Biology subjects

Partridge, J. D.

Publications and source records attributed to Partridge, J. D..

3 recordsLinked to original sources

bioRxiv2025

Texas 2-Step: A new Model for YcgR::c-di-GMP Action at the Flagellar Motor

YcgR is a c-di-GMP effector that inhibits chemotaxis and swimming speed in Escherichia coli and Salmonella. Genetic, biochemical, and structural studies suggest that YcgR interacts with both the bidirectional flagellar rotor and the stator to bias rotation toward counterclockwise (CCW) and reduce motor speed, but the underlying mechanism remains unresolved. Recent cryo-EM structures revealing conformational changes in the rotor-stator complex during directional switching suggested to us a mechanism by which YcgR acts. We call this the Texas 2-Step model, after the country dance in which partners move smoothly in a CCW arc with quick steps followed by slow ones. In this model, YcgR first binds a MotA subunit when the rotor adopts the CCW conformation, in which stators are largely displaced from the C-ring. In the next step, the rotating MotA pentamer delivers YcgR to the rotor protein FliG, thereby slowing motor speed. We provide evidence for the first step of this model, offering testable predictions for future work. ImportanceThe mechanism of YcgR action has been investigated by multiple laboratories using diverse approaches, yet no consensus has emerged. Some studies implicate the rotor, others the stator. A key complication is the involvement of four interacting proteins--MotA, FliG, FliM, and YcgR--with multiple contact sites in several of them. Recent rotor-stator cryo-EM structures revealing conformational changes during directional switching suggested a mechanism that we set out to test. Our experiments show that rotor conformation is crucial for YcgR function.

microbiology↗

bioRxiv2023

Flagellar motor remodeling during swarming requires FliL

FliL is an essential component of the flagellar machinery in some bacteria, but a conditional one in others. The conditional role is for optimal swarming in some bacteria. During swarming, physical forces associated with movement on a surface are expected to exert a higher load on the flagellum, requiring more motor torque to move. Bacterial physiology and morphology are also altered during swarming to cope with the challenges of surface navigation. FliL was reported to enhance motor output in several bacteria and observed to assemble as a ring around ion-conducting stators that power the motor. In this study we identify a common new function for FliL in diverse bacteria - Escherichia coli, Bacillus subtilis and Proteus mirabilis. During swarming, all these bacteria show increased cell speed and a skewed motor bias that suppresses cell tumbling. We demonstrate that these altered motor parameters, or motor remodeling, require FliL. Both swarming and motor remodeling can be restored in an E. coli fliL mutant by complementation with fliL genes from P. mirabilis and B. subtilis, showing conservation of swarming-associated FliL function across phyla. In addition, we demonstrate that the strong interaction we reported earlier between FliL and the flagellar MS-ring protein FliF is confined to the RBM-3 domain of FliF that links the periplasmic rod to the cytoplasmic C-ring. This interaction may explain several phenotypes associated with the absence of FliL.

microbiology↗

bioRxiv2020

Remodeling of Chemotaxis is a Cornerstone of Bacterial Swarming

Many bacteria use flagella-driven motility to swarm or move collectively over a surface terrain. Bacterial adaptations for swarming can include cell elongation, hyper-flagellation, recruitment of special stator proteins and surfactant secretion, among others. We recently demonstrated another swarming adaptation in Escherichia coli, wherein the chemotaxis pathway is remodeled to increase run durations (decrease tumble bias), with running speeds increased as well. We show here that the modification of motility parameters during swarming is not unique to E. coli, but shared by a diverse group of bacteria we examined - Proteus mirabilis, Serratia marcescens, Salmonella enterica, Bacillus subtilis, and Pseudomonas aeruginosa - suggesting that altering the chemosensory physiology is a cornerstone of swarming. ImportanceBacteria within a swarm move characteristically in packs, displaying an intricate swirling motion where hundreds of dynamic packs continuously form and dissociate as the swarm colonizes increasing expanse of territory. The demonstrated property of E. coli to reduce its tumble bias and hence increase its run duration during swarming is expected to maintain/promote side-by-side alignment and cohesion within the bacterial packs. Here we observe a similar low tumble bias in five different bacterial species, both Gram positive and Gram negative, each inhabiting a unique habitat and posing unique problems to our health. The unanimous display of an altered run-tumble bias in swarms of all species examined here suggests that this behavioral adaptation is crucial for swarming.

microbiology↗