1
|
Abstract
Legionella pneumophila (LP) widely exists in natural and artificial water environments, which facilitates LP to infect people. LP infection causes Legionnaires' disease (LD), which is an important but relatively uncommon respiratory infection. Approximately 90% of LD is caused by L. pneumophila serogroup 1 (Lp1). Meteorological conditions may affect the infectivity and virulence of Lp1, but the exact relationship between them is still unclear. In this study, we evaluated the virulence of Lp1 by screening of total 156 Lp1 strains isolated from cooling tower water in different region of China by detecting their abilities to activate NF-κB signaling pathway in vitro. In addition, we screened the distribution of some selected virulence genes in these strains. The virulence, virulence gene distribution and the meteorological factors were analyzed. We found that both the virulence and the distribution of virulence genes had a certain regional and meteorological correlation. Although loss of several virulence genes showed significant effects on the virulence of Lp1 strains, the distribution of virulence genes had very limited effects on the virulence of Lp1. IMPORTANCE LD is likely to be under-recognized in many countries. Due to the widespread existence of LP in natural and artificial water environments, and to the lack of cross-protection against different strains, LP is a potentially serious threat to human health. Therefore, effective monitoring of the virulence of LP in the water environment is very important to prevent and control the prevalence of LD. Understanding the virulence of LP can not only help us to predict the risk of possible outbreaks in advance, but can also enable more targeted clinical treatment. This study highlights the importance of understanding the epidemiology and ecology of LP isolated from public facilities in terms of public health and biology. Due to the potential for water sources to harbor and disseminate LP, and to the fact that geographical conditions influence the virulence of LP, timely and accurate LP virulence surveillance is urgently needed.
Collapse
|
2
|
Budowa IV systemu sekrecji Legionella pneumophilai jego znaczenie w patogenezie. POSTEP HIG MED DOSW 2021. [DOI: 10.2478/ahem-2021-0023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Abstrakt
Bakterie Legionella pneumophila w środowisku naturalnym pasożytują wewnątrz komórek wybranych gatunków pierwotniaków, a po przedostaniu się do sztucznych systemów dystrybucji wody stają się ważnym czynnikiem etiologicznym zapalenia płuc u ludzi. Główną cechą determinującą patogenność tych bakterii jest zdolność do życia i replikacji w makrofagach płucnych, czyli w komórkach wyspecjalizowanych do fagocytozy, zabijania i trawienia mikroorganizmów. Warunkiem wstępnym rozwoju infekcji jest przełamanie mechanizmów bójczych makrofagów i utworzenie wakuoli replikacyjnej LCV (Legionella containing vacuole). Biogeneza wakuoli LCV jest możliwa dzięki sprawnemu funkcjonowaniu IV systemu sekrecji Dot/Icm, który jest wielobiałkowym, złożonym kompleksem umiejscowionym w wewnętrznej i zewnętrznej membranie osłony komórkowej bakterii. System Dot/Icm liczy 27 elementów, na które składają się m.in. kompleks rdzeniowo-transmembranowy, tworzący strukturalny szkielet całego systemu oraz kompleks białek sprzęgających. Geny kodujące komponenty systemu Dot/Icm są zorganizowane na dwóch regionach chromosomu bak-teryjnego. System sekrecji Dot/Icm umożliwia L. pneumophila wprowadzenie do cytozolu komórki gospodarza ponad 300 białek efektorowych, których skoordynowane działanie powoduje utrzymanie integralności błony wakuoli replikacyjnej oraz pozwala na manipulowanie różnymi procesami komórki. Ważnym elementem strategii wewnątrzkomórkowego namnażania się L. pneumophila jest modulowanie transportu pęcherzykowego, interakcja z retikulum endoplazmatycznym oraz zakłócenie biosyntezy białek, procesów autofagii i apoptozy komórki gospodarza. Poznanie złożonych mechanizmów regulacji i funkcji białek efektorowych systemu Dot/Icm ma decydujące znaczenie w zapobieganiu i leczeniu choroby legionistów.
Collapse
|
3
|
Durie CL, Sheedlo MJ, Chung JM, Byrne BG, Su M, Knight T, Swanson M, Lacy DB, Ohi MD. Structural analysis of the Legionella pneumophila Dot/Icm type IV secretion system core complex. eLife 2020; 9:e59530. [PMID: 32876045 PMCID: PMC7511231 DOI: 10.7554/elife.59530] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2020] [Accepted: 09/01/2020] [Indexed: 01/21/2023] Open
Abstract
Legionella pneumophila is an opportunistic pathogen that causes the potentially fatal pneumonia Legionnaires' Disease. This infection and subsequent pathology require the Dot/Icm Type IV Secretion System (T4SS) to deliver effector proteins into host cells. Compared to prototypical T4SSs, the Dot/Icm assembly is much larger, containing ~27 different components including a core complex reported to be composed of five proteins: DotC, DotD, DotF, DotG, and DotH. Using single particle cryo-electron microscopy (cryo-EM), we report reconstructions of the core complex of the Dot/Icm T4SS that includes a symmetry mismatch between distinct structural features of the outer membrane cap (OMC) and periplasmic ring (PR). We present models of known core complex proteins, DotC, DotD, and DotH, and two structurally similar proteins within the core complex, DotK and Lpg0657. This analysis reveals the stoichiometry and contact interfaces between the key proteins of the Dot/Icm T4SS core complex and provides a framework for understanding a complex molecular machine.
Collapse
Affiliation(s)
- Clarissa L Durie
- Life Sciences Institute, University of MichiganAnn ArborUnited States
| | - Michael J Sheedlo
- Department of Pathology, Microbiology, and Immunology, Department of Pathology, Vanderbilt University Medical CenterNashvilleUnited States
| | - Jeong Min Chung
- Life Sciences Institute, University of MichiganAnn ArborUnited States
| | - Brenda G Byrne
- Department of Microbiology and Immunology, University of MichiganAnn ArborUnited States
| | - Min Su
- Life Sciences Institute, University of MichiganAnn ArborUnited States
| | - Thomas Knight
- Department of Microbiology and Immunology, University of MichiganAnn ArborUnited States
| | - Michele Swanson
- Department of Microbiology and Immunology, University of MichiganAnn ArborUnited States
| | - D Borden Lacy
- Department of Pathology, Microbiology, and Immunology, Department of Pathology, Vanderbilt University Medical CenterNashvilleUnited States
- The Veterans Affairs Tennessee Valley Healthcare SystemNashvilleUnited States
- Department of Cell and Developmental Biology, University of MichiganAnn ArborUnited States
| | - Melanie D Ohi
- Life Sciences Institute, University of MichiganAnn ArborUnited States
| |
Collapse
|
4
|
Navarro-Garcia F, Ruiz-Perez F, Cataldi Á, Larzábal M. Type VI Secretion System in Pathogenic Escherichia coli: Structure, Role in Virulence, and Acquisition. Front Microbiol 2019; 10:1965. [PMID: 31543869 PMCID: PMC6730261 DOI: 10.3389/fmicb.2019.01965] [Citation(s) in RCA: 71] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2019] [Accepted: 08/09/2019] [Indexed: 12/18/2022] Open
Abstract
Bacterial pathogens utilize a myriad of mechanisms to invade mammalian hosts, damage tissue sites, and evade the immune system. One essential strategy of Gram-negative bacteria is the secretion of virulence factors through both inner and outer membranes to reach a potential target. Most secretion systems are harbored in mobile elements including transposons, plasmids, pathogenicity islands, and phages, and Escherichia coli is one of the more versatile bacteria adopting this genetic information by horizontal gene transfer. Additionally, E. coli is a bacterial species with members of the commensal intestinal microbiota and pathogens associated with numerous types of infections such as intestinal, urinary, and systemic in humans and other animals. T6SS cluster plasticity suggests evolutionarily divergent systems were acquired horizontally. T6SS is a secretion nanomachine that is extended through the bacterial double membrane; from this apparatus, substrates are conveyed straight from the cytoplasm of the bacterium into a target cell or to the extracellular space. This nanomachine consists of three main complexes: proteins in the inner membrane that are T4SS component-like, the baseplate complex, and the tail complex, which are formed by components evolutionarily related to contractile bacteriophage tails. Advances in the T6SS understanding include the functional and structural characterization of at least 13 subunits (so-called core components), which are thought to comprise the minimal apparatus. So far, the main role of T6SS is on bacterial competition by using it to kill neighboring non-immune bacteria for which antibacterial proteins are secreted directly into the periplasm of the bacterial target after cell-cell contact. Interestingly, a few T6SSs have been associated directly to pathogenesis, e.g., roles in biofilm formation and macrophage survival. Here, we focus on the advances on T6SS from the perspective of E. coli pathotypes with emphasis in the secretion apparatus architecture, the mechanisms of pathogenicity of effector proteins, and the events of lateral gene transfer that led to its spread.
Collapse
Affiliation(s)
- Fernando Navarro-Garcia
- Department of Cell Biology, Centro de Investigación y de Estudios Avanzados del IPN (CINVESTAV-IPN), Mexico City, Mexico
| | - Fernando Ruiz-Perez
- Department of Pediatrics, University of Virginia School of Medicine, Charlottesville, VA, United States
| | - Ángel Cataldi
- Laboratorio de Escherichia coli, Instituto de Agrobiotecnología y Biología Molecular (IABIMO) INTA-CONICET, Buenos Aires, Argentina
| | - Mariano Larzábal
- Laboratorio de Escherichia coli, Instituto de Agrobiotecnología y Biología Molecular (IABIMO) INTA-CONICET, Buenos Aires, Argentina
| |
Collapse
|
5
|
Christie PJ, Gomez Valero L, Buchrieser C. Biological Diversity and Evolution of Type IV Secretion Systems. Curr Top Microbiol Immunol 2019; 413:1-30. [PMID: 29536353 PMCID: PMC5912172 DOI: 10.1007/978-3-319-75241-9_1] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The bacterial type IV secretion systems (T4SSs) are a highly functionally and structurally diverse superfamily of secretion systems found in many species of Gram-negative and -positive bacteria. Collectively, the T4SSs can translocate DNA and monomeric and multimeric protein substrates to a variety of bacterial and eukaryotic cell types. Detailed phylogenomics analyses have established that the T4SSs evolved from ancient conjugation machines whose original functions were to disseminate mobile DNA elements within and between bacterial species. How members of the T4SS superfamily evolved to recognize and translocate specific substrate repertoires to prokaryotic or eukaryotic target cells is a fascinating question from evolutionary, biological, and structural perspectives. In this chapter, we will summarize recent findings that have shaped our current view of the biological diversity of the T4SSs. We focus mainly on two subtypes, designated as the types IVA (T4ASS) and IVB (T4BSS) systems that respectively are represented by the paradigmatic Agrobacterium tumefaciens VirB/VirD4 and Legionella pneumophila Dot/Icm T4SSs. We present current information about the composition and architectures of these representative systems. We also describe how these and a few related T4ASS and T4BSS members evolved as specialized nanomachines through acquisition of novel domains or subunits, a process that ultimately generated extensive genetic and structural mosaicism among this secretion superfamily. Finally, we present new phylogenomics information establishing that the T4BSSs are much more broadly distributed than initially envisioned.
