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: 26.04.2021

Structure of Peptidoglycan

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The Cell Wall of 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 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. Gram-positive bacteria take up the crystal violet stain used in the test, and then appear to be purple-coloured when seen through an optical microscope. This is because the thick peptidoglycan layer in the bacterial cell wall retains the stain after it is washed away from the rest of the sample, in the decolorization stage of the test. Conversely, gram-negative bacteria cannot retain the violet stain after the decolorization step; alcohol used in this stage degrades the outer membrane of gram-negative cells, making the cell wall more porous and incapable of retaining the crystal violet stain. Their peptidoglycan layer is much thinner and sandwiched between an inner cell membrane and a bacterial outer membrane , causing them to take up the counterstain safranin or fuchsine and appear red or pink.

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.

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.

Applied Microbiology pp Cite as. Past attempts at direct measurement of the mechanical characteristics of cells have shown little potential for use with bacteria. However, a technique based on micromanipulation has now been used to compare the mechanical properties of two species of bacteria; Gram-negative Escherichia coli and Gram-positive Staphylococcus epidermis. Gram-negative bacteria have traditionally been considered to be weaker than their Gram-positive counterparts on the basis of them being more susceptible to disintegration by mechanical stress. This observation has been corroborated using micromanipulation, which has directly quantified the differences in cell strength on the basis of bursting force. The bursting force of rapidly growing S.

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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. The differences between Gram positive and Gram negative bacteria are primarily related to their cell wall composition. Gram positive bacteria have cell walls composed mostly of a substance unique to bacteria known as peptidoglycan , or murein. These bacteria stain purple after Gram staining.

The Cell Wall of Bacteria

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.

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.

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.


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