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Lopez AE, Grigoryeva LS, Barajas A, Cianciotto NP. Legionella pneumophila Rhizoferrin Promotes Bacterial Biofilm Formation and Growth within Amoebae and Macrophages. Infect Immun 2023; 91:e0007223. [PMID: 37428036 PMCID: PMC10429650 DOI: 10.1128/iai.00072-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2023] [Accepted: 06/20/2023] [Indexed: 07/11/2023] Open
Abstract
Previously, we showed that Legionella pneumophila secretes rhizoferrin, a polycarboxylate siderophore that promotes bacterial growth in iron-deplete media and the murine lung. Yet, past studies failed to identify a role for the rhizoferrin biosynthetic gene (lbtA) in L. pneumophila infection of host cells, suggesting the siderophore's importance was solely linked to extracellular survival. To test the possibility that rhizoferrin's relevance to intracellular infection was missed due to functional redundancy with the ferrous iron transport (FeoB) pathway, we characterized a new mutant lacking both lbtA and feoB. This mutant was highly impaired for growth on bacteriological media that were only modestly depleted of iron, confirming that rhizoferrin-mediated ferric iron uptake and FeoB-mediated ferrous iron uptake are critical for iron acquisition. The lbtA feoB mutant, but not its lbtA-containing complement, was also highly defective for biofilm formation on plastic surfaces, demonstrating a new role for the L. pneumophila siderophore in extracellular survival. Finally, the lbtA feoB mutant, but not its complement containing lbtA, proved to be greatly impaired for growth in Acanthamoeba castellanii, Vermamoeba vermiformis, and human U937 cell macrophages, revealing that rhizoferrin does promote intracellular infection by L. pneumophila. Moreover, the application of purified rhizoferrin triggered cytokine production from the U937 cells. Rhizoferrin-associated genes were fully conserved across the many sequenced strains of L. pneumophila examined but were variably present among strains from the other species of Legionella. Outside of Legionella, the closest match to the L. pneumophila rhizoferrin genes was in Aquicella siphonis, another facultative intracellular parasite of amoebae.
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Affiliation(s)
- Alberto E. Lopez
- Department of Microbiology and Immunology, Northwestern University Medical School, Chicago, Illinois, USA
| | - Lubov S. Grigoryeva
- Department of Microbiology and Immunology, Northwestern University Medical School, Chicago, Illinois, USA
| | - Armando Barajas
- Department of Microbiology and Immunology, Northwestern University Medical School, Chicago, Illinois, USA
| | - Nicholas P. Cianciotto
- Department of Microbiology and Immunology, Northwestern University Medical School, Chicago, Illinois, USA
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Cianciotto NP. An update on iron acquisition by Legionella pneumophila: new pathways for siderophore uptake and ferric iron reduction. Future Microbiol 2016; 10:841-51. [PMID: 26000653 DOI: 10.2217/fmb.15.21] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Iron acquisition is critical for the growth and pathogenesis of Legionella pneumophila, the causative agent of Legionnaires' disease. L. pneumophila utilizes two main modes of iron assimilation, namely ferrous iron uptake via the FeoB system and ferric iron acquisition through the action of the siderophore legiobactin. This review highlights recent studies concerning the mechanism of legiobactin assimilation, the impact of c-type cytochromes on siderophore production, the importance of legiobactin in lung infection and a newfound role for a bacterial pyomelanin in iron acquisition. These data demonstrate that key aspects of L. pneumophila iron acquisition are significantly distinct from those of long-studied, 'model' organisms. Indeed, L. pneumophila may represent a new paradigm for a variety of other intracellular parasites, pathogens and under-studied bacteria.
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Lindgren H, Lindgren L, Golovliov I, Sjöstedt A. Mechanisms of heme utilization by Francisella tularensis. PLoS One 2015; 10:e0119143. [PMID: 25756756 PMCID: PMC4355490 DOI: 10.1371/journal.pone.0119143] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2014] [Accepted: 01/19/2015] [Indexed: 12/24/2022] Open
Abstract
Francisella tularensis is a highly virulent facultative intracellular pathogen causing the severe disease tularemia in mammals. As for other bacteria, iron is essential for its growth but very few mechanisms for iron acquisition have been identified. Here, we analyzed if and how F. tularensis can utilize heme, a major source of iron in vivo. This is by no means obvious since the bacterium lacks components of traditional heme-uptake systems. We show that SCHU S4, the prototypic strain of subspecies tularensis, grew in vitro with heme as the sole iron source. By screening a SCHU S4 transposon insertion library, 16 genes were identified as important to efficiently utilize heme, two of which were required to avoid heme toxicity. None of the identified genes appeared to encode components of a potential heme-uptake apparatus. Analysis of SCHU S4 deletion mutants revealed that each of the components FeoB, the siderophore system, and FupA, contributed to the heme-dependent growth. In the case of the former two systems, iron acquisition was impaired, whereas the absence of FupA did not affect iron uptake but led to abnormally high binding of iron to macromolecules. Overall, the present study demonstrates that heme supports growth of F. tularensis and that the requirements for the utilization are highly complex and to some extent novel.
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Affiliation(s)
- Helena Lindgren
- Department of Clinical Microbiology, Clinical Bacteriology, and Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå University, Umeå, Sweden
| | - Lena Lindgren
- Department of Clinical Microbiology, Clinical Bacteriology, and Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå University, Umeå, Sweden
| | - Igor Golovliov
- Department of Clinical Microbiology, Clinical Bacteriology, and Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå University, Umeå, Sweden
| | - Anders Sjöstedt
- Department of Clinical Microbiology, Clinical Bacteriology, and Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå University, Umeå, Sweden
- * E-mail:
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Runyen-Janecky LJ. Role and regulation of heme iron acquisition in gram-negative pathogens. Front Cell Infect Microbiol 2013; 3:55. [PMID: 24116354 PMCID: PMC3792355 DOI: 10.3389/fcimb.2013.00055] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2013] [Accepted: 09/10/2013] [Indexed: 12/14/2022] Open
Abstract
Bacteria that reside in animal tissues and/or cells must acquire iron from their host. However, almost all of the host iron is sequestered in iron-containing compounds and proteins, the majority of which is found within heme molecules. Thus, likely iron sources for bacterial pathogens (and non-pathogenic symbionts) are free heme and heme-containing proteins. Furthermore, the cellular location of the bacterial within the host (intra or extracellular) influences the amount and nature of the iron containing compounds available for transport. The low level of free iron in the host, coupled with the presence of numerous different heme sources, has resulted in a wide range of high-affinity iron acquisition strategies within bacteria. However, since excess iron and heme are toxic to bacteria, expression of these acquisition systems is highly regulated. Precise expression in the correct host environment at the appropriate times enables heme iron acquisitions systems to contribute to the growth of bacterial pathogens within the host. This mini-review will highlight some of the recent findings in these areas for gram-negative pathogens.
