Bacteria ~ Useful & Harmful Bacteria

Bacteria | Useful Role of Bacteria | Harmful Role of Bacteria

Bacteria are the most primitive unicellular prokaryotic organisms which do not have a well-defined nucleus and are not enclosed within a nuclear membrane.


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Discovery of Bacteria

Anton von Leeuwenhoek, a Dutch scientist, first observed bacteria in 1675. He named them animalcules.


Ubiquitous in nature, commonly found in air, soil, water, deserts, plants, animals, and in man.

Size of Bacteria

Ranges from 0.2 to 1.5 µm in diameter and 3 to 5 µm in length.

Shape of Bacteria

Coccus: Spherical

MicrococcusSolitary cell of coccus.
DiplococcusOccur in pairs.
StreptococcusOccur in chains
StaphylococcusOccur in clusters.
SpirillaSpiral or twisted


Possess whip-like flagella, which pierce through the cell wall and capsule.

Nutrition of Bacteria

  • Photoautotrophs: Contain chlorophyll and use light energy for the synthesis of food.
  • Chemoautotrophs: Obtain energy by oxidizing inorganic compounds.
  • Saprophytes: Grow on dead and decaying organic matter.
  • Parasites: Obtain their food from a living host on which they grow.
  • Also Read Fungi ~ Useful & Harmful Fungi


  • Aerobic respiration: Absorb atmospheric oxygen.
  • Anaerobic respiration: Do not require free oxygen.

Reproduction of Bacteria

  • Asexual reproduction: Binary fission/cell division
  • Sexual reproduction: Conjugation

Spore formation

Under adverse conditions, several bacteria survive by the formation of spores.


Penicillium notatum, Streptomyces griseus, Penicillium chrysogenum etc.

Useful Role of Bacteria

A. Production of antibiotics

  • The chemical substances produced by a living organism that kill or stop the growth of disease causing microorganisms such as fungi and bacteria are called antibiotics.
  • Antibiotics are used to cure several life-threatening infections in humans, plants and animals.

Some Important Antibiotics:

StreptomycinStreptomyces griseusTuberculosis
ChloromycetinStreptomyces venezuelaeFever, skin rash, typhoid, meningitis
BacitracinBacillus subtilisLocalised eye and skin infections, wound
ErythromycinStreptomyces erythraeusRickettsial fever
PenicillinPenicillium chrysogenumTetanus, diphtheria

B. Production of serums

  • Serum is blood plasma from which fibrinogen has been removed.
  • It is used as a means of prevention against bacterial invasion.

C. Production of vaccine

  • A vaccine is any germ or germ substance introduced into the body to develop resistance to a particular disease.
  • Vaccines confer immunity against specific diseases. They act as antigens and stimulate the body to produce antibodies.

Some Important Vaccines:

TAB vaccine (killed bacteria)Typhoid
BCG vaccine (living, weakened bacteria)Tuberculosis
Triple vaccineDiphtheria, whooping cough, tetanus
Polio vaccinePoliomyelitis virus

D. Production of Toxoids

  • Toxoids are the inactivated toxins of particular bacteria which can stimulate the production of respective antibodies.
  • Toxoids are mostly useful in providing immunity against diphtheria and tetanus.

E. Nitrogen fixation

  • The process of circulation of nitrogen between the atmosphere, soil, plants and animals is called the nitrogen cycle.
  • The process of conversion of free nitrogen from the atmosphere into soluble nitrates by microorganisms is known as biological nitrogen fixation.
  • The microbes which carry out biological nitrogen fixation are commonly called biological nitrogen fixers. Examples: Rhizobium and Azotobacter.

F. Biogas production

  • Gobar gas, biogas or methane production is carried out with the help of bacteria using animal faeces. Examples: Cowdung and urine.
  • Biogas is used as a fuel and for street lighting.

Harmful Role of Bacteria

A. Spoilage of food

Bacteria carry out the process of decay or fermentation, resulting in the spoilage of food materials, such as milk, fruits, vegetables etc., especially during summer. This spoilage can be so severe that
it can also lead to food poisoning.

B. Diseases in Living Beings

Plant Diseases:

DiseasePlant AffectedBacterial Agent
Angular leaf spotCottonXanthomonas malvacearum
Blight cankerPaddyXanthomonas oryzae

Animal Diseases:

DiseaseAnimal AffectedBacterial Agent
AnthraxCattle, sheep, elephantBacillus anthracis
DiphtheriaGuinea pigs, kittens,
Corynebacterium diphtheriae

Human Diseases:

DiseaseBacterial Agent
BronchitisStaphylococcus sp., Haemophilus influenzae
CholeraVibrio cholerae

C. Bioweapons

When pathogenic microorganisms such as bacteria, viruses, fungi, or biological toxins are used deliberately as means to kill or disable plants, animals, and humans, they are known as bioweapons. Examples: Bacillus anthracis, Clostridium botulinum, Clostridium perfringens, etc.

YOU MAY READ Vegetative Propagation and Micropropagation

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