Bacteria break through one-micrometer-square passages by flagellar wrapping.

Area of Science:

• Microbiology
• Biophysics
• Evolutionary Biology

Background:

• Confined micro-environments, such as soil aggregates and intestinal crypts, present significant challenges for bacterial motility.
• The behavior and movement strategies of bacteria in spatially restricted environments are not well understood.
• The stinkbug symbiont, Caballeronia insecticola, must navigate narrow gut passages to reach its symbiotic organ.

Purpose of the Study:

• To investigate bacterial behavior and motility in confined, quasi-one-dimensional spaces.
• To elucidate the mechanism by which Caballeronia insecticola navigates narrow host passages.
• To understand the role of flagellar structure and flexibility in bacterial movement within confined environments.

Main Methods:

• Development of a microfluidic device simulating the host's sorting organ for controlled bacterial confinement.
• Observation and analysis of bacterial cell movement and flagellar dynamics within the microfluidic device.
• Physical simulations and genetic experiments to assess the impact of flagellar hook rigidity on motility and infectivity.

Main Results:

• Caballeronia insecticola exhibits a unique flagellar wrapping behavior, resembling a screw thread, for propulsion in narrow passages.
• This flagellar wrapping mechanism enables smooth and directional movement in quasi-one-dimensional confined spaces.
• Flagellar hook flexibility was identified as crucial for effective wrapping motility and bacterial infectivity; increased rigidity hindered both.

Conclusions:

• Flagellar wrapping is a novel bacterial motility strategy enabling navigation and survival in confined environments.
• This mechanism represents an evolutionary adaptation allowing bacteria to overcome spatial limitations using their existing motility machinery.
• Understanding flagellar wrapping provides insights into bacterial adaptation, symbiosis, and potential targets for controlling microbial infections in confined niches.