Single cell, super-resolution imaging reveals an acid pH-dependent conformational switch in SsrB regulates SPI-2

Andrew Tze Fui Liew, Yong Hwee Foo, Yunfeng Gao, Parisa Zangoui, Moirangthem Kiran Singh, Ranjit Gulvady, Linda Kenney

Research output: Contribution to journalArticle

4 Scopus citations


After Salmonella is phagocytosed, it resides in an acidic vacuole. Its cytoplasm acidifies to pH 5.6; acidification activates pathogenicity island 2 (SPI-2). SPI-2 encodes a type three secretion system whose effectors modify the vacuole, driving endosomal tubulation. Using super-resolution imaging in single bacterial cells, we show that low pH induces expression of the SPI-2 SsrA/B signaling system. Single particle tracking, atomic force microscopy, and single molecule unzipping assays identified pH-dependent stimulation of DNA binding by SsrB. A so-called phosphomimetic form (D56E) was unable to bind to DNA in live cells. Acid-dependent DNA binding was not intrinsic to regulators, as PhoP and OmpR binding was not pH-sensitive. The low level of SPI-2 injectisomes observed in single cells is not due to fluctuating SsrB levels. This work highlights the surprising role that acid pH plays in virulence and intracellular lifestyles of Salmonella; modifying acid survival pathways represents a target for inhibiting Salmonella.

Original languageEnglish (US)
StatePublished - Apr 29 2019



  • <i>s. enterica</i> serovar typhi
  • infectious disease
  • microbiology
  • Salmonella
  • single molecule unzipping
  • single particle tracking
  • SPI-2
  • SsrB
  • super-resolution microscopy

ASJC Scopus subject areas

  • Neuroscience(all)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Immunology and Microbiology(all)

Cite this