Academic literature on the topic 'Legionella pneumophila Dot/Icm'

ABSTRACT The freshwater ciliate Tetrahymena sp. efficiently ingested, but poorly digested, virulent strains of the gram-negative intracellular pathogen Legionella pneumophila. Ciliates expelled live legionellae packaged in free spherical pellets. The ingested legionellae showed no ultrastructural indicators of cell division either within intracellular food vacuoles or in the expelled pellets, while the number of CFU consistently decreased as a function of time postinoculation, suggesting a lack of L. pneumophila replication inside Tetrahymena. Pulse-chase feeding experiments with fluorescent L. pneumophila and Escherichia coli indicated that actively feeding ciliates maintain a rapid and steady turnover of food vacuoles, so that the intravacuolar residence of the ingested bacteria was as short as 1 to 2 h. L. pneumophila mutants with a defective Dot/Icm virulence system were efficiently digested by Tetrahymena sp. In contrast to pellets of virulent L. pneumophila, the pellets produced by ciliates feeding on dot mutants contained very few bacterial cells but abundant membrane whorls. The whorls became labeled with a specific antibody against L. pneumophila OmpS, indicating that they were outer membrane remnants of digested legionellae. Ciliates that fed on genetically complemented dot mutants produced numerous pellets containing live legionellae, establishing the importance of the Dot/Icm system to resist digestion. We thus concluded that production of pellets containing live virulent L. pneumophila depends on bacterial survival (mediated by the Dot/Icm system) and occurs in the absence of bacterial replication. Pellets of virulent L. pneumophila may contribute to the transmission of Legionnaires’ disease, an issue currently under investigation.

ABSTRACT Legionella pneumophila, a causative agent of bacterial pneumonia, survives inside phagocytic cells by avoiding rapid targeting to the lysosome. This bacterium utilizes a type IVB secretion system, encoded by the dot/icm genes, to replicate inside host cells. DotL, a critical component of the Dot/Icm secretion apparatus, functions as the type IV coupling protein. In contrast to most dot/icm genes, which are dispensable for growth on bacteriological media, dotL is required for the viability of wild-type L. pneumophila. Previously we reported that ΔdotL lethality could be suppressed by inactivation of the Dot/Icm complex via mutations in other dot/icm genes. Here we report the isolation of non-dot/icm suppressors of this phenotype. These ΔdotL suppressors include insertions that disrupt the function of the L. pneumophila homologs of cpxR, djlA, lysS, and two novel open reading frames, lpg0742 and lpg1594, that we have named ldsA and ldsB for lethality of ΔdotL suppressor. In addition to suppressing ΔdotL lethality, inactivation of these genes in a wild-type strain background causes a range of defects in L. pneumophila virulence traits, including intracellular growth, implicating these factors in the proper function of the Dot/Icm complex. Consistent with previous data showing a role for the cpx system in regulating expression of several dot/icm genes, the cpxR insertion mutant produced decreased levels of three Dot/Icm proteins, DotA, IcmV, and IcmW. The remaining four suppressors did not affect the steady-state levels of any Dot/Icm protein and are likely to represent the first identified factors necessary for assembly and/or activation of the Dot/Icm secretion complex.

ABSTRACT The Dot/Icm system of Legionella pneumophila triggers activation of caspase-3 during early stages of infection of human macrophages, but apoptosis is delayed until late stages of infection. During early stages of infection of mouse macrophages, the organism triggers rapid caspase-1-mediated cytotoxicity, which is mediated by bacterial flagellin. However, it is not known whether caspase-1 is triggered by L. pneumophila in human macrophages or whether caspase-3 is activated in permissive or nonpermissive mouse macrophages. Using single-cell analyses, we show that the wild-type strain of L. pneumophila does not trigger caspase-1 activation throughout the intracellular infection of human monocyte-derived macrophages (hMDMs), even when the flagellated bacteria escape into the cytoplasm during late stages. Using single-cell analyses, we show that the Dot/Icm system of L. pneumophila triggers caspase-3 but not caspase-1 within permissive A/J mouse bone marrow-derived primary macrophages by 2 to 8 h, but apoptosis is delayed until late stages of infection. While L. pneumophila triggers a Dot/Icm-dependent activation of caspase-1 in nonpermissive BALB/c mouse-derived macrophages, caspase-3 is not activated at any stage of infection. We show that robust intrapulmonary replication of the wild-type strain of L. pneumophila in susceptible A/J mice is associated with late-stage Dot/Icm-dependent pulmonary apoptosis and alveolar inflammation. In the lungs of nonpermissive BALB/c mice, L. pneumophila does not replicate and does not trigger pulmonary apoptosis or alveolar inflammation. Thus, similar to hMDMs, L. pneumophila does not trigger caspase-1 but triggers caspase-3 activation during early and exponential replication in permissive A/J mouse-derived macrophages, and apoptosis is delayed until late stages of infection. The Dot/Icm type IV secretion system is essential for pulmonary apoptosis in the genetically susceptible A/J mice.

