How Bacterias Swim

How Bacteria Swim?

Main ways they use for their locomotion:

1. Mechanism of Swimming Motility (with flagella)

2. Effect of Brownian Motion on trajectory of bacteria (mostly used by non-flagelleted)

Overview

Being micron-sized Brownian motion shows some effect in bacteria’s trajectory resulting in the change of radius.

Fig: Result of effect as distance of bacteria from the surface change, there is change in speed and thus in radius of curvature.

Trajectory

The flagellar filament is left-handed and rotates counterclockwise as observed from right and observing left. On the helix, Two material points are seen with their ‘local’ velocity. Background points increase in value while those in foreground decrease. This diagram also shows the density of the instantaneous drag force resisting helix rotation in the fluid.The overall drag involves a ‘non-zero’ dimension parallel to the helix's axis. As a result, a spinning helix encounters a full fledged net viscous force that is parallel to the helix's axis and it’s orientation is dependent on the helix's orientation and direction of rotation.

Mechanism of Motility

Multi Flagella Model

(i) Rotation rate which is fix is generated by rotatory motor in flagellar filament about axis shown as Unit Vector ‘k’.

(ii) Flexible short hook acts like a torsional spring w.r.t. the axis of the motor.

(iii) Helical filament of flagella is in normal left-handed orientation.

As every helical filament has tapered end its helix radius will tend to become zero near the attachment to the body.

A: Graph of Motors Stiffness(Made Non-Dimensional by Pitch of Flagellar Helices, the frequency of rotation and Viscosity of Fluid) Vs. Θ (Angle Between Helical Axis and Normal to body of Bacteria)

B: Graph of Motors Stiffness(Made Non-Dimensional by Pitch of Flagellar Helices and Viscosity of Fluid) Vs. U (Speed of cell).

There are 4 flagellas on E. Coli, A pusher bacterium has filaments in normal counter clockwise rotation.

its trajectory stiffens over a time period of t=200.

The cell with the flexible hook with the filaments in the back swims much faster than the stiff-hooked cell.

The cell becomes a puller if the direction is reversed and does not swim fast for either orientation. Both the pushers and pullers have identical swimming magnitude, this is due to kinematic reversibility of Stokes flows .

Transition for pusher bacteria is not smooth as compared to stiff hook one. The cause of this instability is due to two-way coupling of cell locomotion and conformation of flagella.

Exp. Observations

The bacteria comprise a spherocylindrical body having helical flagella attached which is built by discrete microparticles to allow efficiency while coupling in fluid.

Conclusion

An optical trap used to measure the basic properties of bacterial propulsion. Some force is needed to know the propulsion matrix, which relates several other motile properties like angular velocity of the flagellum, translational velocity, and torques generated by flagellum.