Do Bacteria Have Cell Walls? 11 Facts You Should Know

Bacteria are the unicellular prokaryotes popularly known to have cell walls with a few exceptions. In this article, we will learn ‘do bacteria have cell walls’?

Most of the bacteria identified have a well-architected cell wall. Various interesting facts regarding bacterial cell walls make it a subject of study amongst all the microbiology enthusiasts.

11 facts to know about bacterial cell walls:

  1. 90 % of bacteria have a cell wall.
  2. Mollicutes are the class of bacteria that lack cell walls; e.g., Mycoplasma
  3. Mycoplasma builds its cell membrane by collecting cholesterol from the environment.
  4. To date, more than 1000 species of the genus Mycoplasma have been identified.
  5. Two different types of cell walls are present in almost all the bacteria: gram-negative cell wall and gram-positive cell wall.
  6. Various pathogenic infections caused by bacteria are contributed by the cell wall of bacteria.
  7. The presence of a thin peptidoglycan layer along with an outer membrane defines a gram-negative bacteria cell wall. 
  8. Several antibiotic drugs act by targeting the cell wall of bacteria.
  9. Teichoic acids are the anionic polymers present in the thick peptidoglycan layer of the gram-positive cell wall.
  10. L-form bacteria are originally not devoid of the cell walls, they lose their wall during the course of evolution.
  11. The outer membrane of a gram-negative bacterium is a lipid bilayer.

Do all bacteria have cell walls?

Bacteria belonging to the class Mollicutes and naturally evolved L-form bacteria are devoid of cell wall.

In the class Mollicutes, the first identified member was Mycoplasma. Several species of the genus Mycoplasma are pathogenic in humans. The absence of a cell wall makes the members of this species resistant to antibiotics that target the synthesis of the cell walls. Also, the lack of cell walls allows these organisms to change their shape easily.

Why do bacteria have a cell wall?

The cell wall protects the cell.

The mesh-like structure of a bacterial cell consisting of peptidoglycan, disaccharides, and amino acids plays a key role in preserving cell shape and structural integrity. The cell wall plays a significant role in protecting the chromosomes and ribosomes present inside a bacterial cell by strongly holding the cell membrane in its place. Also, it prevents the entry of toxic molecules inside the cell.

The cell wall of a bacterium is a stress-bearing structure that helps the bacterium maintain its shape. Bacteria having certain shapes are capable to cope with and adapt to unfavorable and changing external environments.

Various pathogenic infections caused by bacteria are contributed by the cell wall of bacteria. Certain molecules present on the surface of bacterial cell walls act as adhesins that aid in establishing physical contact between the bacteria and the surface of the host organism.

The cell wall of a bacteria allows water to pass through it which in turn pressurizes the plasma membrane against the cell wall. The rigid cell wall of a bacteria aids in balancing the force of water by exerting equal force. Thus, the cell wall of bacteria helps in maintaining the integrity of cells by preventing osmotic lysis.

What type of bacteria has cell walls?

Except for all the species of Mycoplasma and L-form bacteria, all other bacteria have cell walls.

All the gram-positive and gram-negative bacteria have a cell wall, and they are essential for the survival and growth of the bacteria.

Which bacteria do not have a cell wall?

Mycoplasma and L-form bacteria do not have a cell wall.

Mycoplasma lives as parasites or saprotrophs acquiring their nutrition from host organisms. To date, more than 1000 species of the genus Mycoplasma have been identified. These smallest free-living organisms have a wide range of shapes due to the absence of a rigid cell wall.

L-form bacteria isolated by Emmy Klieneberger-Nobel in 1935 are also known as cell wall deficient bacteria. These bacteria got their name L-form from the Lister Institute in London, where it was isolated for the first time.

L-form bacteria can naturally evolve from both gram-positive and gram-negative bacteria during the evolutionary course. These bacteria are being investigated for their potential use in biotechnology, where they can be used for the large-scale production of recombinant proteins.

Bacterial cell wall structure

The bacterial cell wall is a complex multi-layered structure. It is classified into two groups: gram-positive bacterial cell wall and gram-negative bacterial cell wall.

Bacterial cell wall structure has been a topic of major interest since the 1950s. A well-structured cell wall aids the bacteria to survive in an unpredictable and hostile environment. Although the complexity of the cell wall of a bacterium protects it, the semi-permeable nature of the cell wall allows selective passage of waste products from the inside and nutrients from the outside.

The three layers of the gram-negative cell walls are the inner membrane, the peptidoglycan cell wall, and the outer membrane. A prominent example of gram-negative bacteria is Escherichia coli.

do bacteria have cell walls
Gram-negative cell wall from Wikimedia

The outer membrane is a lipid bilayer composed of lipopolysaccharides which are solely present in gram-negative bacteria. The two types of protein identified in the outer membrane are lipoproteins and β-barrel proteins. Passive diffusion of small molecules is facilitated by these transmembrane proteins across the outer membrane.

Few enzymes such as phospholipase and protease also form a part of the outer membrane. Lipopolysaccharides present on the surface of the outer membrane play a crucial role in making the gram-negative bacteria resistant to antibiotics. 

The peptidoglycan layer contributes to the rigidity of the bacterial cell wall. The disaccharide units, N-acetyl glucosamine, and N-acetyl muramic acid are cross-linked by peptide side chains. The key role of peptidoglycan is to maintain the characteristic shape of each bacterium.

Periplasm is a viscous region densely packed with proteins responsible for the biogenesis of cell walls.

The inner membrane of the bacterial cell wall shelters a number of proteins that help in lipid biosynthesis, energy production, and protein secretion. It’s a phospholipid bilayer.

The cell wall of gram-positive bacteria is mainly composed of several layers of peptidoglycan that provide protection against harsh environments.

Teichoic acids the anionic polymers present in the thick peptidoglycan layer constitute 60 % of the gram-positive bacteria cell wall. These peptides are a target of different antibiotic drugs such as beta-lactam. Beta-lactam prevents peptide crosslinking by inactivating transpeptidase which in turn ceases the synthesis of the peptidoglycan cell walls.

Why are bacterial cell walls rigid?

The rigidity of bacterial cell walls is attributed to cross-linked polysaccharides and peptide strands.

The cell wall protects the cell from lysis and prevents the entry of toxic molecules inside the cell. Also, it helps to withstand the turgor pressure generated by the internal molecules of the cell.

Is bacterial cell wall permeable?

The permeability of bacterial cell walls varies across types of bacteria.

The cell wall of a gram-negative bacterium includes an outer membrane of lipopolysaccharides along with a thin layer of peptidoglycan, making it less permeable to different molecules as compared to gram-positive bacteria which do not include an outer membrane.

Do bacterial cells have a chloroplast?

There is no chloroplast in bacteria.

The internal components of a bacterial cell consist of the chromosome that is freely present in the irregularly shaped nucleoid region. Unlike eukaryotic organisms, a bacterial cell does not have membrane-bound organelles and well-defined nuclei. Apart, from the chromosome, bacteria are also known to have numerous ribosomes responsible for protein synthesis.

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