Collapse
Affiliation(s)
- Peter J Christie
- Department of Microbiology and Molecular Genetics, McGovern Medical School, 6431 Fannin St, Houston, TX, 77030, USA.
| | - Laura Gomez Valero
- Institut Pasteur, Biologie des Bactéries Intracellulaires, 75724, Paris, France
- CNRS, UMR 3525, 75724, Paris, France
| | - Carmen Buchrieser
- Institut Pasteur, Biologie des Bactéries Intracellulaires, 75724, Paris, France
- CNRS, UMR 3525, 75724, Paris, France
| |
Collapse
|
6
|
Mancilla M, Saavedra J, Grandón M, Tapia E, Navas E, Grothusen H, Bustos P. The mutagenesis of a type IV secretion system locus of Piscirickettsia salmonis leads to the attenuation of the pathogen in Atlantic salmon, Salmo salar. JOURNAL OF FISH DISEASES 2018; 41:625-634. [PMID: 29251345 DOI: 10.1111/jfd.12762] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2017] [Revised: 11/06/2017] [Accepted: 11/10/2017] [Indexed: 06/07/2023]
Abstract
Piscirickettsiosis is a threatening infectious disease for the salmon industry, due to it being responsible for significant economic losses. The control of outbreaks also poses considerable environmental challenges. Despite Piscirickettsia salmonis having been discovered as the aetiological agent of the disease more than 25 years ago, its pathogenicity remains poorly understood. Among virulence factors identified so far, type four secretion systems (T4SS) seem to play a key role during the infection caused by the bacterium. We report here the genetic manipulation of P. salmonis by means of the transference of plasmid DNA in mating assays. An insertion cassette was engineered for targeting the icmB gene, which encodes a putative T4SS-ATPase and is carried by one of the chromosomal T4SS clusters found within the genome of P. salmonis PM15972A1, a virulent representative of the EM-90-like strain. The molecular characterization of the resulting mutant strain demonstrated that the insertion interrupted the target gene. Further in vitro testing of the icmB mutant showed a dramatic drop in infectivity as tested in CHSE-214 cells, which is in agreement with its attenuated behaviour observed in vivo. Altogether, our results demonstrate that, similar to other facultative intracellular pathogens, P. salmonis' virulence relies on an intact T4SS.
Collapse
Affiliation(s)
- M Mancilla
- Laboratorio de Diagnóstico y Biotecnología, ADL Diagnostic Chile, Puerto Montt, Chile
| | - J Saavedra
- Laboratorio de Diagnóstico y Biotecnología, ADL Diagnostic Chile, Puerto Montt, Chile
| | - M Grandón
- Laboratorio de Diagnóstico y Biotecnología, ADL Diagnostic Chile, Puerto Montt, Chile
| | - E Tapia
- Laboratorio de Diagnóstico y Biotecnología, ADL Diagnostic Chile, Puerto Montt, Chile
| | - E Navas
- Laboratorio de Diagnóstico y Biotecnología, ADL Diagnostic Chile, Puerto Montt, Chile
| | - H Grothusen
- Laboratorio de Diagnóstico y Biotecnología, ADL Diagnostic Chile, Puerto Montt, Chile
| | - P Bustos
- Laboratorio de Diagnóstico y Biotecnología, ADL Diagnostic Chile, Puerto Montt, Chile
| |
Collapse
|
7
|
Population structure and minimum core genome typing of Legionella pneumophila. Sci Rep 2016; 6:21356. [PMID: 26888563 PMCID: PMC4766850 DOI: 10.1038/srep21356] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2015] [Accepted: 01/12/2016] [Indexed: 01/28/2023] Open
Abstract
Legionella pneumophila is an important human pathogen causing Legionnaires’ disease. In this study, whole genome sequencing (WGS) was used to study the characteristics and population structure of L. pneumophila strains. We sequenced and compared 53 isolates of L. pneumophila covering different serogroups and sequence-based typing (SBT) types (STs). We found that 1,896 single-copy orthologous genes were shared by all isolates and were defined as the minimum core genome (MCG) of L. pneumophila. A total of 323,224 single-nucleotide polymorphisms (SNPs) were identified among the 53 strains. After excluding 314,059 SNPs which were likely to be results of recombination, the remaining 9,165 SNPs were referred to as MCG SNPs. Population Structure analysis based on MCG divided the 53 L. pneumophila into nine MCG groups. The within-group distances were much smaller than the between-group distances, indicating considerable divergence between MCG groups. MCG groups were also supplied by phylogenetic analysis and may be considered as robust taxonomic units within L. pneumophila. Among the nine MCG groups, eight showed high intracellular growth ability while one showed low intracellular growth ability. Furthermore, MCG typing also showed high resolution in subtyping ST1 strains. The results obtained in this study provided significant insights into the evolution, population structure and pathogenicity of L. pneumophila.
Collapse
|
8
|
Kubori T, Nagai H. The Type IVB secretion system: an enigmatic chimera. Curr Opin Microbiol 2016; 29:22-9. [DOI: 10.1016/j.mib.2015.10.001] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2015] [Revised: 10/14/2015] [Accepted: 10/15/2015] [Indexed: 10/22/2022]
|
9
|
Nagai H. [Host-pathogen interaction of Legionella pneumophila]. Nihon Saikingaku Zasshi 2015; 69:503-11. [PMID: 25186641 DOI: 10.3412/jsb.69.503] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Legionella are gram-negative bacteria ubiquitously found in freshwater and soil environments. Once inhaled by humans, Legionella infection could result in a severe form of pneumonia known as Legionellosis. Legionella translocate ~300 effector proteins into host cells via the Dot/Icm type IV secretion system, which is central to Legionella pathogenesis. Here I describe a brief review on recent advances in research on the molecular basis of Legionella-eukaryotic-cell interaction.
Collapse
Affiliation(s)
- Hiroki Nagai
- International Research Center for Infectious Diseases, Research Institute for Microbial Diseases, Osaka University
| |
Collapse
|
10
|
Native structure of a type IV secretion system core complex essential for Legionella pathogenesis. Proc Natl Acad Sci U S A 2014; 111:11804-9. [PMID: 25062693 DOI: 10.1073/pnas.1404506111] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Bacterial type IV secretion systems are evolutionarily related to conjugation systems and play a pivotal role in infection by delivering numerous virulence factors into host cells. Using transmission electron microscopy, we report the native molecular structure of the core complex of the Dot/Icm type IV secretion system encoded by Legionella pneumophila, an intracellular human pathogen. The biochemically isolated core complex, composed of at least five proteins--DotC, DotD, DotF, DotG, and DotH--has a ring-shaped structure. Intriguingly, morphologically distinct premature complexes are formed in the absence of DotG or DotF. Our data suggest that DotG forms a central channel spanning inner and outer membranes. DotF, a component dispensable for type IV secretion, plays a role in efficient embedment of DotG into the functional core complex. These results highlight a common scheme for the biogenesis of transport machinery.
Collapse
|
11
|
Reassessing the role of DotF in the Legionella pneumophila type IV secretion system. PLoS One 2013; 8:e65529. [PMID: 23762385 PMCID: PMC3676331 DOI: 10.1371/journal.pone.0065529] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2013] [Accepted: 04/29/2013] [Indexed: 11/19/2022] Open
Abstract
Legionella pneumophila, the causative agent of a severe pneumonia termed Legionnaires’ Disease, survives and replicates within both protozoan hosts and human alveolar macrophages. Intracellular survival is dependent upon secretion of a plethora of protein effectors that function to form a replicative vacuole, evade the endocytic pathway and subvert host immune defenses. Export of these factors requires a type IV secretion system (T4SS) called Dot/Icm that is composed of twenty-seven proteins. This report focuses on the DotF protein, which was previously postulated to have several different functions, one of which centered on binding Dot/Icm substrates. In this report, we examined if DotF functions as the T4SS inner membrane receptor for Dot/Icm substrates. Although we were able to recapitulate the previously published bacterial two-hybrid interaction between DotF and several substrates, the interaction was not dependent on the Dot/Icm substrates’ signal sequences as predicted for a substrate:receptor interaction. In addition, binding did not require the cytoplasmic domain of DotF, which was anticipated to be involved in recognizing substrates in the cytoplasm. Finally, inactivation of dotF did not abolish intracellular growth of L. pneumophila or translocation of substrates, two phenotypes dependent on the T4SS receptor. These data strongly suggest that DotF does not act as the major receptor for Dot/Icm substrates and therefore likely performs an accessory function within the core-transmembrane subcomplex of the L. pneumophila Dot/Icm type IV secretion system.
Collapse
|
12
|
A Type VI secretion system encoding locus is required for Bordetella bronchiseptica immunomodulation and persistence in vivo. PLoS One 2012; 7:e45892. [PMID: 23071529 PMCID: PMC3470547 DOI: 10.1371/journal.pone.0045892] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Accepted: 08/27/2012] [Indexed: 11/19/2022] Open
Abstract
Type VI Secretion Systems (T6SSs) have been identified in numerous Gram-negative pathogens, but the lack of a natural host infection model has limited analysis of T6SS contributions to infection and pathogenesis. Here, we describe disruption of a gene within locus encoding a putative T6SS in Bordetella bronchiseptica strain RB50, a respiratory pathogen that circulates in a broad range of mammals, including humans, domestic animals, and mice. The 26 gene locus encoding the B. bronchiseptica T6SS contains apparent orthologs to all known core genes and possesses thirteen novel genes. By generating an in frame deletion of clpV, which encodes a putative ATPase required for some T6SS-dependent protein secretion, we observe that ClpV contributes to in vitro macrophage cytotoxicity while inducing several eukaryotic proteins associated with apoptosis. Additionally, ClpV is required for induction of IL-1β, IL-6, IL-17, and IL-10 production in J774 macrophages infected with RB50. During infections in wild type mice, we determined that ClpV contributes to altered cytokine production, increased pathology, delayed lower respiratory tract clearance, and long term nasal cavity persistence. Together, these results reveal a natural host infection system in which to interrogate T6SS contributions to immunomodulation and pathogenesis.
Collapse
|
13
|
Putative type VI secretion systems of Vibrio parahaemolyticus contribute to adhesion to cultured cell monolayers. Arch Microbiol 2012; 194:827-35. [DOI: 10.1007/s00203-012-0816-z] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2011] [Revised: 04/01/2012] [Accepted: 04/12/2012] [Indexed: 12/14/2022]
|
14
|
Qin T, Iida KI, Piao Z, Shiota S, Ren H, Shao Z, Yoshida SI. Importance of the icmN gene in the growth of Legionella pneumophila in amoebic cells at low temperature. Can J Microbiol 2012; 58:490-501. [PMID: 22435730 DOI: 10.1139/w2012-011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Legionella pneumophila grows in amoebae and has achieved the ability to grow at various temperatures, although the mechanisms controlling this ability remain poorly understood. The Icm/Dot type IVB secretion system is composed of more than 25 proteins and is known to be essential for intracellular growth. The role of the icmN gene in intracellular multiplication and the effects of culture temperatures on it are not precisely understood. We conducted our investigation using an icmN mutant made by gene replacement mutagenesis. Intracellular growth of the mutant was impaired both in mammalian macrophages and amoeba at 37 °C. In particular, intracellular growth in amoebae was completely impaired at 25 °C. It was found that genes from icmN to icmC formed an operon, i.e., icmN, -M, -L, -E, -G, -C,, and the promoter activity of the icmN operon was stronger at 25 than at 37 °C. It was suggested that icmM and its downstream genes had a secondary promoter that enables icmN mutant grow in amoebae at lower temperatures and macrophages at 37 °C. These results show that the icmN promoter has a low temperature inducible nature, and gene products of the icmN operon require high expression for bacterial proliferation at low temperatures within amoeba.
