[Biology Class Notes] on The Inclusion Bodies- Reservoir of Energy Pdf for EXAM

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:

1. 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.

2. 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

Eg: Negri bodies in Rabies

Paschen bodies in Smallpox

Bollinger bodies in fowlpox

Eg: Torres bodies in Yellow Fever

Cowdry type A in Herpes simplex virus

Cowdry type B in Polio and Adenovirus

Eg: Cowdry type B in Adenovirus

Owl’s eye appearance – Cytomegalovirus

Eg: Warthin-Finkeldey bodies in Measles

Eg: Virus particles in Cucumber mosaic virus

Some of the Diseases that Involve Inclusion Bodies

1. Inclusion of body myositis which affects muscle cells.

2. Amyotrophic lateral sclerosis that affects motor neurons.

3. 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.