Figure 1.
Oxygen depletion triggers speed switching of T4P retraction.
a) Scheme of T4P driven surface motility. Multiple pili adhere to the surface and when they retract, they pull the cell towards the point of attachment. b) Overlay of the speed of twitching motility of multiple bacteria during global speed switching. Full line: fit to eq. 1.
Figure 2.
Components of the proton motive force of N. gonorrhoeae.
(a) Intracellular pH (pHin) and (b) ΔpH-component of the PMF versus extracellular pH (pHex). black: cFDA-SE (N = 100-1000 cells per data point), red: single cell analysis of pHluorin expressing cells (N = 240-530 cells per data point), green spectroscopic analysis of of pHluorin expressing cells (3 independent experiments). Full line in (a): pHin = pHex. (c) Transmembrane potential ΔΨ as a function of pHex (N = 100-200 cells per data point).
Figure 3.
Depletion of proton motive force induces global switching and is fully reversible.
(a) Global switching during injection of 25 µM CCCP. Overlay of speeds of 48 bacterial tracks versus time. Solid line: fit to eq. 1. (b) Global switching during injection of 50 µM CCCP. Overlay of speeds of 40 bacterial tracks. (c) Washing out CCCP is accompanied by switching back to high speed mode. Overlay of speeds of 35 bacterial tracks. (d) Transition rate as obtained by fit to eq. 1.
Figure 4.
Effect of ATP depletion on twitching dynamics by direct inhibition of the ATP synthase.
(a) Kinetics of ATP depletion upon treatment with 50 µM CCCP. Open and closed grey circles depict independent determinations of the relative ATP concentration, respectively. (b) Kinetics of ATP depletion upon treatment with 200 µM DCCD. Open and closed grey circles depict independent determinations of the relative ATP concentration, respectively. (c) Twitching speed averaged over 3 min versus incubation time in 200 µM DCCD.
Figure 5.
Global switching correlates with reduction of transmembrane ΔpH.
(a) Addition of 5 µM nigericin induces global switching (overlay of 31 bacterial tracks). (b) Transmembrane potential ΔΨ before and after nigericin treatment. (c) −61·ΔpH before and after global switching induced by oxygen scavenger treatment at pHex = 6.0.
Figure 6.
Oxygen-dependent mode switching is not conserved in M. xanthus.
(a) Average speeds v of single pilus retraction at 8 pN (62 events) and 30 pN (56 events). (b) Oxygen concentration (black circles) and average speed v of moving bacteria (grey triangles, 5 bacteria per time point) as a function of time.