What is the history of gram-positive Bacteria?
Back in 1884, the Danish bacteriologist Hans Christian Gram developed a staining procedure to view stained bacteria under a light microscope. His staining method is simply called Gram staining. To distinguish between a Gram positive and Gram negative bacterial cell wall. He enlisted a dye, gentian Violet, which perforates the cell wall and cytoplasmic membrane, thus, staining the cytoplasm of the heat-fixed bacteria.
After adding iodine, an insoluble complex is formed, which is maintained by the Gram-positive bacteria cell wall by adding a decolorizer such as ethanol. Therefore, Gram-positive bacteria occur almost purple while Gram-negative not at all and have to be counterstained with a second dye, safranin or fuchsine to appear pink or reddish.
What is the bacterial cell wall?
Bacteria are mostly unicellular organisms, which can be found in a very wide variety of different environments. Therefore, bacterial cell walls deserve special attention because they are essential bacterial structures for protection against a hostile environment.
It is composed of unique components which are not found in nature other than bacteria.
What are the characteristics of the gram-positive bacterial cell wall?
The following are the characteristics of a gram positive bacterial cell wall;
- They lack an outer membrane.
- They have a slim layer of the cytoplasmic lipid layer.
- They have a thick peptidoglycan layer.
- Teichoic acids and lipoids are present, forming lipoteichoic acids.
- A periplasm that is considerably smaller than that of gram-negative bacteria.
The peptidoglycan layer plays a key role in the maintenance of the rigidity of the cell wall by crosslinking with the assistance of DD-transpeptidase. They also have a thin layer of periplasm, as distinguished from that in the Gram negative bacteria. Some have locomotion apparatus, a flagellum with two basal bodies for support unlike gram-negative which has four basal bodies. Some have strong capsules made up of polysaccharides.
What is the shape of the bacterial cell wall?
Gram-positive by definition in shape can be classified as;
Cocci
The singular form is known as coccus, which is a round or oval-shaped bacteria. They occur in pairs or chains or clusters or as singles. For example; The staphylococcus app, and the Streptococcus app. Special districts of cocci include tetrads, Sardines
Bacilli
Rod-shaped, the unique form is known as Bacillus. They are stick-like bacteria with round tapered, square, or swollen ends. For example; the Bacillus app.
Other unique shapes established by Gram-positive bacteria comprise;
Tetrad
A type of cocci shape occurs in square clusters of fours, For example; the Micrococcus app.
Sarcina(octae)
Thick-walled cocci shapes occur in clusters of four, or cubes of eight. For example; the Sarcina app.
For more details, you should read Bacterial Morphology: size, shape, and arrangements
What are the functions of Gram positive cell wall components?
The peptidoglycan in the gram positive cell wall adverts osmotic lysis. The teichoic acids perhaps help make the cell wall stronger. The surface proteins in the bacterial peptidoglycan, depending on the strain and species, carry out a variation of activities.
Some surface proteins function as enzymes. Other proteins serve as adhesins. Adhesins enable the bacterium to adhere intimately to host cells and another surface to colonize those cells and resist flushing.
Many bacteria involved in infection can co-opt the functions of host cells for the bacterium’s benefit. This is done by way of bacterial secretions systems that encourage the bacterium to directly inject bacterial effector molecules into the host cell’s cytoplasm to adapt its cellular machinery or cellular communication to the advantage of the bacteria. The periplasm includes an enzyme for nutrient breakdown.
What is the composition of the gram positive bacterial cell wall?
The composition of Gram-positive cell walls is teichoic acids. Teichoic acids expand through and beyond the rest of the cell wall and are polyalcohols comprised of polymers of glycerol, phosphates, and the sugar alcohol ribitol. it is covalently bound to the peptidoglycan.
The outer surface of the peptidoglycan is embedded with covering proteins that vary with the strain and species of the bacterium. The periplasm is the gelatinous substance between the peptidoglycan and the cytoplasmic membrane.
Peptidoglycan also known as murein, makes up 90% of the bacterial cell wall content. Its major role is to provide shape and maintain cell strength and rigidity. It is a high-quality polymer made up of two identical sugar derivates, named N-acetylglucosamine and N- acetylmuramic acid, and a chain of L-amino acids and three distinct D-amino acids that are rarely organized in proteins i.e; D-glutamic acid, D-alanine, and meso-diaminopimelic acid.
The D-amino acids and the L-amino acids attach to the N- acetylmuramic acid, L- amino acid particularly the L- lysine can restore the meso-diaminopimelic acid. This interconnection of the peptidoglycan subunit makes the peptidoglycan strong to maintain the bacterial shape and integrity, with the ability to be elastic and stretch. Peptidoglycan is also passable enabling molecules to move in and out of the bacterial cell.
What is teichoic acid?
This is a fortified wall made up of copolymers of glycerol. It is water-soluble making up to 50% of the total dry weight of the bacterial cell wall. It is either directly connected to the peptidoglycan, covalently, or to the cell membrane (lipoteichoic acid).
There are two types of teichoic acid
Lipoteichoic acids (LTAs) are teichoic acids that are anchored to the lipid membrane. Wall teichoic acids are teichoic acids that are covalently attached to peptidoglycan.
The direct link to the peptidoglycan in the 6-hydroxyl N- acetylmuramic acid. It is negatively charged and they extend to the peptidoglycan surface, giving the bacterial cell wall active charge. It also provides for retaining the structure of the cell wall.
What are the functions of teichoic acids?
The following are the functions of teichoic acids;
- They are also used as antigens for the serological classification of bacteria.
- They serve as substrates for many autolytic enzymes.
- They play a role in the normal functioning of the cell wall and provide an external permeability barrier to gram-positive bacteria.
- Membrane teichoic acid serves to anchor the underlying membrane.
Conclusion
- Gram-positive bacteria stained purple in color.
- The gram-positive cell wall comprises many related layers of peptidoglycan and lacks an outer membrane.
- Peptidoglycan can lack an outer membrane.
- Teichoic acids and lipoteichoic acids are intertwined through the layers.
- The gram-positive cell wall activates both the body’s innate immune defense and its adaptive immune defenses.
- Cell wall molecules can also trigger adaptive protection.
