cell wall of gram positive and gram negative bacteria pdf file

Cell wall of gram positive and gram negative bacteria pdf file

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Published: 15.04.2021

Structure of Peptidoglycan

Structure of Peptidoglycan

Gram Positive vs. Gram Negative Bacteria

Structure of Peptidoglycan

This test differentiate the bacteria into Gram Positive and Gram Negative Bacteria, which helps in the classification and differentiations of microorganisms. When the bacteria is stained with primary stain Crystal Violet and fixed by the mordant, some of the bacteria are able to retain the primary stain and some are decolorized by alcohol. The cell walls of gram positive bacteria have a thick layer of protein-sugar complexes called peptidoglycan and lipid content is low. Decolorizing the cell causes this thick cell wall to dehydrate and shrink, which closes the pores in the cell wall and prevents the stain from exiting the cell. So the ethanol cannot remove the Crystal Violet-Iodine complex that is bound to the thick layer of peptidoglycan of gram positive bacteria and appears blue or purple in colour. In case of gram negative bacteria, cell wall also takes up the CV-Iodine complex but due to the thin layer of peptidoglycan and thick outer layer which is formed of lipids, CV-Iodine complex gets washed off. Then when again stained with safranin, they take the stain and appears red in color.

It is important to note that not all bacteria have a cell wall. The two different cell wall types can be identified in the lab by a differential stain known as the Gram stain. Originally, it was not known why the Gram stain allowed for such reliable separation of bacterial into two groups. Once the electron microscope was invented in the s, it was found that the staining difference correlated with differences in the cell walls. Here is a website that shows the actual steps of the Gram stain.

Structure of Peptidoglycan

Danish scientist Hans Christian Gram devised a method to differentiate two types of bacteria based on the structural differences in their cell walls. In his test, bacteria that retain the crystal violet dye do so because of a thick layer of peptidoglycan and are called Gram-positive bacteria. In contrast, Gram-negative bacteria do not retain the violet dye and are colored red or pink. Compared with Gram-positive bacteria, Gram-negative bacteria are more resistant against antibodies because of their impenetrable cell wall. These bacteria have a wide variety of applications ranging from medical treatment to industrial use and Swiss cheese production. In a Gram stain test , bacteria are washed with a decolorizing solution after being dyed with crystal violet. On adding a counterstain such as safranin or fuchsine after washing, Gram-negative bacteria are stained red or pink while Gram-positive bacteria retain their crystal violet dye.

Bacterial Cell Wall : The anatomy of bacterial cell structure. Bacterial cells lack a membrane bound nucleus. Their genetic material is naked within the cytoplasm. Ribosomes are their only type of organelle. Bacteria are usually single-celled, except when they exist in colonies. These ancestral cells reproduce by means of binary fission, duplicating their genetic material and then essentially splitting to form two daughter cells identical to the parent.

Earn a free Open University digital badge if you complete this course, to display and share your achievement. Anyone can learn for free on OpenLearn, but signing-up will give you access to your personal learning profile and record of achievements that you earn while you study. Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available. Bacteria are divided into two groups based on how the cell wall appears when they are stained using Gram straining.

Gram Positive vs. Gram Negative Bacteria

Multiple responses of gram-positive and gram-negative bacteria to mixture of hydrocarbons. Most of our knowledge about pollutants and the way they are biodegraded in the environment has previously been shaped by laboratory studies using hydrocarbon-degrading bacterial strains isolated from polluted sites. In present study Gram-positive Mycobacterium s p.

If this really were an assigned self study, by the time you finish, you should be able to:. The process of Gram staining was developed by a Danish bacteriologist Hans Christian Gram who found that bacteria could be differentiated into two large groups based upon different physical properties of their cell walls. Gram-positive bacteria which have a thick peptidoglycan wall retain the crystal violet dye staining them violet or purple , while all other bacteria e. Figure 1. Gram staining of different bacteria.

Most bacteria are classified into two broad categories: Gram positive and Gram negative. These categories are based on their cell wall composition and reaction to the Gram stain test. The Gram staining method, developed by Hans Christian Gram , identifies bacteria based upon the reaction of their cell walls to certain dyes and chemicals.


  • Laurence V. 16.04.2021 at 14:49

    stain in purple during gram staining whereas gram negative bacteria contain a thin peptidoglycan cell wall.

  • Lucrecio B. 16.04.2021 at 16:21

    In bacteriology , gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall.

  • MichГЁle C. 16.04.2021 at 20:43

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