Schematic representation (IMAGE)
Caption
Adaptation of the bacterial type III secretion system to changing pH. (a) Schematic representation of the active T3SS injectisome. Effector proteins (black/blue) are exported from the bacteria to the host cell in a single transport step. The position of the pH sensor protein SctD and one of the dynamic cytosolic T3SS components, SctK, are indicated. Double arrows indicate the exchange of the cytosolic subunits or subcomplexes between the cytosolic and the injectisome-bound state. (b) pH ranges and typical retention times at different parts of the gastrointestinal system. (c) Fluorescent micrographs of live Y. enterocolitica expressing a fluorescently labeled cytosolic T3SS component (EGFP-SctK). Images were taken 10 minutes after bacteria were subjected to the indicated pH. Insets, enlarged single bacteria in "red-hot" color scale. Scale bar, 2 μm. (d) Model of the pH-dependent suppression of T3SS activity. From top: (i) Assembly of the T3SS upon entry into host organisms; cytosolic components bound and exchanging with cytosolic pool. (ii) Prevention of effector translocation upon host cell attachment in low pH environment, because cytosolic components are exclusively cytosolic. (iii) Re-association of cytosolic components to the injectisome and effector translocation upon host cell contact in neutral body parts. The pH sensor protein SctD and the cytosolic components SctK are indicated by D and K, respectively.
Credit
Max Planck Institute for Terrestrial Microbiology/Diepold
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