The bacteria cell wall is an important structure that is a rigid and non-living envelope around the cell.
It is present just above the cell membrane and gives a specific shape to the cell.
Because of this cell wall, bacteria can survive the harshest environmental conditions like drought, heat, chemical exposure, pressure, etc.
If the harsh conditions persist, then the bacteria cell wall forms endospores.
These spores are dormant and give rise to new bacteria when conditions improve. Thus cell wall makes the bacteria immortal.
The bacterial cell wall structure
The bacterial cell wall is made of mucopolysaccharides and mucopeptides.
- The mucopeptide (peptidoglycan) is a polymer of N-acetyl muramic acid (NAM) and N-acetyl glucosamine (NAG).
- Besides them, an amino acid called diaminopimelic acid and a polysaccharide called muramic acid are present in the cell wall.
The structure of the bacterial cell wall is of two types.
One type of cell wall is present in gram-positive bacteria, and the other is present in gram-negative bacteria.
Below you can see the images of structures of two cell walls.
Gram-positive bacteria cell wall
- The cell wall of this bacteria is very rigid.
- It has a thick layer of peptidoglycan that is a combination of protein and carbohydrate molecules.
- Because of this high amount of peptidoglycan layer, the bacteria show blue color when stained with gram stain.
- The layer does not take up the saffron color of the stain, unlike gram-negative bacteria.
- This difference in cell wall structure makes the bacteria susceptible to antibiotics that act on the cell wall.
The cell wall of Gram-Negative bacteria
- This cell wall is entirely different from the one above and the amount of peptidoglycan layer is very much low.
Besides, it is made of three different layers.
a) The uppermost layer is made of lipoproteins.
b) The second layer is made of lipopolysaccharides
c) The bottom layer covering the cell membrane is made of mucopeptides.
Besides, it also has phospholipids, teichoic acid, etc.
This cell wall, when stained with grams stain, it attains a saffron color.
The lipopolysaccharide layer holds the saffron dye in the stain and is responsible for the color.
Functions of bacteria cell wall
- It helps to provide a fixed shape to the cell.
- It facilitates the movement of gases and water into and outside the cell.
- It prevents the cell from getting dried during extremely hot conditions.
- It protects from chemicals and other harsh conditions of the environment. Hence we use heat sterilization to kill bacteria.
- The outermost layer, also called S-layer, helps the bacteria escape phagocytosis by host immune cells.
Benefits to man
It is an essential target in health care for the man to cure bacterial infections.
Antibiotics medicine destroys the cell wall of bacteria, and since human cells don’t have a cell wall, they are unaffected.
Similarly, due to the difference in gram +ve and gram -ve bacteria, an antibiotic with specificity to one type of bacteria can be given.
Thus the presence of cell walls which is safe for bacteria is also a precise target for health care.
But unlike plants, the contents of the wall are entirely different.