E. coli in Motion (Biological and Medical Physics, by Howard C. Berg
By Howard C. Berg
Escherichia coli, often often called E. coli, has been the organism of selection for molecular genetics for many years. Its equipment and cellular habit is likely one of the so much interesting subject matters for cellphone scientists. Scientists and engineers, now not knowledgeable in microbiology, and who want to research extra approximately dwelling machines, can see it as a special instance. This cross-disciplinary monograph covers greater than thirty years of study and is on the market to graduate scholars and scientists alike.
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A formal analysis of a closely related problem, in which a wire is held slantwise and pulled straight downward, is shown in Fig. 1. E. coli carries out this experiment by wrapping the wire into a helix and turning it about the helical axis, as shown, for example, in Figs. 5. The helix behaves like a series of wire segments pulled downward or upward, slantwise, in such a way that the forces generated by each segment in a direction parallel to the helical axis add up, providing the thrust that moves the cell body forward.
The rate at which these displacements are carried out does not matter. Ludwig illustrated this point by imagining a creature with two rigid oars attached to the cell body by hinges, as shown in Fig. 2. The organism strokes its oars rapidly downward and returns them slowly upward. At a low Reynolds number, the cell body moves rapidly upward and then slowly downward, returning to its initial position. At a high Reynolds number, on the other hand, it moves farther during the power stroke than during the recovery stroke.
This was what he was doing in his work on growth of the spore-bearing stalk of the fungus Phycomyces, simply by using a telescope. So I built a microscope that could follow the motion of individual cells of E. coli in three dimensions (Fig. 1). In essence, this is a 31 32 4. 1. The tracking microscope, circa 1974. The lenses, mirrors, and fiber-optic assembly used to dissect the image of a cell was built into the rectangular box extending back from the top of the binocular. Just below the objective is a thermostatted enclosure containing a small chamber in which the bacteria were suspended, mounted on a platform driven by three sets of electromagnetic coils (similar to loudspeaker coils) built into the assembly at the left.