Bipolar lophotrichous Helicobacter suis combine extended and wrapped flagella bundles to exhibit multiple modes of motility

Abstract

The swimming strategies of unipolar flagellated bacteria are well known but little is known about how bipolar bacteria swim. Here we examine the motility of Helicobacter suis, a bipolar gastric-ulcer-causing bacterium that infects pigs and humans. Phase-contrast microscopy of unlabeled bacteria reveals flagella bundles in two conformations, extended away from the body (E) or flipped backwards and wrapped (W) around the body. We captured videos of the transition between these two states and observed three different swimming modes in broth: with one bundle rotating wrapped around the body and the other extended (EW), both extended (EE), and both wrapped (WW). Only EW and WW modes were seen in porcine gastric mucin. The EW mode displayed ballistic trajectories while the other two displayed superdiffusive random walk trajectories with slower swimming speeds. Separation into these two categories was also observed by tracking the mean square displacement of thousands of trajectories at lower magnification. Using the Method of Regularized Stokeslets we numerically calculate the swimming dynamics of these three different swimming modes and obtain good qualitative agreement with the measurements, including the decreased speed of the less frequent modes. Our results suggest that the extended bundle dominates the swimming dynamics.

Figure 1

H. suis flagella dynamics. Arrows point to flagellar bundles, E denotes extended and W denotes wrapped; the cartoons illustrate the flagellar bundle configurations, where flagellar helicity was chosen at random. (A) Movie recorded at 100X and 100 fps in PGM pH6. The bacterium swims with the leading flagellar bundle wrapped around body and lagging flagellar bundle in extended mode in frames 48–52 (run# 33 in Supplementary Table S1). To reverse swimming direction the bundles switch modes in frames 269–273 (run# 34 in Supplementary Table S1). (B) Movie recorded at 100X and 100 fps in BB10 (run# 12 in Supplementary Table S1). The bacterium swims with both bundles in extended position. (C) Movie recorded at 100X and 187 fps in PGM pH6. The bacterium swims with both bundles wrapped around body. (D) Movie recorded at 100X and 100 fps in BB10. The bacterium swims with active wrapped bundle and inactive extended bundle.

Figure 2

Trajectories and body alignment angle of different swimming modes of H. suis swimming in BB10. (A,C,E) Trajectories for modes EW, EE and WW respectively. The trajectories were randomly distributed over the figure for better visualization and do not depict the real position on the movie. (B,D,F) Alignment angle of the center-axis of the body with respect to the x-axis of the video for EW, EE and WW modes respectively. The alignment angle values were translated in the y-axis for better visualization.

Figure 3

Trajectories and body alignment angle of different swimming modes of H. suis swimming in 15 mg/mL PGM at pH6. (A,C) Trajectories for EW and WW modes, respectively. The trajectories and alignment angles were shifted so as to be distributed over the figure for better visualization and do not depict the real position on the movie. (B,D) Alignment angle of the center axis of the body with respect to the x-axis of the image versus time for EW and WW modes respectively. There were no runs in EE mode observed for PGM in this set of bacteria.

Figure 4

MSD and the exponent α for each mode along with speed and body rotation rates for the different modes. (A) MSD vs. time of each trajectory. The green lines are the MSD of EW mode trajectories, maroon lines are the MSD of EE mode trajectories and blue are the MSD of WW mode trajectories. The trajectories in BB10 and PGM were plotted together. Black dashed lines are reference lines for α = 1 and α = 2. (B) Dot plot of α-values for each trajectory separated by mode and medium. The central horizontal lines are the mean values and the vertical bars are the standard deviations. (C) Speed (V), alignment angle frequency (Ω) and V/Ω for the swimming modes of H. suis in BB10 and PGM. Green symbols correspond to EW mode, maroon to EE and blue to WW. Closed circles correspond to BB10 and open symbols to PGM. The horizontal lines indicate the mean while the vertical lines are the standard deviation. 1. Speed of each run separated by mode and media. Each point was calculated as an average of the instantaneous speeds during the individual run. 2. Alignment angle frequency separated by mode and media. Each point was calculated as the average of the frequencies for each run. 3. V/Ω separated by mode and media. Each point was calculated as the average speed of one run divided by the average rotation rate of the same run.

Figure 5

(A,B) Analysis of MSD vs. time of all trajectories in BB10 (A) and PGM (B) along with distributions of the exponent α, run speed and reorientation angle. The blue (red) lines are the MSD of trajectories with α > 1.8 (α ≤ 1.8). Black dashed lines are reference lines for α = 1 and α = 2. (C) Smooth histogram of the α distribution of trajectories in BB10 (black) and PGM (magenta) (D,E). Smooth histogram of v_run (D) and θ_re (E) of H. suis swimming in BB10 (black) and PGM (magenta) at pH6. The histograms have 0.1 bin size for α, 2 μm/s bin size for v_run and 15° bin size for θ_re.

Figure 6

(A) Model for extended-extended mode of motion. Both bundles are left-handed and the motor torque of 2000 pN nm is applied in positive x-directions for each bundle. (B) Rigid body rotation of the flagellum in wrapped mode. (C) Rolling rotation of the filament representing the bundle in wrapped mode; the filament maintains its position relative to the cell body and material points on a cross section move around the cross section. (D) Model showing extended-wrapped swimming with both bundles left-handed while both motors rotate counterclockwise with same torque, set at 2000 pN nm here. (E) Swimming speed and body rotation rate as a function of undetermined rolling rotation rate of wrapped bundle filament. (F) Rigid-body rotation rates of each bundle as a function of undetermined rolling rotation rate. (G) Model showing extended-wrapped swimming with wrapped bundles right-handed while both motors rotate counterclockwise with same torques as in D. (H) Swimming speed and body rotation rate as a function of undetermined rolling rotation rate of wrapped bundle. (I) Rigid-body rotation rates of each bundle as a function of undetermined rolling rotation rate.

Figure 7

(A) Model of bacterium showing wrapped-wrapped swimming with both bundles left-handed while both motors rotate CCW with the same torque, set at 2000 pN nm. (B) Swimming speed and body rotation rate as a function of undetermined rolling rotation rates of each bundle. (C) Rigid-body rotation rates of each bundle as a function of undetermined rolling rotation rates. (D) Model of wrapped-wrapped swimming with one bundle left-handed and the other bundle right-handed while both motors rotate CCW with same torque set at 2000 pN nm. (E) Swimming speed and body rotation rate as a function of undetermined rolling rotation rates of each bundle. (F) Rigid-body rotation rates of each bundle as a function of undetermined rolling rotation rates.

Figure 8

Trajectory of H. suis swimming in BB10 (A) and its respective instantaneous swimming speed (B) and absolute angle change, |Δϕ|, over time (C). The red circles indicate reorientation events.