteins to digest crystalline cellulose. HimarEm1 transposon mutagenesis was used to isolate a mutant with an insertion in CHU_0170 (sprP) that was partially deficient in gliding motility and was unable to digest filter paper cellulose. SprP is similar in sequence to the Porphyromonas gingivalis type IX secretion system (T9SS) protein PorP that is involved in the secretion of gingipain protease virulence factors and to the Flavobacterium johnsoniae T9SS protein SprF that is needed to deliver components of the gliding motility machinery to the cell surface. We developed an efficient method to construct targeted nonpolar mutations in C. hutchinsonii and deleted sprP. The deletion mutant was defective in gliding and failed to digest cellulose, and complementation with sprP on a plasmid restored both abilities. Sequence analysis predicted that CHU_3105 is secreted by the T9SS, and deletion of sprP resulted in decreased levels of extracellular CHU_3105. The results suggest that SprP may function in protein secretion. The T9SS may be required for motility and cellulose utilization because cell surface proteins predicted to be involved in both processes have C-terminal domains that are thought to target them to this secretion system. The efficient genetic tools now available for C. hutchinsonii should allow a detailed analysis of the cellulolytic, gliding motility, and protein secretion machineries of this common but poorly understood bacterium.
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Coburn J, Leong J, Chaconas G. Illuminating the roles of the Borrelia burgdorferi adhesins. Trends Microbiol 2013; 21:372-9. [PMID: 23876218 DOI: 10.1016/j.tim.2013.06.005] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2013] [Revised: 06/13/2013] [Accepted: 06/14/2013] [Indexed: 01/13/2023]
Abstract
The Lyme disease spirochetes, Borrelia burgdorferi (sensu lato), must cause persistent, disseminated infection to be maintained in the natural enzootic cycle. In human Lyme disease, spirochetes spread from the site of a tick bite to colonize multiple tissue sites, causing multisystem clinical manifestations. The Lyme spirochetes produce many adhesive surface proteins that collectively recognize diverse host substrates and cell types and are likely to promote dissemination and chronic infection in a variety of tissues. Recent application of state-of-the-art in vivo imaging technologies is illuminating mechanisms of interaction of B. burgdorferi with the host and the importance of multiple adhesins during mammalian infection.
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Affiliation(s)
- Jenifer Coburn
- Division of Infectious Diseases, Department of Medicine, Medical College of Wisconsin, Milwaukee, WI 53226, USA.
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12
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Abstract
The spirochetes in the Borrelia burgdorferi sensu lato genospecies group cycle in nature between tick vectors and vertebrate hosts. The current assemblage of B. burgdorferi sensu lato, of which three species cause Lyme disease in humans, originated from a rapid species radiation that occurred near the origin of the clade. All of these species share a unique genome structure that is highly segmented and predominantly composed of linear replicons. One of the circular plasmids is a prophage that exists as several isoforms in each cell and can be transduced to other cells, likely contributing to an otherwise relatively anemic level of horizontal gene transfer, which nevertheless appears to be adequate to permit strong natural selection and adaptation in populations of B. burgdorferi. Although the molecular genetic toolbox is meager, several antibiotic-resistant mutants have been isolated, and the resistance alleles, as well as some exogenous genes, have been fashioned into markers to dissect gene function. Genetic studies have probed the role of the outer membrane lipoprotein OspC, which is maintained in nature by multiple niche polymorphisms and negative frequency-dependent selection. One of the most intriguing genetic systems in B. burgdorferi is vls recombination, which generates antigenic variation during infection of mammalian hosts.
