The Polar Legionella Icm/Dot T4SS Establishes Distinct Contact Sites with the Pathogen Vacuole Membrane

Abstract

Legionnaires’ disease is a life-threatening pneumonia, which is characterized by high fever, coughing, shortness of breath, muscle pains, and headaches. The disease is caused by the amoeba-resistant bacterium L. pneumophila found in various soil and aquatic environments and is transmitted to humans via the inhalation of small bacteria-containing droplets.

Migration of Acanthamoeba through Legionella biofilms is regulated by the bacterial Lqs‐LvbR network, effector proteins and the flagellum

“…4), we next tested the role of the Icm/Dot T4SS and secreted effector proteins for amoeba migration in L. pneumophila biofilms. To this end, we used the ΔicmT mutant strain, which lacks a functional Icm/Dot T4SS (Böck et al, 2021), is defective for intracellular growth (Segal and Shuman, 1998), and in contrast to the wild-type strain JR32, does not inhibit cell migration upon infection (Simon et al, 2014). Moreover, we used the ΔlegG1 (lpg1976), ΔppgA (lpg2224) or ΔlegG1-ΔppgA mutant strains, lacking one or two RCC1 repeat effectors, which promote microtubule stabilization, LCV motility and host cell migration (Rothmeier et al, 2013;Swart et al, 2020b).…”

“…Legionella pneumophila replicates intracellularly within free‐living protozoa, which appear to represent the preferential niche in the environment (Fields, 1996; Murga et al ., 2001; Kuiper et al ., 2004). The pathogen governs the interactions with host cells through the Icm/Dot type IV secretion system (T4SS) (Kubori and Nagai, 2016; Ghosal et al ., 2019; Böck et al ., 2021), which transports the impressive number of >300 different ‘effector’ proteins implicated in the formation of a unique, ER‐associated compartment, the Legionella ‐containing vacuole (LCV) (Isberg et al ., 2009; Hubber and Roy, 2010; Finsel and Hilbi, 2015; Personnic et al ., 2016; Qiu and Luo, 2017; Steiner et al ., 2018).…”

Developmental transitions coordinate assembly of the Coxiella burnetii Dot/Icm type IV secretion system

“…Subtomogram averaging and classification analysis of the Dot/Icm machines led to the conclusion that a complete core complex assembles as bacteria transition from the infectious SCV to the replicative LCV form. Multiple studies in L. pneumophila have shown that the Dot/Icm system assembles at cell division sites during bacterial replication and remains localized primarily at the poles of the bacilli [23][24][25][26]35,36 . Most of the "WiFi-like" structures representing an assembled Dot/Icm machine in C. burnetii were identified at the poles of LCV bacilli, suggesting a similar Dot/Icm machine assembly process in both C. burnetii and L. pneumophila.…”

“…It is also possible that the intermembrane tethers represent interaction sites between bacterial adherence factors and the vacuolar membrane that facilitate translocation of Dot/Icm effectors into the host cell by stabilizing intimate contacts. Recently, similar cryo-FIB milling imaging of L. pneumophila inside amoeba hosts showed that the Dot/Icm machine mediates interaction with the vacuolar membrane to form a membrane indentation that facilitates effector secretion 36 . However, we did not observe such a phenomenon between the CCV membrane and C. burnetii secretion machines.…”

The Legionella pneumophila Dot/Icm type IV secretion system and its effectors

“…In line with this model, membrane contact was demonstrated to be essential and sufficient to trigger translocation of effectors into host cells [84]. In the LCV the T4BSS tethers bacterial poles to the vacuole membrane, leading to a distinct indentation of the membrane contact site [85]; however, the molecular cues and mechanisms of host membrane permeation by the T4BSS remain unresolved. In the environment, this setup provides an effective way to swiftly fend off predators and/or maximize exploitation of potentially sporadic encounters with permissive hosts.…”