Is Gram Positive A Bacteria Cell Wall: 9 Interesting Facts


In this post, you will find the information about, Is Gram positive a bacteria cell wall, its structure composition and many more interesting facts.

Is Gram-positive a bacteria cell wall : A bacteria can be gram-positive if its peptidoglycan is thick and gives the purple color to the cell when stained with gram-positive dye crystal violet.

What is gram positive a bacteria cell wall ?

Gram positive bacteria are those having their cell wall made of peptidoglycan. Peptidoglycan is thick in case of  of gram positive bacteria. The size of cell wall ranges from about 20-80nm. Peptidoglycan is consists of two sugar derivatives and peptides.

  The sugars present in peptidoglycan of gram-positive bacteria are modified sugars that have acetyl and amine group. Sugars are arranged horizontally and are joined by β 1-4 glycosidic bond. Chain of amino acids (L-alanine, D-glutamine, L-lysine, and D-alanine) are attached to the side of NAM vertically towards the other glycan chain. The chain of amino acid can be different and vary according to the bacteria specie.

The short peptide chain are linked with other peptide chain by horizontal penta-glycine linkage. The cross linking is executed by penta-glycine linkage. This horizontal and vertical cross-linking forms a 3- Dimensional structure. The structure forms is quite rigid in nature and gives the bacteria its shape and strength especially in case of rod-shaped bacterium.

Structure of gram positive cell wall

Gram positive bacteria have cell wall and cytoplasmic membrane. Cell wall of gram-positive bacteria is made up of peptidoglycan which is composed of two different repeating sugar derivatives and peptide chain. Gram-positive cell wall structure is complex and thick and ranges about 20-80nm in size. The structure consist of peptidoglycan and cytoplasmic membrane.

is gram positive a bacteria cell wall
Structure of Gram positive Cell wall from wikipedia
  • Peptidoglycan is made up of two sugar derivatives, NAG and NAM. They are also called glycans.
  • Glycans are horizontally arranged or joined by β 1-4 glycosidic linkage.
  • Peptides or small chain of amino acid(L-alanine, D-glutamine, L-lysine, and D-alanine) is vertically joined to the NAM molecule.
  • Same the second glycan chain is arranged and joined by cross linking. The one peptide is cross linked with another peptide of glycan with the help of penta-glycine linkage horizontally.
  • Thus, it forms a huge cross linking network in gram positive bacteria.  
  • Apart from this, cell wall of gram-positive bacteria has techoic acid and lipotechoic acid.  
  • Techoic acid are antigenic structures which are embedded in the peptidoglycan layer of gram-positive a cell wall and if it is embedded along with cytoplasmic membrane then it is called lipotechoic acid.

Do all bacteria cells have the gram positive cell wall ?

No, all bacteria cannot be gram-positive, they can be  positive or negative depending upon the bacterial cell wall composition. If the cell wall or peptidoglycan is thick then bacteria is gram-positive and if the bacterial cell wall is thin, then bacteria is considered as gram-negative.

In bacteria, peptidoglycan layer is found outside the cytoplasmic membrane which make its cell wall. This peptidoglycan is allows the dyes to bind and gives purple color when it is stained with crystal violet. By doing this, we can easily differentiate gram-positive bacteria from gram-negative bacteria using differential gram staining technique.

Do gram positive bacteria have thicker or thinner cell wall ?

Gram-positive bacteria consists of  thick peptidoglycan, forming the thick cell wall of bacteria. Bacteria gives off purple color when it is stained with crystal violet using Gram staining technique.

Gram positive bacteria contains cytoplasmic membrane, this structure is common in both gram-positive as well gram-negative bacteria. The second next structure present in gram-positive bacteria is peptidoglycan which is very thick and prominent in comparison to gram-negative bacteria.

Composition of Gram positive bacteria cell wall

As stated earlier that peptidoglycan is made up of two sugar derivatives, NAG and NAM. They are also called glycans. Glycans are horizontally arranged or joined by β 1-4 glycosidic linkage. Peptides or small chain of amino acid(L-alanine, D-glutamine, L-lysine, and D-alanine) is vertically joined to the NAM molecule. Same the second glycan chain is arranged and joined by cross linking.