ABSTRACT Legionella pneumophila is the causative agent of the severe and potentially fatal pneumonia Legionnaires' disease. L. pneumophila is able to replicate within macrophages and protozoa by establishing a replicative compartment in a process that requires the Icm/Dot type IVB secretion system. The signals and regulatory pathways required for Legionella infection and intracellular replication are poorly understood. Mutation of the rpoS gene, which encodes σS, does not affect growth in rich medium but severely decreases L. pneumophila intracellular multiplication within protozoan hosts. To gain insight into the intracellular multiplication defect of an rpoS mutant, we examined its pattern of gene expression during exponential and postexponential growth. We found that σS affects distinct groups of genes that contribute to Legionella intracellular multiplication. We demonstrate that rpoS mutants have a functional Icm/Dot system yet are defective for the expression of many genes encoding Icm/Dot-translocated substrates. We also show that σS affects the transcription of the cpxR and pmrA genes, which encode two-component response regulators that directly affect the transcription of Icm/Dot substrates. Our characterization of the L. pneumophila small RNA csrB homologs, rsmY and rsmZ, introduces a link between σS and the posttranscriptional regulator CsrA. We analyzed the network of σS-controlled genes by mutational analysis of transcriptional regulators affected by σS. One of these, encoding the L. pneumophila arginine repressor homolog gene, argR, is required for maximal intracellular growth in amoebae. These data show that σS is a key regulator of multiple pathways required for L. pneumophila intracellular multiplication.

ABSTRACT Coxiella burnetii, the etiological agent of Q fever, is an obligate intracellular pathogen, whereas Legionella pneumophila, the causative agent of Legionnaires' disease, is a facultative intracellular pathogen. During infection of humans both of these pathogens multiply in alveolar macrophages inside a closed phagosome. L. pneumophila intracellular multiplication was shown to be dependent on the icm/dot system, which probably encodes a type IV-related translocation apparatus. Recently, genes homologous to all of the L. pneumophila icm/dot genes (besides icmR) were found in C. burnetii. To explore the similarities and differences between the icm/dot pathogenesis systems of these two pathogens, interspecies complementation analysis was performed. Nine C. burnetii icm homologous genes (icmT, icmS, icmQ, icmP, icmO, icmJ, icmB, icmW, and icmX) were cloned under regulation of the corresponding L. pneumophila icm genes and examined for the ability to complement L. pneumophila mutants with mutations in these genes. The C. burnetii icmS and icmW homologous genes were found to complement the corresponding L. pneumophila icm mutants to wild-type levels of intracellular growth in both HL-60-derived human macrophages and Acanthamoeba castellanii. In addition, the C. burnetii icmT homologous gene was found to completely complement an L. pneumophila insertion mutant for intracellular growth in HL-60-derived human macrophages, but it only partially complemented the same mutant for intracellular growth in A. castellanii. Moreover, as previously shown for L. pneumophila, the proteins encoded by the C. burnetii icmS and icmW homologous genes were found to interact with one another, and interspecies protein interaction was observed as well. Our results strongly indicate that the Icm/Dot pathogenesis systems of C. burnetii and L. pneumophila have common features.

