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Favaron C, Gabano E, Zanellato I, Gaiaschi L, Casali C, Bottone MG, Ravera M. Effects of Ferrocene and Ferrocenium on MCF-7 Breast Cancer Cells and Interconnection with Regulated Cell Death Pathways. Molecules 2023; 28:6469. [PMID: 37764244 PMCID: PMC10537025 DOI: 10.3390/molecules28186469] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2023] [Revised: 09/01/2023] [Accepted: 09/04/2023] [Indexed: 09/29/2023] Open
Abstract
The effects of ferrocene (Fc) and ferrocenium (Fc+) induced in triple negative human breast cancer MCF-7 cells were explored by immunofluorescence, flow cytometry, and transmission electron microscopy analysis. The different abilities of Fc and Fc+ to produce reactive oxygen species and induce oxidative stress were clearly observed by activating apoptosis and morphological changes after treatment, but also after tests performed on the model organism D. discoideum, particularly in the case of Fc+. The induction of ferroptosis, an iron-dependent form of regulated cell death driven by an overload of lipid peroxides in cellular membranes, occurred after 2 h of treatment with Fc+ but not Fc. However, the more stable Fc showed its effects by activating necroptosis after a longer-lasting treatment. The differences observed in terms of cell death mechanisms and timing may be due to rapid interconversion between the two oxidative forms of internalized iron species (from Fe2+ to Fe3+ and vice versa). Potential limitations include the fact that iron metabolism and mitophagy have not been investigated. However, the ability of both Fc and Fc+ to trigger different and interregulated types of cell death makes them suitable to potentially overcome the shortcomings of traditional apoptosis-mediated anticancer therapies.
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Affiliation(s)
- Cristina Favaron
- Department of Biology and Biotechnology “L. Spallanzani”, University of Pavia, Via Ferrata 9, 27100 Pavia, Italy; (C.F.); (L.G.); (C.C.)
| | - Elisabetta Gabano
- Department of Sustainable Development and Ecological Transition, University of Piemonte Orientale, Piazza S. Eusebio 5, 13100 Vercelli, Italy;
| | - Ilaria Zanellato
- Department of Sciences and Technological Innovation, University of Piemonte Orientale, Viale Teresa Michel 11, 15121 Alessandria, Italy
| | - Ludovica Gaiaschi
- Department of Biology and Biotechnology “L. Spallanzani”, University of Pavia, Via Ferrata 9, 27100 Pavia, Italy; (C.F.); (L.G.); (C.C.)
| | - Claudio Casali
- Department of Biology and Biotechnology “L. Spallanzani”, University of Pavia, Via Ferrata 9, 27100 Pavia, Italy; (C.F.); (L.G.); (C.C.)
| | - Maria Grazia Bottone
- Department of Biology and Biotechnology “L. Spallanzani”, University of Pavia, Via Ferrata 9, 27100 Pavia, Italy; (C.F.); (L.G.); (C.C.)
| | - Mauro Ravera
- Department of Sciences and Technological Innovation, University of Piemonte Orientale, Viale Teresa Michel 11, 15121 Alessandria, Italy
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Peracino B, Monica V, Primo L, Bracco E, Bozzaro S. Iron metabolism in the social amoeba Dictyostelium discoideum: a role for Ferric Chelate Reductases. Eur J Cell Biol 2022; 101:151230. [DOI: 10.1016/j.ejcb.2022.151230] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2022] [Revised: 04/07/2022] [Accepted: 04/25/2022] [Indexed: 11/17/2022] Open
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3
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Molecular Mechanism of Nramp-Family Transition Metal Transport. J Mol Biol 2021; 433:166991. [PMID: 33865868 DOI: 10.1016/j.jmb.2021.166991] [Citation(s) in RCA: 38] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2021] [Revised: 04/02/2021] [Accepted: 04/05/2021] [Indexed: 02/06/2023]
Abstract
The Natural resistance-associated macrophage protein (Nramp) family of transition metal transporters enables uptake and trafficking of essential micronutrients that all organisms must acquire to survive. Two decades after Nramps were identified as proton-driven, voltage-dependent secondary transporters, multiple Nramp crystal structures have begun to illustrate the fine details of the transport process and provide a new framework for understanding a wealth of preexisting biochemical data. Here we review the relevant literature pertaining to Nramps' biological roles and especially their conserved molecular mechanism, including our updated understanding of conformational change, metal binding and transport, substrate selectivity, proton transport, proton-metal coupling, and voltage dependence. We ultimately describe how the Nramp family has adapted the LeuT fold common to many secondary transporters to provide selective transition-metal transport with a mechanism that deviates from the canonical model of symport.