Collapse
Affiliation(s)
- Tian Qin
- Department of Bacteriology, Division of Oral Infectious Diseases and Immunology, Kyushu University, Higashi-ku, Fukuoka 812-8582, Japan.
| | | | | | | | | | | | | |
Collapse
|
15
|
de Pace F, Boldrin de Paiva J, Nakazato G, Lancellotti M, Sircili MP, Guedes Stehling E, Dias da Silveira W, Sperandio V. Characterization of IcmF of the type VI secretion system in an avian pathogenic Escherichia coli (APEC) strain. MICROBIOLOGY (READING, ENGLAND) 2011. [PMID: 21778203 DOI: 10.1099/mic.0.050005–0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The intracellular multiplication factor (IcmF) protein is a component of the recently described type VI secretion system (T6SS). IcmF has been shown to be required for intra-macrophage replication and inhibition of phagosome-lysosome fusion in Legionella pneumophila. In Vibrio cholerae it is involved in motility, adherence and conjugation. Given that we previously reported that two T6SS genes (hcp and clpV) contribute to the pathogenesis of a septicaemic strain (SEPT362) of avian pathogenic Escherichia coli (APEC), we investigated the function of IcmF in this strain. Further elucidation of the virulence mechanisms of APEC is important because this pathogen is responsible for financial losses in the poultry industry, and is closely related to human extraintestinal pathogenic E. coli (ExPEC) strains, representing a potential zoonotic risk, as well as serving as a reservoir of virulence genes. Here we show that an APEC icmF mutant has decreased adherence to and invasion of epithelial cells, as well as decreased intra-macrophage survival. The icmF mutant is also defective for biofilm formation on abiotic surfaces. Additionally, expression of the flagella operon is decreased in the icmF mutant, leading to decreased motility. The combination of these phenotypes culminates in this mutant being altered for infection in chicks. These results suggest that IcmF in APEC may play a role in disease, and potentially also in the epidemiological spread of this pathogen through enhancement of biofilm formation.
Collapse
Affiliation(s)
- Fernanda de Pace
- Department of Genetics, Evolution and Bioagents, Institute of Biology, State University of Campinas - Unicamp, Campinas, SP CP6109, Brazil
| | - Jacqueline Boldrin de Paiva
- Department of Genetics, Evolution and Bioagents, Institute of Biology, State University of Campinas - Unicamp, Campinas, SP CP6109, Brazil
| | | | - Marcelo Lancellotti
- Department of Biochemistry, Institute of Biology, State University of Campinas - Unicamp, Campinas, SP CP6109, Brazil
| | | | - Eliana Guedes Stehling
- Department of Genetics, Evolution and Bioagents, Institute of Biology, State University of Campinas - Unicamp, Campinas, SP CP6109, Brazil
| | - Wanderley Dias da Silveira
- Department of Genetics, Evolution and Bioagents, Institute of Biology, State University of Campinas - Unicamp, Campinas, SP CP6109, Brazil
| | - Vanessa Sperandio
- University of Texas Southwestern Medical Center, Dallas, TX 75390-9048, USA
| |
Collapse
|
16
|
Abstract
Central to Q fever pathogenesis is replication of the causative agent, Coxiella burnetii, within a phagolysosome-like parasitophorous vacuole (PV) in mononuclear phagocytes. C. burnetii modulates PV biogenesis and other host cell functions, such as apoptotic signaling, presumably via the activity of proteins delivered to the host cytosol by a Dot/Icm type IVB secretion system (T4BSS). In this study, we utilized a C. burnetii strain carrying IcmD inactivated by the Himar1 transposon to investigate the requirements for Dot/Icm function in C. burnetii parasitism of human THP-1 macrophage-like cells. The icmD::Tn mutant failed to secrete characterized T4BSS substrates, a defect that correlated with deficient replication, PV development, and apoptosis protection. Restoration of type IVB secretion and intracellular growth of the icmD::Tn mutant required complementation with icmD, -J, and -B, indicating a polar effect of the transposon insertion on downstream dot/icm genes. Induction of icmDJB expression at 1 day postinfection resulted in C. burnetii replication and PV generation. Collectively, these data prove that T4BSS function is required for productive infection of human macrophages by C. burnetii. However, illustrating the metabolic flexibility of C. burnetti, the icmD::Tn mutant could replicate intracellularly when sequestered in a PV generated by wild-type bacteria, where Dot/Icm function is provided in trans, and within a phenotypically similar PV generated by the protozoan parasite Leishmania amazonensis, where host cells are devoid of Dot/Icm T4BSS effector proteins. Coxiella burnetii, the cause of human Q fever, is the only bacterial pathogen known to replicate in a vacuole resembling a phagolysosome. The organism manipulates host macrophages to promote the biogenesis of a vacuolar compartment permissive for growth. By analogy to the well-established cellular microbiology of Legionella pneumophila, the Dot/Icm type IVB secretion system of C. burnetii is implicated as a critical virulence factor in host cell modification that delivers proteins with effector functions directly into the host cell cytosol. Using new genetic tools, we verify that Dot/Icm function is essential for productive infection of human macrophages by C. burnetii. Interestingly, despite the production of homologous secretion systems, L. pneumophila and C. burnetii have strikingly different temporal requirements for Dot/Icm function during their respective infectious cycles.
Collapse
|
17
|
de Pace F, Boldrin de Paiva J, Nakazato G, Lancellotti M, Sircili MP, Guedes Stehling E, Dias da Silveira W, Sperandio V. Characterization of IcmF of the type VI secretion system in an avian pathogenic Escherichia coli (APEC) strain. MICROBIOLOGY-SGM 2011; 157:2954-2962. [PMID: 21778203 DOI: 10.1099/mic.0.050005-0] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The intracellular multiplication factor (IcmF) protein is a component of the recently described type VI secretion system (T6SS). IcmF has been shown to be required for intra-macrophage replication and inhibition of phagosome-lysosome fusion in Legionella pneumophila. In Vibrio cholerae it is involved in motility, adherence and conjugation. Given that we previously reported that two T6SS genes (hcp and clpV) contribute to the pathogenesis of a septicaemic strain (SEPT362) of avian pathogenic Escherichia coli (APEC), we investigated the function of IcmF in this strain. Further elucidation of the virulence mechanisms of APEC is important because this pathogen is responsible for financial losses in the poultry industry, and is closely related to human extraintestinal pathogenic E. coli (ExPEC) strains, representing a potential zoonotic risk, as well as serving as a reservoir of virulence genes. Here we show that an APEC icmF mutant has decreased adherence to and invasion of epithelial cells, as well as decreased intra-macrophage survival. The icmF mutant is also defective for biofilm formation on abiotic surfaces. Additionally, expression of the flagella operon is decreased in the icmF mutant, leading to decreased motility. The combination of these phenotypes culminates in this mutant being altered for infection in chicks. These results suggest that IcmF in APEC may play a role in disease, and potentially also in the epidemiological spread of this pathogen through enhancement of biofilm formation.
Collapse
Affiliation(s)
- Fernanda de Pace
- Department of Genetics, Evolution and Bioagents, Institute of Biology, State University of Campinas - Unicamp, Campinas, SP CP6109, Brazil
| | - Jacqueline Boldrin de Paiva
- Department of Genetics, Evolution and Bioagents, Institute of Biology, State University of Campinas - Unicamp, Campinas, SP CP6109, Brazil
| | | | - Marcelo Lancellotti
- Department of Biochemistry, Institute of Biology, State University of Campinas - Unicamp, Campinas, SP CP6109, Brazil
| | | | - Eliana Guedes Stehling
- Department of Genetics, Evolution and Bioagents, Institute of Biology, State University of Campinas - Unicamp, Campinas, SP CP6109, Brazil
| | - Wanderley Dias da Silveira
- Department of Genetics, Evolution and Bioagents, Institute of Biology, State University of Campinas - Unicamp, Campinas, SP CP6109, Brazil
| | - Vanessa Sperandio
- University of Texas Southwestern Medical Center, Dallas, TX 75390-9048, USA
| |
Collapse
|
18
|
Nagai H, Kubori T. Type IVB Secretion Systems of Legionella and Other Gram-Negative Bacteria. Front Microbiol 2011; 2:136. [PMID: 21743810 PMCID: PMC3127085 DOI: 10.3389/fmicb.2011.00136] [Citation(s) in RCA: 114] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2011] [Accepted: 06/11/2011] [Indexed: 12/03/2022] Open
Abstract
Type IV secretion systems (T4SSs) play a central role in the pathogenicity of many important pathogens, including Agrobacterium tumefaciens, Helicobacter pylori, and Legionella pneumophila. The T4SSs are related to bacterial conjugation systems, and are classified into two subgroups, type IVA (T4ASS) and type IVB (T4BSS). The T4BSS, which is closely related to conjugation systems of IncI plasmids, was originally found in human pathogen L. pneumophila; pathogenesis by L. pneumophila infection requires functional Dot/Icm T4BSS. A zoonotic pathogen, Coxiella burnetii, and an arthropod pathogen, Rickettsiella grylli – both of which carry T4BSSs highly similar to the Legionella Dot/Icm system – are evolutionarily closely related and comprise a monophyletic group. A growing body of bacterial genomic information now suggests that T4BSSs are not limited to Legionella and related bacteria and IncI plasmids. Here, we review the current knowledge on T4BSS apparatus and component proteins, gained mainly from studies on L. pneumophila Dot/Icm T4BSS. Recent structural studies, along with previous findings, suggest that the Dot/Icm T4BSS contains components with primary or higher-order structures similar to those in other types of secretion systems – types II, III, IVA, and VI, thus highlighting the mosaic nature of T4BSS architecture.
Collapse
Affiliation(s)
- Hiroki Nagai
- Research Institute for Microbial Diseases, Osaka University Osaka, Japan
| | | |
Collapse
|
19
|
Al-Quadan T, Kwaik YA. Molecular Characterization of Exploitation of the Polyubiquitination and Farnesylation Machineries of Dictyostelium Discoideum by the AnkB F-Box Effector of Legionella Pneumophila. Front Microbiol 2011; 2:23. [PMID: 21687415 PMCID: PMC3109286 DOI: 10.3389/fmicb.2011.00023] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2011] [Accepted: 01/31/2011] [Indexed: 01/15/2023] Open
Abstract
The Dot/Icm-translocated Ankyrin B (AnkB) F-box effector of Legionella pneumophila is essential for intra-vacuolar proliferation and functions as a platform for the docking of polyubiquitinated proteins to the Legionella-containing vacuole (LCV) within macrophages and ameba. Here we show that ectopically expressed AnkB in Dictyostelium discoideum is targeted to the plasma membrane where it recruits polyubiquitinated proteins and it trans-rescues the intracellular growth defect of the ankB null mutant, which has never been demonstrated for any effector in ameba. Using co-immunoprecipitation and bimolecular fluorescence complementation we show specific interaction of Skp1 of D. discoideum with the F-box domain of AnkB, which has never been demonstrated in ameba. We show that anchoring of AnkB to the cytosolic face of the LCV membrane in D. discoideum is mediated by the host farnesylation of the C-terminal eukaryotic CaaX motif of AnkB and is independent of the F-box and the two ANK domains, which has never been demonstrated in ameba. Importantly, the three host farnesylation enzymes farnesyl transferase, RCE-1, and isoprenyl cysteine carboxyl methyl transferase of D. discoideum are recruited to the LCV in a Dot/Icm-dependent manner, which has never been demonstrated in ameba. We conclude that the polyubiquitination and farnesylation enzymatic machineries of D. discoideum are recruited to the LCV in a Dot/Icm-dependent manner and the AnkB effector exploits the two evolutionarily conserved eukaryotic machineries to proliferate within ameba, similar to mammalian cells. We propose that L. pneumophila has acquired ankB through inter-kingdom horizontal gene transfer from primitive eukaryotes, which facilitated proliferation of L. pneumophila within human cells and the emergence of Legionnaires’ disease.
