“The salmonella containing Vacuole moving with the time (2008)” review Week 5 readings Introduction ● Facultative intracellular pathogens ● Entry to host cell through phagosome like compartment ○ Replicates within Salmonella containing vacuoles ○ Essential for intracellular survival ■ Evasion of host immune responses ■ Sustaining replication ■ Systematic dissemination SCV thesis ● Stage 1 ○ Formation of nascent SCV after bacterial entry ■ Through ruffling mechanisms (T3SS1) ■ Early endosomal markers are acquired ● EEA1 ● Rab5 ● TfR ■ SCV acidic in range (6.0-6.5) ■ T3SS1 effectors ● SipA ○ Actin stabilization ○ SopE, SopB, SopD, SopA ■ Signalling of membrane trafficking ○ SopB ■ Delay in lysosomal fusions ● Stage 2 ○ Loss of early endosomal markers ○ Late endosomal markers are acquired ■ LAMP1/2 ■ Rab 7 ■ Rab11 ■ vATPase ○ Microtubules based SCV in perinuclear regions ○ T3SS2 induced => secretes effectors in host cytosol ■ Triggers acidic environment +SCV maturation ● ex) ○ SseF/SseG = anchors on SCV (MTOC) then modulates host trafficking ○ SpiC = host endosome lysosome fusion ● Stage 3 ○ Intracellular replication starts in 6-8 hours ○ SCV enveloped with network of actin ■ Will make tubular extensions (Sifs) ○ Tubules ■ LAMP1+ Rab7+ ■ Marking of SPI-2 ○ Vacuolar membrane maintained SCV avoids lysosomal degradation Effector System Function SipA T3SS1 Stabilizes actin for invasion; aids early SCV shaping SopB T3SS1 Delays lysosomal fusion via PI(3)P modulation SopD/SopA T3SS1 Influence SCV biogenesis and inflammation SpiC T3SS2 Inhibits endosome-lysosome fusion; impairs vesicle trafficking SseF/SseG T3SS2 Anchor SCV near Golgi/MTOC; prevent dispersion SifA T3SS2 Essential for Sif formation; maintains SCV membrane integrity PipB2 T3SS2 Binds kinesin-1; drives anterograde Sif extension SseJ T3SS2 Lipid-modifying enzyme; opposes SifA function SteC T3SS2 Kinase that promotes F-actin accumulation around SCV SspH2/SseI T3SS2 Modulate cytoskeletal structure, potentially immune suppression Note: many effectors have overlapping roles. This makes difficult in isolation of phenotypes ● Sif Tubules ○ Observed in 4-6 hours of infection ○ LAMP1, microtubes, and RabGTPase ○ Used for nutrient acquisition form the host ■ Used for expansion of ocular space while replicating ■ Avoids autophages ○ Dynamics in Sif ■ SifA = used while formation ■ PipB2 kinesin motor recruitment Sif elongation ■ SseJ = destabilization of Sifs ● SCV host ○ Modified phagosomes ■ Not standard in endosomes + lysosomes ○ Salmonella will prevent fusion and degradative lysosomes ■ Still be able to tap into network ○ Vacuoles will be command center and responsible for vesicular traffics, and cytoskeletal rearrangements ○ Once infected, host cell will be reprogrammed by effectors and maintain niche for salmonella colony