Legionella pneumophila is the causative agent of human Legionnaires' disease. L. pneumophila has been shown to induce apoptosis of T-cells and this may be important pathologically and clinically. The present study has determined the molecular mechanisms underlying L. pneumophila-induced apoptosis, which were unclear. Wild-type L. pneumophila and flagellin-deficient Legionella, but not L. pneumophila lacking a functional type IV secretion system Dot/Icm, replicated in T-cells. However, apoptosis was efficiently induced in T-cells only by wild-type L. pneumophila, and not flagellin-deficient or Dot/Icm-deficient Legionella. Induction of apoptosis involved activation of the initiator caspase 9 and effector caspase 3. Infection with L. pneumophila inhibited phosphorylation of Akt (also known as protein kinase B) and the Akt substrate GSK3β (glycogen synthase kinase 3β), and reduced the levels of β-catenin, a transcriptional activator regulated by GSK3β. It also caused the activation of the pro-apoptotic protein Bax and inhibited the expression of the anti-apoptotic protein XIAP (X-linked inhibitor of apoptosis) via inhibition of the Akt pathway. In conclusion, L. pneumophila induces mitochondria-mediated T-cell apoptosis through inhibition of the Akt/GSK3β signalling pathway.

Abstrakt Bakterie Legionella pneumophila w środowisku naturalnym pasożytują wewnątrz komórek wybranych gatunków pierwotniaków, a po przedostaniu się do sztucznych systemów dystrybucji wody stają się ważnym czynnikiem etiologicznym zapalenia płuc u ludzi. Główną cechą determinującą patogenność tych bakterii jest zdolność do życia i replikacji w makrofagach płucnych, czyli w komórkach wyspecjalizowanych do fagocytozy, zabijania i trawienia mikroorganizmów. Warunkiem wstępnym rozwoju infekcji jest przełamanie mechanizmów bójczych makrofagów i utworzenie wakuoli replikacyjnej LCV (Legionella containing vacuole). Biogeneza wakuoli LCV jest możliwa dzięki sprawnemu funkcjonowaniu IV systemu sekrecji Dot/Icm, który jest wielobiałkowym, złożonym kompleksem umiejscowionym w wewnętrznej i zewnętrznej membranie osłony komórkowej bakterii. System Dot/Icm liczy 27 elementów, na które składają się m.in. kompleks rdzeniowo-transmembranowy, tworzący strukturalny szkielet całego systemu oraz kompleks białek sprzęgających. Geny kodujące komponenty systemu Dot/Icm są zorganizowane na dwóch regionach chromosomu bak-teryjnego. System sekrecji Dot/Icm umożliwia L. pneumophila wprowadzenie do cytozolu komórki gospodarza ponad 300 białek efektorowych, których skoordynowane działanie powoduje utrzymanie integralności błony wakuoli replikacyjnej oraz pozwala na manipulowanie różnymi procesami komórki. Ważnym elementem strategii wewnątrzkomórkowego namnażania się L. pneumophila jest modulowanie transportu pęcherzykowego, interakcja z retikulum endoplazmatycznym oraz zakłócenie biosyntezy białek, procesów autofagii i apoptozy komórki gospodarza. Poznanie złożonych mechanizmów regulacji i funkcji białek efektorowych systemu Dot/Icm ma decydujące znaczenie w zapobieganiu i leczeniu choroby legionistów.

ABSTRACT Legionella longbeachae causes most cases of legionellosis in Australia and may be underreported worldwide due to the lack of L. longbeachae-specific diagnostic tests. L. longbeachae displays distinctive differences in intracellular trafficking, caspase 1 activation, and infection in mouse models compared to Legionella pneumophila, yet these two species have indistinguishable clinical presentations in humans. Unlike other legionellae, which inhabit freshwater systems, L. longbeachae is found predominantly in moist soil. In this study, we sequenced and annotated the genome of an L. longbeachae clinical isolate from Oregon, isolate D-4968, and compared it to the previously published genomes of L. pneumophila. The results revealed that the D-4968 genome is larger than the L. pneumophila genome and has a gene order that is different from that of the L. pneumophila genome. Genes encoding structural components of type II, type IV Lvh, and type IV Icm/Dot secretion systems are conserved. In contrast, only 42/140 homologs of genes encoding L. pneumophila Icm/Dot substrates have been found in the D-4968 genome. L. longbeachae encodes numerous proteins with eukaryotic motifs and eukaryote-like proteins unique to this species, including 16 ankyrin repeat-containing proteins and a novel U-box protein. We predict that these proteins are secreted by the L. longbeachae Icm/Dot secretion system. In contrast to the L. pneumophila genome, the L. longbeachae D-4968 genome does not contain flagellar biosynthesis genes, yet it contains a chemotaxis operon. The lack of a flagellum explains the failure of L. longbeachae to activate caspase 1 and trigger pyroptosis in murine macrophages. These unique features of L. longbeachae may reflect adaptation of this species to life in soil.

