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Fisher DJ, Beare PA. Recent advances in genetic systems in obligate intracellular human-pathogenic bacteria. Front Cell Infect Microbiol 2023; 13:1202245. [PMID: 37404720 PMCID: PMC10315504 DOI: 10.3389/fcimb.2023.1202245] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2023] [Accepted: 05/22/2023] [Indexed: 07/06/2023] Open
Abstract
The ability to genetically manipulate a pathogen is fundamental to discovering factors governing host-pathogen interactions at the molecular level and is critical for devising treatment and prevention strategies. While the genetic "toolbox" for many important bacterial pathogens is extensive, approaches for modifying obligate intracellular bacterial pathogens were classically limited due in part to the uniqueness of their obligatory lifestyles. Many researchers have confronted these challenges over the past two and a half decades leading to the development of multiple approaches to construct plasmid-bearing recombinant strains and chromosomal gene inactivation and deletion mutants, along with gene-silencing methods enabling the study of essential genes. This review will highlight seminal genetic achievements and recent developments (past 5 years) for Anaplasma spp., Rickettsia spp., Chlamydia spp., and Coxiella burnetii including progress being made for the still intractable Orientia tsutsugamushi. Alongside commentary of the strengths and weaknesses of the various approaches, future research directions will be discussed to include methods for C. burnetii that should have utility in the other obligate intracellular bacteria. Collectively, the future appears bright for unraveling the molecular pathogenic mechanisms of these significant pathogens.
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Affiliation(s)
- Derek J. Fisher
- School of Biological Sciences, Southern Illinois University, Carbondale, IL, United States
| | - Paul A. Beare
- Rocky Mountain Laboratory, National Institute of Health, Hamilton, MT, United States
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Kondethimmanahalli C, Ganta RR. Proteome analysis of Ehrlichia chaffeensis containing phagosome membranes revealed the presence of numerous bacterial and host proteins. Front Cell Infect Microbiol 2022; 12:1070356. [PMID: 36619760 PMCID: PMC9816426 DOI: 10.3389/fcimb.2022.1070356] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2022] [Accepted: 12/05/2022] [Indexed: 12/24/2022] Open
Abstract
Tick-transmitted Ehrlichia chaffeensis, the causative agent for human monocytic ehrlichiosis, resides and multiplies within a host cell phagosome. Infection progression of E. chaffeensis includes internalization into a host cell by host cell membrane fusion events following engulfment leading to the formation of E. chaffeensis containing vacuole (ECV). Revealing the molecular composition of ECV is important in understanding the host cellular processes, evasion of host defense pathways and in defining host-pathogen interactions. ECVs purified from infected host cells were analyzed to define both host and bacterial proteomes associated with the phagosome membranes. About 160 bacterial proteins and 2,683 host proteins were identified in the ECV membranes. The host proteins included predominantly known phagosome proteins involved in phagocytic trafficking, fusion of vesicles, protein transport, Ras signaling pathway and pathogenic infection. Many highly expressed proteins were similar to the previously documented proteins of phagosome vacuole membranes containing other obligate pathogenic bacteria. The finding of many bacterial membrane proteins is novel; they included multiple outer membrane proteins, such as the p28-Omps, the 120 kDa protein, preprotein translocases, lipoproteins, metal binding proteins, and chaperonins, although the presence of ankyrin repeat proteins, several Type I and IV secretion system proteins is anticipated. This study demonstrates that ECV membrane is extensively modified by the pathogen. This study represents the first and the most comprehensive description of ECV membrane proteome. The identity of many host and Ehrlichia proteins in the ECV membrane will be a valuable to define pathogenic mechanisms critical for the replication of the pathogen within macrophages.
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Affiliation(s)
| | - Roman R. Ganta
- Center of Excellence for Vector-Borne Diseases, Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, KS, United States
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Mutations in Ehrlichia chaffeensis Genes ECH_0660 and ECH_0665 Cause Transcriptional Changes in Response to Zinc or Iron Limitation. J Bacteriol 2021; 203:e0002721. [PMID: 33875547 PMCID: PMC8316085 DOI: 10.1128/jb.00027-21] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Ehrlichia chaffeensis causes human monocytic ehrlichiosis by replicating within phagosomes of monocytes/macrophages. A function disruption mutation within the pathogen's ECH_0660 gene, which encodes a phage head-to-tail connector protein, resulted in the rapid clearance of the pathogen in vivo, while aiding in induction of sufficient immunity in a host to protect against wild-type infection challenge. In this study, we describe the characterization of a cluster of seven genes spanning from ECH_0659 to ECH_0665, which contained four genes encoding bacterial phage proteins, including the ECH_0660 gene. Assessment of the promoter region upstream of the first gene of the seven genes (ECH_0659) in Escherichia coli demonstrated transcriptional enhancement under zinc and iron starvation conditions. Furthermore, transcription of the seven genes was significantly higher under zinc and iron starvation conditions for E. chaffeensis carrying a mutation in the ECH_0660 gene compared to the wild-type pathogen. In contrast, for the ECH_0665 gene mutant with the function disruption, transcription from the genes was mostly similar to that of the wild type or was moderately downregulated. Recently, we reported that this mutation caused a minimal impact on the pathogen's in vivo growth, as it persisted similarly to the wild type. The current study is the first to describe how zinc and iron contribute to E. chaffeensis biology. Specifically, we demonstrated that the functional disruption in the gene encoding the phage head-to-tail connector protein in E. chaffeensis results in the enhanced transcription of seven genes, including those encoding phage proteins, under zinc and iron limitation. IMPORTANCE Ehrlichia chaffeensis, a tick-transmitted bacterium, causes human monocytic ehrlichiosis by replicating within phagosomes of monocytes/macrophages. A function disruption mutation within the pathogen's gene encoding a phage head-to-tail connector protein resulted in the rapid clearance of the pathogen in vivo, while aiding in induction of sufficient immunity in a host to protect against wild-type infection challenge. In the current study, we investigated if the functional disruption in the phage head-to-tail connector protein gene caused transcriptional changes resulting from metal ion limitations. This is the first study describing how zinc and iron may contribute to E. chaffeensis replication.
