What are inclusion bodies definition types and functions
If someone questions what cell inclusions are or what are inclusion bodies, the answer to both will be the same. Also known as inclusion bodies, these elementary bodies are cytoplasmic inclusions or nuclear aggregates of stable substances like proteins. They freely suspend and float within the cytoplasmic matrix and can also be called cytoplasmic inclusions. Some inclusion bodies lie free in the cytoplasm whereas some are enclosed by a shell. They are usually sites of viral multiplication, thus in a bacterium or eukaryotic cell, therefore, are also referred to as viral inclusion bodies that consist of viral capsid proteins. Inclusion bodies can be an indication of certain diseases like Herpes, Parkinson’s disease, Measles, Rabies and Dementia.
Features of Inclusion Bodies
These act as reserve deposits.
Plenty of nutrients can be stored in them by the cells and utilized when there is deficiency in the environment.
Some of the inclusion bodies in bacteria are very common in a wide variety.
Cell inclusions are generally acidophilic.
These can also be present as crystalline aggregates of virions.
Represent degenerative changes produced by a viral infection.
These are made of virus antigens present at the site where synthesis of virus takes place.
These can be observed as pink structures under microscope when stained with gypsum or methylene blue dye.
Classification of Inclusion Bodies
Inclusion bodies are being classified into two types, namely: Organic Inclusion bodies and inorganic inclusion bodies.
The Organic Inclusion Bodies
Organic inclusion bodies usually contain either (1) glycogen granules or (2) poly-β-hydroxybutyrate (PHB)
Carbon storage reservoirs like glycogen and PHB inclusion bodies provide material for energy and biosynthesis. Glycogen is a polymer of glucose units made up of long chains connected by glycosidic links and branching chains linked by glycosidic bonds. Staining cells with an iodine solution turns them reddish-brown if they contain a lot of glycogen.
Poly-β-hydroxybutyrate (PHB) contains hydroxybutyrate molecules joined by ester bonds between adjacent molecules' carboxyl and hydroxyl groups. Beta hydroxy is the name given because of the portion of the OH group in comparison to the double-bonded Oxygen group. Since the group is repeated several times in the structure, thus it is known as Poly- β-hydroxybutyrate
Cyanobacteria is basically a group of bacteria that can photosynthesise and they have two distinctive organic inclusion bodies:
Large polypeptides with almost equal amounts of two types of amino acids arginine and aspartic acid. One is a basic amino acid, another being an acidic amino acid, which makes up the cyanophycin granules.
Carboxysomes are found in many cyanobacteria and other CO2-fixing bacteria, and they store additional nitrogen for the organism.
The gas vacuole is an amazing organic inclusion body in prokaryotic organisms. Some aquatic prokaryotes rely on it for buoyancy.
Prokaryotes that have gas vacuoles in them can regulate their buoyancy to float at the depth necessary for proper light intensity, oxygen concentration, and nutrient levels. They float upward after new vesicles are formed and down by collapsing vesicles.
Inorganic Inclusion Bodies
In prokaryotes, there are two types of inorganic inclusion bodies:
Granules of Polyphosphate
Many bacteria store phosphate in the form of polyphosphate granules or volutin granules. Polyphosphate is an ester-linked linear polymer of orthophosphates. As a result, volutin granules serve as phosphate storage reservoirs, a key component of cell elements like nucleic acids.
They serve as an energy store in some cells, and polyphosphate can be used as an energy source in processes. These granules are also known as metachromatic granules. They have a metachromatic effect when stained with the blue dyes methylene blue or toluidine blue, which causes them to appear reddish or different shades of the blue spectrum.
Sulfur Granules
Some prokaryotes use sulfur granules to store sulfur temporarily. Photosynthetic bacteria, for example, can use hydrogen sulfide as a photosynthetic electron donor and store the sulfur produced in the periplasmic space or specific cytoplasmic globules.
Metachromatic Inclusions - Some of the large cell inclusions that sometimes stain red with blue dyes like methylene blue are called metachromatic inclusions. These consist of granules that consist of starch and glycogen. In the presence of iodine, the glycogen granules appear reddish brown in color and the starch granules appear blue.
Lipid Inclusions - These appear in various species of Bacillus, Mycobacterium, Azotobacter, and other genera and act as lipid storage material. These can be observed when cells are dyed with fat soluble dyes like Sudan dyes.
Sulfur Granules - These derive energy by oxidizing sulfur and sulfur containing compounds. They may deposit sulfur granules in the cell that serve as an energy reserve.
Carboxysomes - These inclusions contain the enzyme ribulose 1, -5 diphosphate carboxylase. Bacteria use these for a source of carbon for carbon dioxide fixation during photosynthesis.
Magnetosomes - Some bacteria orient themselves within a magnetic field due to the presence of magnetosomes. Magnetosomes are intracellular inclusion bodies or particles of iron oxide mineral called magnetite (Fe3O4). A magnetosome is enclosed by a thin membrane composed of protein, phospholipid and glycoprotein. It imparts a magnetic dipole on a cell allowing itself to exhibit magnetotaxis which is the process of migrating along the earth’s magnetic field. It is found in many aquatic organisms.
Based on the location, either at the nucleus or cytoplasm or at both of these cell organelles, we can classify inclusion bodies in the following categories:
Intranuclear cell inclusions.
Infection inclusion bodies.
Intracytoplasmic inclusion bodies.
Physiological inclusion bodies.