ABSTRACT The Legionella pneumophila-containing phagosome evades endocytic fusion and intercepts endoplasmic reticulum (ER)-to-Golgi vesicle traffic, which is believed to be mediated by the Dot/Icm type IV secretion system. Although phagosomes harboring dot/icm mutants are thought to mature through the endosomal-lysosomal pathway, colocalization studies with lysosomal markers have reported contradictory results. In addition, phagosomes harboring the dot/icm mutants do not interact with endocytosed materials, which is inconsistent with maturation of the phagosomes in the endosomal-lysosomal pathway. Using multiple strategies, we show that the dot/icm mutants defective in the Dot/Icm structural apparatus are unable to maintain the integrity of their phagosomes and escape into the cytoplasm within minutes of entry into various mammalian and protozoan cells in a process independent of the type II secretion system. In contrast, mutants defective in cytoplasmic chaperones of Dot/Icm effectors and rpoS, letA/S, and letE regulatory mutants are all localized within intact phagosomes. Importantly, non-dot/icm L. pneumophila mutants whose phagosomes acquire late endosomal-lysosomal markers are all located within intact phagosomes. Using high-resolution electron microscopy, we show that phagosomes harboring the dot/icm transporter mutants do not fuse to lysosomes but are free in the cytoplasm. Inhibition of ER-to-Golgi vesicle traffic by brefeldin A does not affect the integrity of the phagosomes harboring the parental strain of L. pneumophila. We conclude that the Dot/Icm transporter is involved in maintaining the integrity of the L. pneumophila phagosome, independent of interception of ER-to-Golgi vesicle traffic, which is a novel function of type IV secretion systems.

Legionella pneumophila, the causative agent of Legionnaires' disease, grows within macrophages and manipulates target cell signaling. Formation of a Legionella-containing replication vacuole requires the function of the bacterial type IV secretion system (Dot/Icm), which transfers protein substrates into the host cell cytoplasm. A global microarray analysis was used to examine the response of human macrophage-like U937 cells to low-dose infections with L. pneumophila. The most striking change in expression was the Dot/Icm-dependent up-regulation of antiapoptotic genes positively controlled by the transcriptional regulator nuclear factor κB (NF-κB). Consistent with this finding, L. pneumophila triggered nuclear localization of NF-κB in human and mouse macrophages in a Dot/Icm-dependent manner. The mechanism of activation at low-dose infections involved a signaling pathway that occurred independently of the Toll-like receptor adaptor MyD88 and the cytoplasmic sensor Nod1. In contrast, high multiplicity of infection conditions caused a host cell response that masked the unique Dot/Icm-dependent activation of NF-κB. Inhibition of NF-κB translocation into the nucleus resulted in premature host cell death and termination of bacterial replication. In the absence of one antiapoptotic protein, plasminogen activator inhibitor–2, host cell death increased in response to L. pneumophila infection, indicating that induction of antiapoptotic genes is critical for host cell survival.