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Cinquetti R, Imperiali FG, Bozzaro S, Zanella D, Vacca F, Roseti C, Peracino B, Castagna M, Bossi E. Characterization of Transport Activity of SLC11 Transporters in Xenopus laevis Oocytes by Fluorophore Quenching. SLAS DISCOVERY 2021; 26:798-810. [PMID: 33825579 DOI: 10.1177/24725552211004123] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Membrane proteins are involved in different physiological functions and are the target of pharmaceutical and abuse drugs. Xenopus laevis oocytes provide a powerful heterologous expression system for functional studies of these proteins. Typical experiments investigate transport using electrophysiology and radiolabeled uptake. A two-electrode voltage clamp is suitable only for electrogenic proteins, and uptake measurements require the existence of radiolabeled substrates and adequate laboratory facilities.Recently, Dictyostelium discoideum Nramp1 and NrampB were characterized using multidisciplinary approaches. NrampB showed no measurable electrogenic activity, and it was investigated in Xenopus oocytes by acquiring confocal images of the quenching of injected fluorophore calcein.This method is adequate to measure the variation in emitted fluorescence, and thus transporter activity indirectly, but requires long experimental procedures to collect statistically consistent data. Considering that optimal expression of heterologous proteins lasts for 48-72 h, a slow acquiring process requires the use of more than one batch of oocytes to complete the experiments. Here, a novel approach to measure substrate uptake is reported. Upon injection of a fluorophore, oocytes were incubated with the substrate and the transport activity measured, evaluating fluorescence quenching in a microplate reader. The technique permits the testing of tens of oocytes in different experimental conditions simultaneously, and thus the collection of significant statistical data for each batch, saving time and animals.The method was tested with different metal transporters (SLC11), DMT1, DdNramp1, and DdNrampB, and verified with the peptide transporter PepT1 (SLC15). Comparison with traditional methods (uptake, two-electrode voltage clamp) and with quenching images acquired by fluorescence microscopy confirmed its efficacy.
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Affiliation(s)
| | | | | | - Daniele Zanella
- University of Insubria, Varese, Lombardia, Italy.,The University of Alabama, Birmingham, AL, USA
| | - Francesca Vacca
- University of Insubria, Varese, Lombardia, Italy.,Italian Institute of Technology (IIT), Genova, Italy
| | | | | | | | - Elena Bossi
- University of Insubria, Varese, Lombardia, Italy
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Zn 2+ Intoxication of Mycobacterium marinum during Dictyostelium discoideum Infection Is Counteracted by Induction of the Pathogen Zn 2+ Exporter CtpC. mBio 2021; 12:mBio.01313-20. [PMID: 33531393 PMCID: PMC7858047 DOI: 10.1128/mbio.01313-20] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Microelements are essential for the function of the innate immune system. A deficiency in zinc or copper results in an increased susceptibility to bacterial infections. Macrophages use diverse strategies to restrict intracellular pathogens, including either depriving the bacteria of (micro)nutrients such as transition metals or intoxicating them via metal accumulation. Little is known about the chemical warfare between Mycobacterium marinum, a close relative of Mycobacterium tuberculosis (Mtb), and its hosts. We use the professional phagocyte Dictyostelium discoideum to investigate the role of Zn2+ during M. marinum infection. We show that M. marinum senses toxic levels of Zn2+ and responds by upregulating one of its isoforms of the Zn2+ efflux transporter CtpC. Deletion of ctpC (MMAR_1271) leads to growth inhibition in broth supplemented with Zn2+ as well as reduced intracellular growth. Both phenotypes were fully rescued by constitutive ectopic expression of the Mtb CtpC orthologue demonstrating that MMAR_1271 is the functional CtpC Zn2+ efflux transporter in M. marinum. Infection leads to the accumulation of Zn2+ inside the Mycobacterium-containing vacuole (MCV), achieved by the induction and recruitment of the D. discoideum Zn2+ efflux pumps ZntA and ZntB. In cells lacking ZntA, there is further attenuation of M. marinum growth, presumably due to a compensatory efflux of Zn2+ into the MCV, carried out by ZntB, the main Zn2+ transporter in endosomes and phagosomes. Counterintuitively, bacterial growth is also impaired in zntB KO cells, in which MCVs appear to accumulate less Zn2+ than in wild-type cells, suggesting restriction by other Zn2+-mediated mechanisms. Absence of CtpC further epistatically attenuates the intracellular proliferation of M. marinum in zntA and zntB KO cells, confirming that mycobacteria face noxious levels of Zn2+.
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Olmos J, Pignataro MF, Benítez dos Santos AB, Bringas M, Klinke S, Kamenetzky L, Velazquez F, Santos J. A Highly Conserved Iron-Sulfur Cluster Assembly Machinery between Humans and Amoeba Dictyostelium discoideum: The Characterization of Frataxin. Int J Mol Sci 2020; 21:E6821. [PMID: 32957566 PMCID: PMC7554988 DOI: 10.3390/ijms21186821] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2020] [Revised: 09/05/2020] [Accepted: 09/14/2020] [Indexed: 12/17/2022] Open
Abstract
Several biological activities depend on iron-sulfur clusters ([Fe-S]). Even though they are well-known in several organisms their function and metabolic pathway were poorly understood in the majority of the organisms. We propose to use the amoeba Dictyostelium discoideum, as a biological model to study the biosynthesis of [Fe-S] at the molecular, cellular and organism levels. First, we have explored the D. discoideum genome looking for genes corresponding to the subunits that constitute the molecular machinery for Fe-S cluster assembly and, based on the structure of the mammalian supercomplex and amino acid conservation profiles, we inferred the full functionality of the amoeba machinery. After that, we expressed the recombinant mature form of D. discoideum frataxin protein (DdFXN), the kinetic activator of this pathway. We characterized the protein and its conformational stability. DdFXN is monomeric and compact. The analysis of the secondary structure content, calculated using the far-UV CD spectra, was compatible with the data expected for the FXN fold, and near-UV CD spectra were compatible with the data corresponding to a folded protein. In addition, Tryptophan fluorescence indicated that the emission occurs from an apolar environment. However, the conformation of DdFXN is significantly less stable than that of the human FXN, (4.0 vs. 9.0 kcal mol-1, respectively). Based on a sequence analysis and structural models of DdFXN, we investigated key residues involved in the interaction of DdFXN with the supercomplex and the effect of point mutations on the energetics of the DdFXN tertiary structure. More than 10 residues involved in Friedreich's Ataxia are conserved between the human and DdFXN forms, and a good correlation between mutational effect on the energetics of both proteins were found, suggesting the existence of similar sequence/function/stability relationships. Finally, we integrated this information in an evolutionary context which highlights particular variation patterns between amoeba and humans that may reflect a functional importance of specific protein positions. Moreover, the complete pathway obtained forms a piece of evidence in favor of the hypothesis of a shared and highly conserved [Fe-S] assembly machinery between Human and D. discoideum.