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Honsa ES, Maresso AW. Mechanisms of iron import in anthrax. Biometals 2011; 24:533-45. [PMID: 21258843 DOI: 10.1007/s10534-011-9413-x] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2010] [Accepted: 01/08/2011] [Indexed: 12/18/2022]
Abstract
During an infection, bacterial pathogens must acquire iron from the host to survive. However, free iron is sequestered in host proteins, which presents a barrier to iron-dependent bacterial replication. In response, pathogens have developed mechanisms to acquire iron from the host during infection. Interestingly, a significant portion of the iron pool is sequestered within heme, which is further bound to host proteins such as hemoglobin. The copious amount of heme-iron makes hemoglobin an ideal molecule for targeted iron uptake during infection. While the study of heme acquisition is well represented in Gram-negative bacteria, the systems and mechanism of heme uptake in Gram-positive bacteria has only recently been investigated. Bacillus anthracis, the causative agent of anthrax disease, represents an excellent model organism to study iron acquisition processes owing to a multifaceted lifecycle consisting of intra- and extracellular phases and a tremendous replicative potential upon infection. This review provides an in depth description of the current knowledge of B. anthracis iron acquisition and applies these findings to a general understanding of how pathogenic Gram-positive bacteria transport this critical nutrient during infection.
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Affiliation(s)
- Erin Sarah Honsa
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030, USA
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Differential gene expression in Streptococcus pneumoniae in response to various iron sources. Microb Pathog 2009; 47:101-9. [DOI: 10.1016/j.micpath.2009.05.003] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2008] [Revised: 05/04/2009] [Accepted: 05/07/2009] [Indexed: 11/23/2022]
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Purification of Legiobactin and importance of this siderophore in lung infection by Legionella pneumophila. Infect Immun 2009; 77:2887-95. [PMID: 19398549 DOI: 10.1128/iai.00087-09] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
When cultured in a low-iron medium, Legionella pneumophila secretes a siderophore (legiobactin) that is both reactive in the chrome azurol S (CAS) assay and capable of stimulating the growth of iron-starved legionellae. Using anion-exchange high-pressure liquid chromatography (HPLC), we purified legiobactin from culture supernatants of a virulent strain of L. pneumophila. In the process, we detected the ferrated form of legiobactin as well as other CAS-reactive substances. Purified legiobactin had a yellow-gold color and absorbed primarily from 220 nm and below. In accordance, nuclear magnetic resonance spectroscopy revealed that legiobactin lacks aromatic carbons, and among the 13 aliphatics present, there were 3 carbonyls. When examined by HPLC, supernatants from L. pneumophila mutants inactivated for lbtA and lbtB completely lacked legiobactin, indicating that the LbtA and LbtB proteins are absolutely required for siderophore activity. Independently derived lbtA mutants, but not a complemented derivative, displayed a reduced ability to infect the lungs of A/J mice after intratracheal inoculation, indicating that legiobactin is required for optimal intrapulmonary survival by L. pneumophila. This defect, however, was not evident when the lbtA mutant and its parental strain were coinoculated into the lung, indicating that legiobactin secreted by the wild type can promote growth of the mutant in trans. Legiobactin mutants grew normally in murine lung macrophages and alveolar epithelial cells, suggesting that legiobactin promotes something other than intracellular infection of resident lung cells. Overall, these data represent the first documentation of a role for siderophore expression in the virulence of L. pneumophila.
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Huston WM, Naylor J, Cianciotto NP, Jennings MP, McEwan AG. Functional analysis of the multi-copper oxidase from Legionella pneumophila. Microbes Infect 2008; 10:497-503. [PMID: 18403241 DOI: 10.1016/j.micinf.2008.01.011] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2007] [Revised: 12/20/2007] [Accepted: 01/16/2008] [Indexed: 11/30/2022]
Abstract
Multicopper oxidases have been described to have functions in copper tolerance, manganese oxidation, and iron oxidation in a range of bacteria. The putative cytoplasmic membrane multicopper oxidase from Legionella pneumophila was investigated. The mcoL gene was found to be critical for aerobic extracellular growth under either iron-limiting conditions or in the presence of ferrous Fe(II) iron, as a sole source of this essential metal. The mcoL mutants showed minor growth defects when grown in the presence of Fe(III) as the iron source. In contrast, intracellular growth and survival was not affected by the absence of the mcoL gene regardless of available iron concentration. The evidence presented here could indicate a possible role for mcoL in prevention of the toxic effects of ferrous iron during aerobic conditions. However, a function in high-affinity acquisition of iron could also be possible given the inability of the McoL mutants to grow aerobically under iron-limiting conditions.
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Affiliation(s)
- Wilhelmina M Huston
- Centre for Metals in Biology and School of Molecular and Microbial Sciences, University of Queensland, St Lucia, QLD 4072, Australia
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Chatfield CH, Cianciotto NP. The secreted pyomelanin pigment of Legionella pneumophila confers ferric reductase activity. Infect Immun 2007; 75:4062-70. [PMID: 17548481 PMCID: PMC1951983 DOI: 10.1128/iai.00489-07] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The virulence of Legionella pneumophila is dependent upon its capacity to acquire iron. To identify genes involved in expression of its siderophore, we screened a mutagenized population of L. pneumophila for strains that were no longer able to rescue the growth of a ferrous transport mutant. However, an unusual mutant was obtained that displayed a strong inhibitory effect on the feoB mutant. Due to an insertion in hmgA that encodes homogentisate 1,2-dioxygenase, the mutant secreted increased levels of pyomelanin, the L. pneumophila pigment that is derived from secreted homogentisic acid (HGA). Thus, we hypothesized that L. pneumophila-secreted HGA-melanin has intrinsic ferric reductase activity, converting Fe(3+) to Fe(2+), but that hyperpigmentation results in excessive reduction of iron that can, in the case of the feoB mutant, be inhibitory to growth. In support of this hypothesis, we demonstrated, for the first time, that wild-type L. pneumophila secretes ferric reductase activity. Moreover, whereas the hyperpigmented mutant had increased secreted activity, an lly mutant specifically impaired for pigment production lacked the activity. Compatible with the nature of HGA-melanins, the secreted ferric reductase activity was positively influenced by the amount of tyrosine in the growth medium, resistant to protease, acid precipitable, and heterogeneous in size. Together, these data represent the first demonstration of pyomelanin-mediated ferric reduction by a pathogenic bacterium.
