Anton Von Leeuwenhoek discovered bacteria between 1653 - 1673 with the help of a crude microscope. This was later established by Louis Pasteur (1822 - 1895). Bacteria are unicellular, procaryotic, a-chlorophyllous organisms, of microscopic size.
The largest bacteria are about 12 microns in diameter and cannot be seen without the aid of a microscope. They are ubiquitous - occurring in every natural environment - in the air, water, soil and in and on the bodies of other organisms. Bacteria even colonies the buccal cavity and alimentary canal of humans and ruminants.
Over
2000 species of bacteria have been classified and name of these only a few
cause diseases in humans, animals and plants. The vast majority of bacteria are
saprophytic or free-living. They are extremely important because of their
effects on the human systems.
In
this article, we will explain: List at least six of the general characteristics
of bacteria, describe the structure of bacteria, describe reproduction and
nutrition in bacteria and explain the Economic importance of bacteria.
What are Bacteria?
Bacteria are microscopic, single-celled organisms that exist in their millions, in every
environment, both inside and outside other organisms. Some bacteria are
harmful, but most serve a useful purpose. They support many forms of life, both
plant and animal, and they are used in industrial and medicinal processes.
Bacteria are ubiquitous, mostly free-living organisms often
consisting of one biological cell. They constitute a large domain of
prokaryotic microorganisms. Typically a few micrometres in length, bacteria
were among the first life forms to appear on Earth, and are present in most of
its habitats.
General Characteristics of Bacteria
Do
you remember that living organisms have features that are peculiar to them?
Bacteria do have theirs. You will recall that there are over 2,000 species of bacteria.
They are:
1. Generally
microscopic in nature, they are single celled.
2. They
may be spherical, rod-like or spiral in shape.
3. They
may be motile or non-motile.
4. Aerobic
or anaerobic.
5. They
have no definite nucleus but chromatin granules.
6. The
Cell wall is made up of chitin.
7. Some
are equipped with one or more flagella.
8. They
lack chlorophyll.
9. Spherical
ones are about 0.5mm wide while the rod like are about 2mm - 10mm long.
10.
They inhabit a wide range of natural habitats.
Occurrence of bacteria as Living Organisms
We
need to also consider the occurrence of bacteria as living organisms:
1. They
exist everywhere i.e. in water, air, soil and body of other organisms living or
non-living.
2. They
float in air or dust particles.
3. Abundant
in water bodies and soil to a depth of 30cm.
4. Surplus
in sewage.
5. Occur
in the intestine of all animals.
6. One
gram of fertile soil is estimated to contain 2.5 thousand million while lcms of
fresh milk may contain more than 3000 million bacteria.
Structure of Bacterial Cell
Let
us look at the structure of bacteria:
1. Bacteria
are made up of complex cell wall made up of proteins and carbohydrate,
sometimes impregnated with chitin.
2. No
cellulose.
3. Covering
the cell wall is a slime layer called the capsule or sheath. In this form they
are resistant to drugs and adverse conditions.
4. There
is a definite cytoplasm.
5. No
clearly defined nucleus, but DNA is the nuclear material that is not bounded by
a nuclear membrane.
6. Contains
no membrane bound organelles.
Different Shapes of Bacteria
Again,
let us consider different shapes of bacteria. They have four different forms.
These are:
1. Cocci {Singular =
Coccus}: The cells are spherical or rounded. Depending on how
they cling together after cell division the cocci can further be classified as
diplococci, staphylococci and streptococci.
2. Bacilli (Singular =
bacillus}: The cells are rod-shaped. Some have flagella.
Rod-shaped bacteria may also remain attached end-to-end as in the genus
Lactobacillus.
3. Spirilla (Singular =
spirillum}: The cells are spirally twisted or corksrew
like. Some have flagella. Example is Treponetna.
4. Vibrio:
The cells are comma-shaped Example is Yibrio cholera
Reproduction in Bacteria
You
will find the process of reproduction in bacteria very interesting.
Let
us now consider the details. Reproduction in Bacteria:
1. Mainly
by binary fission, no sexual reproduction.
2. Binary
fission occurs under favourable conditions.
3. The
chromatin material divides mitotically.
4. Cytoplasm
divides along with its content.
5. Two
daughter bacterial cells are formed.
6. Bacillus
subtilis divides 2 - 3 times in an hour.
7. A
single cell may give rise to about 16 million cells in 12 hours.
Sporulation
We now consider this as an occurence that leads to the multiplication in the number of bacteria.
Sporulation goes on as follows:
1. Rod-shaped
bacteria form spores as resting spores.
2. Mass
of protoplasm condenses with thick membrane (endospore).
3. Mother
cell dissolves; endospore remains dormant resisting adverse conditions e.g.
freezing, dryness, high temperature etc.
4. Under
favourable conditions, new bacterial cells emerge.
Gram Reaction
The
gram reaction/test developed in 1884 by Danish Biologist (Christian Gram)
revealed that bacteria can be divided into two natural groups based on their
reaction to the Gram's Stain.
Those bacteria which stain with gram's stain are called Gram Positive, others that do not are called Gram Negative. Gram positive bacteria such as Staphylococcus, Bacillus and Lactobacillus, develop thick walls impregnated with polysaccharides and proteins.
The walls of Gram negative bacteria such as
Salmonella, E coli and Azotobacter are thinner but more complex.
Gram
positive bacteria are purple or violet after staining with Gram's stain while
Gram negative bacteria are pink in colour after the staining reaction.
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