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Affiliation(s)
- Justo Olmos
- Instituto de Biociencias, Biotecnología y Biología Traslacional (iB3), Departamento de Fisiología y Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Intendente Güiraldes 2160, Ciudad Universitaria, Buenos Aires C1428EGA, Argentina; (J.O.); (M.F.P.); (A.B.B.d.S.); (L.K.)
| | - María Florencia Pignataro
- Instituto de Biociencias, Biotecnología y Biología Traslacional (iB3), Departamento de Fisiología y Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Intendente Güiraldes 2160, Ciudad Universitaria, Buenos Aires C1428EGA, Argentina; (J.O.); (M.F.P.); (A.B.B.d.S.); (L.K.)
| | - Ana Belén Benítez dos Santos
- Instituto de Biociencias, Biotecnología y Biología Traslacional (iB3), Departamento de Fisiología y Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Intendente Güiraldes 2160, Ciudad Universitaria, Buenos Aires C1428EGA, Argentina; (J.O.); (M.F.P.); (A.B.B.d.S.); (L.K.)
| | - Mauro Bringas
- Departamento de Química Inorgánica, Analítica y Química Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Instituto de Química Física de los Materiales, Medio Ambiente y Energía (INQUIMAE CONICET), Buenos Aires C1428EGA, Argentina;
| | - Sebastián Klinke
- Fundación Instituto Leloir, IIBBA-CONICET, and Plataforma Argentina de Biología Estructural y Metabolómica PLABEM, Av. Patricias Argentinas 435, Buenos Aires C1405BWE, Argentina;
| | - Laura Kamenetzky
- Instituto de Biociencias, Biotecnología y Biología Traslacional (iB3), Departamento de Fisiología y Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Intendente Güiraldes 2160, Ciudad Universitaria, Buenos Aires C1428EGA, Argentina; (J.O.); (M.F.P.); (A.B.B.d.S.); (L.K.)
- IMPaM, CONICET, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires C1121ABG, Argentina
| | - Francisco Velazquez
- Instituto de Biociencias, Biotecnología y Biología Traslacional (iB3), Departamento de Fisiología y Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Intendente Güiraldes 2160, Ciudad Universitaria, Buenos Aires C1428EGA, Argentina; (J.O.); (M.F.P.); (A.B.B.d.S.); (L.K.)
- Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales (IQUIBICEN)—(UBA/CONICET), Buenos Aires C1428EGA, Argentina
| | - Javier Santos
- Instituto de Biociencias, Biotecnología y Biología Traslacional (iB3), Departamento de Fisiología y Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Intendente Güiraldes 2160, Ciudad Universitaria, Buenos Aires C1428EGA, Argentina; (J.O.); (M.F.P.); (A.B.B.d.S.); (L.K.)
- Consejo Nacional de Investigaciones Científicas y Técnicas, Rivadavia 1917, Buenos Aires C1033AAJ, Argentina
- Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires. Intendente Güiraldes 2160, Ciudad Universitaria, Buenos Aires C1428EGA, Argentina
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Knobloch P, Koliwer-Brandl H, Arnold FM, Hanna N, Gonda I, Adenau S, Personnic N, Barisch C, Seeger MA, Soldati T, Hilbi H. Mycobacterium marinum produces distinct mycobactin and carboxymycobactin siderophores to promote growth in broth and phagocytes. Cell Microbiol 2020; 22:e13163. [PMID: 31945239 DOI: 10.1111/cmi.13163] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2019] [Accepted: 12/22/2019] [Indexed: 02/06/2023]
Abstract
Mycobacterium marinum is a model organism for pathogenic Mycobacterium species, including Mycobacterium tuberculosis, the causative agent of tuberculosis. These pathogens enter phagocytes and replicate within the Mycobacterium-containing vacuole, possibly followed by vacuole exit and growth in the host cell cytosol. Mycobacteria release siderophores called mycobactins to scavenge iron, an essential yet poorly soluble and available micronutrient. To investigate the role of M. marinum mycobactins, we purified by organic solvent extraction and identified by mass spectrometry the lipid-bound mycobactin (MBT) and the water-soluble variant carboxymycobactin (cMBT). Moreover, we generated by specialised phage transduction a defined M. marinum ΔmbtB deletion mutant predicted to be defective for mycobactin production. The M. marinum ΔmbtB mutant strain showed a severe growth defect in broth and phagocytes, which was partially complemented by supplying the mbtB gene on a plasmid. Furthermore, purified Fe-MBT or Fe-cMBT improved the growth of wild type as well as ΔmbtB mutant bacteria on minimal plates, but only Fe-cMBT promoted the growth of wild-type M. marinum during phagocyte infection. Finally, the intracellular growth of M. marinum ΔmbtB in Acanthamoeba castellanii amoebae was restored by coinfection with wild-type bacteria. Our study identifies and characterises the M. marinum MBT and cMBT siderophores and reveals the requirement of mycobactins for extra- and intracellular growth of the pathogen.