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Affiliation(s)
- Christa H Chatfield
- Department of Microbiology-Immunology, Northwestern University Medical School, 320 East Superior Street, Chicago, IL 60611-3010, USA
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Cianciotto NP. Iron acquisition by Legionella pneumophila. Biometals 2006; 20:323-31. [PMID: 17180462 DOI: 10.1007/s10534-006-9057-4] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2006] [Accepted: 11/28/2006] [Indexed: 11/29/2022]
Abstract
For nearly 20 years, it was believed that Legionella pneumophila does not produce siderophores. Yet, we have now determined that L. pneumophila secretes a siderophore (legiobactin) that is detectable by the CAS assay. We have optimized conditions for legiobactin expression, shown its biological activity, and found genes (lbtAB) involved in its production and secretion. LbtA is homologous with siderophore synthetases from E. coli (aerobactin), Sinorhizobium (rhizobactin), and Bordetella (alcaligin), while LbtB is a member of the major facilitator superfamily of multidrug efflux pumps. Mutants lacking lbtAB produce 40-70% less CAS reactivity. The lbtA mutant is also defective for growth in deferrated media containing citrate, indicating that legiobactin is required in conditions of severe iron limitation. lbtAB mutants grow normally in macrophages and amoebae host cells as well as within the lungs of mice. L. pneumophila does express lbtA in macrophages, suggesting that legiobactin has a dispensable role in infection. Legiobactin is iron repressed and does not react in the Csáky and Arnow assays. Anion-exchange HPLC has been used to purify legiobactin, and thus far, structural analysis suggests that the molecule is similar but not identical to rhizobactin, rhizoferrin, and alcaligin. The residual CAS reactivity present in supernatants of the lbtAB mutants suggests that L. pneumophila might produce a second siderophore. Besides siderophores, we have determined that ferrous iron transport, encoded by feoB, is critical for L. pneumophila growth in low-iron conditions, in host cells, and in the mammalian lung. Some of our other studies have discovered a critical, yet undefined, role for the L. pneumophila cytochrome c maturation locus in low-iron growth, intracellular infection, and virulence.
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Affiliation(s)
- Nicholas P Cianciotto
- Department of Microbiology-Immunology, Northwestern University Medical School, 320 East Superior Street, Chicago, IL 60611-3010, USA.
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Lück PC, Steinert M. Pathogenese, Diagnostik und Therapie der Legionella-Infektion. Bundesgesundheitsblatt Gesundheitsforschung Gesundheitsschutz 2006; 49:439-49. [PMID: 16596363 DOI: 10.1007/s00103-006-1254-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Legionella species are ubiquitous in aquatic environments. About 50 years ago they entered the engineered (technical) environment, i.e. warm water systems with zones of stagnation. Since that time they represent a hygienic problem. After transmission to humans via aerosols legionellae might cause Legionella pneumonia (legionnaires' disease) or influenza-like respiratory infections (Pontiac fever). Epidemiological data suggest that Legionella strains might differ substantially in their virulence properties. Although the molecular basis is not understood L. pneumophila serogroup 1 especially MAb 3/1-positive strains cause the majority of infections. The main virulence feature is the ability to multiply intracellularly. After uptake into macrophages legionellae multiply in a specialized vacuole and finally lyse their host cells. Several bacterial factors like surface components, secretion systems and iron uptake systems are involved in this process. Since the clinical picture of Legionella pneumonia does not allow differentiation from pneumoniae caused by other pathogens, microbiological diagnostic methods are needed to establish the diagnosis. Cultivation of legionellae from clinical specimens, detection of antigens and DNA in patients' samples and detection of antibodies in serum samples are suitable methods. However, none of the diagnostic tests presently available offers the desired quality with respect to sensitivity and specificity. Therefore, the standard technique is to use several diagnostic tests in parallel. Advantages and disadvantages of the diagnostic procedures are discussed. Therapeutic options for Legionella infections are newer macrolides like azithromycin and chinolones (ciprofloxacin, levofloxacin and moxifloxacin).
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Affiliation(s)
- P C Lück
- Institut für Medizinische Mikrobiologie, Nationales Konsiliarlabor für Legionellen, TU-Dresden, Fiedlerstrasse 42, 01307 Dresden.
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De Buck E, Maes L, Meyen E, Van Mellaert L, Geukens N, Anné J, Lammertyn E. Legionella pneumophila Philadelphia-1 tatB and tatC affect intracellular replication and biofilm formation. Biochem Biophys Res Commun 2005; 331:1413-20. [PMID: 15883032 DOI: 10.1016/j.bbrc.2005.04.060] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2005] [Indexed: 11/25/2022]
Abstract
Legionella pneumophila is a facultative intracellular human pathogen and an important cause of Legionnaires' disease, a severe form of pneumonia. Recently, we showed the presence of a putative twin-arginine translocation (Tat) pathway in L. pneumophila Philadelphia-1. This secretion pathway is used to transport completely folded proteins across the cytoplasmic membrane. The importance of the Tat pathway in L. pneumophila was investigated by constructing a tatB and a tatC mutant. Functionality of the Tat pathway was shown using a proven heterologous Tat substrate. It was shown that tatB and tatC are involved in intracellular replication in Acanthamoeba castellanii and differentiated U937 cells, and in biofilm forming ability. A putative Legionella Tat substrate was identified via 2D gel electrophoresis.
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Affiliation(s)
- Emmy De Buck
- Laboratory of Bacteriology, Rega Institute for Medical Research, Katholieke Universiteit Leuven, Minderbroedersstraat 10, B-3000 Louvain, Belgium
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Rossier O, Cianciotto NP. The Legionella pneumophila tatB gene facilitates secretion of phospholipase C, growth under iron-limiting conditions, and intracellular infection. Infect Immun 2005; 73:2020-32. [PMID: 15784543 PMCID: PMC1087389 DOI: 10.1128/iai.73.4.2020-2032.2005] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Our previous mutational analysis of Legionella pneumophila demonstrated a role for type II protein (Lsp) secretion and iron acquisition in intracellular infection and virulence. In gram-negative bacteria, the twin-arginine translocation (Tat) pathway is involved in secretion of proteins, including components of respiratory complexes, across the inner membrane to the periplasm. To assess the significance of Tat for L. pneumophila, tatB mutants were characterized. The mutants exhibited normal growth in standard media but grew slowly under low-iron conditions. They were also impaired in the Nadi assay, indicating that the function of cytochrome c oxidase is influenced by tatB. Consistent with this observation, a subunit of the cytochrome c reductase was shown to be a Tat substrate. Supernatants of the tatB mutants showed a 30% reduction in phospholipase C activity while maintaining normal levels of other Lsp secreted activities. When tested for infection of U937 macrophages, the tatB mutants showed a 10-fold reduction in growth. Double mutants lacking tatB and Lsp secretion were even more defective, suggesting tatB has an intracellular role that is independent of Lsp. tatB mutants were also impaired 20-fold in Hartmannella vermiformis amoebae cultured in the presence of an iron chelator. All mutant phenotypes were complemented by reintroduction of an intact tatB. Thus, L. pneumophila tatB plays a role in the formation of a respiratory complex, growth under low-iron conditions, the secretion of a phospholipase C activity, and intracellular infection.