The genus Legionella consists of environmental bacteria which are the causative agents of the severe pneumonia Legionnaires’ disease. L. longbeachae and L. pneumophila are able to replicate intracellularly in human alveolar macrophages and aquatic or soil amoebae. In order to replicate within host cells the bacteria establish a compartment derived from the endoplasmatic reticulum (ER) which is called “Legionella-containing vacuole” (LCV). A bacterial intracellular multiplication/defective in organelle transport (Icm/Dot) type IV secretion system (T4SS) is essential for the formation of this LCV. The Icm/Dot T4SS enables translocation of effector proteins into the host cell. More than 100 effector proteins are presumably translocated during an L. longbeachae infection whereas around 300 translocated effector proteins are known for L. pneumophila. During maturation the LCV communicates with vesicles from the endocytic vesicle trafficking pathway, avoids fusion with lysosomes and instead fuses with the ER. Phosphoinositides (PI) such as phosphatitdylinositol-4-phosphate (PtdIns(4)P) are enriched on the LCV which mediate the binding of Icm/Dot translocated effector proteins like SidCLpn (substrate of Icm/Dot transporter) as well as its paralogous protein SdcALpn. The 73 kDa effector SidM but not the 106 kDa SidCLpn was found in a previous phosphoinositide pulldown assay with L. pneumophila lysate to be the major PtdIns(4)P binding protein. Using L. longbeachae lysate we showed binding of the 111 kDa SidCLlo to PtdIns(4)P in a phosphoinositide pulldown. This result was confirmed by protein-lipid overlay assays using “PIP-strips”. In further analysis the P4C (PtdIns(4)P-binding of SidC) domain was identified as a 19 kDa domain of SidCLlo located in the amino acid region 609 to 782. This P4C domain was located in the same region as the 20 kDa SidCLpn_P4C domain of L. pneumophila. Both P4C domains can be used as LCV markers. This was shown with GST-tagged proteins binding to LCVs in a cell homogenate. The two P4C domains show a sequence identity of only 45% and the full-length protein of 40%. Circular dichroism measurements revealed that the secondary structure of the two proteins is similar. Moreover, isothermal titration calorimetric measurements indicated a 3.4 higher affinity of SidCLlo towards PtdIns(4)P compared with SidCLpn. In RAW 264.7 macrophages infected with L. longbeachae we showed that endogenous SidCLlo as well as heterologously produced SidCLpn is translocated to the LCV in an Icm/Dot-dependent manner. The deletion of the sidCLlo gene led to a reduced recruitment of calnexin to the LCV in infected Dictyostelium discoideum. This effect was complemented by adding plasmid-encoded SidCLlo, SidCLpn or SdcALpn. The same recruitment defect for a L. pneumophila strain lacking the sidCLpn and sdcALpn genes was complemented by the production of SidCLlo and SidCLpn as published before. Therefore, these effectors play a role for pathogen-host interactions by promoting the recruitment of ER to the LCV. L. longbeachae or L. pneumophila wild-type strains outcompeted their sidC deletion mutant in a competition assay in Acanthamoeba castellanii. However neither of the deletion mutants were impaired in their growth in single strain replication experiments. In summary despite of the small sequence identity and the higher binding affinity to PtdIns(4)P of SidCLlo compared to SidCLpn both effector proteins seem to have similar functions during an infection of Legionella. For the characterization of L. longbeachae-containing vacuoles through proteomic analysis, LCVs had to be isolated from infected D. discoideum or RAW 264.7 macrophages. Endogenous SidCLlo or heterologously produced SidCLpn were used as LCV markers for the isolation. Pathogen vacuoles harbouring L. longbeachae were isolated by immuno-affinity purification using antibodies specifically recognizing SidCLlo or SidCLpn. Future investigations aim at optimizing the LCV purification protocol for L. longbeachae to determine the proteome composition of the L. longbeachae-containing vacuole.
