Distinct chemotactic behavior in the original Escherichia coli K-12 depending on forward-and-backward swimming, not on run-tumble movements.
Scientific reports 10:1 (2020) 15887
Abstract:
Most motile bacteria are propelled by rigid, helical, flagellar filaments and display distinct swimming patterns to explore their favorable environments. Escherichia coli cells have a reversible rotary motor at the base of each filament. They exhibit a run-tumble swimming pattern, driven by switching of the rotational direction, which causes polymorphic flagellar transformation. Here we report a novel swimming mode in E. coli ATCC10798, which is one of the original K-12 clones. High-speed tracking of single ATCC10798 cells showed forward and backward swimming with an average turning angle of 150°. The flagellar helicity remained right-handed with a 1.3 μm pitch and 0.14 μm helix radius, which is consistent with the feature of a curly type, regardless of motor switching; the flagella of ATCC10798 did not show polymorphic transformation. The torque and rotational switching of the motor was almost identical to the E. coli W3110 strain, which is a derivative of K-12 and a wild-type for chemotaxis. The single point mutation of N87K in FliC, one of the filament subunits, is critical to the change in flagellar morphology and swimming pattern, and lack of flagellar polymorphism. E. coli cells expressing FliC(N87K) sensed ascending a chemotactic gradient in liquid but did not spread on a semi-solid surface. Based on these results, we concluded that a flagellar polymorphism is essential for spreading in structured environments.Assembly and dynamics of the bacterial flagellum
Annual Review of Microbiology Annual Reviews 74 (2020) 181-200
Abstract:
The bacterial flagellar motor is the most complex structure in the bacterial cell, driving the ion-driven rotation of the helical flagellum. The ordered expression of the regulon and the assembly of the series of interacting protein rings, spanning the inner and outer membranes to form the ∼45–50-nm protein complex, have made investigation of the structure and mechanism a major challenge since its recognition as a rotating nanomachine about 40 years ago. Painstaking molecular genetics, biochemistry, and electron microscopy revealed a tiny electric motor spinning in the bacterial membrane. Over the last decade, new single-molecule and in vivo biophysical methods have allowed investigation of the stability of this and other large protein complexes, working in their natural environment inside live cells. This has revealed that in the bacterial flagellar motor, protein molecules in both the rotor and stator exchange with freely circulating pools of spares on a timescale of minutes, even while motors are continuously rotating. This constant exchange has allowed the evolution of modified components allowing bacteria to keep swimming as the viscosity or the ion composition of the outside environment changes.Cryo-EM structures provide insight into how E. coli F1Fo ATP synthase accommodates symmetry mismatch
Nature Communications Springer Nature 11:1 (2020) 2615
Abstract:
F1Fo ATP synthase functions as a biological rotary generator that makes a major contribution to cellular energy production. It comprises two molecular motors coupled together by a central and a peripheral stalk. Proton flow through the Fo motor generates rotation of the central stalk, inducing conformational changes in the F1 motor that catalyzes ATP production. Here we present nine cryo-EM structures of E. coli ATP synthase to 3.1–3.4 Å resolution, in four discrete rotational sub-states, which provide a comprehensive structural model for this widely studied bacterial molecular machine. We observe torsional flexing of the entire complex and a rotational sub-step of Fo associated with long-range conformational changes that indicates how this flexibility accommodates the mismatch between the 3- and 10-fold symmetries of the F1 and Fo motors. We also identify density likely corresponding to lipid molecules that may contribute to the rotor/stator interaction within the Fo motor.Load-dependent adaptation near zero load in the bacterial flagellar motor
Interface Royal Society 16:159 (2019) 20190300
Abstract:
The bacterial flagellar motor is an ion-powered transmembrane protein complex which drives swimming in many bacterial species. The motor consists of a cytoplasmic ‘rotor’ ring and a number of ‘stator’ units, which are bound to the cell wall of the bacterium. Recently, it has been shown that the number of functional torque-generating stator units in the motor depends on the external load, and suggested that mechanosensing in the flagellar motor is driven via a ‘catch bond’ mechanism in the motor’s stator units. We present a method that allows us to measure—on a single motor—stator unit dynamics across a large range of external loads, including near the zero-torque limit. By attaching superparamagnetic beads to the flagellar hook, we can control the motor’s speed via a rotating magnetic field. We manipulate the motor to four different speed levels in two different ion-motive force (IMF) conditions. This framework allows for a deeper exploration into the mechanism behind load-dependent remodelling by separating out motor properties, such as rotation speed and energy availability in the form of IMF, that affect the motor torque. The bacterial flagellar motor (BFM) is an ion-driven nanomachine that drives swimming in a variety of bacterial species. The BFM couples the flow of cations (protons, in Escherichia coli) across the bacterial membrane to induce rotation in the flagellum, spinning the filament like a propeller to move the bacterium forward. The flagellar motor generates torque through interactions between the motor’s stator and rotor; specifically, torque is generated via an interaction between a stator unit (in E. coli, comprising the proteins MotA and MotB) and FliG protein ‘spokes’ that line the rotor’s cytoplasmic C-ring (figure 1a). The BFM’s stator can be composed of between 1 and at least 11 independent units.Simultaneous tracking of Pseudomonas aeruginosa motility in liquid and at the solid-liquid interface reveals differential roles for the flagellar stators
mSystems American Society for Microbiology 4:5 (2019) e00390-19