Collapse
Affiliation(s)
- Tasneem Al-Quadan
- Department of Microbiology and Immunology, College of Medicine, University of Louisville Louisville, KY, USA
| | | |
Collapse
|
20
|
Abstract
The genus Legionella contains more than 50 species, of which at least 24 have been associated with human infection. The best-characterized member of the genus, Legionella pneumophila, is the major causative agent of Legionnaires' disease, a severe form of acute pneumonia. L. pneumophila is an intracellular pathogen, and as part of its pathogenesis, the bacteria avoid phagolysosome fusion and replicate within alveolar macrophages and epithelial cells in a vacuole that exhibits many characteristics of the endoplasmic reticulum (ER). The formation of the unusual L. pneumophila vacuole is a feature of its interaction with the host, yet the mechanisms by which the bacteria avoid classical endosome fusion and recruit markers of the ER are incompletely understood. Here we review the factors that contribute to the ability of L. pneumophila to infect and replicate in human cells and amoebae with an emphasis on proteins that are secreted by the bacteria into the Legionella vacuole and/or the host cell. Many of these factors undermine eukaryotic trafficking and signaling pathways by acting as functional and, in some cases, structural mimics of eukaryotic proteins. We discuss the consequences of this mimicry for the biology of the infected cell and also for immune responses to L. pneumophila infection.
Collapse
|
21
|
Moliner C, Fournier PE, Raoult D. Genome analysis of microorganisms living in amoebae reveals a melting pot of evolution. FEMS Microbiol Rev 2010. [DOI: 10.1111/j.1574-6976.2009.00209.x] [Citation(s) in RCA: 130] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
|
22
|
Weber B, Hasic M, Chen C, Wai SN, Milton DL. Type VI secretion modulates quorum sensing and stress response in Vibrio anguillarum. Environ Microbiol 2009; 11:3018-28. [PMID: 19624706 DOI: 10.1111/j.1462-2920.2009.02005.x] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Type VI protein secretion systems (T6SS) are essential for virulence of several Gram-negative bacteria. In this study, we identified a T6SS in Vibrio anguillarum, a marine bacterium that causes a hemorrhagic septicemia in fish. A partial operon vtsA-H (vibrio type six secretion) was sequenced and shown to encode eight proteins. VtsE-H are signature proteins found in other T6SSs, while VtsA-D are not associated with T6SS studied so far. In-frame deletions were made in each gene. Secretion of a haemolysin-co-regulated-like protein (Hcp), a protein secreted by all studied T6SSs, was decreased in VtsE-H. Unexpectedly, VtsA, VtsC and VtsD activated while VtsB and VtsE-H repressed hcp expression. The T6SS proteins also regulated expression of two extracellular proteases, EmpA and PrtV, but inversely to Hcp expression. This regulation was indirect as T6S positively regulated expression of the stress-response regulator RpoS and the quorum-sensing regulator VanT, which positively regulate protease expression. Moreover, VtsA-H proteins were not needed for virulence but did play a role in various stress responses. Thus, these data characterize a new role for T6S in the ecology of bacteria and we hypothesize this role to be a signal sensing mechanism that modulates the expression of regulators of the general stress response.
Collapse
Affiliation(s)
- Barbara Weber
- Department of Molecular Biology, Umeå University, S-901 87 Umeå, Sweden
| | | | | | | | | |
Collapse
|
23
|
|
24
|
Filloux A, Hachani A, Bleves S. The bacterial type VI secretion machine: yet another player for protein transport across membranes. MICROBIOLOGY-SGM 2008; 154:1570-1583. [PMID: 18524912 DOI: 10.1099/mic.0.2008/016840-0] [Citation(s) in RCA: 270] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Several secretion systems have evolved that are widespread among Gram-negative bacteria. Recently, a new secretion system was recognized, which is named the type VI secretion system (T6SS). The T6SS components are encoded within clusters of genes initially identified as IAHP for IcmF-associated homologous proteins, since they were all found to contain a gene encoding an IcmF-like component. IcmF was previously reported as a component of the type IV secretion system (T4SS). However, with the exception of DotU, other T4SS components are not encoded within T6SS loci. Thus, the T6SS is probably a novel kind of complex multi-component secretion machine, which is often involved in interaction with eukaryotic hosts, be it a pathogenic or a symbiotic relationship. The expression of T6SS genes has been reported to be mostly induced in vivo. Interestingly, expression and assembly of T6SSs are tightly controlled at both the transcriptional and the post-translational level. This may allow a timely control of T6SS assembly and function. Two types of proteins, generically named Hcp and VgrG, are secreted via these systems, but it is not entirely clear whether they are truly secreted effector proteins or are actually components of the T6SS. The precise role and mode of action of the T6SS is still unknown. This review describes current knowledge about the T6SS and summarizes its hallmarks and its differences from other secretion systems.
Collapse
Affiliation(s)
- Alain Filloux
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires, UPR9027, CNRS-IBSM, 31 Chemin Joseph Aiguier, 13402 Marseille cedex 20, France.,Imperial College London, Division of Cell and Molecular Biology, Centre for Molecular Microbiology and Infection, South Kensington Campus, Flowers Building, London SW7 2AZ, UK
| | - Abderrahman Hachani
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires, UPR9027, CNRS-IBSM, 31 Chemin Joseph Aiguier, 13402 Marseille cedex 20, France.,Imperial College London, Division of Cell and Molecular Biology, Centre for Molecular Microbiology and Infection, South Kensington Campus, Flowers Building, London SW7 2AZ, UK
| | - Sophie Bleves
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires, UPR9027, CNRS-IBSM, 31 Chemin Joseph Aiguier, 13402 Marseille cedex 20, France
| |
Collapse
|
25
|
Bingle LE, Bailey CM, Pallen MJ. Type VI secretion: a beginner's guide. Curr Opin Microbiol 2008; 11:3-8. [PMID: 18289922 DOI: 10.1016/j.mib.2008.01.006] [Citation(s) in RCA: 425] [Impact Index Per Article: 26.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2007] [Revised: 01/16/2008] [Accepted: 01/18/2008] [Indexed: 10/22/2022]
Abstract
Type VI secretion is a newly described mechanism for protein transport across the cell envelope of Gram-negative bacteria. Components that have been partially characterised include an IcmF homologue, the ATPase ClpV, a regulatory FHA domain protein and the secreted VgrG and Hcp proteins. Type VI secretion is clearly a key virulence factor for some important pathogenic bacteria and has been implicated in the translocation of a potential effector protein into eukaryotic cells by at least one organism (Vibrio cholerae). However, type VI secretion systems (T6SSs) are widespread in nature and not confined to known pathogens. In accordance with the general rule that the expression of protein secretion systems is tightly regulated, expression of type VI secretion is controlled at both transcriptional and post-transcriptional levels.
Collapse
Affiliation(s)
- Lewis Eh Bingle
- Centre for Systems Biology, University of Birmingham, Edgbaston, Birmingham, UK.
| | | | | |
Collapse
|
26
|
Bandyopadhyay P, Liu S, Gabbai CB, Venitelli Z, Steinman HM. Environmental mimics and the Lvh type IVA secretion system contribute to virulence-related phenotypes of Legionella pneumophila. Infect Immun 2006; 75:723-35. [PMID: 17101653 PMCID: PMC1828514 DOI: 10.1128/iai.00956-06] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Legionella pneumophila, the causative organism of Legionnaires' disease, is a fresh-water bacterium and intracellular parasite of amoebae. This study examined the effects of incubation in water and amoeba encystment on L. pneumophila strain JR32 and null mutants in dot/icm genes encoding a type IVB secretion system required for entry, delayed acidification of L. pneumophila-containing phagosomes, and intracellular multiplication when stationary-phase bacteria infect amoebae and macrophages. Following incubation of stationary-phase cultures in water, mutants in dotA and dotB, essential for function of the type IVB secretion system, exhibited entry and delay of phagosome acidification comparable to that of strain JR32. Following encystment in Acanthamoeba castellanii and reversion of cysts to amoeba trophozoites, dotA and dotB mutants exhibited intracellular multiplication in amoebae. The L. pneumophila Lvh locus, encoding a type IVA secretion system homologous to that in Agrobacterium tumefaciens, was required for restoration of entry and intracellular multiplication in dot/icm mutants following incubation in water and amoeba encystment and was required for delay of phagosome acidification in strain JR32. These data support a model in which the Dot/Icm type IVB secretion system is conditionally rather than absolutely required for L. pneumophila virulence-related phenotypes. The data suggest that the Lvh type IVA secretion system, previously thought to be dispensable, is involved in virulence-related phenotypes under conditions mimicking the spread of Legionnaires' disease from environmental niches. Since environmental amoebae are implicated as reservoirs for an increasing number of environmental pathogens and for drug-resistant bacteria, the environmental mimics developed here may be useful in virulence studies of other pathogens.
Collapse
Affiliation(s)
- Purnima Bandyopadhyay
- Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, USA
| | | | | | | | | |
Collapse
|
27
|
Brzuszkiewicz E, Brüggemann H, Liesegang H, Emmerth M, Ölschläger T, Nagy G, Albermann K, Wagner C, Buchrieser C, Emődy L, Gottschalk G, Hacker J, Dobrindt U. How to become a uropathogen: comparative genomic analysis of extraintestinal pathogenic Escherichia coli strains. Proc Natl Acad Sci U S A 2006; 103:12879-84. [PMID: 16912116 PMCID: PMC1568941 DOI: 10.1073/pnas.0603038103] [Citation(s) in RCA: 256] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2006] [Indexed: 01/16/2023] Open
Abstract
Uropathogenic Escherichia coli (UPEC) strain 536 (O6:K15:H31) is one of the model organisms of extraintestinal pathogenic E. coli (ExPEC). To analyze this strain's genetic basis of urovirulence, we sequenced the entire genome and compared the data with the genome sequence of UPEC strain CFT073 (O6:K2:H1) and to the available genomes of nonpathogenic E. coli strain MG1655 (K-12) and enterohemorrhagic E. coli. The genome of strain 536 is approximately 292 kb smaller than that of strain CFT073. Genomic differences between both UPEC are mainly restricted to large pathogenicity islands, parts of which are unique to strain 536 or CFT073. Genome comparison underlines that repeated insertions and deletions in certain parts of the genome contribute to genome evolution. Furthermore, 427 and 432 genes are only present in strain 536 or in both UPEC, respectively. The majority of the latter genes is encoded within smaller horizontally acquired DNA regions scattered all over the genome. Several of these genes are involved in increasing the pathogens' fitness and adaptability. Analysis of virulence-associated traits expressed in the two UPEC O6 strains, together with genome comparison, demonstrate the marked genetic and phenotypic variability among UPEC. The ability to accumulate and express a variety of virulence-associated genes distinguishes ExPEC from many commensals and forms the basis for the individual virulence potential of ExPEC. Accordingly, instead of a common virulence mechanism, different ways exist among ExPEC to cause disease.
