Inclusions:

Inclusion bodies can be divided into two types:

Inclusion bodies not bounded by a membrane and lie free in the cytoplasm. Ex. Polyphosphate granules, cyanophycingranules and some glycogen granules.

Inclusion bodies enclosed by a membrane about 2-4nm thick. Ex.PolyB-hydroxybutyrate granules, some glycogen and sulfur granules, carboxysomes and gas vacuoles.

Organic inclusion bodies:

Glycogen:

Polymer of glucose units composed of long chains formed by alpha (1-4) glycosidic bonds and branching chains connected to themby alpha (1-6)glycosidic bonds. Ex. glycogen and starch, and their presence can be demonstrated when iodine is applied to the cells (glycogen granules appear reddish brown and starch granules appear blue).

Poly B- hydroxybutyrate:

Contains beta-hydroxybutyrate molecules joined by ester bonds between the carboxyl and hydroxyl groups of adjacent molecules. Appear in various species of Mycobacterium, Bacillus, Azotobacter , Spirillum and other genera. Lipid inclusions are revealed by use of fat-soluble dyes, such as Sudan dyes.

Glycogen and PHB are carbon storage reservoirs providing material for energy and biosynthesis (Fig. 12).

 

Fig. 12 . Poly B- hydroxybutyrate inclusions

Cyanophycin granules:

Cyanobacteria are composed of large amino acids containing approximately equal amounts of amino acids arginine and aspartic acid. These are used to store extra nitrogen for the bacteria.

Carboxysomes:

These are polyhedral and hexagonal inclusions that contain the enzyme ribulose 1,5-diphosphate carboxylase. ·Bacteria that use carbon dioxide as their sole source of carbon require this enzyme for carbon dioxide fixation during photosynthesis (Ex.nitrifying bacteria, cyanobacteria, and Thiobacilli ).

Gas vacuoles:

These are hollow cavities found in many aquatic prokaryotes, including cyanobacteria, anoxygenic photosynthetic bacteria and halobacteria. Each vacuole consists of rows of several individual gas vesicles, which are hollow cylinders covered by protein. Their function is to maintain buoyancy so that the cells can remain at the depth in the water appropriate for them to receive sufficient amounts of oxygen, light and nutrients. They are impermeable to water and permeable to atmospheric gases.