Tad pili with adaptable tips mediate contact-dependent killing during bacterial predation

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.