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Capsules and Slime Layers

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Capsule Slime Layer

Many bacterial cells secrete a capsule or a slime layer as an extracellular material. A slime layer is loosely attached to the bacterium and can be washed away, while a capsule is firmly attached to the bacterium and has distinct boundaries.

This article will study slime layer and capsule, slime capsule definition and bacterial capsule and slime layer.

Slime Layer and Capsule

  • The capsule is a polysaccharide film that extends beyond the cell envelope and is thus considered part of the bacterial cell's outer envelope. It's a well-organized layer that's difficult to remove and can cause a variety of diseases. The capsule, which can be present in both gram-negative and gram-positive bacteria, is distinct from the second lipid membrane, the bacterial outer membrane, which only exists in gram-negative bacteria and contains lipopolysaccharides and lipoproteins. 

  • A slime layer is created when the amorphous viscid secretion (that makes up the capsule) diffuses into the surrounding medium and persists as a loose secretion. 

  • The glycocalyx is a term that refers to both the capsule and the slime layer.

Detailed Composition of Slime Capsule

Composition of Capsule

While most bacterial capsules are made of polysaccharides, some organisms, such as Bacillus anthracis, use other materials, such as poly-D-glutamic acid. Since most capsules are so tightly packed, most standard stains cannot penetrate the capsule, making them difficult to stain. A sample is stained with a dark dye, such as India ink, to make it easier to see encapsulated bacteria under a microscope. The capsule's arrangement prevents the stain from entering the cell. Bacterial capsules appear as a light halo around the cell against a dark background when viewed.

Functions of Capsule

The capsule is referred to as a virulence factor because it increases bacteria's capacity to cause disease (e.g. prevents phagocytosis). The capsule will protect cells from eukaryotic cells like macrophages engulfing them.


Number six Phagocytosis can involve the presence of a capsule-specific antibody. Water is also present in the capsules, which prevents the bacteria from drying out. Bacterial viruses and most hydrophobic toxic products, such as detergents, are also excluded.  Immunity to one form of capsule does not mean immunity to the others. Capsules also aid in the adhesion of cells to surfaces. Polysaccharide encapsulated bacteria are a group of bacteria that have a capsule.

Slime Layer of Bacteria

A slime layer in bacteria is an unorganized layer of extracellular material that covers bacteria cells and is easily removed (e.g. by centrifugation). Exopolysaccharides, glycoproteins, and glycolipids make up the majority of this. As a result, the slime layer is assumed to be a branch of the glycocalyx.

Although slime layers and capsules are most commonly found in bacteria, archaea may also have these structures. This structure and role knowledge are also transferable to these microorganisms.

Structure of Slime Layer

  • Slime layers are amorphous and vary in thickness, with different amounts formed depending on the cell type and environment. These layers appear as strands hanging extracellularly and forming net-like structures between cells separated by 1-4m. Researchers believe that after 9 days of development, a cell's formation of the slime layer will slow, possibly due to slower metabolic activity.

  • A bacterial capsule is similar to a slime layer, but it is more rigid. In comparison to their slime layer counterparts, capsules are more structured and difficult to extract. An S-layer is a highly structured but separate structure. S-layers are glycoprotein-based structures that incorporate themselves into the cell wall and provide rigidity and protection to the cells. The cell's rigidity is not aided by a slime layer because it is loose and flowing.

Functions of Slime Layer

  • The slime layer's job is to protect bacteria cells from environmental threats including antibiotics and desiccation. Bacteria can adhere to smooth surfaces like prosthetic implants and catheters, as well as other smooth surfaces like Petri dishes, due to the slime layer. The cells adhered to the culture vessel without any additional appendages, depending solely on extracellular material, according to the researchers.

  • A slime layer, though primarily composed of polysaccharides, can be overproduced to the point that the cell may rely on it as additional food storage during a famine. In addition, ground-dwelling prokaryotes can produce a slime layer to prevent excessive drying caused by annual temperature and humidity changes.

  • Bacterial colonies can be able to withstand chemical sterilization with chlorine, iodine, and other chemicals, leaving autoclaving or boiling water flushing as the only surefire method of decontamination.

Difference Between Capsule and Slime Layer


Slime Layer 

It is a glycocalyx layer consisting of tightly associated polysaccharide molecules with the cell wall.

It is a glycocalyx layer consisting of loosely associated glycoprotein molecules.

The capsule is composed of polysaccharides.

The Slime layer is composed of glycoprotein, glycolipids, and exopolysaccharide.

It is thicker than the slime layer.

It is a thin layer.

It is tightly bound to the cell wall

It is loosely bound to the cell wall.

Well organized layer

Unorganized layer

Acts as a virulence factor.

It helps the cell to prevent dehydration and nutrient loss.

Layers Outside the Cell Wall

A cell membrane is found in every cell. A cell wall is present in the majority of bacteria. Bacteria, on the other hand, may or may not have a few additional layers. If existent, these would be located outside of the cell membrane as well as the cell wall.


A polysaccharide layer entirely encases the cell in a bacterial capsule. It is well-organized and densely packed, which explains why it does not stain under the microscope. Desiccation, hydrophobic poisonous chemicals (i.e. detergents), and bacterial viruses are just some of the hazards that the capsule protects the cell from. The capsule can boost bacterial pathogens' potential to cause disease while also protecting them from phagocytosis (engulfment by white blood cells known as phagocytes). Finally, it can aid in surface attachment.