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Affiliation(s)
- Paulina Knobloch
- Institute of Medical Microbiology, University of Zürich, Zürich, Switzerland
| | | | - Fabian M Arnold
- Institute of Medical Microbiology, University of Zürich, Zürich, Switzerland
| | - Nabil Hanna
- Department of Biochemistry, Faculty of Sciences, University of Geneva, Geneva, Switzerland
| | - Imre Gonda
- Institute of Medical Microbiology, University of Zürich, Zürich, Switzerland
| | - Sophia Adenau
- Institute of Medical Microbiology, University of Zürich, Zürich, Switzerland
| | - Nicolas Personnic
- Institute of Medical Microbiology, University of Zürich, Zürich, Switzerland
| | - Caroline Barisch
- Department of Biochemistry, Faculty of Sciences, University of Geneva, Geneva, Switzerland
| | - Markus A Seeger
- Institute of Medical Microbiology, University of Zürich, Zürich, Switzerland
| | - Thierry Soldati
- Department of Biochemistry, Faculty of Sciences, University of Geneva, Geneva, Switzerland
| | - Hubert Hilbi
- Institute of Medical Microbiology, University of Zürich, Zürich, Switzerland
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Type II Secretion Promotes Bacterial Growth within the Legionella-Containing Vacuole in Infected Amoebae. Infect Immun 2019; 87:IAI.00374-19. [PMID: 31405960 DOI: 10.1128/iai.00374-19] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2019] [Accepted: 08/08/2019] [Indexed: 12/30/2022] Open
Abstract
It was previously determined that the type II secretion system (T2SS) promotes the ability of Legionella pneumophila to grow in coculture with amoebae. Here, we discerned the stage of intracellular infection that is potentiated by comparing the wild-type and T2SS mutant legionellae for their capacity to parasitize Acanthamoeba castellanii Whereas the mutant behaved normally for entry into the host cells and subsequent evasion of degradative lysosomes, it was impaired in the ability to replicate, with that defect being first evident at approximately 9 h postentry. The replication defect was initially documented in three ways: by determining the numbers of CFU recovered from the lysates of the infected monolayers, by monitoring the levels of fluorescence associated with amoebal monolayers infected with green fluorescent protein (GFP)-expressing bacteria, and by utilizing flow cytometry to quantitate the amounts of GFP-expressing bacteria in individual amoebae. By employing confocal microscopy and newer imaging techniques, we further determined the progression in volume and shape of the bacterial vacuoles and found that the T2SS mutant grows at a decreased rate and does not attain maximally sized phagosomes. Overall, the entire infection cycle (i.e., entry to egress) was considerably slower for the T2SS mutant than it was for the wild-type strain, and the mutant's defect was maintained over multiple rounds of infection. Thus, the T2SS is absolutely required for L. pneumophila to grow to larger numbers in its intravacuolar niche within amoebae. Combining these results with those of our recent analysis of macrophage infection, T2SS is clearly a major component of L. pneumophila intracellular infection.
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Buracco S, Peracino B, Andreini C, Bracco E, Bozzaro S. Differential Effects of Iron, Zinc, and Copper on Dictyostelium discoideum Cell Growth and Resistance to Legionella pneumophila. Front Cell Infect Microbiol 2018; 7:536. [PMID: 29379774 PMCID: PMC5770829 DOI: 10.3389/fcimb.2017.00536] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2017] [Accepted: 12/26/2017] [Indexed: 12/29/2022] Open
Abstract
Iron, zinc, and copper play fundamental roles in eucaryotes and procaryotes, and their bioavailability regulates host-pathogen interactions. For intracellular pathogens, the source of metals is the cytoplasm of the host, which in turn manipulates intracellular metal traffic following pathogen recognition. It is established that iron is withheld from the pathogen-containing vacuole, whereas for copper and zinc the evidence is unclear. Most infection studies in mammals have concentrated on effects of metal deficiency/overloading at organismal level. Thus, zinc deficiency or supplementation correlate with high risk of respiratory tract infection or recovery from severe infection, respectively. Iron, zinc, and copper deficiency or overload affects lymphocyte proliferation/maturation, and thus the adaptive immune response. Whether they regulate innate immunity at macrophage level is open, except for iron. The early identification in a mouse mutant susceptible to mycobacterial infection of the iron transporter Nramp1 allowed dissecting Nramp1 role in phagocytes, from the social amoeba Dictyostelium to macrophages. Nramp1 regulates iron efflux from the phagosomes, thus starving pathogenic bacteria for iron. Similar studies for zinc or copper are scant, due to the large number of copper and zinc transporters. In Dictyostelium, zinc and copper transporters include 11 and 6 members, respectively. To assess the role of zinc or copper in Dictyostelium, cells were grown under conditions of metal depletion or excess and tested for resistance to Legionella pneumophila infection. Iron shortage or overload inhibited Dictyostelium cell growth within few generations. Surprisingly, zinc or copper depletion failed to affect growth. Zinc or copper overloading inhibited cell growth at, respectively, 50- or 500-fold the physiological concentration, suggesting very efficient control of their homeostasis, as confirmed by Inductively Coupled Plasma Mass Spectrometry quantification of cellular metals. Legionella infection was inhibited or enhanced in cells grown under iron shortage or overload, respectively, confirming a major role for iron in controlling resistance to pathogens. In contrast, zinc and copper depletion or excess during growth did not affect Legionella infection. Using Zinpyr-1 as fluorescent sensor, we show that zinc accumulates in endo-lysosomal vesicles, including phagosomes, and the contractile vacuole. Furthermore, we provide evidence for permeabilization of the Legionella-containing vacuole during bacterial proliferation.
