CELL INCLUSIONS IN BACTERIA

 CELL INCLUSIONS

—     Within the cytoplasm of prokaryotic cells, several kinds of reserve deposits, known as Inclusions or Cell Inclusions or Inclusion bodies.

·  Cells may accumulate certain nutrients when they are plentiful and use them when the environment is deficient.

·       Some inclusions arc common to a wide variety of bacteria, whereas others are limited to a small number of species and therefore serve as a basis for identification.

TYPES OF CELL INCLUSIONS

a)     Metachromatic Granules

b)     Polysaccharide Granules

c)     Lipid Inclusions

d)     Sulfur Granules

e)     Carboxysomes

a) Metachromatic granules

·  Metachromatic granules are large inclusions that take their name from the fact that they sometimes stain red with certain blue dyes such as Methylene blue (Metachromasia).

·   Metachromatic Granules are made up of Polymetaphosphates and also called as Volutins or Volutin Granules or Babe Ernst Granules or Polar Bodies.

·   Volutin represents a reserve of Inorganic phosphate (polyphosphate) that can be used in the synthesis of ATP. It is generally formed by cells that grow in phosphate - rich environments.

·   Metachromatic granules are present in Bacteria (Corynebacterium diphtheriae, Spirillum sp., Rhizobium sp. and some Bacillus sp.), Algae, Fungi and Protozoa.

b) Polysaccharide Granules

·       Polysaccharide granules are also called as Polyglucan granules or Hydrophilic granules.

·       Polysaccharide granules typically consist of Glycogen and Starch.

·     In the presence of Iodine, Glycogen granules appears in Red and Starch granules appears in Blue.

·       Polysaccharide granules are deposited by the bacteria themselves inside their cells when simple sugars like Glucose, Sucrose or Fructose are present for Polysaccharide (Glucan) synthesis.

·       Polysaccharide granules are present in Clostridium sp. and some Coliform bacteria and act as an importance source for Carbohydrate metabolism in bacteria.

c) Lipid Inclusions

·       Lipid Inclusions are also called as Sudanophilic granules or Poly – β – hydroxybutyrate (PHB).

·       Lipid inclusions are revealed by staining cells with fat-soluble dyes, such as Sudan dyes.

·   PHB Granules are formed during Lipid synthesis, Acetate or Butyrate metabolism, Nitrogen deficiency conditions or Denitrification process.

·     During Lipid biosynthesis, Acetyl CoA is condensed into Aceto - Acetyl CoA and further reduced to β – hydrobybutyryl CoA. Polymerization of this compound results in formation of PHB.

·       Lipid inclusions appear in various species of Mycobacterium, Bacillus, Rhizobium, Azotobacter, Spirillum, Alcaligenes and other Soil bacteria.  

d) Sulfur Granules

·       Sulfur Granules are also called as Sulfur Globules.

·       Sulfur Granules are Cytoplasmic globules of the element Sulfur.

·       Sulfur Granules are present in the "Sulfur bacteria" which grow in Sulfur rich environment that belong to the genus Thiobacillus thiooxidans, Chromatium sp. and Chlorobium sp. derive energy by oxidizing sulfur and sulfur-containing compounds.

·     The Sulfur bacteria may deposit sulfur granules in the cell, where they serve as an energy reserve.

e) Carboxysomes

·  Carboxysomes are the bacterial Cell inclusions that contain the enzyme Ribulose 1,5 - diphosphate carboxylase.

·   Photosynthetic bacteria use Carbon-di-oxide as their sole source of carbon and require this enzyme for Carbon-di-oxide fixation.

·       Carboxysomes containing bacteria are Nitrifying bacteria, Cyanobacteria and Thiobacilli.