Collapse
Affiliation(s)
- Elzbieta Brzuszkiewicz
- *Göttingen Genomics Laboratory, Institute of Microbiology and Genetics, Georg-August-Universität Göttingen, Grisebachstrasse 8, 37077 Göttingen, Germany
- Institute for Molecular Biology of Infectious Diseases, Bayerische Julius-Maximilians-Universität Würzburg, Röntgenring 11, 97070 Würzburg, Germany
| | - Holger Brüggemann
- *Göttingen Genomics Laboratory, Institute of Microbiology and Genetics, Georg-August-Universität Göttingen, Grisebachstrasse 8, 37077 Göttingen, Germany
- Laboratoire de Génomique des Microorganismes Pathogènes, Institut Pasteur, 75724 Paris Cedex 15, France
| | - Heiko Liesegang
- *Göttingen Genomics Laboratory, Institute of Microbiology and Genetics, Georg-August-Universität Göttingen, Grisebachstrasse 8, 37077 Göttingen, Germany
| | - Melanie Emmerth
- Institute for Molecular Biology of Infectious Diseases, Bayerische Julius-Maximilians-Universität Würzburg, Röntgenring 11, 97070 Würzburg, Germany
| | - Tobias Ölschläger
- Institute for Molecular Biology of Infectious Diseases, Bayerische Julius-Maximilians-Universität Würzburg, Röntgenring 11, 97070 Würzburg, Germany
| | - Gábor Nagy
- Institute of Medical Microbiology and Immunology, University of Pécs, Szigeti ut 12, 7624 Pécs, Hungary
| | - Kaj Albermann
- Biomax Informatics AG, Lochhamerstrasse 9, 82152 Martinsried, Germany; and
| | - Christian Wagner
- Biomax Informatics AG, Lochhamerstrasse 9, 82152 Martinsried, Germany; and
| | - Carmen Buchrieser
- Laboratoire de Génomique des Microorganismes Pathogènes, Institut Pasteur, 75724 Paris Cedex 15, France
| | - Levente Emődy
- Institute of Medical Microbiology and Immunology, University of Pécs, Szigeti ut 12, 7624 Pécs, Hungary
| | - Gerhard Gottschalk
- *Göttingen Genomics Laboratory, Institute of Microbiology and Genetics, Georg-August-Universität Göttingen, Grisebachstrasse 8, 37077 Göttingen, Germany
| | - Jörg Hacker
- Institute for Molecular Biology of Infectious Diseases, Bayerische Julius-Maximilians-Universität Würzburg, Röntgenring 11, 97070 Würzburg, Germany
| | - Ulrich Dobrindt
- Institute for Molecular Biology of Infectious Diseases, Bayerische Julius-Maximilians-Universität Würzburg, Röntgenring 11, 97070 Würzburg, Germany
| |
Collapse
|
28
|
Miyake M, Watanabe T, Koike H, Molmeret M, Imai Y, Abu Kwaik Y. Characterization of Legionella pneumophila pmiA, a gene essential for infectivity of protozoa and macrophages. Infect Immun 2005; 73:6272-82. [PMID: 16177298 PMCID: PMC1230894 DOI: 10.1128/iai.73.10.6272-6282.2005] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The ability of Legionella pneumophila to cause pneumonia is dependent on intracellular replication within alveolar macrophages. The Icm/Dot secretion apparatus is essential for the ability of L. pneumophila to evade endocytic fusion, to remodel the phagosome by the endoplasmic reticulum (ER), and to replicate intracellularly. Protozoan and macrophage infectivity (pmi) mutants of L. pneumophila, which include 11 dot/icm mutants, exhibit defects in intracellular growth and replication within both protozoa and macrophages. In this study we characterized one of the pmi loci, pmiA. In contrast to the parental strain, the pmiA mutant is defective in cytopathogenicity for protozoa and macrophages. This is a novel mutant that exhibits a partial defect in survival within U937 human macrophage-like cells but exhibits a severe growth defect within Acanthamoeba polyphaga, which results in elimination from this host. The intracellular defects of this mutant are complemented by the wild-type pmiA gene on a plasmid. In contrast to phagosomes harboring the wild-type strain, which exclude endosomal-lysosomal markers, the pmiA mutant-containing phagosomes acquire the late endosomal-lysosomal markers LAMP-1 and LAMP-2. In contrast to the parental strain-containing phagosomes that are remodeled by the ER, there was a decrease in the number of ER-remodeled phagosomes harboring the pmiA mutant. Among several Legionella species examined, the pmiA gene is specific for L. pneumophila. The predicted amino acid sequence of the PmiA protein suggests that it is a transmembrane protein with three membrane-spanning regions. PmiA is similar to several hypothetical proteins produced by bacteria with a type IV secretion apparatus. Importantly, the defect in pmiA abolishes the pore-forming activity, which has been attributed to the Icm/Dot type IV secretion system. However, the mutant is sensitive to NaCl, and this sensitivity is abrogated in the icm/dot mutants. These results suggest that PmiA is a novel virulence factor that is involved in intracellular survival and replication of L. pneumophila in macrophages and protozoan cells.
Collapse
Affiliation(s)
- Masaki Miyake
- Department of Microbiology, School of Pharmaceutical Sciences, University of Shizuoka, Suruga-ku, Shizuoka-shi, Japan.
| | | | | | | | | | | |
Collapse
|
29
|
Parsons DA, Heffron F. sciS, an icmF homolog in Salmonella enterica serovar Typhimurium, limits intracellular replication and decreases virulence. Infect Immun 2005; 73:4338-45. [PMID: 15972528 PMCID: PMC1168621 DOI: 10.1128/iai.73.7.4338-4345.2005] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Salmonella enterica serovar Typhimurium utilizes macrophages to disseminate from the intestine to deeper tissues within the body. While S. enterica serovar Typhimurium has been shown to kill its host macrophage, it can persist intracellularly beyond 18 h postinfection. To identify factors involved in late stages of infection, we screened a transposon library made in S. enterica serovar Typhimurium for the ability to persist in J774 macrophages at 24 h postinfection. Through this screen, we identified a gene, sciS, found to be homologous to icmF in Legionella pneumophila. icmF, which is required for intracellular multiplication, is conserved in several gram-negative pathogens, and its homolog appears to have been acquired horizontally in S. enterica serovar Typhimurium. We found that an sciS mutant displayed increased intracellular numbers in J774 macrophages when compared to the wild-type strain at 24 h postinfection. sciS was maximally transcribed at 27 h postinfection and is repressed by SsrB, an activator of genes required for promoting intracellular survival. Finally, we demonstrate that an sciS mutant is hypervirulent in mice when administered intragastrically. Taken together, these data indicate a role for SciS in controlling intracellular bacterial levels at later stages of infection and attenuating virulence in a murine host.
Collapse
Affiliation(s)
- Duncan A Parsons
- Department of Molecular Microbiology and Immunology, Oregon Health and Science University, 3181 SW Sam Jackson Park Rd., L220, Portland, Oregon 97201, USA.
| | | |
Collapse
|
30
|
Buscher BA, Conover GM, Miller JL, Vogel SA, Meyers SN, Isberg RR, Vogel JP. The DotL protein, a member of the TraG-coupling protein family, is essential for Viability of Legionella pneumophila strain Lp02. J Bacteriol 2005; 187:2927-38. [PMID: 15838018 PMCID: PMC1082803 DOI: 10.1128/jb.187.9.2927-2938.2005] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Legionella pneumophila is able to survive inside phagocytic cells by an internalization route that bypasses fusion of the nascent phagosome with the endocytic pathway to allow formation of a replicative phagosome. The dot/icm genes, a major virulence system of L. pneumophila, encode a type IVB secretion system that is required for intracellular growth. One Dot protein, DotL, has sequence similarity to type IV secretion system coupling proteins (T4CPs). In other systems, coupling proteins are not required for viability of the organism. Here we report the first example of a strain, L. pneumophila Lp02, in which a putative T4CP is essential for viability of the organism on bacteriological media. This result is particularly surprising since the majority of the dot/icm genes in Lp02 are dispensable for growth outside of a host cell, a condition that does not require a functional Dot/Icm secretion complex. We were able to isolate suppressors of the Delta dotL lethality and found that many contained mutations in other components of the Dot/Icm secretion system. A systematic analysis of dot/icm deletion mutants revealed that the majority of them (20 of 26) suppressed the lethality phenotype, indicating a partially assembled secretion system may be the source of Delta dotL toxicity in the wild-type strain. These results are consistent with a model in which the DotL protein plays a role in regulating the activity of the L. pneumophila type IV secretion apparatus.
Collapse
Affiliation(s)
- Benjamin A Buscher
- Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO 63110, USA
| | | | | | | | | | | | | |
Collapse
|
31
|
Albers U, Reus K, Shuman HA, Hilbi H. The amoebae plate test implicates a paralogue of lpxB in the interaction of Legionella pneumophila with Acanthamoeba castellanii. MICROBIOLOGY-SGM 2005; 151:167-182. [PMID: 15632436 DOI: 10.1099/mic.0.27563-0] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Legionella pneumophila is a bacterial parasite of freshwater amoebae which also grows in alveolar macrophages and thus causes the potentially fatal pneumonia Legionnaires' disease. Intracellular growth within amoebae and macrophages is mechanistically similar and requires the Icm/Dot type IV secretion system. This paper reports the development of an assay, the amoebae plate test (APT), to analyse growth of L. pneumophila wild-type and icm/dot mutant strains spotted on agar plates in the presence of Acanthamoeba castellanii. In the APT, wild-type L. pneumophila formed robust colonies even at high dilutions, icmT, -R, -P or dotB mutants failed to grow, and icmS or -G mutants were partially growth defective. The icmS or icmG mutant strains were used to screen an L. pneumophila chromosomal library for genes that suppress the growth defect in the presence of the amoebae. An icmS suppressor plasmid was isolated that harboured the icmS and flanking icm genes, indicating that this plasmid complements the intracellular growth defect of the mutant. In contrast, different icmG suppressor plasmids rendered the icmG mutant more cytotoxic for A. castellanii without enhancing intracellular multiplication in amoebae or RAW264.7 macrophages. Deletion of individual genes in the suppressor plasmids inserts identified lcs (Legionella cytotoxic suppressor) -A, -B, -C and -D as being required for enhanced cytotoxicity of an icmG mutant strain. The corresponding proteins show sequence similarity to hydrolases, NlpD-related metalloproteases, lipid A disaccharide synthases and ABC transporters, respectively. Overexpression of LcsC, a putative paralogue of the lipid A disaccharide synthase LpxB, increased cytotoxicity of an icmG mutant but not that of other icm/dot or rpoS mutant strains against A. castellanii. Based on sequence comparison and chromosomal location, lcsB and lcsC probably encode enzymes involved in cell wall maintenance and peptidoglycan metabolism. The APT established here may prove useful to identify other bacterial factors relevant for interactions with amoeba hosts.