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Affiliation(s)
- Simona Buracco
- Department of Clinical and Biological Sciences, University of Torino, Turin, Italy
| | - Barbara Peracino
- Department of Clinical and Biological Sciences, University of Torino, Turin, Italy
| | - Claudia Andreini
- Magnetic Resonance Center (CERM), University of Florence, Florence, Italy
| | - Enrico Bracco
- Department of Oncology, University of Torino, Turin, Italy
| | - Salvatore Bozzaro
- Department of Clinical and Biological Sciences, University of Torino, Turin, Italy
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Barisch C, Kalinina V, Lefrançois LH, Appiah J, López-Jiménez AT, Soldati T. Localization of all four ZnT zinc transporters in Dictyostelium and impact of ZntA and B knockout on bacteria killing. J Cell Sci 2018; 131:jcs.222000. [DOI: 10.1242/jcs.222000] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2018] [Accepted: 10/17/2018] [Indexed: 01/26/2023] Open
Abstract
Professional phagocytes have developed an extensive repertoire of autonomous immunity strategies to ensure killing of bacteria. Besides phagosome acidification and the generation of reactive oxygen species, deprivation of nutrients and the lumenal accumulation of toxic metals are essential to kill ingested bacteria or inhibit growth of intracellular pathogens. We use the soil amoeba Dictyostelium discoideum, a professional phagocyte that digests bacteria for nutritional purposes, to decipher the role of zinc poisoning during phagocytosis of non-pathogenic bacteria and visualize the temporal and spatial dynamics of compartmentalized, free zinc using fluorescent probes. Immediately after particle uptake, zinc is delivered to phagosomes by fusion with “zincosomes” of endosomal origin, but also by the action of one or more zinc transporters. We localize the four Dictyostelium ZnT transporters to endosomes, the contractile vacuole and the Golgi apparatus, and study the impact of znt knockouts on zinc homeostasis. Finally, we show that zinc is delivered into the lumen of Mycobacterium smegmatis-containing vacuoles, and that Escherichia coli deficient in the zinc efflux P1B-type ATPase ZntA is killed faster than wild type bacteria.
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Affiliation(s)
- Caroline Barisch
- Department of Biochemistry, Faculty of Science, University of Geneva, 30 quai Ernest-Ansermet, Science II, 1211 Geneva-4, Switzerland
| | - Vera Kalinina
- Department of Biochemistry, Faculty of Science, University of Geneva, 30 quai Ernest-Ansermet, Science II, 1211 Geneva-4, Switzerland
- Present address: Institute of Cytology, Russian Academy of Sciences, Tikhoretsky ave. 4, 194064 St. Petersburg, Russia
| | - Louise H. Lefrançois
- Department of Biochemistry, Faculty of Science, University of Geneva, 30 quai Ernest-Ansermet, Science II, 1211 Geneva-4, Switzerland
| | - Joddy Appiah
- Department of Biochemistry, Faculty of Science, University of Geneva, 30 quai Ernest-Ansermet, Science II, 1211 Geneva-4, Switzerland
| | - Ana T. López-Jiménez
- Department of Biochemistry, Faculty of Science, University of Geneva, 30 quai Ernest-Ansermet, Science II, 1211 Geneva-4, Switzerland
| | - Thierry Soldati
- Department of Biochemistry, Faculty of Science, University of Geneva, 30 quai Ernest-Ansermet, Science II, 1211 Geneva-4, Switzerland
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Yu HZ, Zhang SZ, Ma Y, Fei DQ, Li B, Yang LA, Wang J, Li Z, Muhammad A, Xu JP. Molecular Characterization and Functional Analysis of a Ferritin Heavy Chain Subunit from the Eri-Silkworm, Samia cynthia ricini. Int J Mol Sci 2017; 18:ijms18102126. [PMID: 29036914 PMCID: PMC5666808 DOI: 10.3390/ijms18102126] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2017] [Revised: 10/05/2017] [Accepted: 10/06/2017] [Indexed: 01/16/2023] Open
Abstract
Ferritins are conserved iron-binding proteins that are primarily involved in iron storage, detoxification and the immune response. Despite the importance of ferritin in organisms, little is known about their roles in the eri-silkworm (Samia cynthia ricini). We previously identified a ferritin heavy chain subunit named ScFerHCH in the S. c. ricini transcriptome database. The full-length S. c. ricini ferritin heavy chain subunit (ScFerHCH) was 1863 bp and encoded a protein of 231 amino acids with a deduced molecular weight of 25.89 kDa. Phylogenetic analysis revealed that ScFerHCH shared a high amino acid identity with the Bombyx mori and Danaus plexippus heavy chain subunits. Higher ScFerHCH expression levels were found in the silk gland, fat body and midgut of S. c. ricini by reverse transcription quantitative polymerase chain reaction (RT-qPCR) and Western blotting. Injection of Staphylococcus aureus and Pseudomonas aeruginosa was associated with an upregulation of ScFerHCH in the midgut, fat body and hemolymph, indicating that ScFerHCH may contribute to the host’s defense against invading pathogens. In addition, the anti-oxidation activity and iron-binding capacity of recombinant ScFerHCH protein were examined. Taken together, our results suggest that the ferritin heavy chain subunit from eri-silkworm may play critical roles not only in innate immune defense, but also in organismic iron homeostasis.