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Affiliation(s)
- Ombeline Rossier
- Department of Microbiology and Immunology, Northwestern University Medical School, 320 East Superior St., Chicago, IL 60611, USA
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Flieger A, Rydzewski K, Banerji S, Broich M, Heuner K. Cloning and characterization of the gene encoding the major cell-associated phospholipase A of Legionella pneumophila, plaB, exhibiting hemolytic activity. Infect Immun 2004; 72:2648-58. [PMID: 15102773 PMCID: PMC387885 DOI: 10.1128/iai.72.5.2648-2658.2004] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.9] [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, is an intracellular pathogen of amoebae, macrophages, and epithelial cells. The pathology of Legionella infections involves alveolar cell destruction, and several proteins of L. pneumophila are known to contribute to this ability. By screening a genomic library of L. pneumophila, we found an additional L. pneumophila gene, plaB, which coded for a hemolytic activity and contained a lipase consensus motif in its deduced protein sequence. Moreover, Escherichia coli harboring the L. pneumophila plaB gene showed increased activity in releasing fatty acids predominantly from diacylphospho- and lysophospholipids, demonstrating that it encodes a phospholipase A. It has been reported that culture supernatants and cell lysates of L. pneumophila possess phospholipase A activity; however, only the major secreted lysophospholipase A PlaA has been investigated on the molecular level. We therefore generated isogenic L. pneumophila plaB mutants and tested those for hemolysis, lipolytic activities, and intracellular survival in amoebae and macrophages. Compared to wild-type L. pneumophila, the plaB mutant showed reduced hemolysis of human red blood cells and almost completely lost its cell-associated lipolytic activity. We conclude that L. pneumophila plaB is the gene encoding the major cell-associated phospholipase A, possibly contributing to bacterial cytotoxicity due to its hemolytic activity. On the other hand, in view of the fact that the plaB mutant multiplied like the wild type both in U937 macrophages and in Acanthamoeba castellanii amoebae, plaB is not essential for intracellular survival of the pathogen.
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Affiliation(s)
- Antje Flieger
- Robert Koch-Institut, Berlin. Institut für Molekulare Infektionsbiologie, Julius-Maximilians Universität Würzburg, Würzburg, Germany.
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Mazoy R, Osorio CR, Toranzo AE, Lemos ML. Isolation of mutants of Vibrio anguillarum defective in haeme utilisation and cloning of huvA, a gene coding for an outer membrane protein involved in the use of haeme as iron source. Arch Microbiol 2003; 179:329-38. [PMID: 12647036 DOI: 10.1007/s00203-003-0529-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2002] [Revised: 01/17/2003] [Accepted: 01/29/2003] [Indexed: 10/20/2022]
Abstract
The isolation of Vibrio anguillarum mutants lacking the ability to use haemin and haemoglobin as the only iron sources, as well as the identification of a gene involved in haeme utilisation are described. One of the isolated mutants defective in haeme utilisation lacked an iron-regulated outer membrane protein of 79-kDa. Although growth on haeme as iron source was completely abolished, the haemin and haemoglobin binding activities remained intact in the mutant, suggesting that the absent protein is not the only one involved in haeme binding. The wild-type phenotype in this mutant was restored by transformation with a cosmid clone (pML1) containing a 21-kb DNA fragment isolated from a gene library derived from the parental strain of V. anguillarum. Sequence analysis of pML1 subclones led to the finding of an ORF, huvA, that codes for a 79-kDa protein (HuvA) and whose sequence shows high identity with haeme receptors from Vibrio choleare (HutA) and Vibrio vulnificus (HupA). The sequence of huvA from the V. anguillarum haeme-utilisation mutant revealed a single mutation, leading to the synthesis of a truncated HuvA protein of 70 kDa. The parental strain and the cosmid-complemented mutant showed a higher degree of virulence for fish than the mutant strain in experimental infections in which fish were previously overloaded with haemin. This finding suggests that haeme uptake plays an important role in V. anguillarum multiplication in fish tissues when free haeme is available.
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Affiliation(s)
- Ramón Mazoy
- Departamento de Microbiología y Parasitología, Universidad de Santiago de Compostela, Facultad de Biología e Instituto de Acuicultura, 15782, Santiago de Compostela, Spain
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Toptchieva A, Sisson G, Bryden LJ, Taylor DE, Hoffman PS. An inducible tellurite-resistance operon in Proteus mirabilis. MICROBIOLOGY (READING, ENGLAND) 2003; 149:1285-1295. [PMID: 12724390 DOI: 10.1099/mic.0.25981-0] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Tellurite resistance (Te(r)) is widespread in nature and it is shown here that the natural resistance of Proteus mirabilis to tellurite is due to a chromosomally located orthologue of plasmid-borne ter genes found in enteric bacteria. The P. mirabilis ter locus (terZABCDE) was identified in a screen of Tn5lacZ-generated mutants of which one contained an insertion in terC. The P. mirabilis terC mutant displayed increased susceptibility to tellurite (Te(s)) and complementation with terC carried on a multicopy plasmid restored high-level Te(r). Primer extension analysis revealed a single transcriptional start site upstream of terZ, but only with RNA harvested from bacteria grown in the presence of tellurite. Northern blotting and reverse transcriptase-PCR (RT-PCR) analyses confirmed that the ter operon was inducible by tellurite and to a lesser extent by oxidative stress inducers such as hydrogen peroxide and methyl viologen (paraquat). Direct and inverted repeat sequences were identified in the ter promoter region as well as motifs upstream of the -35 hexamer that resembled OxyR-binding sequences. Finally, the 390 bp intergenic promoter region located between orf3 and terZ showed no DNA sequence identity with any other published ter sequences, whereas terZABCDE genes exhibited 73-85 % DNA sequence identity. The ter operon was present in all clinical isolates of P. mirabilis and Proteus vulgaris tested and is inferred for Morganella and Providencia spp. based on screening for high level Te(r) and preliminary PCR analysis. Thus, a chromosomally located inducible tellurite resistance operon appears to be a common feature of the genus Proteus.
