The entry ofSalmonellain a distinct tight compartment revealed at high temporal and ultrastructural resolution

Abstract

Salmonella enterica induces membrane ruffling and genesis of macropinosomes during its interactions with epithelial cells. This is achieved through the type three secretion system-1, which first mediates bacterial attachment to host cells and then injects bacterial effector proteins to alter host behaviour. Next, Salmonella enters into the targeted cell within an early membrane-bound compartment that matures into a slow growing, replicative niche called the Salmonella Containing Vacuole (SCV). Alternatively, the pathogen disrupts the membrane of the early compartment and replicate at high rate in the cytosol. Here, we show that the in situ formed macropinosomes, which have been previously postulated to be relevant for the step of Salmonella entry, are key contributors for the formation of the mature intracellular niche of Salmonella. We first clarify the primary mode of type three secretion system-1 induced Salmonella entry into epithelial cells by combining classical fluorescent microscopy with cutting edge large volume electron microscopy. We observed that Salmonella, similarly to Shigella, enters epithelial cells inside tight vacuoles rather than in large macropinosomes. We next apply this technology to visualise rupturing Salmonella containing compartments, and we use extended time-lapse microscopy to establish early markers that define which Salmonella will eventually hyper replicate. We show that at later infection stages, SCVs harbouring replicating Salmonella have previously fused with the in situ formed macropinosomes. In contrast, such fusion events could not be observed for hyper-replicating Salmonella, suggesting that fusion of the Salmonella entry compartment with macropinosomes is the first committed step of SCV formation.

Human GBP1 binds LPS to initiate assembly of a caspase-4 activating platform on cytosolic bacteria

“…1f). Since in epithelial cells a subset of Salmonella escape from the Salmonella-containing vacuole (SCV) into the cytosol within the first hour after entry 18,19 , we hypothesized that Salmonella could activate the non-canonical inflammasome as previously observed in mouse macrophages 20 . To test this, we infected naive or IFNγ-primed wild-type, CASP4 -/and GSDMD -/-HeLa ( Supplementary Fig.…”

Shigella hijacks the exocyst to cluster macropinosomes for efficient vacuolar escape

“…Previously we noted that the IAMs formed during S. typhimurium infection can fuse with the early entry compartment of S. typhimurium. [6,32]. Proteomic analysis of the IAMs during S. typhimurium infection also suggests specific SNARE proteins involved for the BCV-IAM fusion, implying a…”

Presence of SopE and mode of infection result in increasedSalmonella‐containing vacuole damage and cytosolic release during host cell infection bySalmonella enterica

“…Salmonella-infected cells have been comprehensively described by Birmingham et al (2006). Detailed ultrastructural analyses showed that invading Salmonella inhabits individual macropinosomes (Fredlund et al, 2018) and works in our group showed that this individuality is maintained in later stages of infection (Krieger et al, 2014). The demand for membranes to build SCV with individual Salmonella could exceed the supply in case to high rates of invasion, thus promoting instability.…”