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Affiliation(s)
- Hai-Zhong Yu
- School of Life Sciences, Anhui Agricultural University, Hefei 230036, China.
| | - Shang-Zhi Zhang
- School of Life Sciences, Anhui Agricultural University, Hefei 230036, China.
| | - Yan Ma
- School of Life Sciences, Anhui Agricultural University, Hefei 230036, China.
| | - Dong-Qiong Fei
- School of Life Sciences, Anhui Agricultural University, Hefei 230036, China.
| | - Bing Li
- School of Life Sciences, Anhui Agricultural University, Hefei 230036, China.
| | - Li-Ang Yang
- School of Life Sciences, Anhui Agricultural University, Hefei 230036, China.
| | - Jie Wang
- School of Life Sciences, Anhui Agricultural University, Hefei 230036, China.
| | - Zhen Li
- School of Life Sciences, Anhui Agricultural University, Hefei 230036, China.
| | - Azharuddin Muhammad
- School of Life Sciences, Anhui Agricultural University, Hefei 230036, China.
| | - Jia-Ping Xu
- School of Life Sciences, Anhui Agricultural University, Hefei 230036, China.
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12
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Brenz Y, Ohnezeit D, Winther-Larsen HC, Hagedorn M. Nramp1 and NrampB Contribute to Resistance against Francisella in Dictyostelium. Front Cell Infect Microbiol 2017; 7:282. [PMID: 28680861 PMCID: PMC5478718 DOI: 10.3389/fcimb.2017.00282] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2017] [Accepted: 06/09/2017] [Indexed: 12/16/2022] Open
Abstract
The Francisella genus comprises highly pathogenic bacteria that can cause fatal disease in their vertebrate and invertebrate hosts including humans. In general, Francisella growth depends on iron availability, hence, iron homeostasis must be tightly regulated during Francisella infection. We used the system of the professional phagocyte Dictyostelium and the fish pathogen F. noatunensis subsp. noatunensis (F.n.n.) to investigate the role of the host cell iron transporters Nramp (natural resistance associated macrophage proteins) during Francisella infection. Like its mammalian ortholog, Dictyostelium Nramp1 transports iron from the phagosome into the cytosol, whereas the paralog NrampB is located on the contractile vacuole and controls, together with Nramp1, the cellular iron homeostasis. In Dictyostelium, Nramp1 localized to the F.n.n.-phagosome but disappeared from the compartment dependent on the presence of IglC, an established Francisella virulence factor. In the absence of Nramp transporters the bacteria translocated more efficiently from the phagosome into the host cell cytosol, its replicative niche. Increased escape rates coincided with increased proteolytic activity in bead-containing phagosomes indicating a role of the Nramp transporters for phagosomal maturation. In the nramp mutants, a higher bacterial load was observed in the replicative phase compared to wild-type host cells. Upon bacterial access to the cytosol of wt cells, mRNA levels of bacterial iron uptake factors were transiently upregulated. Decreased iron levels in the nramp mutants were compensated by a prolonged upregulation of the iron scavenging system. These results show that Nramps contribute to host cell immunity against Francisella infection by influencing the translocation efficiency from the phagosome to the cytosol but not by restricting access to nutritional iron in the cytosol.
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Affiliation(s)
- Yannick Brenz
- Department of Parasitology, Bernhard Nocht Institute for Tropical MedicineHamburg, Germany
| | - Denise Ohnezeit
- Institute for Medical Microbiology, Hygiene and Virology, University Medical Center Hamburg-EppendorfHamburg, Germany
| | - Hanne C Winther-Larsen
- Centre for Integrative Microbial Evolution and Department of Pharmaceutical Biosciences, University of OsloOslo, Norway
| | - Monica Hagedorn
- Department of Life Sciences and Chemistry, Jacobs UniversityBremen, Germany
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13
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Huber RJ. Using the social amoeba Dictyostelium to study the functions of proteins linked to neuronal ceroid lipofuscinosis. J Biomed Sci 2016; 23:83. [PMID: 27881166 PMCID: PMC5122030 DOI: 10.1186/s12929-016-0301-0] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2016] [Accepted: 11/15/2016] [Indexed: 12/12/2022] Open
Abstract
Neuronal ceroid lipofuscinosis (NCL), also known as Batten disease, is a debilitating neurological disorder that affects both children and adults. Thirteen genetically distinct genes have been identified that when mutated, result in abnormal lysosomal function and an excessive accumulation of ceroid lipofuscin in neurons, as well as other cell types outside of the central nervous system. The NCL family of proteins is comprised of lysosomal enzymes (PPT1/CLN1, TPP1/CLN2, CTSD/CLN10, CTSF/CLN13), proteins that peripherally associate with membranes (DNAJC5/CLN4, KCTD7/CLN14), a soluble lysosomal protein (CLN5), a protein present in the secretory pathway (PGRN/CLN11), and several proteins that display different subcellular localizations (CLN3, CLN6, MFSD8/CLN7, CLN8, ATP13A2/CLN12). Unfortunately, the precise functions of many of the NCL proteins are still unclear, which has made targeted therapy development challenging. The social amoeba Dictyostelium discoideum has emerged as an excellent model system for studying the normal functions of proteins linked to human neurological disorders. Intriguingly, the genome of this eukaryotic soil microbe encodes homologs of 11 of the 13 known genes linked to NCL. The genetic tractability of the organism, combined with its unique life cycle, makes Dictyostelium an attractive model system for studying the functions of NCL proteins. Moreover, the ability of human NCL proteins to rescue gene-deficiency phenotypes in Dictyostelium suggests that the biological pathways regulating NCL protein function are likely conserved from Dictyostelium to human. In this review, I will discuss each of the NCL homologs in Dictyostelium in turn and describe how future studies can exploit the advantages of the system by testing new hypotheses that may ultimately lead to effective therapy options for this devastating and currently untreatable neurological disorder.
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Affiliation(s)
- Robert J Huber
- Department of Biology, Trent University, 2140 East Bank Drive, Peterborough, ON, K9J 7B8, Canada.