Slime Layer

A bacterial slime layer is similar to a capsule in that it is made up of polysaccharides and surrounds the cell completely. It also protects against a variety of dangers, including desiccation and antibiotics. It may also enable surface adhesion. So, what is the difference between it and the capsule? In contrast to a capsule, which integrates tightly around the bacterial cell wall, a slime layer is a loose, unstructured coating that is easily removed off the cell that created it.

Did you Know?

Since there are so many bacteria that are becoming immune to antimicrobial agents like antibiotics (which prevent cell growth or simply destroy the cell), new research is being published on new drugs that reduce virulence factors in certain bacteria. Anti-virulent drugs inhibit bacteria's pathogenic properties, enabling the host to fight them or antimicrobial agents to function. Staphylococcus aureus is a pathogenic bacteria that causes a variety of human infections and possesses a variety of virulence factors, including biofilm formation, quorum sensing, and exotoxins, to name a few.

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FAQs on Capsules and Slime Layers

1. What are the Functions of Bacteria Capsules and Slime Layers?

A slime layer is a non-rigid matrix that can be easily deformed and cannot keep India Ink out. Many cells and their outer barriers make up biofilms. Both capsules and slime layers have two primary functions: defense and adhesion.

2. What is the Composition of the Slime Layer?

A slime layer in bacteria is an unorganized layer of extracellular material that covers bacteria cells and is easily removed (e.g. by centrifugation). Exopolysaccharides, glycoproteins, and glycolipids make up the majority of this. As a result, the slime layer is assumed to be a branch of the glycocalyx.

3. Is Glycocalyx Present in All Bacteria?

The glycocalyx is a viscous outer layer of fibres that spreads from the bacterium that is secreted by all bacteria. A capsule is a large, tightly bound glycocalyx that adheres to the cell wall.

4. What are the functions of the capsule?

Following are the functions of capsule:

  • Prevent Desiccation and Drying of the Cell: capsular polysaccharide binds a large amount of water, making the cell resistant to drying.

  • It protects against mechanical injury, temperature, and drying, among other things.

  • Attachment: The capsule aids in surface attachment. Streptococcus mutations that cause dental caries, for example, adhere to the surface of the teeth via their capsule.

  • Anti-phagocytic: Capsules are resistant to WBC phagocytosis.

  • The capsule prevents the bacteriophage from attaching to the cell surface.

  • When the nutrient supply in the cell is low, the capsule serves as a source of sustenance.

  • Repulsion occurs when microorganisms with the same charge encapsulated resist one other.

5. What are the key points about capsules?

Following are some points about capsules:

  • A capsule is a 0.2m thick viscous layer that is securely connected to the cell wall of capsulated bacteria.

  • Slime layers are weakly linked to the cell wall and can be washed away or lost during subculture.

  • The capsule is made up of 98 percent water and 2% carbohydrate, glycoprotein/polypeptide, or both.

  • The capsule of acetic acid bacteria is made up of homopolysaccharide (hemicellulose)

  • Leuconostoc capsules are made of cellulose, which contains glucose or fructose.

  • The capsule of Klebsiella pneumonia is composed of glucose, galactose, rhamnose, and other sugars.

  • A polypeptide (Polymer of D-glutamic acid) is used in Bacillus anthracis capsules, while L-amino acids are used in Streptococci capsules.

  • The structure of a capsule is extremely delicate. It can be washed away with vigor.

  • The capsule is the bacteria's most essential pathogenicity component.

  • A negative staining approach is used to visualize the capsule.

6. What is the slime layer and does it protect against phagocytosis?

The slime layer, which surrounds the bacterial cell, is an easily removable, diffuse, disorganized coating of extracellular material. It is made up mostly of polysaccharides and can be used to trap nutrients, enhance cell motility, bind cells together, or attach to smooth surfaces.

Many Gram-positive and Gram-negative bacteria exude a hydrophilic slime layer made up mostly of high-molecular-weight polysaccharides. The cell is also protected from phagocytosis by the capsule. The capsule's slipperiness prevents germs from being taken up by phagocytic cells.

7. Where are capsules found and what is capsule stain?

Capsules are found just outside of gram-positive bacteria's murein (peptidoglycan) layer and gram-negative bacteria's outer membrane (lipopolysaccharide layer). The capsule appears like a mesh or network of thin strands in electron microscopy.

Capsule stain is a sort of differential stain that uses acidic and basic dyes to stain background and bacterial cells, respectively, in order to visualize the presence of capsules. The bacteria is surrounded by a capsule that is generated in the cytoplasm and released to the outside of the cell.

8. Where can I find notes on capsules and slimes?

Vedantu provides notes and questions on capsules and slimes. Professional educators produce content in such a way that it is easily understood and remembered by students. It covers capsules and slimes, as well as their functions and differences. Vedantu also provides students in grades 1 through 12 with study materials and a variety of competitive exams. Notes, important topics and questions, revision notes, and other material are among the contents. On Vedantu, you may access all of these resources for free. Students must first register on the Vedantu website in order to access all of these tools. Vedantu's mobile app also allows you to register.

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