Inclusion bodies can be present in a bacterium or eukaryotic cell in the form of cystic lesions, fungal infections, virus infected cells, bacterial infections, autoimmune diseases, neoplasms and blood dyscrasias.
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Examples of Viral Inclusion Bodies
Acidophilic Intracytoplasmic Inclusion Bodies (eosinophilic)
Eg: Negri bodies in Rabies
Paschen bodies in Smallpox
Bollinger bodies in fowlpox
Acidophilic Intranuclear Inclusion Bodies (Eosinophilic)
Eg: Torres bodies in Yellow Fever
Cowdry type A in Herpes simplex virus
Cowdry type B in Polio and Adenovirus
Intranuclear Basophilic Inclusions
Eg: Cowdry type B in Adenovirus
Owl’s eye appearance - Cytomegalovirus
Both Intranuclear and Intracytoplasmic
Eg: Warthin-Finkeldey bodies in Measles
Viral Inclusion Bodies in Plants
Eg: Virus particles in Cucumber mosaic virus
Some of the Diseases that Involve Inclusion Bodies
Inclusion of body myositis which affects muscle cells.
Amyotrophic lateral sclerosis that affects motor neurons.
Dementia with lewy inclusions that affect cerebral neurons.
How to Prevent the Formation of Inclusion Bodies?
The cell inclusions are made of denatured aggregates of proteins (inactive), and several techniques have been developed to prevent the inclusion bodies formation. These help in the solubilisation and recovery of active proteins. The techniques are mentioned as follows:
Usage of weaker promoters to slow down the rate of protein expression.
Using low copy number plasmids.
Co-expression of chaperone.
Using specific E.coli strains.
Fusing the target protein with a soluble partner.
Lowering of the expression temperature.
FAQs on Inclusion Bodies in Cells Structure and Biological Role
1. What are inclusion bodies in biology?
Inclusion bodies are non-living cytoplasmic structures found inside cells that store nutrients, pigments, or secretory products. Unlike organelles, they are usually not membrane-bound and are temporary accumulations of substances.
- Common in prokaryotic cells such as bacteria.
- May store food reserves like glycogen or lipids.
- Can also contain pigments or waste materials.
2. What is the function of inclusion bodies in cells?
The main function of inclusion bodies is storage of reserve materials and other cellular substances. They act as intracellular deposits that support cell survival and metabolism.
- Store energy sources like glycogen granules.
- Accumulate lipid droplets for energy.
- Contain pigments such as melanin in some cells.
- Help bacteria store inorganic materials like polyphosphate granules.
3. Are inclusion bodies membrane-bound?
Most inclusion bodies are non-membrane-bound structures in the cytoplasm. They lack a surrounding lipid bilayer, which distinguishes them from true organelles like mitochondria or the nucleus.
- Appear as granules or droplets in the cytoplasm.
- Often visible under a light microscope.
- Function mainly as storage deposits.
4. What are examples of inclusion bodies in prokaryotic cells?
Common examples of inclusion bodies in prokaryotic cells include glycogen granules, polyphosphate granules, and sulfur granules. These inclusions help bacteria store nutrients and inorganic compounds.
- Glycogen granules – store glucose as an energy reserve.
- Polyphosphate granules (volutin granules) – store phosphate.
- Sulfur granules – found in sulfur bacteria.
- Gas vacuoles – help in buoyancy in aquatic bacteria.
5. What is the difference between inclusion bodies and organelles?
The key difference is that inclusion bodies are non-living storage deposits, whereas organelles are living, functional structures within the cell. Organelles carry out specific metabolic functions, while inclusion bodies mainly store materials.
- Inclusion bodies: usually non-membrane-bound, temporary, storage role.
- Organelles: membrane-bound (in eukaryotes), permanent, perform active functions like respiration or protein synthesis.
6. What are inclusion bodies in bacteria?
In bacteria, inclusion bodies are cytoplasmic storage granules that contain reserve nutrients or inorganic materials. They help bacteria survive nutrient deficiency and environmental stress.
- Store carbon as glycogen or lipids.
- Store phosphate as volutin granules.
- May contain sulfur in sulfur-oxidizing bacteria.
7. What are viral inclusion bodies?
Viral inclusion bodies are abnormal aggregates of viral particles or proteins formed inside infected host cells. They are often seen in the cytoplasm or nucleus during viral infections.
- Formed due to viral replication.
- May serve as sites of viral assembly.
- Used in diagnosis of certain viral diseases.
8. What are inclusion bodies in eukaryotic cells?
In eukaryotic cells, inclusion bodies are stored materials or pigments present in the cytoplasm but not considered true organelles. They are temporary accumulations of substances.
- Glycogen granules in liver and muscle cells.
- Lipid droplets in adipose tissue.
- Melanin granules in skin cells.
9. How are inclusion bodies formed?
Inclusion bodies are formed by the accumulation of synthesized materials within the cytoplasm when they are produced faster than they are used. This leads to visible deposits inside the cell.
- Excess glucose is converted to glycogen and stored.
- Excess fatty acids form lipid droplets.
- Bacteria accumulate inorganic compounds like phosphate.
10. Why are inclusion bodies important in microbiology?
Inclusion bodies are important in microbiology because they help identify bacteria and understand their metabolic capabilities. Certain inclusions are characteristic of specific bacterial groups.
- Presence of volutin granules helps identify Corynebacterium species.
- Sulfur granules indicate sulfur-oxidizing bacteria.
- Gas vacuoles explain buoyancy in aquatic microbes.