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Affiliation(s)
- Anna Toptchieva
- Department of Microbiology and Immunology, Dalhousie University, Sir Charles Tupper Medical Building, College Street, Halifax, Nova Scotia, Canada B3H 4H7
| | - Gary Sisson
- Department of Microbiology and Immunology, Dalhousie University, Sir Charles Tupper Medical Building, College Street, Halifax, Nova Scotia, Canada B3H 4H7
| | - Louis J Bryden
- Department of Microbiology and Immunology, Dalhousie University, Sir Charles Tupper Medical Building, College Street, Halifax, Nova Scotia, Canada B3H 4H7
| | - Diane E Taylor
- Department of Medical Microbiology and Immunology, 1-28 Medical Science Building, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
| | - Paul S Hoffman
- Division of Infectious Diseases, Department of Medicine, Dalhousie University, Sir Charles Tupper Medical Building, College Street, Halifax, Nova Scotia, Canada B3H 4H7
- Department of Microbiology and Immunology, Dalhousie University, Sir Charles Tupper Medical Building, College Street, Halifax, Nova Scotia, Canada B3H 4H7
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17
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Robey M, Cianciotto NP. Legionella pneumophila feoAB promotes ferrous iron uptake and intracellular infection. Infect Immun 2002; 70:5659-69. [PMID: 12228295 PMCID: PMC128349 DOI: 10.1128/iai.70.10.5659-5669.2002] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In order to determine the role of ferrous iron transport in Legionella pathogenesis, we identified and mutated the feoB gene in virulent Legionella pneumophila strain 130b. As it is in Escherichia coli, the L. pneumophila feoB gene was contained within a putative feoAB operon. L. pneumophila feoB insertion mutants exhibited decreased ferrous but not ferric iron uptake compared to the wild type. Growth on standard buffered charcoal yeast extract agar or buffered yeast extract broth was unaffected by the loss of L. pneumophila FeoB. However, the L. pneumophila feoB mutant had a reduced ability to grow on buffered charcoal yeast extract agar with a reduced amount of its usual iron supplementation, a phenotype that could be complemented by the addition of feoB in trans. In unsupplemented buffered yeast extract broth, the feoB mutant also had a growth defect, which was further exacerbated by the addition of the ferrous iron chelator, 2,2'-dipyridyl. The feoB mutant was also 2.5 logs more resistant to streptonigrin than wild-type 130b, confirming its decreased ability to acquire iron during extracellular growth. Decreased replication of the feoB mutant was noted within iron-depleted Hartmannella vermiformis amoebae and human U937 cell macrophages. The reduced intracellular infectivity of the feoB mutant was complemented by the introduction of a plasmid containing feoAB. The L. pneumophila feoB gene conferred a modest growth advantage for the wild type over the mutant in a competition assay within the lungs of A/J mice. Taken together, these results indicate that L. pneumophila FeoB is a ferrous iron transporter that is important for extracellular and intracellular growth, especially in iron-limited environments. These data represent the first evidence for the importance of ferrous iron transport for intracellular replication by a human pathogen.
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Affiliation(s)
- Marianne Robey
- Department of Microbiology-Immunology, Northwestern University Medical School, Chicago, Illinois 60611, USA
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18
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Abstract
Legionella pneumophila is naturally found in fresh water were the bacteria parasitize within protozoa. It also survives planctonically in water or biofilms. Upon aerosol formation via man-made water systems, L. pneumophila can enter the human lung and cause a severe form of pneumonia, called Legionnaires' disease. The pathogenesis of Legionnaires' disease is largely due to the ability of L. pneumophila to invade and grow within macrophages. An important characteristic of the intracellular survival strategy is the replication within the host vacuole that does not fuse with endosomes or lysosomes. In recent times a great number of bacterial virulence factors which affect growth of L. pneumophila in both macrophages and protozoa have been identified. The ongoing Legionella genome project and the use of genetically tractable surrogate hosts are expected to significantly contribute to the understanding of bacterium-host interactions and the regulation of virulence traits during the infection cycle. Since person-to-person transmission of legionellosis has never been observed, the measures for disease prevention have concentrated on eliminating the pathogen from water supplies. In this respect detection and analysis of Legionella in complex environmental consortia become increasingly important. With the availability of new molecular tools this area of applied research has gained new momentum.
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Affiliation(s)
- Michael Steinert
- Institut für Molekulare Infektionsbiologie, Universität Würzburg, Würzburg, Germany.
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19
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Viswanathan VK, Kurtz S, Pedersen LL, Abu-Kwaik Y, Krcmarik K, Mody S, Cianciotto NP. The cytochrome c maturation locus of Legionella pneumophila promotes iron assimilation and intracellular infection and contains a strain-specific insertion sequence element. Infect Immun 2002; 70:1842-52. [PMID: 11895946 PMCID: PMC127876 DOI: 10.1128/iai.70.4.1842-1852.2002] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Previously, we obtained a Legionella pneumophila mutant, NU208, that is hypersensitive to iron chelators when grown on standard Legionella media. Here, we demonstrate that NU208 is also impaired for growth in media that simply lack their iron supplement. The mutant was not, however, impaired for the production of legiobactin, the only known L. pneumophila siderophore. Importantly, NU208 was also highly defective for intracellular growth in human U937 cell macrophages and Hartmannella and Acanthamoeba amoebae. The growth defect within macrophages was exacerbated by treatment of the host cells with an iron chelator. Sequence analysis demonstrated that the transposon disruption in NU208 lies within an open reading frame that is highly similar to the cytochrome c maturation gene, ccmC. CcmC is generally recognized for its role in the heme export step of cytochrome biogenesis. Indeed, NU208 lacked cytochrome c. Phenotypic analysis of two additional, independently derived ccmC mutants confirmed that the growth defect in low-iron medium and impaired infectivity were associated with the transposon insertion and not an entirely spontaneous second-site mutation. trans-complementation analysis of NU208 confirmed that L. pneumophila ccmC is required for cytochrome c production, growth under low-iron growth conditions, and at least some forms of intracellular infection. Although ccm genes have recently been implicated in iron assimilation, our data indicate, for the first time, that a ccm gene can be required for bacterial growth in an intracellular niche. Complete sequence analysis of the ccm locus from strain 130b identified the genes ccmA-H. Interestingly, however, we also observed that a 1.8-kb insertion sequence element was positioned between ccmB and ccmC. Southern hybridizations indicated that the open reading frame within this element (ISLp 1) was present in multiple copies in some strains of L. pneumophila but was absent from others. These findings represent the first evidence for a transposable element in Legionella and the first identification of an L. pneumophila strain-specific gene.
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Affiliation(s)
- V K Viswanathan
- Department of Microbiology and Immunology, Northwestern University Medical School, Chicago, Illinois 60611, USA
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20
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Heuner K, Dietrich C, Skriwan C, Steinert M, Hacker J. Influence of the alternative sigma(28) factor on virulence and flagellum expression of Legionella pneumophila. Infect Immun 2002; 70:1604-8. [PMID: 11854250 PMCID: PMC127743 DOI: 10.1128/iai.70.3.1604-1608.2002] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The fliA gene of Legionella pneumophila encoding the alternative sigma(28) factor was inactivated by introducing a kanamycin resistance cassette. Electron microscopy and Western blot analysis revealed that the fliA mutant strain is aflagellate and expresses no flagellin. Reporter gene assays indicated that the flaA promoter is not active in the fliA mutant strain. The fliA mutant strain multiplied less effectively in coculture with amoebae than the wild-type strain and was not able to replicate in coculture with Dictyostelium discoideum.
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Affiliation(s)
- Klaus Heuner
- Institut für Molekulare Infektionsbiologie, Universität Würzburg, 97070 Würzburg, Germany.
