Economic importance of Bacteria ”Biological Classification” Botany Notes Chapter 2, for Class 12-CBSE

Economic importance of Bacteria

Bacteria play significant role in day to day activates of human beings.

1.Beneficial activities

a) Role in agriculture

i) Decay and decomposition of organic matter : they bring about decay and decomposition of dead remains of plants and animals. These are the most important for mineral cycling

ii) Sewage disposal : The bacteria decompose the organic matter present in the sewage, converting into simpler inorganic substances. The inorganic substances thus formed, being soluble, pass out through filter along with water which is highly useful of irrigation purposes, g., Clostridium, E. Coli.

iii) Nitrogen cycle : The proteins present in dead remains of living organisms are converted into amino acids by different types of saprophytic bacteria. Amino acid are converted into ammonia by ammonifying bacteria (Bacillus vulgaris, B. ramosus). Nitrifying bacteria convert ammonium salts first into nitrites (Nitrosomonas, Nitrococcus)  which are subsequently converted into nitrates (Nitrobacter). In presence of denitrifying bacteria (pseudomonas denitrificans) , nitrates and nitrites of soil are converted to gaseous nitrogen.

iv) Nitrogen Fixation : It is the biological process in which atmospheric nitrogen is converted into nitrogenous compounds by nitrogen fixing bacteria. These bacteria are of 2 types : a) Free living b) Symbiotic

a) Free living bacteria are Azotobacter and Beijerinckia (aerobic) and Clostridium (anaerobic).

b) Common symbiotic bacteria are Rhizobium Leguminosarum and Xanthomonas. These convert nitrogen into ammonia which is directly converted into amino acids by plants.

v) Manure preparation : Saprotrophic bacteria help in preparation of farmyard manure by converting farm refuse, dung and other organic wastes into humus.

b) Role in industry : Man has utilized the metabolic activates of bacteria in preparation of a number of industrial products as listed below :

i) Butter milk and sour cream

ii) Yoghurt

iii) Cheese

iv) Vinegar

v) Retting of fibres : Retting is a controlled microbial decomposition for separation of fibres. The tissues are immersed in water tanks where anaerobic butyric acid bacteria dissolve the pectin of middle lamella of cells, thus, separating the fibres. Clostridium perfringens and Pseudomonas fluorescence are useful in this process.

vi) Curing of leaves : To improve the flavor and taste in tea, using Micrococcus candidans and in tobacco leaves by Bacillus megatherium.

vii) Single cell proteins (SCP) : like – Methylohilus methyoltropus and Rhodopseudomonas capsulata.

c) Role in Medicine : Bacteria have been used extensively in preparation of antibiotics, vaccines, serums and vitamins.

i) Antibiotics : The term antibiotic was given by Waksman, who discovered streptomycin, these are the organic substances produced by microorganisms which inhibit the growth of other organisms (mostly pathogens) but do not affect the growth of organisms secreting these. The first commercial antibiotic penicillin was discovered by Flemming (1959) from a fungus called Penicillium.

Some antibiotics of eubacterial origin :

  1. a) Bacitracin ……………………… Bacillus licheniformis
  2. b) Polymixin ……………………… Bacillus polymyxa
  3. c) Gramicidin …………………….. B. brevis
  4. d) Subtilin …………………………. B.subtilis
  5. ii) Vaccine production

vaccines and serums against typhoid, cholera TB, pertussis, tetanus and diphtheria are made with the help of bacteria or their toxins e.g., DPT ( against diphtheria, pertussis and tetanus), TT(against tetanus), BCG (Bacille of Calmette – Guerin against TB ) , DT ( against diphtheria and tetanus)

iii) Vitamins : Escherichia coli present in human intestine produces large quantities of B- complex vitamin K. bacteria are utilized in industrial production of a number of vitamins like riboflavin from clostridium butylicum, Cobalarmin (B12) from Bacillus megatherium and Pseudomonas denitrificans.

iv) Pollution control : Pseudomonas putida degrades petroleum wastes. Flavobacterium can decompose 2 , 4-D. DDT can be decomposed by Acetobacter aerogens. Gange’s water contains Bdellovibiro bacteriovorus that maintains purity of its water.

Harmful activates

i) Spoilage of food : Saprophytic bacteria cause decay of vegetables, fruit, meat, bread and other foods, making these unfit for human consumption. Some bacteria even produce strong toxins in the infected food stuffs which cause food poisoning when consumed.

ii) Deterioration of Domestic Articles : Some saprophytic bacteria like Cellulomonas, Spirochaete cytophaga cause deterioration of domestic articles of daily use such as leather, woolen, canvas articles etc.

iii) Denitrification of Soils : Denitrifying bacteria like Thiobacillus denitrificans,  Micrococcus denitrificans and Pseudomonas convert nitrates and nitrites present in the soil into gaseous nitrogen, thus depleting the soil nitrogen, thereby decreasing soil fertility.

iv) Desulphurification : Desulphovibrio desulphuricans.

v) Diseases : Common disease of humans, animals and plants are listed below respectively –