Collapse
Affiliation(s)
- Urs Albers
- Institute of Microbiology, Swiss Federal Institute of Technology (ETH), Wolfgang-Pauli Str. 10, HCI G405, 8093 Zürich, Switzerland
| | - Katrin Reus
- Institute of Microbiology, Swiss Federal Institute of Technology (ETH), Wolfgang-Pauli Str. 10, HCI G405, 8093 Zürich, Switzerland
| | - Howard A Shuman
- Department of Microbiology, College of Physicians and Surgeons, Columbia University, 701 West 168th Street, New York, NY 10032, USA
| | - Hubert Hilbi
- Institute of Microbiology, Swiss Federal Institute of Technology (ETH), Wolfgang-Pauli Str. 10, HCI G405, 8093 Zürich, Switzerland
| |
Collapse
|
32
|
Sexton JA, Miller JL, Yoneda A, Kehl-Fie TE, Vogel JP. Legionella pneumophila DotU and IcmF are required for stability of the Dot/Icm complex. Infect Immun 2004; 72:5983-92. [PMID: 15385502 PMCID: PMC517559 DOI: 10.1128/iai.72.10.5983-5992.2004] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Legionella pneumophila utilizes a type IV secretion system (T4SS) encoded by 26 dot/icm genes to replicate inside host cells and cause disease. In contrast to all other L. pneumophila dot/icm genes, dotU and icmF have homologs in a wide variety of gram-negative bacteria, none of which possess a T4SS. Instead, dotU and icmF orthologs are linked to a locus encoding a conserved cluster of proteins designated IcmF-associated homologous proteins, which has been proposed to constitute a novel cell surface structure. We show here that dotU is partially required for L. pneumophila intracellular growth, similar to the known requirement for icmF. In addition, we show that dotU and icmF are necessary for optimal plasmid transfer and sodium sensitivity, two additional phenotypes associated with a functional Dot/Icm complex. We found that these effects are due to the destabilization of the T4SS at the transition into the stationary phase, the point at which L. pneumophila becomes virulent. Specifically, three Dot proteins (DotH, DotG, and DotF) exhibit decreased stability in a DeltadotU DeltaicmF strain. Furthermore, overexpression of just one of these proteins, DotH, is sufficient to suppress the intracellular growth defect of the DeltadotU DeltaicmF mutant. This suggests a model where the DotU and IcmF proteins serve to prevent DotH degradation and therefore function to stabilize the L. pneumophila T4SS. Due to their wide distribution among bacterial species and their genetic linkage to known or predicted cell surface structures, we propose that this function in complex stabilization may be broadly conserved.
Collapse
Affiliation(s)
- Jessica A Sexton
- Department of Molecular Microbiology, Washington University, St. Louis, Missouri 63110, USA
| | | | | | | | | |
Collapse
|
33
|
VanRheenen SM, Duménil G, Isberg RR. IcmF and DotU are required for optimal effector translocation and trafficking of the Legionella pneumophila vacuole. Infect Immun 2004; 72:5972-82. [PMID: 15385501 PMCID: PMC517542 DOI: 10.1128/iai.72.10.5972-5982.2004] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2004] [Revised: 04/12/2004] [Accepted: 06/01/2004] [Indexed: 12/21/2022] Open
Abstract
The gram-negative bacterium Legionella pneumophila causes a severe form of pneumonia called Legionnaires' disease, characterized by bacterial replication within alveolar macrophages. Prior to intracellular replication, the vacuole harboring the bacterium must first escape trafficking to the host lysosome, a process that is dependent on the Dot/Icm type IV secretion system. To identify genes required for intracellular growth, bacterial mutants were isolated that were delayed in escape from the macrophage but which retain a minimally functional Dot/Icm machinery. The mutations were found in eight distinct genes, including three genes known to be required for optimal intracellular growth. Two of these genes, icmF and dotU, are located at one end of a cluster of genes that encode the type IV secretion system, yet both icmF and dotU lack orthologs in other type IV translocons. DotU protein is degraded in the early postexponential phase in wild-type L. pneumophila and at all growth phases in an icmF mutant. IcmF contains an extracytoplasmic domain(s) based on accessibility to a membrane-impermeant amine-reactive reagent. In the absence of either gene, L. pneumophila targets inappropriately to LAMP-1-positive compartments during macrophage infection, is defective in the formation of replicative vacuoles, and is impaired in the translocation of the effector protein SidC. Therefore, although IcmF and DotU do not appear to be part of the core type IV secretion system, these proteins are necessary for an efficiently functioning secretion apparatus.
Collapse
Affiliation(s)
- Susan M VanRheenen
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA
| | | | | |
Collapse
|
34
|
Abstract
Although many bacteria are known to be naturally competent for DNA uptake, this ability varies dramatically between species and even within a single species, some isolates display high levels of competence while others seem to be completely nontransformable. Surprisingly, many nontransformable bacterial strains appear to encode components necessary for DNA uptake. We believe that many such strains are actually competent but that this ability has been overlooked because standard laboratory conditions are inappropriate for competence induction. For example, most strains of the gram-negative bacterium Legionella pneumophila are not competent under normal laboratory conditions of aerobic growth at 37 degrees C. However, it was previously reported that microaerophilic growth at 37 degrees C allows L. pneumophila serogroup 1 strain AA100 to be naturally transformed. Here we report that another L. pneumophila serogroup 1 strain, Lp02, can also be transformed under these conditions. Moreover, Lp02 can be induced to high levels of competence by a second set of conditions, aerobic growth at 30 degrees C. In contrast to Lp02, AA100 is only minimally transformable at 30 degrees C, indicating that Lp02 is hypercompetent under these conditions. To identify potential causes of hypercompetence, we isolated mutants of AA100 that exhibited enhanced DNA uptake. Characterization of these mutants revealed two genes, proQ and comR, that are involved in regulating competence in L. pneumophila. This approach, involving the isolation of hypercompetent mutants, shows great promise as a method for identifying natural transformation in bacterial species previously thought to be nontransformable.
Collapse
Affiliation(s)
- Jessica A Sexton
- Department of Molecular Microbiology, Washington University, Campus Box 8230, 660 S. Euclid Ave., St. Louis, MO 63110, USA.
| | | |
Collapse
|
35
|
Zusman T, Feldman M, Halperin E, Segal G. Characterization of the icmH and icmF genes required for Legionella pneumophila intracellular growth, genes that are present in many bacteria associated with eukaryotic cells. Infect Immun 2004; 72:3398-409. [PMID: 15155646 PMCID: PMC415720 DOI: 10.1128/iai.72.6.3398-3409.2004] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Legionella pneumophila, the causative agent of Legionnaires' disease, replicates intracellularly within a specialized phagosome of mammalian and protozoan host cells, and the Icm/Dot type IV secretion system has been shown to be essential for this process. Unlike all the other known Icm/Dot proteins, the IcmF protein, which was described before, and the IcmH protein, which is characterized here, have homologous proteins in many bacteria (such as Yersinia pestis, Salmonella enterica, Rhizobium leguminosarum, and Vibrio cholerae), all of which associate with eukaryotic cells. Here, we have characterized the L. pneumophila icmH and icmF genes and found that both genes are present in 16 different Legionella species examined. The icmH and icmF genes were found to be absolutely required for intracellular multiplication in Acanthamoeba castellanii and partially required for intracellular growth in HL-60-derived human macrophages, for immediate cytotoxicity, and for salt sensitivity. Mutagenesis of the predicted ATP/GTP binding site of IcmF revealed that the site is partially required for intracellular growth in A. castellanii. Analysis of the regulatory region of the icmH and icmF genes, which were found to be cotranscribed, revealed that it contains at least two regulatory elements. In addition, an icmH::lacZ fusion was shown to be activated during stationary phase in a LetA- and RelA-dependent manner. Our results indicate that although the icmH and icmF genes probably have a different evolutionary origin than the rest of the icm/dot genes, they are part of the icm/dot system and are required for L. pneumophila pathogenesis.
Collapse
Affiliation(s)
- Tal Zusman
- Department of Molecular Microbiology and Biotechnology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel
| | | | | | | |
Collapse
|
36
|
Ohnishi H, Mizunoe Y, Takade A, Tanaka Y, Miyamoto H, Harada M, Yoshida SI. Legionella dumoffii DjlA, a member of the DnaJ family, is required for intracellular growth. Infect Immun 2004; 72:3592-603. [PMID: 15155669 PMCID: PMC415686 DOI: 10.1128/iai.72.6.3592-3603.2004] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Legionella dumoffii is one of the common causes of Legionnaires' disease and is capable of replicating in macrophages. To understand the mechanism of survival within macrophages, transposon mutagenesis was employed to isolate the genes necessary for intracellular growth. We identified four defective mutants after screening 790 transposon insertion mutants. Two transposon insertions were in genes homologous to icmB or dotC, within dot/icm loci, required for intracellular multiplication of L. pneumophila. The third was in a gene whose product is homologous to the 17-kDa antigen forming part of the VirB/VirD4 type IV secretion system of Bartonella henselae. The fourth was in the djlA (for "dnaj-like A") gene. DjlA is a member of the DnaJ/Hsp40 family. Transcomplementation of the djlA mutant restored the parental phenotype in J774 macrophages, A549 human alveolar epithelial cells, and the amoeba Acanthamoeba culbertsoni. Using confocal laser-scanning microscopy and transmission electron microscopy, we revealed that in contrast to the wild-type strain, L. dumoffii djlA mutant-containing phagosomes were unable to inhibit phagosome-lysosome fusion. Transmission electron microscopy also showed that in contrast to the virulent parental strain, the djlA mutant was not able to recruit host cell rough endoplasmic reticulum. Furthermore, the stationary-phase L. dumoffii djlA mutants were more susceptible to H2O2, high osmolarity, high temperature, and low pH than was their parental strain. These results indicate that DjlA is required for intracellular growth and organelle trafficking, as well as bacterial resistance to environmental stress. This is the first report demonstrating that a single DjlA-deficient mutant exhibits a distinct phenotype.
Collapse
Affiliation(s)
- Hiroko Ohnishi
- Department of Bacteriology, Faculty of Medical Sciences, Kyushu University, Fukuoka 812-8582, Japan
| | | | | | | | | | | | | |
Collapse
|
37
|
Miyamoto H, Yoshida SI, Taniguchi H, Shuman HA. Virulence conversion of Legionella pneumophila by conjugal transfer of chromosomal DNA. J Bacteriol 2003; 185:6712-8. [PMID: 14594847 PMCID: PMC262088 DOI: 10.1128/jb.185.22.6712-6718.2003] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In this study, we examined whether virulence conversion occurs in Legionella pneumophila by conjugal transfer of chromosomal DNA. A virulent strain, K6, which has the genes for Kmr and LacZ+ transposed in the chromosome of strain Philadelphia-1, which belongs to serogroup 1, was used as one parent, and an avirulent strain, Chicago-2S, which is a spontaneous streptomycin-resistant derivative of strain Chicago-2 belonging to serogroup 6, was used as the other parent. Experiments in which K6 (approximately 2.6 x 10(9) CFU) and Chicago-2S (approximately 8.9 x 10(9) CFU) were mated typically yielded 10(3) Kmr Smr LacZ+ transconjugants. Thirty-two (about 2.8%) of 1,152 transconjugants belonging to serogroup 6 acquired the ability to grow intracellularly in Acanthamoeba castellanii and guinea pig macrophages. When guinea pigs were infected with sublethal doses of Legionella aerosols generated from one of these transconjugants (HM1011), they developed a severe pneumonia similar to that caused by donor strain K6. These results show that avirulent strain Chicago-2S changed into virulent strain HM1011 through conjugation with virulent strain K6. Furthermore, we showed that Legionella chromosomal virulence genes (icm-dot locus) were horizontally transferred by the conjugation system. The chromosomal conjugation system may play a role(s) in the evolution of L. pneumophila.
