Extra Cellular Matrix

It is attached to the cell wall and is made of polysaccharide or polypeptide, or a combination of both, to form a viscous layer. If it is thick, structured and adheres strongly to the cell wall, it is called a Capsule. If it is disorganized and loosely attached to the cell wall it is called a Slime layer. Both capsule and slime layer do not take up simple stains but can be observed by negative staining with India Ink or Negrosin. 

Functions of Capsules - (a). Adhere to surfaces to form colonies. (b). Antiphagocytic. (c). Antigenic. (d). Protect the organism from dehydration. 

Structures for Movement

a. Flagellum
Made of the protein flagellin and consists of a filament, hook, and basal body. The basal region has a rod and rings. Gram positive organisms have 2 rings, one in the cell wall and one in the cell membrane. Gram negative organisms have 4 rings, 2 in the cell wall and 2 in the cell membrane.


 

Flagella have different numbers and arrangements:
 
 Monotrichous  Lophotrichous

 Amphitrichous

  Peritrichous


 
 
 Counterclockwise rotation is for smooth swimming towards an attractant. Clockwise rotation is for backward or reverse movement. With peritrichous flagella clockwise rotation results in tumbling to change direction. 

b. Axial Filaments - 

Found in Spirochetes and are similar to flagella, but are located between the cell wall and an outer sheath, and are attached to one end of the organism.

Copyright 1996 by the Faculty Resource Center

Sylvester McKenna & Devabrata Mondal
Long Island University, Brooklyn Campus