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Tad pili with adaptable tips mediate contact-dependent killing during bacterial predation
Julien Herrou1, Laetitia My2, Caroline L Monteil3
1Aix Marseille Univ, CNRS, LCB, Marseille, France. jherrou@imm.cnrs.fr.
Abstract:
The predatory bacterium, Myxococcus xanthus, kills its prey by contact, using a putative Tight Adherence pilus, known as the Kil system, along with a protein complex resembling the basal body a type-III secretion system, named the "needleless" T3SS*. In this work, we provide direct evidence that Myxococcus polymerizes a Kil pilus at the prey contact site, which is constituted by the major pilin KilP. We also genetically demonstrate that the predation function of this pilus is linked to four different minor pilin complexes, which work in specific combinations to detect and kill phylogenetically diverse bacterial species. Structural models of the Kil pilus suggest that these minor pilin complexes form interchangeable "Tips", exposing variable domains at the extremity of the pilus to interact with prey cells. Remarkably, the activity of these Tips also depends on the T3SS*, revealing a tight functional connection between the Kil system and the T3SS*. While these Tips are mostly restricted to predatory bacteria, genomic and structural analyses suggest that in other bacteria, including pathogens, Tad pili are also customized and functionalized by similar minor pilin complexes exposing variable domains.
Insights
The predatory bacterium Myxococcus xanthus uses a specialized pilus (Kil system) and a needleless type-III secretion system (T3SS*) to hunt prey. Minor pilin complexes form interchangeable tips on the pilus, enabling detection and killing of diverse bacteria.
Area of Science:
- Microbiology
- Bacterial Predation
- Molecular Biology
Background:
- Myxococcus xanthus is a predatory bacterium that kills prey by direct contact.
- This predation involves a putative Tight Adherence pilus (Kil system) and a needleless type-III secretion system (T3SS*).
Purpose of the Study:
- To provide direct evidence for Kil pilus polymerization at prey contact sites.
- To genetically demonstrate the role of minor pilin complexes in predation specificity.
- To elucidate the functional connection between the Kil system and the T3SS*.
Main Methods:
- Direct visualization of Kil pilus polymerization.
- Genetic analysis of minor pilin complex function in predation.
- Structural modeling of the Kil pilus.
- Genomic and structural analyses of related pili in other bacteria.
Main Results:
- Myxococcus xanthus polymerizes a Kil pilus composed of KilP major pilin at prey contact sites.
- Four distinct minor pilin complexes function as interchangeable 'Tips' to detect and kill diverse bacterial prey.
- Tip activity is dependent on the T3SS*, indicating a functional linkage between the Kil system and T3SS*.
- Genomic data suggest similar minor pilin complex customization in other bacteria, including pathogens.
Conclusions:
- The Kil system, with its variable minor pilin tips and T3SS* dependence, represents a sophisticated mechanism for bacterial predation.
- These findings reveal a conserved principle of pilus functionalization by interchangeable tip complexes, applicable beyond predatory bacteria.
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