Table : 2

   Name of causal organism                       Name of the human diseases

 Shigella dysenteriae, S. sonnei, S. boydis-                    Bacillary dysentery

Clostridium botulinum  –                                                         botulism

Vibrio cholera                                                                Cholera

Leptotrichia bucccalis                                                     Dental plaque

Corynebacterium diphtheriae                                         Diphtheria

 Salmonella typhimurium staphylococcus aureus   –     Food poisoning

 Clostridium perfringens                                                          Gangrene

Escherichia coli, Salmonella                                          Gastroenteritis

 Neisseria gonorrhoeae or Salmonella                                     Gonorrhoea

 Mycobacterium leprae (Hensen’s bacillus)                             Leprosy

Neisseria meningitidis                                                    Meningitis

Heliobacter pylori –                                                        Peptic ulcer

Staphylococcus aureus                                                  Pimples

Yersinia pestis                                                               Plague

Diplococcus pneumonia                                                          Pneumonia

Streptococcus species                                                    Rheumatic fever

Treponema pallidum                                                     Syphilis

Clostridium tetani                                                                   Tetanus

Streptococcus pyrogenes                                                         Tonsilitis

Mycobacterium tuberculosis                                          Tuberculosis

Salmonella typhosa / typhi                                            Typhoid

Gardineralla vaginalis                                                    Vaginitis

Bordetella pertussis / Hemophilous pertusis                           Whooping cough

Salmonella typhimurium                                               Enteric fever (paratyphoid)

Mycoplasma hominis    –                  Male sterility and female abortion in humans


Table : 3

Name of causal organism                          Name of the animal diseases

Brucella sui                                                          Brucellosis

Clostridium chanvei                                   Black leg

Bacillus anthracis                                                 Anthrax

Salmonella abortusovis                              Abortion

Table : 3

Name of causal organism                          Name of the plant diseases

Pseudomonas solanacearum                       Potato wilt

Xanthomonas citri                                               Citrus canker

Agrobacterium tumefaciens                        Crown gall

Erwinia amylovora                                     Fire blight of apple

Xanthomonas oryzae                                  Bacterial blight of rice

Xanthomonas malvacearum                       angular leaf spot of Gossypium

Canthomonas phaseoli                               Bean blight of Phaseolus

Pseudomonas rubrilineans                          Red stripe of sugarcane

Eruinia cartovora                                                 Soft rot of carrot

Corynebacterium tritici                               Tundu (bacterial rot) of wheat

Xanthomonas campestris                           Black rot of cabbage

Streptomyces scabies                                 Potato scab

Pseudomonas tobaci                                   Wild fire of tobacco


  1. Spherical bacteria with chain like arrangement of different length is
    1. Diplococcus
    2. Staphylococcus
    3. Streptococcus
    4. Sarcina
  2. Select incorrect statement w.r.t eubacteria
    1. Have very simple structure
    2. Peptidoglycan nature of cell wall
    3. Heterotrophs are most abundant in nature
    4. Show most simple metabolic diversity
  3. Gram positive bacteria differs from Gram negative bacteria in the
    1. Presence of NAG and NAM
    2. Absence of diaminopimelic acid
    3. Presence of L-alanine
    4. Absence of D-glutamic acid
  4. Bacterial cell envelope is
    1. Glycocalyx only
    2. Cell wall only
    3. Glycocalyx and nucleoid
    4. Glycocalyx, cell wall and plasma membrane
  5. Nucleoid is
    1. Histoneless linear ss- DNA
    2. Circular DNA with histone proteins
    3. Circular DNA packaged with polyamines
    4. DNA with free ends
  6. Bacteria capable of switching over to anaerobic mode to get energy for their survival, are called
    1. Facultative anaerobes
    2. Obligate anaerobes
    3. Obligate aerobes
    4. Facultative aerobes
  7. Find odd one out w.r.t. phototrophic nutrition
    1. Chromatium and chlorobium
    2. Rhodopseudomonas and Thiospirillum
    3. Chloronema and Chloroflexus
    4. Pseudomonas and Clostridium
  8. Mark the incorrect option (w.r.t. nitrifying bacteria0
    1. Nitrococcus
    2. Leptothrix
    3. Nitrobacter
    4. Ntiorocysits
  9. Genetic recombination in which a small double stranded piece of DNA is transferred from donor bacterium to recipient bacterium by a bacteriophage was first demonstrated by
    1. Griffith
    2. Lederberg and Tatum
    3. Zinder and Lederberg
    4. Avery
  10. Select correct match

Column – I                                        Column – II

a.Retting of fibres                                       i) Pseudomonas putida

  1. Pollution control ii) Pseudomonas fluorescence
  2. Riboflavin iii) Bacillus brevis
  3. Gramicidin iv) Clostridium butylicum

1) a(ii), b(i), c(iv), d(iii)

2) a(ii), b(i), c(iii), d(iv)

3) a(i), b(iii), c(iv), d(iii)

4) a(iii), b(i), c(iv), d(ii)


Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.