A few vital and cardinal characteristic features of ‘bacteria’ are as enumerated under : 1. Shape 2. Size 3. Reproduction 4. Formation of Colony 5. Mutation 6. Motility 7. Food and Oxygen Requirements 8. Temperature Requirements
CHARACTERISTIC
FEATURES
A few
vital and cardinal characteristic features of ‘bacteria’ are as enumerated under :
There are
three principal forms of bacteria,
namely :
(a) Spherical or Ovoid —
bacteria occur as single cells (micrococci), or in pairs (diplococci), clusters (staphylococci), chains (streptococci) or cubical groups (sarcinae)
;
(b) Rod-shaped — bacteria are termed as bacilli, more oval ones are known as coccobacilli, and those forming a chain
are called as streptobacilli ; and
(c) Spiral — bacteria are rigid (spirilla), flexible (spirochaetes) or curved (vibrios).
An
average rod-shaped bacterium measures approximately 1 μm in diameter and 4 μm in length. They usually vary in
size considerably from < 0.5 to 1.0 μm in
diameter to 10–20 μm in
length in some of the longer spiral forms.
It has
been observed that simple cell division
is the usual method of reproduction, whereas cer-tain bacteria give rise to buds or branches that eventually break off. The growth rate is
substantially affected on account of changes in temperature, nutrition, and
other factors.
Importantly,
bacilli can produce reproductive
cells invariably termed as spores,
whose relatively thick coatings are highly resistant to adverse environmental
conditions. In the event of a better congenial environment the spores commence to grow. Besides, spores are difficult to kill as they
are highly resistant to heat as well as disinfectant action.
A group
of bacteria growing in one particular place is known as a colony. A colony is invariably comprised of the ‘descendants of a single cell’. It has
been found that colonies differ in shape, size, colour, texture, type of
margin, and several other characteristic features. Interestingly, each species
of bacteria has a characteristic type of colony formation.
Evidently,
a majority of bacteria, like all living organisms, do possess the ability to
adapt their shape or functions when encountered with distinct changes in their
environment, but there are certain degree of limits to this ability. However,
they may also mutate to adapt to some potentially lethal sub-stances, for instance
: antibiotics.
It has
been duly observed that none of the ovoid or spherical cocci are capable of
moving, but certain bacilli and spiral forms do exhibit absolute independent
movement. It is, however, pertinent to mention here that the power of
locomotion exclusively depends on the possession one or more flagella, slender
whiplike appendages which more or less work like propellars.
Bacteria
are of different types based upon their food
and oxygen requirements as given below :
(a) Heterotrophic : require
organic material as food,
(b) Parasites : feed on living organisms,
(c) Saprophytes : feed on non-living organic
material,
(d) Autotrophic : i.e.,
self-nourishing–obtain their energy from inorganic substances, including most
of the soil bacteria,
(e) Aerobes : essentially require oxygen for
their very existence and growth, and
(f) Anaerobes : do not require oxygen for their
existence and growth. e.g., most
bacteria found in the GIT.
Although
some bacteria live at very low temperature or very high temperature ; however,
the optimum temperature for a majority of pathogens is 37 °C (98.6 °F).
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