Die Gattung Legionella besteht aus opportunistischen Pathogenen, die Auslöser für die schwere Lungenentzündung Legionärskrankheit sind. Die Legionella-Spezies L. longbeachae sowie L. pneumophila vermehren sich intrazellulär in humanen alveolaren Makrophagen sowie in aquatischen oder im Boden lebenden Amöben. Ein vom endoplasmatischen Retikulum (ER) abstammendes Kompartiment ist notwendig für die intrazelluläre Replikation. Diese Nische wird als „Legionella-containing vacuole“ (LCV) bezeichnet. Die Bildung der LCV benötigt ein „intracellular multiplication/defective in organelle transport“ (Icm/Dot) Typ IV Sekretionssystem (T4SS), das Effektorproteine in die Wirtszelle transportiert. Zurzeit sind über 100 vermutete Effektorproteine für L. longbeachae und etwa 300 Effektorproteine für L. pneumophila beschrieben. Im Verlauf eines Reifungsprozesses kommuniziert die LCV mit endosomalen Vesikeln, verhindert eine Fusion mit den Lysosomen und fusioniert mit dem ER. Phosphoinositide wie das PtdIns(4)P wurden auf der LCV gefunden. Diese dienen als Bindestellen für die durch das Icm/Dot translozierten Effektorproteine wie das SidCLpn und sein paraloges Protein SdcALpn. In einer früheren Studie wurde in einem Phosphoinositid-Pulldown Experiment das 73 kDa Effektorprotein SidM aber nicht das 106 kDa Protein SidCLpn als Bindepartner von PtdIns(4)P nachgewiesen. Wir konnten in einem Phosphoinositid-Pulldown Experiment mit L. longbeachae Lysat zeigen, dass das 111 kDa homologe Protein von SidCLpn SidCLlo der Bindepartner von L. longbeachae für PtdIns(4)P ist. Ein 19 kDa großes SidCLlo- Fragment im Bereich der Aminosäuren 609 bis 782 konnte identifiziert werden, das für die Bindung von SidCLlo an PtdIns(4)P notwendig ist. Interessanterweise liegt die früher beschriebene 20 kDa große P4C Domäne von SidCLpn in der gleichen Region. Durch Inkubation von GST-gekoppelten SidCLlo_P4C-Proteinen mit L. pneumophila Zellhomogenat konnten wir zeigen, dass SidCLlo_P4C die Vakuole von L. pneumophila homogen dekoriert. Daher kann SidCLlo_P4C genauso wie das SidCLpn_P4C als LCV Marker benutzt werden. Die P4C Domänen besitzen eine Sequenzhomologie von 45% und SidCLlo und SidCLpn zeigen eine Sequenzhomologie von 40%. Mittels zirkularer Dichroismus Messung konnte gezeigt werden, dass die beiden Proteine ähnliche Sekundärstrukturen besitzen. Mittels isothermer Titrationskalorimetrie konnten wir zeigen, dass SidCLlo eine 3.4-fach höhere Bindeaffinität zu PtdIns(4)P besitzt als SidCLpn. In infizierten RAW 264.7 Makrophagen konnte wir zeigen, dass L. longbeachae nicht nur sein eigenes endogen produzierten SidCLlo sondern auch ein heterolog exprimiertes SidCLpn in einer Icm/Dot abhängigen Art und Weise auf die LCV transloziert. Frühere Studien zeigten, dass in einer sidC-sdcALpn Deletionsmutante die ER Rekrutierung zu der LCV in infizierten D. discoideum Zellen beeinträchtigt ist. Wir konnten zeigen, dass die heterologe Produktion von SidCLlo diesen Rekrutierungsfehler komplementieren kann, ebenso wie Plasmid-kodiertes SidCLpn oder SdcALpn. Die Deletion vom Gen sidCLlo in L. longbeachae führt ebenfalls zu einer verminderten Rekrutierung von ER-Markern zur LCV in infizierten D. discoideum. Dieser Effekt konnte durch eine Produktion von SidCLlo, SidCLpn und SdcALpn komplementiert werden. Die SidC Deletionsstämme von L. longbeachae oder L. pneumophila replizierten in Acanthamoeba castellanii wie die entsprechenden Wildtyp-Stämme, aber in direkter Konkurrenz wurden die Deletionsmutanten von den Wildtyp-Stämmen verdrängt. Insgesamt scheinen trotz der geringen Sequenzidentität und der höheren Bindeaffinität von SidCLlo im Vergleich zu SidCLpn zu PtdIns(4)P beide Effektorproteine ähnliche Funktionen im Infektionsweg von Legionella wahr zu nehmen. Für die Charakterisierung von L. longbeachae-enthaltenden Vakuolen in einer Proteomanalyse müssen LCVs aus D. discoideum oder RAW 264.7 Makrophagen isoliert werden. Endogenes SidCLlo oder heterolog produziertes SidCLpn wurden als Vakuolen- Marker für die Isolation von L. longbeachae-enthaltenen Vakuolen verwendet. L. longbeachae-enthaltene Vakuolen wurden in einer Immunaffinitätsaufreinigung mit Hilfe spezifischer Antikörper gegen SidCLlo oder SidCLpn isoliert. Weitere Studien zielen auf die Verbesserung der Vakuolen-Isolation von L. longbeachae, um das Proteom dieser LCV zu charakterisieren.

