CLASSIFICATION OF BACTERIA ON THE
BASIS OF NUMBER AND ORGANISATION OF FLAGELLA
A flagellum is a lash-like
appendage that protrudes from the cell body of certain prokaryotic and
eukaryotic cells. The word flagellum in Latin means whip. The primary role
of the flagellum is locomotion but it also often has function as a
sensory organelle,
being sensitive to chemicals and temperatures outside the cell. Flagella are
organelles defined by function rather than structure. There are large
differences between different types of flagellum; the prokaryotic and
eukaryotic flagella differ greatly in protein composition, structure, and
mechanism of propulsion, however both are used for swimming.
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| fig: The tail like portion is the flagella |
Different species of bacteria have different numbers and arrangements of flagella.
- Atrichous bacteria lack flagellum.
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| Fig: Atrichous Bacteria |
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- Monotrichous bacteria have a single flagellum that occur at or near one end of bacterium. (e.g., Vibrio cholerae).
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| fig: A monotrichous bacteria |
- Lophotrichous bacteria have multiple flagella located at the same spot on the bacteria's surfaces which act in concert to drive the bacteria in a single direction. In many cases, the bases of multiple flagella are surrounded by a specialized region of the cell membrane.
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| fig: A Lophotrichous Bacteria |
- Amphitrichous bacteria have a single flagellum on each of two opposite ends (only one flagellum operates at a time, allowing the bacteria to reverse course rapidly by switching which flagellum is active).
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| Fig: Amphitrichous Bacteria |
- Peritrichous bacteria have flagella projecting in all directions (e.g., E. coli).
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| Fig: A Peritrichous bacteria |
