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Monotrichous distribution means that each cell has a single flagellum. If the flagellum is located at the end of the cell, the cell is said to have monotrichous polar distribution, as is the case with Pseudomonas sp. (see picture at left). Amphitrichous bacteria have a single flagellum at each pole. |
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Lophotrichous distribution is a pattern in which bacteria appear to have a tuft ("lopho") of hair ("trichous") at one or both ends. Spirillum is an example of this type of distribution (see picture at left). |
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Peritrichous flagella are distributed uniformly over the surface of each bacterial cell. This pattern is characteristic for highly motile organisms like Proteus vulgaris (see picture). |
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A fourth type of flagellar distribution is the axial filament characteristic of the Spirochetes (see picture at left).
Hundreds of individual periplasmic flagella are bundled together to create a struture that allows spinning and flexing motility.
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FLAGELLAR ULTRASTRUCTURE
Flagellar ultrastructure is fundamentally different in the eukaryotes and the prokaryotes. Only
prokaryotic flagella will be discussed here. Bacteria possessing flagella have basal bodies
embedded in the plasma membrane as anchoring mechanisms. The Gram-negative bacteria have
an additional basal body embedded in the outer membrane.
| Flagellar basal bodies and hooks in a Gram-negative bacterial cell. |
Flagellar basal bodies and hooks in a Gram-positive bacterial cell. |
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BACTERIAL MOVEMENT
Bacterial movement is produced through the action of the flagella (see the diagrams below).
Bacteria move toward attractive stimuli and away from harmful substances and waste products
in the process known as chemotaxis. Monotrichous bacteria
move forward in a simple response to chemotactic stimuli, the counterclockwise
rotation of the flagellum. This forward movement is termed the "run".
Negative chemotaxis causes clockwise rotation of the flagellum and results in a random
tumbling motion. Peritrichous bacteria move in a similar fashion, even
though the situation is somewhat complicated by a requirement for bundling of the flagella
to produce coordinated action during counterclockwise rotation. The "tumble" in peritrichous
bacteria is the result of bundle disruption during clockwise flagellar rotation.
| Movement in Monotrichous Bacteria | Movement in Peritrichous Bacteria |
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Bacterial chemotaxis is controlled by a complex series of events
beginning with the binding of an attractant molecule to a cell surface chemoreceptor. Chemoreceptors
are often clustered at the ends of rod-shaped cells like E. coli. Chemoreceptors do
not influence flagellar motion directly, but convey information through a phosphorylation
cascade. Information about the environment can be translated into motion within 200 milliseconds.
A return to steady-state is assured by a coordinated feedback loop that quickly causes a reversion
to original levels of protein phosphorylation in the absence of stimuli.
References:
Blair, D.F. (1995) How bacteria sense and swim. Ann. Rev. Microbiol. 49: 489 - 522.
Doetsch, R.N. and Sjoblad, R.D. (1980) Flagellar structure and function in eubacteria. Ann. Rev. Microbiol. 34: 69 - 108.
Manson, M.D. (1992) "Bacterial motility and chemotaxis" In Advances in microbial physiology, vol 33, A.H. Rose,
editor, 277-346. New York: Academic Press.
Related Topics:
Bacterial Spore Formation
Bacterial Physiology