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21
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Robey M, O'Connell W, Cianciotto NP. Identification of Legionella pneumophila rcp, a pagP-like gene that confers resistance to cationic antimicrobial peptides and promotes intracellular infection. Infect Immun 2001; 69:4276-86. [PMID: 11401964 PMCID: PMC98497 DOI: 10.1128/iai.69.7.4276-4286.2001] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In the course of characterizing a locus involved in heme utilization, we identified a Legionella pneumophila gene predicted to encode a protein with homology to the product of the Salmonella enterica serovar Typhimurium pagP gene. In Salmonella, pagP increases resistance to the bactericidal effects of cationic antimicrobial peptides (CAMPs). Mutants with insertions in the L. pneumophila pagP-like gene were generated and showed decreased resistance to different structural classes of CAMPs compared to the wild type; hence, this gene was designated rcp for resistance to cationic antimicrobial peptides. Furthermore, Legionella CAMP resistance was induced by growth in low-magnesium medium. To determine whether rcp had any role in intracellular survival, mutants were tested in the two most relevant host cells for Legionnaires' disease, i.e., amoebae and macrophages. These mutants exhibited a 1,000-fold-decreased recovery during a Hartmannella vermiformis coculture. Complementation of the infectivity defect could be achieved by introduction of a plasmid containing the intact rcp gene. Mutations in rcp consistently reduced both the numbers of bacteria recovered during intracellular infection and their cytopathic capacity for U937 macrophages. The rcp mutant was also more defective for lung colonization of A/J mice. Growth of rcp mutants in buffered yeast extract broth was identical to that of the wild type, indicating that the observed differences in numbers of bacteria recovered from host cells were not due to a generalized growth defect. However, in low-Mg(2+) medium, the rcp mutant was impaired in stationary-phase survival. This is the first demonstration of a pagP-like gene, involved in resistance to CAMPs, being required for intracellular infection and virulence.
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Affiliation(s)
- M Robey
- Department of Microbiology-Immunology, Northwestern University Medical School, Chicago, Illinois 60611, USA
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22
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Rossier O, Cianciotto NP. Type II protein secretion is a subset of the PilD-dependent processes that facilitate intracellular infection by Legionella pneumophila. Infect Immun 2001; 69:2092-8. [PMID: 11254562 PMCID: PMC98134 DOI: 10.1128/iai.69.4.2092-2098.2001] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Previously, we had demonstrated that a Legionella pneumophila prepilin peptidase (pilD) mutant does not produce type IV pili and shows reduced secretion of enzymatic activities. Moreover, it displays a distinct colony morphology and a dramatic reduction in intracellular growth within amoebae and macrophages, two phenotypes that are not exhibited by a pilin (pilE(L)) mutant. To determine whether these pilD-dependent defects were linked to type II secretion, we have constructed two new mutants of L. pneumophila strain 130b. Mutations were introduced into either lspDE, which encodes the type II outer membrane secretin and ATPase, or lspFGHIJK, which encodes the pseudopilins. Unlike the wild-type and pilE(L) strains, both lspDE and lspG mutants showed reduced secretion of six pilD-dependent enzymatic activities; i.e., protease, acid phosphatase, p-nitrophenol phosphorylcholine hydrolase, lipase, phospholipase A, and lysophospholipase A. However, they exhibited a colony morphology different from that of the pilD mutant, suggesting that their surfaces are distinct. The pilD, lspDE, and lspG mutants were similarly and greatly impaired for growth within Hartmannella vermiformis, indicating that the intracellular defect of the peptidase mutant in amoebae is explained by the loss of type II secretion. When assessed for infection of U937 macrophages, both lsp mutants exhibited a 10-fold reduction in intracellular multiplication and a diminished cytopathic effect. Interestingly, the pilD mutant was clearly 100-fold more defective than the type II secretion mutants in U937 cells. These results suggest the existence of a novel pilD-dependent mechanism for promoting L. pneumophila intracellular infection of human cells.
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Affiliation(s)
- O Rossier
- Department of Microbiology and Immunology, Northwestern University Medical School, Chicago, Illinois 60611, USA
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23
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Carroll JA, Coleman SA, Smitherman LS, Minnick MF. Hemin-binding surface protein from Bartonella quintana. Infect Immun 2000; 68:6750-7. [PMID: 11083791 PMCID: PMC97776 DOI: 10.1128/iai.68.12.6750-6757.2000] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2000] [Accepted: 09/06/2000] [Indexed: 11/20/2022] Open
Abstract
Bartonella quintana, the agent of trench fever and a cause of endocarditis and bacillary angiomatosis in humans, has the highest reported in vitro hemin requirement for any bacterium. We determined that eight membrane-associated proteins from B. quintana bind hemin and that a approximately 25-kDa protein (HbpA) was the dominant hemin-binding protein. Like many outer membrane proteins, HbpA partitions to the detergent phase of a Triton X-114 extract of the cell and is heat modifiable, displaying an apparent molecular mass shift from approximately 25 to 30 kDa when solubilized at 100 degrees C. Immunoblots of purified outer and inner membranes and immunoelectron microscopy with whole cells show that HbpA is strictly located in the outer membrane and surface exposed, respectively. The N-terminal sequence of mature HbpA was determined and used to clone the HbpA-encoding gene (hbpA) from a lambda genomic library. The hbpA gene is 816 bp in length, encoding a predicted immature protein of approximately 29.3 kDa and a mature protein of 27.1 kDa. A Fur box homolog with 53% identity to the Escherichia coli Fur consensus is located upstream of hbpA and may be involved in regulating expression. BLAST searches indicate that the closest homologs to HbpA include the Bartonella henselae phage-associated membrane protein, Pap31 (58.4% identity), and the OMP31 porin from Brucella melitensis (31.7% identity). High-stringency Southern blots indicate that all five pathogenic Bartonella spp. possess hbpA homologs. Recombinant HbpA can bind hemin in vitro; however, it does not confer a hemin-binding phenotype upon E. coli. Intact B. quintana treated with purified anti-HbpA Fab fragments show a significant (P < 0.004) dose-dependent decrease in hemin binding relative to controls, suggesting that HbpA plays an active role in hemin acquisition and therefore pathogenesis. HbpA is the first potential virulence determinant characterized from B. quintana.