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MESH Headings
- Alleles
- Animals
- Antigenic Variation
- Antigens, Bacterial/genetics
- Antigens, Bacterial/immunology
- Antigens, Bacterial/metabolism
- Bacterial Outer Membrane Proteins/genetics
- Bacterial Outer Membrane Proteins/metabolism
- Bacterial Proteins/genetics
- Bacterial Proteins/immunology
- Bacterial Proteins/metabolism
- Bacteriophages/genetics
- Bacteriophages/metabolism
- Bacteriophages/pathogenicity
- Borrelia burgdorferi/genetics
- Borrelia burgdorferi/immunology
- Borrelia burgdorferi/pathogenicity
- Borrelia burgdorferi/virology
- DNA, Bacterial/genetics
- DNA, Bacterial/metabolism
- Electroporation
- Evolution, Molecular
- Genes, Bacterial
- Genetic Variation
- Humans
- Ixodes/microbiology
- Linkage Disequilibrium
- Lipoproteins/genetics
- Lipoproteins/immunology
- Lipoproteins/metabolism
- Lyme Disease/microbiology
- Plasmids/genetics
- Plasmids/metabolism
- Prophages/genetics
- Prophages/metabolism
- Recombination, Genetic
- Selection, Genetic
- Species Specificity
- Transduction, Genetic
- Transformation, Genetic
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Affiliation(s)
- Dustin Brisson
- Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Dan Drecktrah
- Division of Biological Sciences, The University of Montana, Missoula, Montana 59812
| | - Christian H. Eggers
- Department of Biomedical Sciences, Quinnipiac University, Hamden, Connecticut 06518
| | - D. Scott Samuels
- Division of Biological Sciences, The University of Montana, Missoula, Montana 59812
- Center for Biomolecular Structure and Dynamics, The University of Montana, Missoula, Montana 59812
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Reversing bacterial resistance to antibiotics by phage-mediated delivery of dominant sensitive genes. Appl Environ Microbiol 2011; 78:744-51. [PMID: 22113912 DOI: 10.1128/aem.05741-11] [Citation(s) in RCA: 128] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Pathogen resistance to antibiotics is a rapidly growing problem, leading to an urgent need for novel antimicrobial agents. Unfortunately, development of new antibiotics faces numerous obstacles, and a method that resensitizes pathogens to approved antibiotics therefore holds key advantages. We present a proof of principle for a system that restores antibiotic efficiency by reversing pathogen resistance. This system uses temperate phages to introduce, by lysogenization, the genes rpsL and gyrA conferring sensitivity in a dominant fashion to two antibiotics, streptomycin and nalidixic acid, respectively. Unique selective pressure is generated to enrich for bacteria that harbor the phages carrying the sensitizing constructs. This selection pressure is based on a toxic compound, tellurite, and therefore does not forfeit any antibiotic for the sensitization procedure. We further demonstrate a possible way of reducing undesirable recombination events by synthesizing dominant sensitive genes with major barriers to homologous recombination. Such synthesis does not significantly reduce the gene's sensitization ability. Unlike conventional bacteriophage therapy, the system does not rely on the phage's ability to kill pathogens in the infected host, but instead, on its ability to deliver genetic constructs into the bacteria and thus render them sensitive to antibiotics prior to host infection. We believe that transfer of the sensitizing cassette by the constructed phage will significantly enrich for antibiotic-treatable pathogens on hospital surfaces. Broad usage of the proposed system, in contrast to antibiotics and phage therapy, will potentially change the nature of nosocomial infections toward being more susceptible to antibiotics rather than more resistant.
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14
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Abstract
Veillonellae are one of the most prevalent and predominant microorganisms in both the supra- and subgingival plaques of the human oral cavity. Veillonellae's mutualistic relationships with the early, middle, and late colonizers of the oral cavity make them an important component of oral biofilm ecology. Unlike other ubiquitous early colonizers in the oral cavity, surprisingly little is known about Veillonella biology due to our lack of ability to genetically transform this group of bacteria. The objective of this study was to test the transformability of veillonellae. Using Veillonella parvula strain PK1910, we first obtained spontaneous mutations conferring streptomycin resistance. These mutations all carry a K43N substitution in the RpsL protein. Using the mutated rpsL gene as a selection marker, a variety of conditions were tested and optimized for electroporation. With the optimized protocol, we were able to introduce the first targeted mutation into the chromosome of V. parvula PK1910. Although more studies are needed to develop a robust genetic manipulation system in veillonellae, our results demonstrated, for the first time, that V. parvula is transformable, at least for strain PK1910.
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Affiliation(s)
- Jinman Liu
- Department of Oral Biology, College of Dentistry, The University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
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15
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Development and use of a gene deletion strategy for Flavobacterium johnsoniae to identify the redundant gliding motility genes remF, remG, remH, and remI. J Bacteriol 2011; 193:2418-28. [PMID: 21421754 DOI: 10.1128/jb.00117-11] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cells of Flavobacterium johnsoniae exhibit rapid gliding motility over surfaces. Cell movement is thought to involve motor complexes comprised of Gld proteins that propel the cell surface adhesin SprB. The four distal genes of the sprB operon (sprC, sprD, sprB, and sprF) are required for normal motility and for formation of spreading colonies, but the roles of the remaining three genes (remF, remG, and fjoh_0982) are unclear. A gene deletion strategy was developed to determine whether these genes are involved in gliding. A spontaneous streptomycin-resistant rpsL mutant of F. johnsoniae was isolated. Introduction of wild-type rpsL on a plasmid restored streptomycin sensitivity, demonstrating that wild-type rpsL is dominant to the mutant allele. The gene deletion strategy employed a suicide vector carrying wild-type rpsL and used streptomycin for counterselection. This approach was used to delete the region spanning remF, remG, and fjoh_0982. The mutant cells formed spreading colonies, demonstrating that these genes are not required for normal motility. Analysis of the genome revealed a paralog of remF (remH) and a paralog of remG (remI). Deletion of remH and remI had no effect on motility of wild-type cells, but cells lacking remF and remH, or cells lacking remG and remI, formed nonspreading colonies. The motility defects resulting from the combination of mutations suggest that the paralogous proteins perform redundant functions in motility. The rpsL counterselection strategy allows construction of unmarked mutations to determine the functions of individual motility proteins or to analyze other aspects of F. johnsoniae physiology.
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