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Wang Y, Nair ADS, Alhassan A, Jaworski DC, Liu H, Trinkl K, Hove P, Ganta CK, Burkhardt N, Munderloh UG, Ganta RR. Multiple Ehrlichia chaffeensis Genes Critical for Its Persistent Infection in a Vertebrate Host Are Identified by Random Mutagenesis Coupled with In Vivo Infection Assessment. Infect Immun 2020; 88:e00316-20. [PMID: 32747600 PMCID: PMC7504954 DOI: 10.1128/iai.00316-20] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Accepted: 07/23/2020] [Indexed: 12/14/2022] Open
Abstract
Ehrlichia chaffeensis, a tick-transmitted obligate intracellular rickettsial agent, causes human monocytic ehrlichiosis. In recent reports, we described substantial advances in developing random and targeted gene disruption methods to investigate the functions of E. chaffeensis genes. We reported earlier that the Himar1 transposon-based random mutagenesis is a valuable tool in defining E. chaffeensis genes critical for its persistent growth in vivo in reservoir and incidental hosts. The method also aided in extending studies focused on vaccine development and immunity. Here, we describe the generation and mapping of 55 new mutations. To define the critical nature of the bacterial genes, infection experiments were carried out in the canine host with pools of mutant organisms. Infection evaluation in the physiologically relevant host by molecular assays and by xenodiagnoses allowed the identification of many proteins critical for the pathogen's persistent in vivo growth. Genes encoding proteins involved in biotin biosynthesis, protein synthesis and fatty acid biosynthesis, DNA repair, electron transfer, and a component of a multidrug resistance (MDR) efflux pump were concluded to be essential for the pathogen's in vivo growth. Three known immunodominant membrane proteins, i.e., two 28-kDa outer membrane proteins (P28/OMP) and a 120-kDa surface protein, were also recognized as necessary for the pathogen's obligate intracellular life cycle. The discovery of many E. chaffeensis proteins crucial for its continuous in vivo growth will serve as a major resource for investigations aimed at defining pathogenesis and developing novel therapeutics for this and related pathogens of the rickettsial family Anaplasmataceae.
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Affiliation(s)
- Ying Wang
- Center of Excellence for Vector-Borne Diseases (CEVBD), Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, USA
| | - Arathy D S Nair
- Center of Excellence for Vector-Borne Diseases (CEVBD), Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, USA
| | - Andy Alhassan
- Center of Excellence for Vector-Borne Diseases (CEVBD), Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, USA
- Department of Pathobiology, School of Veterinary Medicine, St. George's University, West Indies, Grenada
| | - Deborah C Jaworski
- Center of Excellence for Vector-Borne Diseases (CEVBD), Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, USA
| | - Huitao Liu
- Center of Excellence for Vector-Borne Diseases (CEVBD), Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, USA
| | - Kathleen Trinkl
- Center of Excellence for Vector-Borne Diseases (CEVBD), Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, USA
| | - Paidashe Hove
- Center of Excellence for Vector-Borne Diseases (CEVBD), Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, USA
- Department of Pathobiology, School of Veterinary Medicine, St. George's University, West Indies, Grenada
| | - Charan K Ganta
- Center of Excellence for Vector-Borne Diseases (CEVBD), Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, USA
| | - Nicole Burkhardt
- Department of Entomology, University of Minnesota, St. Paul, Minnesota, USA
| | - Ulrike G Munderloh
- Department of Entomology, University of Minnesota, St. Paul, Minnesota, USA
| | - Roman R Ganta
- Center of Excellence for Vector-Borne Diseases (CEVBD), Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, USA
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Adelabu OA, Iweriebor BC, Okoh AI, Obi LC. Phylogenetic profiling for zoonotic Ehrlichia spp. from ixodid ticks in the Eastern Cape, South Africa. Transbound Emerg Dis 2019; 67:1247-1256. [PMID: 31880098 DOI: 10.1111/tbed.13460] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2019] [Revised: 12/19/2019] [Accepted: 12/19/2019] [Indexed: 01/08/2023]
Abstract
