Bacterial Flagella & its ultrastructure / Classification of bacteria based on flagellar arrangement

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In this video, the ultrastructure of bacterial flagella, and the bacterial classification based on flagellar arrangement are discussed here:
Flagella are thread like locomotor appendages extending outward from the plasma membrane and cell wall. Bacterial flagella are slender, rigid structures, about 20 nm across and up to 20 μm long. Flagella are so thin they cannot be observed directly with a bright-field microscope but must be stained with special techniques designed to increase their thickness. The detailed structure of a flagellum can only be seen in the electron microscope.
The bacteria are classified into five categories based on the flagellar arrangement. They are:
1. Atrichous: - These bacteria has no flagella. Example: Corynebacterium diptheriae.
2. Monotrichous bacteria (trichous means hair) have one flagellum; if it is located at an end, it is said to be a polar flagellum. Example: - Vibro cholerae.
3. Amphitrichous bacteria (amphi means on both sides) have a single flagellum at each pole. Example: Rhodospirillum rubrum.
4. Lophotrichous bacteria (lopho means tuft) have a cluster of flagella at one or both ends. Example: Spirillum volutans.
5. Peritrichous: Flagella are spread evenly over the whole surface of peritrichous (peri means around) bacteria. Example: Escherichia coli.
Transmission electron microscope studies have shown that the bacterial flagellum is composed of three parts.
(1) The longest and most obvious portion is the flagellar filament, which extends from the cell surface to the tip.
(2) The basal body is embedded in the cell; and
(3) a short, curved segment, the flagellar hook, links the filament to its basal body and acts as a flexible coupling.
Filament :
The filament is a hollow, rigid cylinder constructed of subunits of the protein flagellin, which ranges in molecular weight from 30,000 to 60,000 daltons, depending on the bacterial species.
The filament ends with a capping protein. Some bacteria have sheaths surrounding their flagella. For example, Vibrio cholerae has a lipopolysaccharide sheath.
The hook and basal body are quite different from the filament.
Hook:
Slightly wider than the filament, the hook is made of different protein subunits.
It consists of different proteins. The length of the hook is longer in gram positive than gram negative bacteria.
Basal body:
The basal body is the most complex part of a flagellum.
In transmission electron micrographs of the basal bodies of E. coli and most other gram-negative bacteria, the basal body appears to have four rings, L ring, P ring, S ring, and M ring, connected to a central rod. It is now known that the S ring and M ring are different portions of the same protein, and they are now referred to as the MS ring. On the cytoplasmic side of the MS ring is the C ring, which was discovered later. Gram-positive bacteria have only two rings-an inner ring connected to the plasma membrane and an outer one probably attached to the peptidoglycan.