SCientifiC RepoRts | 7: 16771 | DOI:10.1038/s41598-017-16428-9
A polar bundle of agella can drive
bacterial swimming by pushing,
pulling, or coiling around the cell
, Veronika Waljor
, Robert Großmann
, Marco J. Kühn
, Kai M. Thormann
& Carsten Beta
Bacteria swim in sequences of straight runs that are interrupted by turning events. They drive their
swimming locomotion with the help of rotating helical agella. Depending on the number of agella
and their arrangement across the cell body, dierent run-and-turn patterns can be observed. Here,
we present uorescence microscopy recordings showing that cells of the soil bacterium Pseudomonas
putida that are decorated with a polar tuft of helical agella, can alternate between two distinct
swimming patterns. On the one hand, they can undergo a classical push-pull-push cycle that is well
known from monopolarly agellated bacteria but has not been reported for species with a polar
bundle of multiple agella. Alternatively, upon leaving the pulling mode, they can enter a third slow
swimming phase, where they propel themselves with their helical bundle wrapped around the cell
body. A theoretical estimate based on a random-walk model shows that the spreading of a population
of swimmers is strongly enhanced when cycling through a sequence of pushing, pulling, and wrapped
agellar congurations as compared to the simple push-pull-push pattern.
Swimming motility is ubiquitous in the living world. It is essential for many biological functions, such as the
search for nutrients, sexual reproduction, or the spreading of diseases
. Among microbial swimmers, bacteria
are one of the largest and most prominent classes
. ey propel themselves with the help of helical agella that
are connected to rotary motors in their cell wall. Bacteria typically move in a sequence of persistent runs that
are interrupted by random reorientation events. e most thoroughly studied example, the intestinal bacterium
Escherichia coli, displays several agella distributed across its cell envelope (peritrichous agellation). Upon coun-
terclockwise rotation of their motors, they form a coherent agellar bundle that pushes the cell forward in a run.
When one or several of the motors reverse their sense of rotation, the bundle disassembles and a random reorien-
tation of the cell body occurs (tumble), setting the direction of the next run
Over the past years, it became clear that, depending on the number and the arrangement of agella, a variety
of swimming patterns may emerge that dier from the classical run-and-tumble strategy of E. coli. For exam-
ple, bacteria that are decorated with a single agellum at their cell pole (monotrichous agellation) typically
display sharp reversals in their swimming direction
, but may also exhibit more complex maneuvers, such as
the run-reverse-ick pattern of Vibrio sp.
. We have recently concentrated our research on the soil bacterium
that propels itself with a tu of helical agella attached to the posterior pole of its elongated
cell body (lophotrichous agellation)
. Similar to monotrichous bacteria, P. putida swims in straight runs that are
interrupted by sharp reversals in the swimming direction. But in addition, also events with small turning angles
centered around θ = 0° occurred. In contrast to other bacterial swimmers, P. putida may also change its swim-
ming speed between two dierent levels when reversing its swimming direction. However, not every reversal is
associated with a speed change.
These findings pose several fundamental questions regarding the swimming strategy of P. putida.
Monotrichous bacteria induce reversal events by changing the sense of rotation of their agellar motor. ese
University of Potsdam, Institute of Physics and Astronomy, 14476, Potsdam, Germany.
Université Côte d’Azur,
Laboratoire J. A. Dieudonné, UMR 7351 CNRS, F-06108, Nice Cedex 02, France.
Institut für Mikrobiologie und
Molekularbiologie, Justus-Liebig-Universität Giessen, 35392, Giessen, Germany. Correspondence and requests for
materials should be addressed to C.B. (email: email@example.com)
Received: 8 August 2017
Accepted: 6 November 2017
Published: xx xx xxxx