Early trafficking and intracellular replication of Legionella longbeachaea within an ER-derived late endosome-like phagosome

Abstract

SummaryLegionella pneumophila is the predominant cause of Legionnaires' disease in the USA and Europe in contrast to Legionella longbeachaea, which is the leading cause of the disease in Western Australia. The ability of L. pneumophila to replicate intracellularly is triggered at the post-exponential phase along with expression of other virulence traits, such as motility. We show that while motility of L. longbeachaea is triggered upon growth transition into postexponential phase, its ability to proliferate intracellularly is totally independent of the bacterial growth phase. Within macrophages, L. pneumophila replicates in a phagosome that excludes early and late endocytic markers and is surrounded by the rough endoplasmic reticulum (RER). In contrast, the L. longbeachaea phagosome colocalizes with the early endosomal marker early endosomal antigen 1 (EEA1) and the late endosomal markers lysosomal associated membrane glycoprotein 2 (LAMP-2) and mannose 6-phosphate receptor (M6PR), and is surrounded by the RER. The L. longbeachaea phagosome does not colocalize with the vacuolar ATPase (vATPase) proton pump, and the lysosomal luminal protease Cathepsin D, or the lysosomal tracer Texas red Ovalbumin (TROV). Intracellular proliferation of L. longbeachaea occurs in LAMP-2-positive phagosomes that are remodelled by the RER. Despite their distinct trafficking, both L. longbeachaea and L. pneumophila can replicate in communal phagosomes whose biogenesis is predominantly modulated by L. longbeachaea into LAMP-2-positive phagosomes. In addition, the L. pneumophila dotA mutant is rescued for intracellular replication if it co-inhabits the phagosome with L. longbeachaea. During late stages of infection, L. longbeachaea escape into the cytoplasm, prior to lysis of the macrophage, similar to L. pneumophila. We conclude that the L. longbeachaea phagosome matures to a non-acidified late endosome-like stage that is remodelled by the RER, indicating an idiosyncratic trafficking of L. longbeachaea compared with other intracellular pathogens, and a divergence in its intracellular lifestyle from L. pneumophila. In addition, re-routing biogenesis of the L. pneumophila phagosome into a late endosome controlled by L. longbeachaea has no effect on intracellular replication.

Exclusion of Actin-Binding Protein p57/Coronin-1 from Bacteria-Containing Phagosomes in Macrophages Infected with Legionella

“…27,28) L. longbeachea, which is a human pathogen as well, replicates in RER-surrounded phagosomes that acquire late endosomal marker LAMP-1 while excluding lysosomal markers such as cathepsin D and TROv. 29) Phagosomes containing L. gratiana have not been characterized in this sense. However, our data may suggest that common mechanisms are involved in the exclusion of p57/coronin-1 from bacteria-containing phagosomes upon infection by L. pneumophila or L. gratiana.…”

Computational modeling and experimental validation of the Legionella and Coxiella virulence-related type-IVB secretion signal

“…Therefore, we decided to examine ORFs that received a score above 5 in L. longbeachae as a representative Legionella species. This pathogenic Legionella species has been shown previously to have different intracellular characteristics in comparison to L. pneumophila (29). Using the same secretion signal model described above, 128 L. longbeachae ORFs obtained a score above 5 (Dataset S4).…”

The Legionella longbeachae Icm/Dot Substrate SidC Selectively Binds Phosphatidylinositol 4-Phosphate with Nanomolar Affinity and Promotes Pathogen Vacuole-Endoplasmic Reticulum Interactions

“…The formation of LCVs by L. pneumophila has been studied in some detail. In contrast, knowledge about the formation of LCVs by L. longbeachae is very limited, but the process appears to be different (17).…”