Ticks are obligate hematophagous parasite of vertebrate that transmit a range of pathogenic microorganisms that can cause diseases in livestock and humans. The range of tick-borne disease causative agents infecting domestic animals and humans has recently increased. Several significant zoonotic tick-borne diseases such as ehrlichiosis among others are on the increase worldwide. This study was designed to investigate the occurrence of zoonotic Ehrlichia spp. from samples collected from livestock in selected communities in the Eastern Cape Province, South Africa. Tick samples were manually collected from domesticated animals in selected homesteads. The ticks were morphologically identified to species and tested for Ehrlichia infection via polymerase chain reaction (PCR), using genus-specific disulphide bond formation protein (dsbA) gene primers. This was followed by sequence analysis of amplicons and phylogeny. Of the 1,200 ticks collected, Amblyomma hebraeum was most prevalent (n = 335; 27.9%), followed by Rhipicephalus appendiculatus (n = 274; 22.8%), Rhipicephalus decoloratus; (n = 224; 18.7%) and Rhipicephalus eversti eversti (n = 200, 16.7%). Ehrlichia DNA was detected in 19/1,200 (1.6%) of the screened DNA samples. A homology search of the generated sequences revealed a high percentage of identity between 95% and 98% with other homologous dsbA gene sequences of other Ehrlichia species in GenBank. Phylogenetic analysis showed that the obtained sequences clustered unambiguously with other Ehrlichia sequences from different geographical regions of the world. We concluded that Ehrlichial pathogens are vectored by the ticks collected from domesticated animals in the study areas, thus suggesting concern for public health, as some of the recovered pathogens are zoonotic in nature and could pose serious public health risk through human exposure to tick bites.
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Affiliation(s)
- Olusesan Adeyemi Adelabu
- SAMRC Microbial Water Quality Monitoring Centre, University of Fort Hare, Alice, South Africa.,Applied and Environmental Microbiology Research Group (AEMREG), Department of Biochemistry and Microbiology, University of Fort Hare, Alice, South Africa
| | | | - Anthony Ifeanyi Okoh
- SAMRC Microbial Water Quality Monitoring Centre, University of Fort Hare, Alice, South Africa.,Applied and Environmental Microbiology Research Group (AEMREG), Department of Biochemistry and Microbiology, University of Fort Hare, Alice, South Africa
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Kondethimmanahalli C, Liu H, Ganta RR. Proteome Analysis Revealed Changes in Protein Expression Patterns Caused by Mutations in Ehrlichia chaffeensis. Front Cell Infect Microbiol 2019; 9:58. [PMID: 30937288 PMCID: PMC6431617 DOI: 10.3389/fcimb.2019.00058] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2018] [Accepted: 02/25/2019] [Indexed: 01/31/2023] Open
Abstract
The tick-borne rickettsial pathogen, Ehrlichia chaffeensis, causes monocytic ehrlichiosis in people and other vertebrate hosts. Mutational analysis in E. chaffeensis genome aids in better understanding of its infection and persistence in host cells and in the development of attenuated vaccines. Our recent RNA deep sequencing study revealed that three genomic mutations caused global changes in the gene expression patterns, which in turn affect the ability of pathogen's survival in a host and the host's ability to induce protection against the pathogen. In this follow-up study, we document the impact of mutations on the pathogen's global protein expression and the influence of protein abundance on a mutant's attenuation and protection of vertebrate host against infection. iTRAQ labeling and mass spectrometry analysis of E. chaffeensis wildtype and mutants identified 564 proteins covering about 63% of the genome. Mutation in ECH_0379 gene encoding for an antiporter protein, causing attenuated growth in vertebrate hosts, led to overexpression of p28 outer membrane proteins, molecular chaperons, and metabolic enzymes, while a mutation downstream to the ECH_0490 gene that caused minimal impact on the pathogen's in vivo growth resulted in major changes in the expression of outer membrane proteins, transcriptional regulators and T4SS proteins. ECH_0660 gene mutation, causing the pathogen's rapid clearance and offering protection against wild type infection challenge in a vertebrate host, had a minimal impact on proteome similar to our prior observations from transcriptome analysis. While the global proteome data revealed fewer translated proteins compared to the transcripts identified from RNA deep sequencing analysis, there is a great deal of correlation noted between the global proteome and transcriptome analysis. Further, global proteome analysis, including the assessment of 2D resolved total and immunoproteomes revealed greater variations in the highly immunogenic p28-Omp proteins.
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Affiliation(s)
- Chandramouli Kondethimmanahalli
- Department of Diagnostic Medicine/Pathobiology, Center of Excellence for Vector-Borne Diseases, College of Veterinary Medicine, Kansas State University, Manhattan, KS, United States
| | - Huitao Liu
- Department of Diagnostic Medicine/Pathobiology, Center of Excellence for Vector-Borne Diseases, College of Veterinary Medicine, Kansas State University, Manhattan, KS, United States
| | - Roman R Ganta
- Department of Diagnostic Medicine/Pathobiology, Center of Excellence for Vector-Borne Diseases, College of Veterinary Medicine, Kansas State University, Manhattan, KS, United States
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