The PilT retraction ATPase promotes both extension and retraction of the MSHA type IVa pilus in Vibrio cholerae

Abstract

Diverse bacterial species use type IVa pili (T4aP) to interact with their environments. The dynamic extension and retraction of T4aP is critical for their function, but the mechanisms that regulate this dynamic activity remain poorly understood. T4aP are typically extended via the activity of a dedicated extension motor ATPase and retracted via the action of an antagonistic retraction motor ATPase called PilT. These motors are generally functionally independent, and loss of PilT commonly results in T4aP hyperpiliation due to undeterred pilus extension. However, for the mannose-sensitive hemagglutinin (MSHA) T4aP of Vibrio cholerae, the loss of PilT unexpectedly results in a loss of surface piliation. Here, we employ a combination of genetic and cell biological approaches to dissect the underlying mechanism. Our results demonstrate that PilT is necessary for MSHA pilus extension in addition to its well-established role in promoting MSHA pilus retraction. Through a suppressor screen, we also provide genetic evidence that the MshA major pilin impacts pilus extension. Together, these findings contribute to our understanding of the factors that regulate pilus extension and describe a previously uncharacterized function for the PilT motor ATPase.

Sulfolobus acidocaldariusadhesion pili power twitching motility in the absence of a dedicated retraction ATPase

“…Two bacterial species, Caulobacter crescentus and Vibrio cholerae, are also known to lack a retraction ATPase and it was shown that the assembly ATPase PilB is responsible for both pilus assembly and retraction (Ellison et al, 2017;Ellison et al, 2019;Hughes et al, 2022). In our case, it is likely that the adhesion pili assembly ATPase AapE also coordinates pilus retraction.…”

“…For many years PilT was thought to be essential for retraction of type IV pili, leading to the proposal that archaeal pili are not capable of retraction and do not employ twitching motility (Chaudhury et al, 2018;Denise et al, 2019;Beeby, 2019). Recent work, however, has revealed the existence of PilT-independent retraction mechanisms in at least some bacteria (Ellison et al, 2017;Ellison et al, 2019;Hughes et al, 2022). While performing live-cell, time-lapse imaging of S. acidocaldarius at their normal growth temperature (75°C) we observed a type of surface-motility reminiscent of bacterial twitching motility (Charles-Orszag et al, 2021), challenging the idea that type IV pili in these cells are unable to retract.…”

Adhesion pilus retraction powers twitching motility in the thermoacidophilic crenarchaeon Sulfolobus acidocaldarius

“…Interestingly, bacterial Tad pili are thought to have been acquired from archaea through horizontal gene transfer 29 . In the bacterial pathogen Vibrio cholerae , PilT promotes both pilus assembly and retraction 32 . Finally, type IV pili of the bacterial pathogen Neisseria gonorrhoeae exhibit slow, ATPase-independent retraction, which can be enhanced by PilT homologs 43 .…”

“…For many years PilT was thought to be essential for retraction of type IV pili, leading to the proposal that archaeal pili are not capable of retraction and do not employ twitching motility 3,28,29 . Recent work, however, revealed that some bacteria exhibit PilT-independent pilus retraction [30][31][32] . While performing livecell, time-lapse imaging of the model hyperthermophilic crenarchaeon Sulfolobus acidocaldarius at their normal growth temperature (75 °C) we previously observed a type of surface-motility reminiscent of bacterial twitching motility 33 , challenging the idea that type IV pili in these cells are unable to retract.…”