Visualizing the Translocation and Localization of Bacterial Type III Effector Proteins by Using a Genetically Encoded Reporter System

Appl Environ Microbiol. 2016 Apr 18;82(9):2700-2708. doi: 10.1128/AEM.03418-15. Print 2016 May.


Bacterial type III secretion system (T3SS) effector proteins are critical determinants of infection for many animal and plant pathogens. However, monitoring of the translocation and delivery of these important virulence determinants has proved to be technically challenging. Here, we used a genetically engineered LOV (light-oxygen-voltage) sensing domain derivative to monitor the expression, translocation, and localization of bacterial T3SS effectors. We found the Escherichia coli O157:H7 bacterial effector fusion Tir-LOV was functional following its translocation and localized to the host cell membrane in discrete foci, demonstrating that LOV-based reporters can be used to visualize the effector translocation with minimal manipulation and interference. Further evidence for the versatility of the reporter was demonstrated by fusing LOV to the C terminus of the Shigella flexneri effector IpaB. IpaB-LOV localized preferentially at bacterial poles before translocation. We observed the rapid translocation of IpaB-LOV in a T3SS-dependent manner into host cells, where it localized at the bacterial entry site within membrane ruffles.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Escherichia coli O157 / genetics
  • Escherichia coli O157 / metabolism
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / metabolism
  • Genes, Reporter*
  • Genetic Engineering / methods
  • HeLa Cells
  • Host-Pathogen Interactions
  • Humans
  • Optical Imaging
  • Protein Domains
  • Shigella flexneri / genetics
  • Shigella flexneri / metabolism
  • Type III Secretion Systems / analysis
  • Type III Secretion Systems / genetics
  • Type III Secretion Systems / metabolism*


  • Bacterial Proteins
  • Escherichia coli Proteins
  • Type III Secretion Systems
  • ipaB protein, Shigella