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Affiliation(s)
- J A Carroll
- Microscopy Branch, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, Hamilton, Montana 59840, USA
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24
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Viswanathan VK, Edelstein PH, Pope CD, Cianciotto NP. The Legionella pneumophila iraAB locus is required for iron assimilation, intracellular infection, and virulence. Infect Immun 2000; 68:1069-79. [PMID: 10678909 PMCID: PMC97250 DOI: 10.1128/iai.68.3.1069-1079.2000] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Legionella pneumophila, a facultative intracellular parasite of human alveolar macrophages and protozoa, causes Legionnaires' disease. Using mini-Tn10 mutagenesis, we previously isolated a L. pneumophila mutant that was hypersensitive to iron chelators. This mutant, NU216, and its allelic equivalent, NU216R, were also defective for intracellular infection, particularly in iron-deficient host cells. To determine whether NU216R was attenuated for virulence, we assessed its ability to cause disease in guinea pigs following intratracheal inoculation. NU216R-infected animals yielded 1,000-fold fewer bacteria from their lungs and spleen compared to wild-type-130b-infected animals that had received a 50-fold-lower dose. Moreover, NU216R-infected animals subsequently cleared the bacteria from these sites. While infection with 130b resulted in high fever, weight loss, and ruffled fur, inoculation with NU216R did not elicit any signs of disease. DNA sequence analysis revealed that the transposon insertion in NU216R lies in the first open reading frame of a two-gene operon. This open reading frame (iraA) encodes a 272-amino-acid protein that shows sequence similarity to methyltransferases. The second open reading frame (iraB) encodes a 501-amino-acid protein that is highly similar to di- and tripeptide transporters from both prokaryotes and eukaryotes. Southern hybridization analyses determined that the iraAB locus was largely limited to strains of L. pneumophila, the most pathogenic of the Legionella species. A newly derived mutant containing a targeted disruption of iraB showed reduced ability to grow under iron-depleted extracellular conditions, but it did not have an infectivity defect in the macrophage-like U937 cells. These data suggest that iraA is critical for virulence of L. pneumophila while iraB is involved in a novel method of iron acquisition which may utilize iron-loaded peptides.
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Affiliation(s)
- V K Viswanathan
- Department of Microbiology, Northwestern University Medical School, Chicago, Illinois 60611, USA
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25
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Liles MR, Scheel TA, Cianciotto NP. Discovery of a nonclassical siderophore, legiobactin, produced by strains of Legionella pneumophila. J Bacteriol 2000; 182:749-57. [PMID: 10633110 PMCID: PMC94339 DOI: 10.1128/jb.182.3.749-757.2000] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The mechanisms by which Legionella pneumophila, a facultative intracellular parasite and the agent of Legionnaires' disease, acquires iron are largely unexplained. Several earlier studies indicated that L. pneumophila does not elaborate siderophores. However, we now present evidence that supernatants from L. pneumophila cultures can contain a nonproteinaceous, high-affinity iron chelator. More specifically, when aerobically grown in a low-iron, chemically defined medium (CDM), L. pneumophila secretes a substance that is reactive in the chrome azurol S (CAS) assay. Importantly, the siderophore-like activity was only observed when the CDM cultures were inoculated to relatively high density with bacteria that had been grown overnight to log or early stationary phase in CDM or buffered yeast extract. Inocula derived from late-stationary-phase cultures, despite ultimately growing, consistently failed to result in the elaboration of siderophore-like activity. The Legionella CAS reactivity was detected in the culture supernatants of the serogroup 1 strains 130b and Philadelphia-1, as well as those from representatives of other serogroups and other Legionella species. The CAS-reactive substance was resistant to boiling and protease treatment and was associated with the <1-kDa supernatant fraction. As would also be expected for a siderophore, the addition of 0.5 or 2.0 microM iron to the cultures repressed the expression of the CAS-reactive substance. Interestingly, the supernatants were negative in the Arnow, Csáky, and Rioux assays, indicating that the Legionella siderophore was not a classic catecholate or hydroxamate and, hence, might have a novel structure. We have designated the L. pneumophila siderophore legiobactin.
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Affiliation(s)
- M R Liles
- Department of Microbiology and Immunology, Northwestern University Medical School, Chicago, Illinois 60611, USA
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26
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Segal G, Shuman HA. Legionella pneumophila utilizes the same genes to multiply within Acanthamoeba castellanii and human macrophages. Infect Immun 1999; 67:2117-24. [PMID: 10225863 PMCID: PMC115946 DOI: 10.1128/iai.67.5.2117-2124.1999] [Citation(s) in RCA: 231] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In previous reports we described a 22-kb Legionella pneumophila chromosomal locus containing 18 genes. Thirteen of these genes (icmT, -R, -Q, -P, -O, -M, -L, -K, -E, -C, -D, -J, and -B) were found to be completely required for intracellular growth and killing of human macrophages. Three genes (icmS, -G, and -F) were found to be partially required, and two genes (lphA and tphA) were found to be dispensable for intracellular growth and killing of human macrophages. Here, we analyzed the requirement of these genes for intracellular growth in the protozoan host Acanthamoeba castellanii, a well-established important environmental host of L. pneumophila. We found that all the genes that are completely required for intracellular growth in human macrophages are also completely required for intracellular growth in A. castellanii. However, the genes that are partially required for intracellular growth in human macrophages are completely required for intracellular growth in A. castellanii. In addition, the lphA gene, which was shown to be dispensable for intracellular growth in human macrophages, is partially required for intracellular growth in A. castellanii. Our results indicate that L. pneumophila utilizes the same genes to grow intracellularly in both human macrophages and amoebae.
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Affiliation(s)
- G Segal
- Department of Microbiology, College of Physicians & Surgeons, Columbia University, New York, New York 10032, USA
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27
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Graber KR, Smoot LM, Actis LA. Expression of iron binding proteins and hemin binding activity in the dental pathogen Actinobacillus actinomycetemcomitans. FEMS Microbiol Lett 1998; 163:135-42. [PMID: 9673015 DOI: 10.1111/j.1574-6968.1998.tb13037.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
Actinobacillus actinomycetemcomitans was found to express a polypeptide immunologically related to the Neisseria gonorrhoeae FbpA iron binding protein. In addition, the expression of hitB and hitC homologs was detected by Northern blot analysis. This periodontal pathogen also expresses a polypeptide homologous to the 31-kDa Haemophilus influenzae protein, which shows amino acid sequence homology with the FimA and YfeA proteins from Streptococcus parasanguis and Yersinia pestis, respectively. Both A. actinomycetemcomitans protein homologs were located within the periplasmic space, and their synthesis was regulated by the iron and hemin concentration of the culture medium. Southern and Western blot analysis together with molecular cloning revealed the presence of a Fur-like repressor, which may control the iron regulation of gene expression in this bacterium. Cultivation in the presence of hemin or Congo red revealed the ability of this organism to bind hemin. This binding activity was further confirmed by isolating Escherichia coli DH5 alpha clones that produced red and brown colonies on agar plates containing Congo red and hemin, respectively, after transformation with an A. actinomycetemcomitans gene library.
