Cell Structure of Bacteria

The detailed structure of bacteria can be studied only under the electron microscope. The ultrastructure of bacterium reveals the following cell structure.

Mucilage layer:

It is the outermost layer present in the bacterial cell. If it is in the form of loose sheath then it is called slime layer and if it is found in the form of thick and tough sheath it is called capsule. It is made up of a type of polysaccharide. It is the protective layer. It protects the bacterial cell from drying, harmful chemicals acids, drugs etc.

Cell Wall

It is a rigid structure present inner to mucilage layer. It is made up of murein or peptidoglycan. It gives shape and structural support to the cell.

Protoplasm

It is differentiated into three parts;

Cell membrane

Cytoplasm

Nuclear body

Cell membrane:

It is a semi-permeable membrane present inner to the cell wall and works as outer covering layer of cytoplasm. It is made up of lipid, protein and a small amount of carbohydrate.

Cytoplasm

It is viscous, granular substance present between the cell membrane and nuclear body. It contains ribosomes, mesosome, chromatophore, extra circular DNA, RNA and food reserved material in the form of glycogen, lipid, and volutin granule. Double membrane-bound cell organelles like mitochondria, endoplasmic, reticulum, Golgi bodies and plastids are absent.

Nuclear body

The nucleus is an incipient type which lacks a well-organized nucleus. It lacks nuclear membrane and nucleolus which is also called nucleoid. DNA is long, double-stranded and without histone protein. Such DNA is also called naked DNA or circular DNA. DNA is commonly called bacterial chromosome. DNA carries all genetic information.

Extra circular DNA or plasmid is found in the cytoplasm which is a short fragment of circular DNA. It carries genetic information about fertility factor and resistance factor.

Ribosomes:

They are of 70s type. They are of two type;

• Free ribosome
• Fixed ribosome

Free ribosomes are found freely in the cytoplasm and fixed ribosomes are found attached to the cell membrane. It helps in protein synthesis. Sometimes the chain of ribosomes is found which are called polyribosomes.

Chromatophores

They are single membrane bound sac-like thylakoids which are found freely in the cytoplasm. Chromatophores are the site for photosynthesis. They are found only in photosynthetic bacteria.

Mesosomes:

They are finger-like infolding or projection of cell membrane. They increase the surface area for respiration. They contain respiratory enzymes. Mesosomes are present in gram-positive bacteria and absent in gram-negative bacteria. In gram-negative respiration occurs directly from the inner surface of cell membrane.

Gas vacuole:

The gas vacuole is found in bacteria. They help in floating in liquid.

Food reserved material is found in the form of lipid and glycogen. Volatingranule is also found which is inorganic granule and store phosphate.

Flagella

Flagella are the long fine thin thread like protoplasmic extension or appendages. They help bacteria to swim in liquid.

Pilli:

They are a short fine thin thread like protoplasmic appendages. They help in the attachment of bacteria with other at the time of conjugation.