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14
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Hao X, Lüthje F, Rønn R, German NA, Li X, Huang F, Kisaka J, Huffman D, Alwathnani HA, Zhu YG, Rensing C. A role for copper in protozoan grazing - two billion years selecting for bacterial copper resistance. Mol Microbiol 2016; 102:628-641. [PMID: 27528008 DOI: 10.1111/mmi.13483] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/12/2016] [Indexed: 12/28/2022]
Abstract
The Great Oxidation Event resulted in integration of soft metals in a wide range of biochemical processes including, in our opinion, killing of bacteria by protozoa. Compared to pressure from anthropologic copper contamination, little is known on impacts of protozoan predation on maintenance of copper resistance determinants in bacteria. To evaluate the role of copper and other soft metals in predatory mechanisms of protozoa, we examined survival of bacteria mutated in different transition metal efflux or uptake systems in the social amoeba Dictyostelium discoideum. Our data demonstrated a strong correlation between the presence of copper/zinc efflux as well as iron/manganese uptake, and bacterial survival in amoebae. The growth of protozoa, in turn, was dependent on bacterial copper sensitivity. The phagocytosis of bacteria induced upregulation of Dictyostelium genes encoding the copper uptake transporter p80 and a triad of Cu(I)-translocating PIB -type ATPases. Accumulated Cu(I) in Dictyostelium was monitored using a copper biosensor bacterial strain. Altogether, our data demonstrate that Cu(I) is ultimately involved in protozoan predation of bacteria, supporting our hypothesis that protozoan grazing selected for the presence of copper resistance determinants for about two billion years.
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Affiliation(s)
- Xiuli Hao
- Key Laboratory of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, China
| | - Freja Lüthje
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Regin Rønn
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Nadezhda A German
- Department of Pharmaceutical Sciences, Texas Tech University Health Sciences Center, Amarillo, TX, USA
| | - Xuanji Li
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Fuyi Huang
- Key Laboratory of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, China
| | - Javan Kisaka
- Department of Chemistry, Western Michigan University, Kalamazoo, MI, USA
| | - David Huffman
- Department of Chemistry, Western Michigan University, Kalamazoo, MI, USA
| | - Hend A Alwathnani
- Department of Botany and Microbiology, King Saud University, Riyadh, Saudi Arabia
| | - Yong-Guan Zhu
- Key Laboratory of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, China
| | - Christopher Rensing
- Key Laboratory of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, China.,J. Craig Venter Institute, La Jolla, CA, USA
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15
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Buracco S, Peracino B, Cinquetti R, Signoretto E, Vollero A, Imperiali F, Castagna M, Bossi E, Bozzaro S. Dictyostelium Nramp1, which is structurally and functionally similar to mammalian DMT1 transporter, mediates phagosomal iron efflux. J Cell Sci 2015; 128:3304-16. [PMID: 26208637 PMCID: PMC4582194 DOI: 10.1242/jcs.173153] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2015] [Accepted: 07/21/2015] [Indexed: 01/01/2023] Open
Abstract
The Nramp (Slc11) protein family is widespread in bacteria and eukaryotes, and mediates transport of divalent metals across cellular membranes. The social amoeba Dictyostelium discoideum has two Nramp proteins. Nramp1, like its mammalian ortholog (SLC11A1), is recruited to phagosomal and macropinosomal membranes, and confers resistance to pathogenic bacteria. Nramp2 is located exclusively in the contractile vacuole membrane and controls, synergistically with Nramp1, iron homeostasis. It has long been debated whether mammalian Nramp1 mediates iron import or export from phagosomes. By selectively loading the iron-chelating fluorochrome calcein in macropinosomes, we show that Dictyostelium Nramp1 mediates iron efflux from macropinosomes in vivo. To gain insight in ion selectivity and the transport mechanism, the proteins were expressed in Xenopus oocytes. Using a novel assay with calcein, and electrophysiological and radiochemical assays, we show that Nramp1, similar to rat DMT1 (also known as SLC11A2), transports Fe(2+) and manganese, not Fe(3+) or copper. Metal ion transport is electrogenic and proton dependent. By contrast, Nramp2 transports only Fe(2+) in a non-electrogenic and proton-independent way. These differences reflect evolutionary divergence of the prototypical Nramp2 protein sequence compared to the archetypical Nramp1 and DMT1 proteins.
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Affiliation(s)
- Simona Buracco
- Department of Clinical and Biological Sciences, University of Torino, AOU S. Luigi, Orbassano 10043, Italy
| | - Barbara Peracino
- Department of Clinical and Biological Sciences, University of Torino, AOU S. Luigi, Orbassano 10043, Italy
| | - Raffaella Cinquetti
- Department of Biotechnology and Life Sciences, University of Insubria, Via J. H. Dunant 3, Varese 21100, Italy
| | - Elena Signoretto
- Department of Pharmacological and Biomolecular Sciences, Università degli Studi di Milano, Via Trentacoste 2, Milano 20133, Italy
| | - Alessandra Vollero
- Department of Biotechnology and Life Sciences, University of Insubria, Via J. H. Dunant 3, Varese 21100, Italy
| | - Francesca Imperiali
- Department of Biotechnology and Life Sciences, University of Insubria, Via J. H. Dunant 3, Varese 21100, Italy
| | - Michela Castagna
- Department of Pharmacological and Biomolecular Sciences, Università degli Studi di Milano, Via Trentacoste 2, Milano 20133, Italy
| | - Elena Bossi
- Department of Biotechnology and Life Sciences, University of Insubria, Via J. H. Dunant 3, Varese 21100, Italy
| | - Salvatore Bozzaro
- Department of Clinical and Biological Sciences, University of Torino, AOU S. Luigi, Orbassano 10043, Italy
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16
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Bergmann S, Steinert M. From Single Cells to Engineered and Explanted Tissues: New Perspectives in Bacterial Infection Biology. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2015; 319:1-44. [PMID: 26404465 DOI: 10.1016/bs.ircmb.2015.06.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Cell culture techniques are essential for studying host-pathogen interactions. In addition to the broad range of single cell type-based two-dimensional cell culture models, an enormous amount of coculture systems, combining two or more different cell types, has been developed. These systems enable microscopic visualization and molecular analyses of bacterial adherence and internalization mechanisms and also provide a suitable setup for various biochemical, immunological, and pharmacological applications. The implementation of natural or synthetical scaffolds elevated the model complexity to the level of three-dimensional cell culture. Additionally, several transwell-based cell culture techniques are applied to study bacterial interaction with physiological tissue barriers. For keeping highly differentiated phenotype of eukaryotic cells in ex vivo culture conditions, different kinds of microgravity-simulating rotary-wall vessel systems are employed. Furthermore, the implementation of microfluidic pumps enables constant nutrient and gas exchange during cell cultivation and allows the investigation of long-term infection processes. The highest level of cell culture complexity is reached by engineered and explanted tissues which currently pave the way for a more comprehensive view on microbial pathogenicity mechanisms.