Collapse
Affiliation(s)
- Hiroshi Miyamoto
- Department of Microbiology, University of Occupational and Environmental Health, Yahatanishi-ku, Kitakyushu 807-8555, Japan.
| | | | | | | |
Collapse
|
38
|
Gal-Mor O, Segal G. Identification of CpxR as a positive regulator of icm and dot virulence genes of Legionella pneumophila. J Bacteriol 2003; 185:4908-19. [PMID: 12897011 PMCID: PMC166489 DOI: 10.1128/jb.185.16.4908-4919.2003] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
To date, 24 Legionella pneumophila genes (icm and dot genes) have been shown to be required for intercellular growth and host cell killing. A previous report indicated that the regulation of these genes is complicated and probably involves several regulatory proteins. In this study, a genetic screen performed in Escherichia coli identified the CpxR response regulator as an activator of the L. pneumophila icmR gene. Construction of an L. pneumophila cpxR insertion mutant showed that the expression of icmR is regulated by CpxR. In addition, a conserved CpxR binding site (GTAAA) was identified in the icmR regulatory region and L. pneumophila His-tagged CpxR protein was shown to bind to the icmR regulatory region using a mobility shift assay. Besides its dramatic effect on the icmR level of expression, the CpxR regulator was also found to affect the expression of the icmV-dotA and icmW-icmX operons, but to a lesser extent. The role of CpxA, the cognate sensor kinase of CpxR, was also examined and its effect on the icmR level of expression was found to be less pronounced than the effect of CpxR. The RpoE sigma factor, which was shown to coregulate genes together with CpxR, was examined as well, but it did not influence icm and dot gene expression. In addition, when the cpxR mutant strain, in which the expression of the icmR gene was dramatically reduced, and the cpxA and rpoE mutant strains were examined for their ability to grow inside Acanthamoeba castellanii and HL-60-derived human macrophages, no intracellular growth defect was observed. This study presents the first evidence for a direct regulator (CpxR) of an icm-dot virulence gene (icmR). The CpxR regulator together with other regulatory factors probably concerts with the expression of icm and dot genes to result in successful infection.
Collapse
Affiliation(s)
- Ohad Gal-Mor
- Department of Molecular Microbiology and Biotechnology, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Ramat-Aviv, Tel-Aviv 69978, Israel
| | | |
Collapse
|
39
|
Ko KS, Lee HK, Park MY, Kook YH. Mosaic structure of pathogenicity islands in Legionella pneumophila. J Mol Evol 2003; 57:63-72. [PMID: 12962307 DOI: 10.1007/s00239-002-2452-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
A gene complex, dot/icm, located in two independent chromosomal loci of L. pneumophila, the causative agent of Legionnaires' disease, is related to virulence. To investigate the evolutionary pattern of these pathogenicity islands of L. pneumophila, portions of four genes in the dot/icm complex, namely, dotA, dotB, icmB, and icmT, were amplified, sequenced, and phylogenetically analyzed, in addition to rpoB, which encodes an RNA polymerase beta-subunit. The nucleotide sequences and phylogenetic analyses of these five genes of 96 L. pneumophila strains revealed that several subgroups of L. pneumophila proliferated clonally. However, incongruent gene tree topologies and the results of statistical testing (Templeton Willcoxon signed-ranked and incongruence length differences tests) indicated that the evolutionary histories of these genes within the pathogenicity islands are not uniform, and that they constitute a mosaic structure. In addition, the nonuniform grouping of some reference strains suggests that intraspecific recombination might be still occurring in nature or in the laboratory.
Collapse
Affiliation(s)
- Kwan Soo Ko
- Department of Microbiology and Cancer Research Institute, Seoul National University Hospital, Seoul 110-799, Republic of Korea
| | | | | | | |
Collapse
|
40
|
Zusman T, Yerushalmi G, Segal G. Functional similarities between the icm/dot pathogenesis systems of Coxiella burnetii and Legionella pneumophila. Infect Immun 2003; 71:3714-23. [PMID: 12819052 PMCID: PMC161977 DOI: 10.1128/iai.71.7.3714-3723.2003] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Coxiella burnetii, the etiological agent of Q fever, is an obligate intracellular pathogen, whereas Legionella pneumophila, the causative agent of Legionnaires' disease, is a facultative intracellular pathogen. During infection of humans both of these pathogens multiply in alveolar macrophages inside a closed phagosome. L. pneumophila intracellular multiplication was shown to be dependent on the icm/dot system, which probably encodes a type IV-related translocation apparatus. Recently, genes homologous to all of the L. pneumophila icm/dot genes (besides icmR) were found in C. burnetii. To explore the similarities and differences between the icm/dot pathogenesis systems of these two pathogens, interspecies complementation analysis was performed. Nine C. burnetii icm homologous genes (icmT, icmS, icmQ, icmP, icmO, icmJ, icmB, icmW, and icmX) were cloned under regulation of the corresponding L. pneumophila icm genes and examined for the ability to complement L. pneumophila mutants with mutations in these genes. The C. burnetii icmS and icmW homologous genes were found to complement the corresponding L. pneumophila icm mutants to wild-type levels of intracellular growth in both HL-60-derived human macrophages and Acanthamoeba castellanii. In addition, the C. burnetii icmT homologous gene was found to completely complement an L. pneumophila insertion mutant for intracellular growth in HL-60-derived human macrophages, but it only partially complemented the same mutant for intracellular growth in A. castellanii. Moreover, as previously shown for L. pneumophila, the proteins encoded by the C. burnetii icmS and icmW homologous genes were found to interact with one another, and interspecies protein interaction was observed as well. Our results strongly indicate that the Icm/Dot pathogenesis systems of C. burnetii and L. pneumophila have common features.
Collapse
Affiliation(s)
- Tal Zusman
- Department of Molecular Microbiology & Biotechnology, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Ramat-Aviv, Tel-Aviv 69978, Israel
| | | | | |
Collapse
|
41
|
Abstract
Evidence for the involvement of type IV protein secretion systems in bacterial virulence is accumulating. Many of the substrate proteins secreted by type IV systems either hijack or interfere with specific host cell pathways. These substrates can be injected directly into host cells via the type IV apparatus or are secreted by the type IV machinery in a state that allows them to gain access to cellular targets without the further assistance of the type IV system. Arguably, the protein substrates of most type IV secretion systems remain undiscovered. Here, we review the activities of known type IV substrates and discuss the putative roles of unidentified substrates.
Collapse
Affiliation(s)
- Hiroki Nagai
- Section of Microbial Pathogenesis, Yale University School of Medicine, Boyer Center for Molecular Medicine, Room 354b, 295 Congress Avenue, New Haven, CT 06536, USA
| | | |
Collapse
|
42
|
Gal-Mor O, Segal G. The Legionella pneumophila GacA homolog (LetA) is involved in the regulation of icm virulence genes and is required for intracellular multiplication in Acanthamoeba castellanii. Microb Pathog 2003; 34:187-94. [PMID: 12668142 DOI: 10.1016/s0882-4010(03)00027-5] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Legionella pneumophila, the causative agent of legionnaires' disease, is a broad-host-range facultative intracellular pathogen. Thus far, 24 genes (icm/dot genes) required for L. pneumophila intracellular growth, have been discovered. In this study, a deletion substitution was constructed in the L. pneumophila homolog of the gacA response regulator (letA) and its involvement in L. pneumophila pathogenicity and icm/dot gene expression was characterized. The letA mutant constructed had no intracellular growth defect when analyzed in HL-60 derived human macrophages, but it was found to be severely attenuated for intracellular growth in the protozoan host Acanthamoeba castellanii. The growth defect in amoebae was fully complemented by introducing the L. pneumophila letA gene on a plasmid. In addition, the LetA regulator was found to be involved in the expression of three icm genes (icmT, icmP and icmR). The level of expression of the icmT::lacZ and icmR::lacZ fusions was found to be higher, while the level of expression of the icmP::lacZ fusion was found to be lower when analyzed in the letA mutant strain, in comparison to the wild-type strain. We concluded that LetA has a moderate effect on icm/dot gene expression, but it probably plays a major role in the expression of L. pneumophila genes required for intracellular growth in protozoan hosts. A similar host specific phenotype was previously described for the RpoS sigma factor and the type II general secretion system of L. pneumophila.
Collapse
Affiliation(s)
- Ohad Gal-Mor
- Department of Molecular Microbiology & Biotechnology, George S Wise Faculty of Life Sciences, Tel-Aviv University, Ramat-Aviv, Tel-Aviv 69978, Israel
| | | |
Collapse
|
43
|
Chopra P, Singh A, Koul A, Ramachandran S, Drlica K, Tyagi AK, Singh Y. Cytotoxic activity of nucleoside diphosphate kinase secreted from Mycobacterium tuberculosis. EUROPEAN JOURNAL OF BIOCHEMISTRY 2003; 270:625-34. [PMID: 12581202 DOI: 10.1046/j.1432-1033.2003.03402.x] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Pathogenicity of Mycobacterium tuberculosis is closely related to its ability to survive and replicate in the hostile environment of macrophages. For some pathogenic bacteria, secretion of ATP-utilizing enzymes into the extracellular environment aids in pathogen survival via P2Z receptor-mediated, ATP-induced death of infected macrophages. A component of these enzymes is nucleoside diphosphate kinase (Ndk). The ndk gene was cloned from M. tuberculosis H37Rv and expressed in Escherichia coli. Ndk was secreted into the culture medium by M. tuberculosis, as determined by enzymatic activity and Western blotting. Purified Ndk enhanced ATP-induced macrophage cell death, as assayed by the release of [14C]adenine. A catalytic mutant of Ndk failed to enhance ATP-induced macrophage cell death, and periodate-oxidized ATP (oATP), an irreversible inhibitor of P2Z receptor, blocked ATP/Ndk-induced cell death. Purified Ndk was also found to be autophosphorylated with broad specificity for all nucleotides. Conversion of His117-->Gln, which is part of the nucleotide-binding site, abolished autophosphorylation. Purified Ndk also showed GTPase activity. Collectively, these results indicate that secreted Ndk of M. tuberculosis acts as a cytotoxic factor for macrophages, which may help in dissemination of the bacilli and evasion of the immune system.
