Types of bacteria and their characteristics

Types of bacteria

there are four types of bacteria on the basis of their shape.


These are spherical (rounded) bacteria. Due to the arrangment, these bacteria are of four kinds.

  • Monococc-us: single rounded bacteria.
  • Diplo-Cocci: these are in groups of two rounded bacteria.
  • Strepto-Cocci: these bacteria are arranged in chain like manner.
  • Staphylo-Cocci: these bacteria are present in groups or bundles.

When bacteria are in the group of four cells they are called Tetrad  or sarcina and when in the group of eight cells they are called octant.


These are rod-shaped bacteria. These are also of different types.

  • Mono-bacillus: single rod-shaped bacteria.
  • Diplo-bacilli: group of two rod-shaped bacteria.
  • Strepto-bacilli: chain like rod-shaped bacteria.
  • Staphylo-bacilli: groups of many rod-shapped bacteria.
  • Spirilli

These are spiral shaped bacteria. They are never found in groups. They are single bacteria.

4. VibroThey are comma shaped.they are also not found in groups. They are single bacteria.

Structure of a bacterial cell

A typical bacterial cell shows the following structure.

(1)Flagella (2) Pilli (Capsule) (4) Cell wall (5) Cell membrane (Cytoplasm (Mesosome(8) Nuclear Material


Flagella are the locomotors organs of bacteria. These are thread like structures; arise from the outer surface of bacterial cells. The flagella are found in Bacilli bacteria.


These are hollow filament like structures present on their body. The Pilli do not take part in locomotion. They are involved in the process of conjugation (reproduction).


It is the outer additional protective layer present around the cell wall. It is made up of polysaccharides. It is found only in some bacteria.

4.Cell wall

It is the layer around the bacterial cell. It protects the inner parts of cell and also provides a definite shape to bacterial cell. It is composed of sugars, amino acids and chitin. Cellulose is absent. The cell wall also has a compound, called Peptidoglycon. It provides strength to bacterial cell and helps to maintain the shape.

5.Cell Membrane (Plasma membrane)

On the inner side of cell wall, around the cyoplasm cell membrane is present. It is semi-permeable and controls osmotic properties of cell. The cell membrane is composed of proteins and lipids.


The inner substance of bacterial cell is called cytoplasm. It contains granules of glycogen and fats, and proteins as reserve food. It does not have Endoplasmic reticulum, Mitochondria,Glogi bodies, Plastids etc, but it contains ribosomes  for protein synthesis.

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