Cross linking between glycans and peptides from Wikipedia

The one peptide is cross linked with another peptide of glycan with the help of penta-glycine linkage horizontally. Thus, it forms a huge cross linking network in gram positive bacteria. Gram-positive bacteria contains techoic acid and lipotechoic acid. Techoic acid is embedded in the peptidoglycan layer and if the techoic acid is present along with the cytoplasmic membrane then it is called lipotechoic acid. These structures are highly antigenic.

Gram-positive cell wall structure is complex and thick and ranges about 20-80nm in size. The structure consist of peptidoglycan and cytoplasmic membrane.

When is the bacteria cell wall gram positive?

Gram staining is a technique by which we can easily determine whether the bacterial cell wall  is gram positive or gram negative type. In bacteria, peptidoglycan layer is found outside the cytoplasmic membrane which make its cell wall. This peptidoglycan is allows the dyes to bind and gives purple color when it is stained with crystal violet, which is what makes staining techniques such as Gram staining work so well.

Hans Christian Gram developed a technique called Gram Staining in which he used different dyes to differentiate the bacteria on the basis of cell wall. Crystal violet is a first dye applied to the dry mount bacterial culture.  
All the cells stained purple. Now, the mordant called Gram’s Iodine is applied over the mount. Mordant allows the binding of dye with them to form large complex.  
Washing with water removes excess dye and water. In order to differentiate the gram-positive bacteria from gram-negative, the crucial step is applied, adding ethanol over the mount. 
Ethanol act as differentiator which tightens the peptidoglycan layer and therefore the violet-lugol complex is remain trapped in the bacterium.  
While for gram-negative bacteria, ethanol solubilizes the outer membrane, therefore the violet-lugol complex moves out when it is washed with water. Counter stain is applied to stain those bacteria who might have lost the violet- lugol complex.  After drying and observing under microscope, we can easily differentiate the bacteria by seeing the color of the cell. Those bacteria who stained purple are gram-positive while those which are seen pink are considered as gram-negative.

Why is the bacteria cell wall gram positive?

Bacterial cell wall is said to be gram-positive because it has thick peptidoglycan and it stains purple and can be seen as purple colored cells under the microscope at 100X.

Glycans are horizontally arranged or joined by β 1-4 glycosidic linkage. Peptides or small chain of amino acid(L-alanine, D-glutamine, L-lysine, and D-alanine) is vertically joined to the NAM molecule. Same the second glycan chain is arranged and joined by cross linking. The one peptide is cross linked with another peptide of glycan with the help of penta-glycine linkage horizontally. Thus, it forms a huge cross linking network in gram positive bacteria.

Functions of gram positive cell wall

  • The crucial function of cell wall is that it maintains the osmotic balance inside and outside the cell  which restricts the cell to burst from osmotic pressure.
  • During cell division, bacteria forms two daughter cells, the newly formed cells are juvenile and lacks peptidoglycan and internal condition of cell is hyper-osmotic, it takes quite time to synthesize cell wall. After synthesizing the cell wall, it prevents cell bursting.
  • A structure called techoic acid aslo known as glycopolymer, plays a crucial function in gram-positive cell wall, it develops the net negative charge of the cell, which is required for the production of proton motive force.
  • Gram-positive cell wall maintains the shape of the bacteria, specifically in rod-shaped bacterium.
  • Techoic acid plays a role in cell division. Also provide resistance to the beta lactam antibiotics, high salt concentration as well as high temperatures.
  • Since, the peptidoglycan is relatively porous, some nutrient substances are very much larger that it cannot pass through it. So, peptidoglycan allow to pass the exoenzymes from cytoplasm through it, so that they can break it into smaller components for the cell.

Conclusion

To wrap up this post, we conclude that gram-positive bacteria have thick cell wall which can be easily determine by using gram staining technique. Peptidoglycan makes the cell wall of the bacteria. It functions as providing rigidity, strength and shape to the cell.

Saif Ali

Hi, I am Saif Ali. I obtained my Master's degree in Microbiology and have one year of research experience in water microbiology from  National Institute of Hydrology, Roorkee. Antibiotic resistant microorganisms and soil bacteria, particularly PGPR, are my areas of interest and expertise. Currently, I'm focused on developing antibiotic alternatives. I'm always trying to discover new things from my surroundings.  My goal is to provide readers with easy-to-understand microbiology articles. If you have a bug, treat it with caution and avoid using antibiotics to combat SUPERBUGS. Let's connect via LinkedIn.

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