Cytoplasm and Its Contents

The cytoplasm is inside the cell membrane and is mostly water by composition. However, it has a semifluid nature due to a suspension of carbohydrates, enzymes, inorganic ions, lipids, and proteins. Within this suspension can be found the nuclear region, ribosomes, storage products, and endospores.

Instead of a nucleus, bacterial cells have a nuclear region or nucleoid. The nuclear region consists mostly of genetic material in one large and circular chromosome. In addition to the chromosome, some bacteria have small molecules of genetic material, called plasmids, that contain additional genetic information.

FIGURE 3.4 Beggiatoa.

Ribosomes are small spherical bodies that serve as sites for protein synthesis. Ribosomes are abundant in the cytoplasm, and often they are found in long chains known as polyribosomes.

There are several storage products or inclusions that may be found in bacterial cells. These products include stored food, volutin granules, and sulfur granules. Food may be stored in the form of glycogen (glucose polymer), starch, and poly-P-hydroxybutyrate (PHB). Phosphorus-accumulating organisms or poly-P bacteria including Acinobacter store phosphorus in long chains of polyphosphate known as volutin granules.Volutin granules also are known as metachromatic granules, because they display metachromasia. Metachromasia is not a stain of uniform color produced by a simple stain. It is the production of different intensities of color. Sulfur-oxidizing bacteria including the filamentous organisms Beggiatoa (Figure 3.4) and Thiothrix oxidize sulfides (HS-) as an energy source. The product from the oxidation of sulfide is insoluble elemental sulfur (S°) that is stored as a granule in the cytoplasm.

Endospores are produced by only a small number of bacteria including species of Bacillus and Clostridium. Endospores are dormant reproduction bodies of active vegetative bacteria. They contain very little water and are highly resistant to harsh environmental conditions including acidity, desiccation, heat, and some disinfectants. When conditions become favorable, the endospores germinate.

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