PilY1 Promotes Legionella pneumophila Infection of Human Lung Tissue Explants and Contributes to Bacterial Adhesion, Host Cell Invasion, and Twitching Motility

Abstract

Legionnaires' disease is an acute fibrinopurulent pneumonia. During infection Legionella pneumophila adheres to the alveolar lining and replicates intracellularly within recruited macrophages. Here we provide a sequence and domain composition analysis of the L. pneumophila PilY1 protein, which has a high homology to PilY1 of Pseudomonas aeruginosa. PilY1 proteins of both pathogens contain a von Willebrand factor A (vWFa) and a C-terminal PilY domain. Using cellular fractionation, we assigned the L. pneumophila PilY1 as an outer membrane protein that is only expressed during the transmissive stationary growth phase. PilY1 contributes to infection of human lung tissue explants (HLTEs). A detailed analysis using THP-1 macrophages and A549 lung epithelial cells revealed that this contribution is due to multiple effects depending on host cell type. Deletion of PilY1 resulted in a lower replication rate in THP-1 macrophages but not in A549 cells. Further on, adhesion to THP-1 macrophages and A549 epithelial cells was decreased. Additionally, the invasion into non-phagocytic A549 epithelial cells was drastically reduced when PilY1 was absent. Complementation variants of a PilY1-negative mutant revealed that the C-terminal PilY domain is essential for restoring the wild type phenotype in adhesion, while the putatively mechanosensitive vWFa domain facilitates invasion into non-phagocytic cells. Since PilY1 also promotes twitching motility of L. pneumophila, we discuss the putative contribution of this newly described virulence factor for bacterial dissemination within infected lung tissue.

Peptidyl-Prolyl- cis / trans -Isomerases Mip and PpiB of Legionella pneumophila Contribute to Surface Translocation, Growth at Suboptimal Temperature, and Infection

“…Construction of isogenic L. pneumophila knockout mutants. For analysis of L. pneumophila PpiB, isogenic knockout mutants of the wild type and the Mip mutant strain were generated via homologous recombination as previously described (56). Up-and downstream flanking regions of ppiB with overhangs of 1 to 1.5 kb complementary to the 5= and 3= regions of the open reading frame of the respective resistance gene were amplified and merged together in a joining PCR.…”

Dual Role of Mechanisms Involved in Resistance to Predation by Protozoa and Virulence to Humans

“…A mutation of FlaA reduces the efficiency of invasion of A. castellanii and macrophage due to reduced motility ( Dietrich et al, 2001 ; Schell et al, 2016a ). In addition, PilY1 is responsible for the biogenesis of the type IV pili, which is important for twitching motility, surface attachment and host cell invasion ( Hoppe et al, 2017 ). PilY1 is also involved in inhibition of fusion of the lysosome with the phagosome in the social amoebae D. discoideum and a mutant of PilY1 demonstrated reduced intracellular growth in macrophage ( Shevchuk et al, 2014 ).…”

The Flagellar Regulon of Legionella—A Review

“…Twitching motility is based on a functional type IV pilus. The ability to move forward by twitching has been reported for L. pneumophila (Coil and Anne, 2009 ; Hoppe et al, 2017 ). In addition, sliding motility, a surfactant-mediated motility, has been described for L. pneumophila (Stewart et al, 2009 ).…”