Collapse
Affiliation(s)
- Puneet Chopra
- Institute of Genomics and Integrative Biology, Mall Road, Delhi, India
| | | | | | | | | | | | | |
Collapse
|
44
|
Bladergroen MR, Badelt K, Spaink HP. Infection-blocking genes of a symbiotic Rhizobium leguminosarum strain that are involved in temperature-dependent protein secretion. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2003; 16:53-64. [PMID: 12580282 DOI: 10.1094/mpmi.2003.16.1.53] [Citation(s) in RCA: 164] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Rhizobium leguminosarum strain RBL5523 is able to form nodules on pea, but these nodules are ineffective for nitrogen fixation. The impairment in nitrogen fixation appears to be caused by a defective infection of the host plant and is host specific for pea. A Tn5 mutant of this strain, RBL5787, is able to form effective nodules on pea. We have sequenced a 33-kb region around the phage-transductable Tn5 insertion. The Tn5 insertion was localized to the 10th gene of a putative operon of 14 genes that was called the imp (impaired in nitrogen fixation) locus. Several highly similar gene clusters of unknown function are present in Pseudomonas aeruginosa, Vibrio cholerae, Edwardsiella ictaluri, and several other animal pathogens. Homology studies indicate that several genes of the imp locus are involved in protein phosphorylation, either as a kinase or dephosphorylase, or contain a phosphoprotein-binding module called a forkhead-associated domain. Other proteins show similarity to proteins involved in type III protein secretion. Two dimensional gel electrophoretic analysis of the secreted proteins in the supernatant fluid of cultures of RBL5523 and RBL5787 showed the absence in the mutant strain of at least four proteins with molecular masses of approximately 27 kDa and pIs between 5.5 and 6.5. The production of these proteins in the wild-type strain is temperature dependent. Sequencing of two of these proteins revealed that their first 20 amino acids are identical. This sequence showed homology to that of secreted ribose binding proteins (RbsB) from Bacilus subtilis and V. cholerae. Based on this protein sequence, the corresponding gene encoding a close homologue of RbsB was cloned that contains a N-terminal signal sequence that is recognized by type I secretion systems. Inoculation of RBL5787 on pea plants in the presence of supernatant of RBL5523 caused a reduced ability of RBL5787 to nodulate pea and fix nitrogen. Boiling of this supernatant before inoculation restored the formation of effective nodules to the original values, indicating that secreted proteins are indeed responsible for the impaired phenotype. These data suggest that the imp locus is involved in the secretion to the environment of proteins, including periplasmic RbsB protein, that cause blocking of infection specifically in pea plants.
Collapse
Affiliation(s)
- M R Bladergroen
- Institute of Molecular Plant Sciences, Leiden University, Wassenaarseweg 64, 2333 AL Leiden, The Netherlands
| | | | | |
Collapse
|
45
|
Pallen M, Chaudhuri R, Khan A. Bacterial FHA domains: neglected players in the phospho-threonine signalling game? Trends Microbiol 2002; 10:556-63. [PMID: 12564991 DOI: 10.1016/s0966-842x(02)02476-9] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Forkhead-associated (FHA) domains bind phospho-threonine peptides and are known to mediate phosphorylation-dependent protein-protein interactions in a variety of eukaryotic settings. However, their role in bacterial physiology and signalling has been largely neglected. We have surveyed bacterial FHA domains and discovered that they are implicated in many bacterial processes, including regulation of cell shape, type III secretion, sporulation, pathogenic and symbiotic host-bacterium interactions, carbohydrate storage and transport, signal transduction and ethambutol resistance. The way is now open to identify the targets of each FHA domain, and their roles in cellular physiology, and perhaps even to develop novel FHA-blocking antibacterial agents.
Collapse
Affiliation(s)
- Mark Pallen
- Division of Immunity & Infection, Birmingham University Medical School, UK.
| | | | | |
Collapse
|
46
|
Das S, Chakrabortty A, Banerjee R, Chaudhuri K. Involvement of in vivo induced icmF gene of Vibrio cholerae in motility, adherence to epithelial cells, and conjugation frequency. Biochem Biophys Res Commun 2002; 295:922-8. [PMID: 12127983 DOI: 10.1016/s0006-291x(02)00782-9] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Previously, using global transcription profile approach icmF gene of Vibrio cholerae was identified as an in vivo induced gene. In the present study, the icmF gene of V. cholerae O395 was cloned, sequenced, and used to construct an icmF insertion mutant. This IcmF is homologous to Legionella pneumophila IcmF, belonging to the icm cassette responsible for macrophage killing and intracellular survival of the organism. The icmF insertion mutant exhibited reduced motility and increased adherence to human intestinal epithelial cells. The presence of ATP-GTP-binding site suggests further a possible role of IcmF as a signaling molecule. Triparental-mating assay, with the mutant as a recipient, showed higher conjugation frequency than wild type. We propose that the increased adherence to epithelial cell line and increased conjugation frequency of the mutant result from some sort of cell surface reorganization.
Collapse
Affiliation(s)
- Soumita Das
- Biophysics Division, Human Genetics and Genomics Group, Indian Institute of Chemical Biology, Jadavpur, 4, Raja S.C. Mullick Road, Calcutta, India
| | | | | | | |
Collapse
|
47
|
Rankin S, Li Z, Isberg RR. Macrophage-induced genes of Legionella pneumophila: protection from reactive intermediates and solute imbalance during intracellular growth. Infect Immun 2002; 70:3637-48. [PMID: 12065505 PMCID: PMC128052 DOI: 10.1128/iai.70.7.3637-3648.2002] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A promoter-probe strategy was devised to identify genes specifically expressed by Legionella pneumophila during growth within the macrophage. Random fragments from the L. pneumophila chromosome were inserted upstream of a promoterless phage T4 td gene, and fragments that led to complementation of thymine auxotrophy during intracellular growth of the bacterium were identified. Two different selection strategies were employed to eliminate promoters that were also active during extracellular growth of the bacterium. Some of these genes were identified independently by using both of the selection strategies. The factors identified include orthologs of efflux-mediated resistance determinants and transporters, a transporter involved in protection from osmotic stress, a stress response GTP-binding protein, a response regulator, a sensor kinase, and two systems that increase the reducing potential of the bacterium, one of which encodes the L. pneumophila ortholog of ahpC. Five of the clones analyzed here were fusions to promoters that were closely linked to genes encoding three-component chemiosmotic efflux pumps that export heavy metals or toxic organic compounds. Analysis of ahpC gene expression indicates that levels increased at least sevenfold during intracellular growth of the bacterium. Inactivation of several of the genes at their chromosomal loci had no effect on the intracellular growth rate of L. pneumophila in cultured macrophages. This suggests that a number of genes with increased expression during intracellular growth may be part of redundant systems that allow survival and growth under the conditions encountered within host cells.
Collapse
Affiliation(s)
- Susannah Rankin
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA
| | | | | |
Collapse
|
48
|
Gal-Mor O, Zusman T, Segal G. Analysis of DNA regulatory elements required for expression of the Legionella pneumophila icm and dot virulence genes. J Bacteriol 2002; 184:3823-33. [PMID: 12081952 PMCID: PMC135176 DOI: 10.1128/jb.184.14.3823-3833.2002] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
To investigate the regulation of the Legionella pneumophila icm and dot genes required for intracellular growth, a series of nine icm::lacZ fusions were constructed. These icm::lacZ fusions were found to have different levels of expression in L. pneumophila, and five of them were more highly expressed at stationary phase than at exponential phase. When the expression of these fusions in Escherichia coli was tested, all of them were found to be expressed but three of them had dramatic changes in their levels of expression in comparison to those in L. pneumophila. Site-directed and PCR random mutagenesis with these icm::lacZ fusions was used to identify DNA regulatory elements of icm genes. Four icm genes (icmT, icmP, icmQ, and icmM) that had low levels of expression in L. pneumophila were found to contain a 6-bp sequence (TATACT) essential for their expression. This sequence was shown by primer extension to serve as their -10 promoter elements. A similar sequence, which constitutes the -10 promoter elements of the icmV, icmW, and icmR genes which had high levels of expression in L. pneumophila, was also identified. In addition, regulatory elements that probably serve as binding sites for transcription regulators were found in these genes. Altogether, 12 regulatory elements, 7 of which constitute the -10 promoter elements of the icm genes, were found. Even though all the icm and dot genes are part of one system required for L. pneumophila intracellular growth and even though their promoters are probably recognized by the vegetative sigma factor, it seems that they are subjected to different regulation mediated by several regulatory factors.
Collapse
Affiliation(s)
- Ohad Gal-Mor
- Department of Molecular Microbiology and Biotechnology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat-Aviv, Israel
| | | | | |
Collapse
|
49
|
Samrakandi MM, Cirillo SLG, Ridenour DA, Bermudez LE, Cirillo JD. Genetic and phenotypic differences between Legionella pneumophila strains. J Clin Microbiol 2002; 40:1352-62. [PMID: 11923356 PMCID: PMC140379 DOI: 10.1128/jcm.40.4.1352-1362.2002] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Legionnaires' disease is a potentially lethal pneumonia that is primarily due to infection by the species Legionella pneumophila, although more than 40 other species are known. Certain L. pneumophila subgroups, particularly serogroup 1, are associated with the majority of the epidemics. The genetic bases for these differences in virulence have not been determined. Three strains, AA100, JR32, and Lp01, have been used in many molecular pathogenesis studies of L. pneumophila. We found genetic differences between these strains by PCR and Southern analyses that may be related to their ability to cause disease. We also examined the distribution of these genetic loci in clinical and environmental isolates of Legionella and found a correlation between the presence of two of these loci, rtxA and lvh, and the ability to cause disease in humans. Examination of the interactions of these strains with host cells suggested that they differ in important phenotypic characteristics including adherence, entry, and intracellular replication. Furthermore, in the mouse model of infection they display differing levels of replication in lungs. These studies emphasize the importance of further investigation into the genetic makeup of these strains, which is likely to lead to the identification of additional factors involved in Legionella pathogenesis.
Collapse
Affiliation(s)
- Mustapha M Samrakandi
- Department of Veterinary and Biomedical Sciences, University of Nebraska, Lincoln, Lincoln, Nebraska 68583, USA
| | | | | | | | | |
Collapse
|
50
|
Zusman T, Gal-Mor O, Segal G. Characterization of a Legionella pneumophila relA insertion mutant and toles of RelA and RpoS in virulence gene expression. J Bacteriol 2002; 184:67-75. [PMID: 11741845 PMCID: PMC134777 DOI: 10.1128/jb.184.1.67-75.2002] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
To investigate the involvement of RelA in the regulation of Legionella pneumophila virulence, a deletion substitution was constructed in the relA gene. The relA knockout resulted in an undetectable level of ppGpp in the cells during the stationary phase, but the original level was restored when the relA gene product was supplied on a plasmid. The effect of the relA mutation was examined with two systems that are known to be expressed during the stationary phase in L. pneumophila. Pigment production was found to be dependent on the relA gene product, and only one-half as much pigment was produced by the relA mutant as by the wild-type strain. Flagellum gene expression was also found to be dependent on the relA gene product, as determined with a flaA::lacZ fusion. However, the relA gene product was found to be dispensable for intracellular growth both in HL-60-derived human macrophages and in the protozoan host Acanthamoeba castellanii. To determine the involvement of the relA gene product in expression of L. pneumophila genes required for intracellular growth (icm/dot genes), nine icm::lacZ fusions were constructed, and expression of these fusions in the wild-type strain was compared with their expression in relA mutant strains. Expression of only one of the icm::lacZ fusions was moderately reduced in the relA mutant strain. Expression of the nine icm::lacZ fusions was also examined in a strain containing an insertion in the gene that codes for the stationary-phase sigma factor RpoS, and similar results were obtained. We concluded that RelA is dispensable for intracellular growth of L. pneumophila in the two hosts examined and that both RelA and RpoS play minor roles in L. pneumophila icm/dot gene expression.
Collapse
Affiliation(s)
- Tal Zusman
- Department of Molecular Microbiology & Biotechnology, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Ramat-Aviv, Tel-Aviv 69978, Israel
| | | | | |
Collapse
|