Gram positive and Gram negative bacteria are the most common types of bacteria. Gram-positive bacteria have extensive coatings of peptidoglycan in their cell walls. Gram-positive cells turn purple when stained with a Gram stain method. Gram negative bacteria have a thin covering of peptidoglycan on their cell walls. An outer membrane with lipopolysaccharide (LPS) molecules is also part of the cell wall. When Gram negative bacteria are stained with a Gram stain, they turn pink. Exotoxins are produced by both Gram positive and Gram negative bacteria, while only Gram negative bacteria create endotoxins.
Gram positive cell wall
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The Gram-positive cell wall displays as a broad, dense wall 20-80 nm thick, with several interconnecting layers of peptidoglycan in electron micrographs ). Peptidoglycan makes up 60 to 90% of the Gram-positive cell wall chemically. The peptidoglycan is thought to be laid down in Gram-positive bacteria in cables of multiple cross-linked glycan strands around 50 nm wide. These wires are then cross-linked to add to the cell wall’s strength.
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Teichoic acids and lipoteichoic acids are found in Gram-positive bacteria’s cell walls. Teichoic acids are polyalcohols made up of polymers of glycerol, phosphates, and the sugar alcohol ribitol that are covalently attached to the peptidoglycan and extend across and beyond the rest of the cell wall. Lipoteichoic acids are teichoic acids that are covalently linked to cytoplasmic membrane lipids.
Functions of the Gram-Positive Cell Wall Components
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Osmotic lysis is prevented by the peptidoglycan in Gram-positive cell walls.
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Teichoic acids are thought to aid in the strengthening of cell walls
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Depending on the strain and species, the surface proteins in the bacterial peptidoglycan perform a variety of functions.
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Some surface proteins have the ability to act as enzymes.
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Adhesins are other proteins. Adhesins allow the bacterium to stick to host cells and other surfaces, allowing it to colonise them and resist washing.
Many bacteria that cause infections have the potential to co-opt host cell processes for their own gain. This is accomplished using bacterial secretion systems, which allow the bacteria to directly inject bacterial effector molecules into the host cell’s cytoplasm in order to modify the host cell’s cellular machinery or cellular communication to the bacteria’s benefit. They accomplish this by developing secretion systems like the type 3 secretion system, which produces injectisomes, which are hollow, needle-like tubes. For example, certain bacteria inject invasions into the cytoplasm of the host cell, allowing the bacteria to enter the cell.
Gram negative cell wall
The gelatinous material that lies between both the outer membrane, the peptidoglycan, and the cytoplasmic membrane is known as periplasm. This 15nm-wide periplasmic region contains a variety of hydrolytic enzymes for food degradation, periplasmic associated proteins for ATP-binding cassette (ABC) transport, and chemoreceptors for chemotaxis.
Functions of the Gram-Negative Cell Wall Components
The innate immune system and the adaptive immune system are the two immune systems in the human body. Innate immunity is a nonspecific antigen defence mechanism that a host employs instantly or within a few hours after being exposed to practically any microorganism. This is the immune system that one is born with, and it is the body’s first response to eradicate microorganisms and avoid infection. Antigen-specific defence mechanisms that take several days to become protective and are designed to react with and eliminate a specific antigen are referred to as adaptive (acquired) immunity. This is the immunity that one builds during the course of one’s life.
Difference between gram positive and gram negative cell wall
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Gram positive bacteria have a thick peptidoglycan layer without an outer lipid membrane, whereas Gram negative bacteria have a thin peptidoglycan layer with an outer lipid membrane.
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When referring to their structure rather than their staining properties, Gram positive bacteria are called monoderms because they lack an outer lipid membrane. Gram negative bacteria have an outer lipid membrane, which is why they are referred to as diderms in terms of their physical structure.
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Gram-positive bacteria have a distinct purple colour when seen under a light microscope following Gram staining. This is due to the purple crystal violet stain staying in the thick peptidoglycan layer of the cell wall. Gram negative bacteria look pale reddish in colour under a light microscope. Because their cell walls are unable to hold the crystal violet stain, they are solely coloured by the safranin counterstain.
Conclusion
Gram-positive bacteria stain purple following Gram staining due to the nature of their cell wall. The Gram-positive cell wall is made up of numerous interconnected peptidoglycan layers and does not have an outside membrane. In the hypotonic environment in which most bacteria live, peptidoglycan resists osmotic lysis. Through the peptidoglycan layers, teichoic acids and lipoteichoic acids are intertwined. Adhesins, secretion systems, and enzymes are all possible functions of surface proteins embedded in the cell wall. Both the body’s innate and adaptive immune responses are activated by Gram-positive cell walls. Gram negative bacteria have a thin covering of peptidoglycan on their cell walls. When Gram negative bacteria are stained with a Gram stain, they turn pink.