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Affiliation(s)
- Simone Bergmann
- Institute of Microbiology, Technische Universität Braunschweig, Braunschweig, Lower Saxony, Germany
| | - Michael Steinert
- Institute of Microbiology, Technische Universität Braunschweig, Braunschweig, Lower Saxony, Germany
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17
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Veyrier FJ, Cellier MF. Metal economy in host-microbe interactions. Front Cell Infect Microbiol 2015; 4:190. [PMID: 25629009 PMCID: PMC4292787 DOI: 10.3389/fcimb.2014.00190] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2014] [Accepted: 12/19/2014] [Indexed: 01/30/2023] Open
Affiliation(s)
- Frédéric J Veyrier
- Institut Pasteur Paris, France ; Institut National de la Recherche Scientifique-Institut Armand Frappier Laval, Canada
| | - Mathieu F Cellier
- Institut National de la Recherche Scientifique-Institut Armand Frappier Laval, Canada
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18
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Weber S, Stirnimann CU, Wieser M, Frey D, Meier R, Engelhardt S, Li X, Capitani G, Kammerer RA, Hilbi H. A type IV translocated Legionella cysteine phytase counteracts intracellular growth restriction by phytate. J Biol Chem 2014; 289:34175-88. [PMID: 25339170 DOI: 10.1074/jbc.m114.592568] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The causative agent of Legionnaires' pneumonia, Legionella pneumophila, colonizes diverse environmental niches, including biofilms, plant material, and protozoa. In these habitats, myo-inositol hexakisphosphate (phytate) is prevalent and used as a phosphate storage compound or as a siderophore. L. pneumophila replicates in protozoa and mammalian phagocytes within a unique "Legionella-containing vacuole." The bacteria govern host cell interactions through the Icm/Dot type IV secretion system (T4SS) and ∼300 different "effector" proteins. Here we characterize a hitherto unrecognized Icm/Dot substrate, LppA, as a phytate phosphatase (phytase). Phytase activity of recombinant LppA required catalytically essential cysteine (Cys(231)) and arginine (Arg(237)) residues. The structure of LppA at 1.4 Å resolution revealed a mainly α-helical globular protein stabilized by four antiparallel β-sheets that binds two phosphate moieties. The phosphates localize to a P-loop active site characteristic of dual specificity phosphatases or to a non-catalytic site, respectively. Phytate reversibly abolished growth of L. pneumophila in broth, and growth inhibition was relieved by overproduction of LppA or by metal ion titration. L. pneumophila lacking lppA replicated less efficiently in phytate-loaded Acanthamoeba castellanii or Dictyostelium discoideum, and the intracellular growth defect was complemented by the phytase gene. These findings identify the chelator phytate as an intracellular bacteriostatic component of cell-autonomous host immunity and reveal a T4SS-translocated L. pneumophila phytase that counteracts intracellular bacterial growth restriction by phytate. Thus, bacterial phytases might represent therapeutic targets to combat intracellular pathogens.
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Affiliation(s)
- Stephen Weber
- From the Max von Pettenkofer Institute, Department of Medicine, Ludwig-Maximilians University Munich, 80336 Munich, Germany
| | - Christian U Stirnimann
- the Laboratory of Biomolecular Research, Department of Biology and Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Mara Wieser
- the Laboratory of Biomolecular Research, Department of Biology and Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Daniel Frey
- the Laboratory of Biomolecular Research, Department of Biology and Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Roger Meier
- the Scientific Center for Optical and Electron Microscopy, ETH Zurich, 8093 Zurich, Switzerland
| | - Sabrina Engelhardt
- the Institute of Veterinary Physiology and Zurich Center for Integrative Human Physiology (ZIHP), Vetsuisse Faculty, University of Zurich, 8057 Zurich, Switzerland, and
| | - Xiaodan Li
- the Laboratory of Biomolecular Research, Department of Biology and Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Guido Capitani
- the Laboratory of Biomolecular Research, Department of Biology and Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Richard A Kammerer
- the Laboratory of Biomolecular Research, Department of Biology and Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Hubert Hilbi
- From the Max von Pettenkofer Institute, Department of Medicine, Ludwig-Maximilians University Munich, 80336 Munich, Germany, the Institute of Medical Microbiology, Department of Medicine, University of Zurich, 8006 Zurich, Switzerland
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