Pathogenic diversification of the gut commensal Providencia alcalifaciens via acquisition of a second type III secretion system
Related Experiment Video
Updated: Jun 13, 2025
Coincubation Assay for Quantifying Competitive Interactions between Vibrio fischeri Isolates
Published on: July 22, 2019
Jessica A Klein1, Alexander V Predeus2, Aimee R Greissl1
1Paul G. Allen School for Global Health, College of Veterinary Medicine, Washington State University, Pullman, Washington, USA.
Abstract:
Providencia alcalifaciens is a Gram-negative bacterium found in various water and land environments and organisms, including insects and mammals. Some P. alcalifaciens strains encode gene homologs of virulence factors found in pathogenic Enterobacterales members, such as Salmonella enterica serovar Typhimurium and Shigella flexneri. Whether these genes are pathogenic determinants in P. alcalifaciens is not known. In this study, we investigated P. alcalifaciens-host interactions at the cellular level, focusing on the role of two type III secretion systems (T3SS) belonging to the Inv-Mxi/Spa family. T3SS1b is widespread in Providencia spp. and encoded on the chromosome. A large plasmid that is present in a subset of P. alcalifaciens strains, primarily isolated from diarrheal patients, encodes for T3SS1a. We show that P. alcalifaciens 205/92 is internalized into eukaryotic cells, lyses its internalization vacuole, and proliferates in the cytosol. This triggers caspase-4-dependent inflammasome responses in gut epithelial cells. The requirement for the T3SS1a in entry, vacuole lysis, and cytosolic proliferation is host cell type-specific, playing a more prominent role in intestinal epithelial cells than in macrophages or insect cells. In a bovine ligated intestinal loop model, P. alcalifaciens colonizes the intestinal mucosa and induces mild epithelial damage with negligible fluid accumulation in a T3SS1a- and T3SS1b-independent manner. However, T3SS1b was required for the rapid killing of Drosophila melanogaster. We propose that the acquisition of two T3SS has allowed P. alcalifaciens to diversify its host range, from a highly virulent pathogen of insects to an opportunistic gastrointestinal pathogen of animals.
Insights
Providencia alcalifaciens utilizes two type III secretion systems (T3SS) to interact with hosts. The study reveals T3SS1a is crucial for invading host cells, while T3SS1b aids in insect pathogenicity, enabling host range expansion.
Area of Science:
- Microbiology
- Cell Biology
- Pathogen Host Interactions
Background:
- Providencia alcalifaciens is a Gram-negative bacterium found in diverse environments.
- Some strains possess virulence factor gene homologs found in known pathogens like Salmonella and Shigella.
- The pathogenic role of these genes in P. alcalifaciens remains largely unknown.
Purpose of the Study:
- To investigate cellular-level interactions between P. alcalifaciens and host cells.
- To elucidate the role of two specific type III secretion systems (T3SS1a and T3SS1b) in P. alcalifaciens pathogenesis.
- To understand how these T3SS contribute to host specificity and disease potential.
Main Methods:
- Cellular invasion assays using various eukaryotic cell types (intestinal epithelial cells, macrophages, insect cells).
- Analysis of bacterial intracellular survival, vacuole lysis, and proliferation.
- In vivo studies using a bovine ligated intestinal loop model.
- Assessment of bacterial virulence in Drosophila melanogaster.
Main Results:
- P. alcalifaciens invades eukaryotic cells, lyses vacuoles, and proliferates intracellularly, triggering inflammasome responses.
- T3SS1a is essential for entry, vacuole lysis, and cytosolic proliferation in a host cell-dependent manner.
- T3SS1a and T3SS1b are not required for intestinal colonization and mild damage in a bovine model.
- T3SS1b is critical for rapid killing of Drosophila melanogaster.
Conclusions:
- P. alcalifaciens employs distinct T3SS for different host interactions.
- T3SS1a facilitates intracellular survival in mammalian cells, particularly intestinal epithelial cells.
- T3SS1b contributes to insect pathogenicity.
- The acquisition of two T3SS enables P. alcalifaciens to adapt as an opportunistic gastrointestinal pathogen and a potent insect pathogen.