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Affiliation(s)
- K R Graber
- Department of Microbiology, Miami University, Oxford, OH 45056, USA
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28
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Liles MR, Viswanathan VK, Cianciotto NP. Identification and temperature regulation of Legionella pneumophila genes involved in type IV pilus biogenesis and type II protein secretion. Infect Immun 1998; 66:1776-82. [PMID: 9529113 PMCID: PMC108120 DOI: 10.1128/iai.66.4.1776-1782.1998] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/1997] [Accepted: 01/27/1998] [Indexed: 02/07/2023] Open
Abstract
Previously, we had isolated by transposon mutagenesis a Legionella pneumophila mutant that appeared defective for intracellular iron acquisition. While sequencing in the proximity of the mini-Tn10 insertion, we found a locus that had a predicted protein product with strong similarity to PilB from Pseudomonas aeruginosa. PilB is a component of the type II secretory pathway, which is required for the assembly of type IV pili. Consequently, the locus was cloned and sequenced. Within this 4-kb region were three genes that appeared to be organized in an operon and encoded homologs of P. aeruginosa PilB, PilC, and PilD, proteins essential for pilus production and type II protein secretion. Northern blot analysis identified a transcript large enough to include all three genes and showed a substantial increase in expression of this operon when L. pneumophila was grown at 30 degrees C as opposed to 37 degrees C. The latter observation was then correlated with an increase in piliation when bacteria were grown at the lower temperature. Southern hybridization analysis indicated that the pilB locus was conserved within L. pneumophila serogroups and other Legionella species. These data represent the first isolation of type II secretory genes from an intracellular parasite and indicate that the legionellae express temperature-regulated type IV pili.
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Affiliation(s)
- M R Liles
- Department of Microbiology-Immunology, Northwestern University, Chicago, Illinois 60611, USA
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29
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Guerry P, Perez-Casal J, Yao R, McVeigh A, Trust TJ. A genetic locus involved in iron utilization unique to some Campylobacter strains. J Bacteriol 1997; 179:3997-4002. [PMID: 9190817 PMCID: PMC179210 DOI: 10.1128/jb.179.12.3997-4002.1997] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Two genes involved in iron utilization in Campylobacter coli VC167 T1 have been characterized. The cfrA gene encodes a protein with a predicted Mr of 77,653 which, after processing of the leader sequence, has a predicted Mr of 75,635. This protein has significant sequence identity to siderophore receptors of several bacteria, and site-specific mutants defective in cfrA do not synthesize one of two major iron-repressible outer membrane proteins. An adjacent gene encodes a TonB-like protein; a mutant in this gene lost the ability to utilize hemin, ferrichrome, and enterochelin as iron sources. The cfrA and tonB genes of VC167 T1 hybridized to all strains of C. coli and most strains of C. jejuni examined but did not hybridize to several other strains of C. jejuni, suggesting that the thermophilic campylobacters can be separated into two categories based on the presence of these two iron utilization genes.
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Affiliation(s)
- P Guerry
- Enteric Diseases Program, Naval Medical Research Institute, Bethesda, Maryland 20889, USA.
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30
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Abstract
Streptococcus pneumoniae is a causative agent of bacterial pneumonia, otitis media, meningitis, and bacteremia. It causes considerable morbidity and mortality throughout the world, especially among children, the elderly, and immunocompromised individuals. We have demonstrated previously that the growth of S. pneumoniae is limited under iron-depleted conditions and can be restored by the addition of either hemin or hemoglobin. In the present study, we showed that S. pneumoniae had the ability to bind hemin and that the level of hemin binding activity was not affected by supplementation of the growth medium with iron. Approximately 70 to 80% of the hemin binding activity was mediated by proteinase-resistant components, and the remainder was mediated by proteins. Hemin binding proteins were located in both soluble extract and envelope fractions of pneumococcal cells. By batch affinity chromatography, a major hemin binding polypeptide with an apparent molecular mass of 43 kDa was identified in the cell lysate of S. pneumoniae. Polyclonal antibodies against this polypeptide were raised. By immunoblot analysis, this hemin binding polypeptide was localized in the envelope and did not exhibit any variation in molecular weight among all serotypes tested. The subcellular distribution of hemin binding activity may have functional implications.
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Affiliation(s)
- S S Tai
- Department of Microbiology, College of Medicine, Howard University, Washington, DC 20059, USA
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31
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Hickey EK, Cianciotto NP. An iron- and fur-repressed Legionella pneumophila gene that promotes intracellular infection and encodes a protein with similarity to the Escherichia coli aerobactin synthetases. Infect Immun 1997; 65:133-43. [PMID: 8975903 PMCID: PMC174567 DOI: 10.1128/iai.65.1.133-143.1997] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Legionella pneumophila, a parasite of alveolar macrophages, requires iron for intra- and extracellular growth. Although its mechanisms for iron assimilation are poorly understood, this bacterium produces Fur, a protein that can repress gene transcription in response to iron concentration. Because iron- and Fur-regulated genes are important for infection in other bacteria, the identification of similar genes in L. pneumophila was undertaken. A wild-type strain of L. pneumophila was randomly mutated with a mini-Tn10' lacZ transposon, and the resulting gene fusions were tested for iron regulation by assessing beta-galactosidase production in the presence and absence of iron chelators. Of the initial six mutants with iron-repressed lacZ fusions, two strains, NU229 and NU232, possessed fusions that were stably iron regulated. To assay for Fur regulation, the levels of beta-galactosidase were measured in strains no longer producing Fur. As in a number of pathogenic bacteria, L. pneumophila fur could not be insertionally inactivated, but spontaneous Fur- derivatives were generated by selecting for manganese resistance. Strain NU229 contained a Fur-repressed fusion based on derepression of lacZ expression in its manganese-resistant derivative. Extracellular growth of NU229 in bacteriological media was similar to that of wild-type strain 130b. To assess the role of an iron- and Fur-regulated (frgA) gene in intracellular infection, the ability of NU229 to grow within U937 cell monolayers was tested. Quantitative infection assays demonstrated that intracellular growth of NU229 was impaired as much as 80-fold. Reconstruction of the mutant by allelic exchange proved that the infectivity defect in NU229 was due to the inactivation of frgA and not to a second-site mutation. Subsequently, complementation of the interrupted gene by an intact plasmid-encoded gene demonstrated that the infectivity defect was due to the loss of frgA and not to a polar effect. Nucleotide sequence analysis revealed that the 63-kDa FrgA protein has homology with the aerobactin synthetases IucA and IucC of Escherichia coli, raising the possibility that L. pneumophila encodes a siderophore which is required for optimal intracellular replication. Southern hybridization analysis determined that frgA is specific to L. pneumophila.
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Affiliation(s)
- E K Hickey
- Department of Microbiology-Immunology, Northwestern University, Chicago, Illinois 60611, USA
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O'Connell WA, Dhand L, Cianciotto NP. Infection of macrophage-like cells by Legionella species that have not been associated with disease. Infect Immun 1996; 64:4381-4. [PMID: 8926117 PMCID: PMC174385 DOI: 10.1128/iai.64.10.4381-4384.1996] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
We assessed the ability of Legionella species that have not been associated with disease to infect macrophage-like U937 cells. Two of fourteen species tested exhibited a 50% infective dose that was within I log unit of that of virulent L. pneumophila. Indeed, intracellular CFU of L. jamestowniensis and L. parisiensis increased 100-fold over a 72-h period. These data indicate that additional legionellae can flourish within phagocytes and therefore, can, if given the opportunity, cause disease.
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Affiliation(s)
- W A O'Connell
- Department of Microbiology-Immunology, Northwestern University, Chicago, Illinois 60611, USA
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