Viscous drag on the flagellum activates Bacillus subtilis entry into the K‐state

Abstract

Bacillus subtilis flagella are not only required for locomotion but also act as sensors that monitor environmental changes. Although how the signal transmission takes place is poorly understood, it has been shown that flagella play an important role in surface sensing by transmitting a mechanical signal to control the DegS-DegU two-component system. Here we report a role for flagella in the regulation of the K-state, which enables transformability and antibiotic tolerance (persistence). Mutations impairing flagellar synthesis are inferred to increase DegU-P, which inhibits the expression of ComK, the master regulator for the K-state, and reduces transformability. Tellingly, both deletion of the flagellin gene and straight filament (hagA233V) mutations increased DegU phosphorylation despite the fact that both mutants had wild type numbers of basal bodies and the flagellar motors were functional. We propose that higher viscous loads on flagellar motors result in lower DegU-P levels through an unknown signaling mechanism. This flagellar-load based mechanism ensures that cells in the motile subpopulation have a 10-fold enhanced likelihood of entering the K-state and taking up DNA from the environment. Further, our results suggest that the developmental states of motility and competence are related and most commonly occur in the same epigenetic cell type.

Impaired competence in flagellar mutants ofBacillus subtilisis connected to the regulatory network governed by DegU

“…By additionally investigating a strain harboring a degU-yfp fusion, Diethmaier et al also suggested an increased level of DegU~P to be present in the hag-mutant (Diethmaier et al, 2017), which is consistent with our conclusions. In addition, the authors detected a reduced expression of comK in a strain with the degU32 variant, which produces a form of DegU~P with higher stability (Diethmaier et al, 2017).…”

“…At this point however, we cannot provide a reasonable explanation for the increased transformation frequency of Δhag degU32. Diethmaier et al proposed that increased DegU~P and lower comK expression in the flagellar mutants and in a strain with straight flagella was caused by a lower viscous load (Diethmaier et al, 2017). In line with this report, we also observed that higher viscosity in the medium resulted in an increased transformation frequency.…”

“…Both studies, however, report a negative effect of the deletion of flagellar components on competence development. The extent to which wild type and mutant differ in competence development is in the same order of magnitude between the studies: for example Diethmaier et al observe a 10-fold reduced number of comG expressing-cells in Δhag (Diethmaier et al, 2017), whereas our flow cytometry experiments showed a slightly lower, 5-fold reduction. Additionally, by investigating the transformation frequency in a cheA mutant, we could also show that the chemotactic response does not seem to have an influence on competence development.…”

“…In a recently published study, similar effects were observed even though different methods have been used: Diethmaier and colleagues found that the expression of comK is lower in deletion mutants of the fla/che operon, hag, and the second stator gene motB (Diethmaier et al, 2017).…”

“…These results suggest that 195 altering the phosphorylation state of DegU in flagellar mutants can revert the negative impact on 196 competence, which was caused by a lack of motility. 197 In a recently published study, similar effects were observed even though different methods have 218 been used: Diethmaier and colleagues found that the expression of comK is lower in deletion 219 mutants of the fla/che operon, hag, and the second stator gene motB (Diethmaier et al, 2017). 220…”