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Some bacterial cell walls possess a net charge of negative at their outer surface due to the presence of lipopolysaccharides and phospholipids that helps to protect themselves in the presence of undesirable compounds or some other adverse conditions.
What is the gram-negative bacteria cell wall?
Most of the bacteria cell wall is around 10-25nm in thickness and the main account for about 20 to 30% of the dry weight of the cell. The most bacteria cell wall has a few layers of an outer membrane and peptidoglycan. It is made up of a substance commonly known as a mucopeptide or peptidoglycan.
Most of the outer membrane of this bacteria has a porins-like structure that is permeable for different types of desirable ions.
The bacteria also contain periplasm or periplasmic space, which means the space between the outer membrane and cytoplasmic membrane which is generally filled with some proteins and degrading enzymes that help in the molecule transportation. Due to the presence of such a layer, the gram-negative bacteria are never caused or affected by some other compounds such as enzymes, salts, dyes, antibodies, detergent, etc.
Do all bacteria cells have a gram-negative cell wall?
No, some of the bacteria have a gram-positive bacterial cell wall. If the bacteria possess only a few layers of peptidoglycan and a thinner structure then such types of bacteria come in the category of gram-negative while if bacteria possess many layers of peptidoglycan with rigid and thick-like structures with also contain teichoic acids that can be linked to the plasma membrane and also span the layers of peptidoglycan, they are known as a gram-positive type of bacteria.
The cell wall of gram-positive bacteria also known as murein has repeating units of NAG-N-acetyl glucosamine and NAM N-acetylmuramic acid while gram-negative bacteria have phospholipids and lipoproteins and lack teichoic acid.
Do gram-negative bacteria have a thicker or thinner cell wall?
Gram-negative bacteria do not contain a thick layer of peptidoglycan. The peptidoglycan is loosely distributed between the outer and inner cell membrane. The gram negative bacteria has additional outer membrane which consist of phospholipids and lipopolysaccharides. The lipopolysaccharide possesses or provides a negative charge to the cell wall of gram-negative bacteria. Mostly such bacteria are pathogenic.
The bacteria contain a thin peptidoglycan layer, cytoplasmic membrane, and lipopolysaccharide present in the outer membrane of the bacterial cell wall. The bacteria also contain periplasm or periplasmic space, which means the space between the outer membrane and cytoplasmic membrane. Such a space has a loose network of peptidoglycan chains, commonly known as a layer of peptidoglycan.
Some examples are Escherichia coli, Salmonella typhi, Xanthomonas citri, Klebsiella pneumonia, Azotobacter chrococcum, Vibrio cholera, Beijerinckia indica, and many more
When is the bacteria cell wall gram-negative?
There is an additional layer of lipid over the peptidoglycan layer, due to which the cell is impermeable to crystal violet stain but applied on ethanol, the lipid layer is dissolved leaving the peptidoglycan layer exposed.
The outer layer of cell wall is a one kind of protective layer of gram-negative bacteria that doesn’t retain the stain of crystal violet. The stain of crystal violet is mainly used during the gram staining method of bacterial differentiation. Such gram-negative bacteria are mostly pathogenic. When the counter-stain safranin is applied the cell takes up the stain and appears pink. simply, the pink colonies appear only after it is treated with crystal violet, safranin, etc. Such a method of identifying gram-negative bacteria is known as simple staining.
Why is the bacteria cell wall gram-negative?
The bacterial cell wall has a net charge of negative due to the presence of a lot of phosphate groups lining up on a surface that aid the transport of peptidoglycan from within the cell to the outside. The outer layer of gram-negative bacteria is generally made up of polysaccharides and phospholipids that also help to confer such a negative net charge.
The lipopolysaccharides have a total of three parts include, Lipid A, O antigen, and Core polysaccharide that contribute to the negative charge of the bacterial surface because the core polysaccharide in it contains charged phosphate and charged sugars.
Compositions of gram-negative cell wall
The cell wall of gram-negative bacteria is more complex compared to the gram-positive bacteria with has a very rigid structure. A couple of layers contain around 5 to 10% of the total cell wall.
The bacteria contain a thin peptidoglycan layer, cytoplasmic membrane, and lipopolysaccharide present in the outer membrane of the bacterial cell wall. The outer layer of gram-negative bacteria is generally made up of polysaccharides and phospholipids that also help to confer such a negative net charge.
Structures of gram-negative cell wall
Functions of cell wall
- The cell wall of bacteria gives support to the organelles or inner cellular parts, protection, and gives defined shape.
- The cell wall is also protected from internal pressure, and damage by some other tough or rigid structure maintains the cell from mechanical injury and allows desired material to pass in and out of the cell.
- The bacterial cell wall possesses a layer that is constructed by crosslinked carbohydrate polymers commonly refer to as peptidoglycan. During the condition of osmotic lysis, the peptidoglycan layer of the bacterial cell wall protects the bacteria. The peptidoglycan layer of this bacteria plays a very important role as a barrier and also acts as a main structural component of the cell wall.
- Another most important function of the cell wall is to act as a permeability barrier for a different types of molecules and compounds. The cell wall of this bacteria also possesses some porin-like structure for the transport of desirable molecules from the outside to the inside of the cell.
The gram-negative bacteria are mostly pathogenic and usually possess only a few layers of peptidoglycan and a thinner structure, such types of bacteria can easily identify via the method of simple staining that usually gives pink in color.