What are Cell Inclusions?
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.
(Image will be uploaded soon)
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 The Inclusion Bodies- Reservoir of Energy
1. Why are some granules called metachromatic granules?
They are called metachromatic granules because they appear red or a different shade of blue when stained with the blue dyes methylene blue or toluidine blue. These are orthophosphate linear polymers joined by an ester bond. Nucleic acid contains phosphorus, which is a crucial component. Metachromatic granules are made up of polymerised phosphate and are used to store inorganic phosphate and energy. Polymeric esters of poly-hydroxybutyric acid or similar chemicals are found in many bacteria's lipid droplets.
2. What are gas vacuoles?
Gas vacuoles are clusters of hollow cylindrical structures known as gas vesicles found in amoeba for food storage. The walls of gas vesicles are made entirely of a single small protein. These protein subunits come together to form a rigid confined cylinder that is hollow, impervious to water, but porous to atmospheric gasses. They can also be found within some bacteria. You can get the detailed information regarding other cell organelles on the Vedantu app or website. Also, you can download study materials that have been specifically designed for the students.
3. How can we visualize PHB?
PHB, also known as Poly- β-hydroxybutyrate, is an organic inclusion body that accumulates in distinct bodies that are readily stained with Sudan black for light microscopy and are seen as empty "holes" in the electron microscope. This can happen as the inclusion bodies are able to dissolve in the solvents that are ultimately used to prepare the specimens for electron microscopy.
4. Why are inclusion bodies formed?
Overexpression of heterologous proteins causes inclusion bodies. They are dense, spherical, aggregated proteins that form in the cytoplasm of prokaryotes. Inclusion bodies have been hypothesized to operate as viral factories and play an essential role in the viral replication cycle because they include all of the proteins required for viral RNA production. When the yield of the native protein is low due to severe proteolysis, inclusion bodies are often advantageous.
5. Why is Carboxysome important?
Carboxysomes are structures, polyhedral in shape that contain the enzyme ribulose-1, 5-bisphosphate carboxylase, also known as Rubisco. It is a crucial enzyme in the process of converting CO2 from the atmosphere into sugar, which is known as CO2 fixation. The enzyme forms a paracrystalline arrangement in the carboxysome, which acts as an enzyme reserve. Carboxysomes may also act as a CO2 fixation site.
