Bacteria are
the smallest organisms having a cellular structure. They are unicellular prokaryotic
organisms classified as microorganisms. The study of bacteria is called
bacteriology.
Occurrence
The bacteria
occupy many environments, such as:
soil, dust, water, air, in and on animals and plants and they can even be found
in hot springs at temperature at 70° C or higher. Their numbers are enormous;
one gram of fertile soil is estimated to contain 100 million and 1 cm3
of fresh milk may contain more than 3000 million bacteria
Morphology of Bacteria
The
morphology refers to size, shape, arrangement and structure of bacterial cells.
Size of Bacterial Cell
Bacteria are
unicellular and very small. Most of them are approximately 0.5 to 1.0 μm in diameter
and from 0.1 to 10 μm in length.
Shape of Bacterial Cell
The shape of
a bacterial cell is governed by its rigid cell wall. Most bacteria have
constant shape but some have cells that exhibit a variety of shape
According to
their shape the bacteria can be generally classified as:
Cocci: These are sphere-shaped bacteria,
for example Streptococcus pneumoniae
causing pneumonia.
Bacilli: These are rod-like bacteria, for
example Lactobacillus found in milk.
Spirilla: They are rigid helical bacteria.
These are usually curved with a twist or turn. The spirillum may have less than
one complete twist and called vibrioid or one or more complete twists known as helical.
Spirochetes: These are flexible and can twist and
control their shape whereas the spirilla are relatively rigid.
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