Dissertação de Mestrado em Biologia Celular e Molecular apresentada à Faculdade de Ciências e Tecnologia
Legionella pneumophila é o principal agente da Doença dos Legionários, uma pneumonia severa e ocasionalmente mortal. Esta bactéria gram negativa, é ubíqua em ambientes aquáticos não salinos e em sistemas artificiais de água, replicando-se dentro de protozários aquáticos (principalmente amebas), mas também dentro de macrófagos alveolares humanos.A virulência de L. pneumophila depende da sua capacidade de remodelar o vacuolo fagocítico, denominado “Legionella-containing vacuole” (LCV), para criar um nicho replicativo prevenindo a fusão do fagossoma com o lisossoma, evitando assim o sistema imunitário do hospedeiro. Para realizar estas tarefas, L. pneumophila efectua a translocação de numerosos efectores bacterianos para a célula hospedeira através do sistema de secreção Dot/Icm Tipo IV (T4BSS). Este sistema de secreção é responsável pela translocação um vasto número de efectores que modulam diversas atividades da célula hospedeira. Apesar do elevado número de efetores identificados, apenas alguns são considerados críticos para o crescimento intracelular da bactéria, como a proteína SdhA. Esta proteína é importante para a manutenção da integridade do LCV em macrófagos, uma vez que na sua ausência o LCV é fragmentado resultando na morte da célula hospedeira e da bactéria.Nos últimos anos o uso de Galleria mellonella como um modelo de infeção para o estudo de agentes patogénicos tem aumentado devido a existência de uma correlação entre a virulência de bactérias patogénicas em insetos e nos modelos em mamíferos. Neste inseto, a mortalidade induzida por L. pneumophila é dependente da dose e do sistema de secreção Dot/Icm T4BSS funcional. Para além disso, a utilização de G. mellonella na determinação da função e relevância de efetores do Dot/Icm T4BSS, como o SdhA, na virulência desta bactéria já foi demonstrada.O objetivo principal deste estudo foi determinar se o efetor SdhA translocado por Dot/Icm T4BSS e crucial para a virulência de L. pneumophila em G. mellonella, é está envolvido em diferenças de virulência em estirpes de L. pneumophila não relacionadas, isoladas de diferentes ambientes e com origens genéticas distintas, usando a larva G. mellonella como um modelo de infeção.Neste estudo verificámos que a virulência da maioria das estirpes de L. pneumophila é dependente do efetor SdhA. Para além disso, a relevância deste efector na infeção por L. pneumophila variou entre as estirpes analisadas. Assim, concluímos que o efector SdhA é responsável pelos níveis distintos de virulência observados entre estirpes de L. pneumophila isoladas de ambientes distintos e com diferentes contextos genéticos. Adicionalmente, detetámos pela primeira vez a existência de redundância funcional para SdhA na infeção em G. mellonella entre estirpes de L. pneumophila
Legionella pneumophila is the major agent of Legionnaire´s Disease (LD) a severe and occasionally fatal pneumonia. This gram negative bacteria that is ubiquitous in freshwater environments and in many man-made water systems, replicates within aquatic protozoa (mainly amoeba), but also within human alveolar macrophages.L. pneumophila virulence depends on the ability to use the phagocytic vacuole, namely Legionella-containing vacuole (LCV), to create a replicative niche preventing phagosome-lysosome fusion and evade the host immune system. To accomplish these tasks L. pneumophila translocate numerous bacterial effectors into the host cell though Dot/Icm Type IV Secretion System (TB4SS). This secretion system is responsible for the translocation of vast number of effectors that modulate diverse host cell functions. Despite this large number of recognized effectors only a few are considered to be critical for intracellular growth and disease, such as SdhA protein. This protein is crucial for the maintenance of LCV integrity in macrophages, since in the absence of this effector occurs the LCV disruption resulting in the death of both host cell and bacterium.An increase in use of G. mellonella as an infection model for human pathogens occurred in the last year due the existence of a large correlation between virulence of bacterial pathogens in the insect and in mammalian models. In this insect, mortality induced by this L. pneumophila is both dose and functional Dot/Icm T4BSS-depedent. Moreover, the suitability of G. mellonella to determine the role of Dot/Icm T4BSS effectors, such SdhA, in virulence of this bacterium was already demonstrated.The main objective of this study was to determine if the role of the crucial virulence-related Dot/Icm T4BSS effector SdhA induce different levels of virulence among unrelated L. pneumophila strains, isolated from different environments and with distinct genetic backgrounds, using G. mellonella larvae as an infection model.In this study the majority of L. pneumophila strains induced a sdhA-dependent larval mortality. In addition, relevant differences on the role of sdhA were observed among the studied strains. In sum, SdhA induced different levels of virulence among unrelated L. pneumophila strains in G. mellonella infection. Importantly, some degree of functional redundancy towards SdhA was detected for the first time in a L. pneumophila strain.