Differential Effects of Iron, Zinc, and Copper on Dictyostelium discoideum Cell Growth and Resistance to Legionella pneumophila

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.

Mycobacterium marinum produces distinct mycobactin and carboxymycobactin siderophores to promote growth in broth and phagocytes

“…Pathogenic mycobacteria, such as M. marinum or M. tuberculosis , replicate in host cells in a distinct, membrane‐bound pathogen vacuole called MCV, followed by rupture of the vacuole membrane and exit of the bacteria to the cytoplasm (Cardenal‐Munoz et al, ; Koliwer‐Brandl et al, ; Russell, ). The MCV represents a metal ion‐poor environment (Chao et al, ), which is depleted of iron due to the activity of NRAMP‐1, a proton‐driven transporter of ferric iron (Bozzaro, Buracco, & Peracino, ; Buracco et al, ; Buracco, Peracino, Andreini, Bracco, & Bozzaro, ; Peracino, Buracco, & Bozzaro, ).…”

“…Russell, 2016). The MCV represents a metal ion-poor environment (Chao et al, 2019), which is depleted of iron due to the activity of NRAMP-1, a proton-driven transporter of ferric iron Buracco et al, 2015;Buracco, Peracino, Andreini, Bracco, & Bozzaro, 2017;.…”

Zn2+ intoxication of Mycobacterium marinum during Dictyostelium discoideum infection is counteracted by induction of the pathogen Zn2+ exporter CtpC

“…Here we focused on the Zn 2+ -mediated battle between M. marinum and its host D. discoideum. D. discoideum has previously served as model to uncover the role of transition metals in the resistance to intracellular pathogens Buracco et al, 2017;Buracco et al, 2015;Peracino et al, 2006). For example, it has been shown that whilst Fe 2+ participates in D. discoideum resistance to M. avium or Legionella pneumophila Buracco et al, 2017;Buracco et al, 2015;Peracino et al, 2006), Cu 2+ or Zn 2+ do not affect the infection by the latter (Buracco et al, 2017).…”

“…It has been recently shown that, in D. discoideum, free Zn 2+ accumulates inside (i) the CV network, (ii) zincosomes, endosomal compartments with lysosomal and post-lysosomal characteristics, and (iii) phagosomes containing beads and nonpathogenic bacteria such as Escherichia coli or M. smegmatis Buracco et al, 2017) (Fig. 1A).…”

Evasion of phagotrophic predation by protist hosts and innate immunity of metazoan hosts byLegionella pneumophila

“…The drawback to understanding how metazoan hosts have contributed to L. pneumophila evolution is that the evolutionary biology of the immune response has been studied in only two L. pneumophila natural hosts, Dictyostelium discoideum and C. elegans (Buracco, Peracino, Andreini, Bracco, & Bozzaro, 2017;Cardenal-Muñoz, Barisch, Lefrançois, López-Jiménez, & Soldati, 2018;Dunn et al, 2017;Mori, Mode, & Pieters, 2018;Swart, Harrison, Eichinger, Steinert, & Hilbi, 2018;L. Li & Faucher, 2016 Protists resistant to L. pneumophila have also been identified, but their relationship is poorly understood (Amaro, Wang, Gilbert, Roger Anderson, & Shuman, 2015).…”