1. Microorganisms or Microbes
n Microbes are organisms which cannot be seen by naked eyes.
n Occurrence: These can be found everywhere, i.e., in soil, water, air and inside the bodies of living organisms. They can be found in thermal vents, deep in soil, under snow as well as in acidic environment.
n Diversity: Microbes are of various varieties—protozoa, bacteria, fungi, plant viruses, viroids and prions.
2. Microbes in Household Products
(i) Curd
l Curd is formed by adding a small amount of curd to milk, which acts as a starter or inoculum.
l Lactobacillus/lactic acid bacteria (LAB) present in starter, multiply at suitable temperature and convert milk into curd.
l Acids released by LAB during the growth, coagulates and partially digest milk protein, casein.
l Benefits of LAB:
(a) Increases vitamin B12 amount thus increasing nutrient quality of milk.
(b) Checks disease-causing microbes in stomach.
(ii) Dough
l Dough is formed by fermentation by bacteria.
l Bread is made by fermentation by Saccharomyces cerevisiae or commonly called baker’s yeast.
l CO2 released during the process of fermentation gives the puffy appearance to dough.
l It is used to make foods like idli, dosa, bread, etc.
(iii) Toddy
l It is a traditional drink of Southern India.
l It is made by fermentation of sap from palm trees by bacteria.
(iv) Cheese
l Cheese is formed by partial degradation of milk by different microorganisms.
l Swiss cheese is formed by the bacterium Propionibacterium sharmanii. Its characteristic feature is formation of large holes due to production of large amount of CO2.
l Roquefort cheese is formed by ripening with the fungi Penicillium roqueforti for a particular flavour.
3. Microbes in Industrial Products
n Large-scale production of various compounds in industries is done in very large vessels called fermentors.
(i) Fermented beverages
l Beverages are formed by fermenting malted cereals and fruit juices with Saccharomyces cerevisiae or brewer’s yeast to produce ethanol.
l Formation of different types of alcoholic drinks depends on raw material and type of processing.
l Wine and beer are produced without distillation.
l Whisky, brandy and rum are formed by distillation.
(ii) Antibiotics
l Antibiotics are chemical substances produced by some microorganisms which can kill or retard the growth of other disease-causing microorganisms.
l Penicillin, discovered by Alexander Fleming, was the first antibiotic to be discovered.
l Discovery of penicillin: While working on Staphylococcus bacteria, Fleming observed the growth of mould around which the bacteria did not grow. It was found to be a chemical, penicillin, produced by Penicillium notatum.
l The function of penicillin as an antibiotic was established by Ernest Chain and Howard Florey.It was used to treat American soldiers wounded in World War II. Fleming, Chain and Florey were awarded Nobel prize in 1945 for their discovery.
l Diseases cured by antibiotics include plague, whooping cough (kali khansi), diphtheria (gal ghotu) and leprosy (kusht rog).
(iii) Organic acids and alcohol
l The following organic acids are produced by microbial metabolic actions:
S. No. | Organic acid | Microbe | Type of microbe |
(i) | Citric acid | Aspergillus niger | Fungi |
(ii) | Acetic acid (Vinegar) | Acetobacter aceti | Bacteria |
(iii) | Butyric acid | Clostridium butylicum | Bacteria |
(iv) | Lactic acid | Lactobacillus sps. | Bacteria |
l Ethanol is produced by yeast (Saccharomyces cerevisiae).
(iv) Enzymes
l Some important enzymes commercially produced are as follows:
S. No. | Enzyme | Uses |
(i) | Lipase | (a) Used in detergent formulations. (b) Helps in removing oily stains from laundry. |
(ii) | Pectinase and protease | Used for clarifying bottled juices. |
(iii) | Streptokinase (produced by Streptococcus and modified by genetic engineering) | Used as ‘clot-buster’ for removing clots from blood vessels of patients who have undergone myocardial infarction. |
(iv) | Invertase produced by yeast | To invert sugar for ice creams and confectioneries. |
(v) Bioactive molecules
S. No. | Molecule | Source organism | Use |
(i) | Cyclosporin A | Trichoderma polysporum (fungus) | Used as immunosuppressive agent in organ transplant patients. |
(ii) | Statin | Monascus purpureus (fungus) | Used as blood-cholesterol lowering agent. It competitively inhibits enzymes for cholesterol synthesis. |
4. Microbes in Sewage Treatment
n Sewage is the muni cipal waste water, containing large quantities of human excreta.
n Need for sewage treatment: Sewage contains large amounts of organic matter and pathogenic microbes. Before discharging into natural bodies, sewage is made less polluting.
n Sewage is treated in sewage treatment plants (STPs).
n Ganga Action Plan and Yamuna Action Plan have been initiated by Ministry of Environment and Forests, under which large number of STPs will be build to treat sewage before their discharge in rivers to reduce their pollution.
n Sewage treatment is carried out in two stages:
(i) Primary treatment or physical treatment
l It is the physical removal of large and small particles from sewage.
l First, the floating debris is removed by sequential filtration by passing through wire mesh screens.
l Then, the grit (soil and small pebbles) are removed by sedimentation in settling tanks. The sediment is called primary sludge and the supernatant is the effluent.
l The effluent is taken for secondary treatment.
(ii) Secondary treatment or biological treatment
l Primary effluent is passed into large aeration tanks with constant mechanical agitation and air supply.
l Useful aerobic microbes grow rapidly and form flocs.
l Flocs are masses of bacteria associated with fungal filaments to form mesh-like structures.
l The growing microbes consume organic matter and thus reduce the biochemical oxygen demand (BOD).
l When BOD of sewage has reduced, the effluent is passed into settling tank.
l Here, the bacterial flocs settle and the sediment is called activated sludge.
l A small part of the sludge is used as an inoculum in the aeration tank and the remaining part is passed into large tanks called anaerobic sludge digesters.
l In the digesters, heterotrophic microbes anaerobically digest bacteria and fungi in sludge producing mixture of gases such as methane, hydrogen sulphide (H2S) and CO2, which form the biogas.
l Effluent is now released into rivers and streams.
Biological Oxygen Demand (BOD)
n BOD refers to the amount of oxygen consumed if all the organic matter in one litre of water is oxidised by bacteria.
n BOD measures the amount of organic matter in water by measuring the rate of oxygen uptake by microbes, thus it is measure of organic matter present in water.
n Higher BOD indicates higher polluting potential.
5. Microbes in Production of Biogas
n Biogas is a mixture of inflammable gases (methane, CO2, etc) produced by microbial activity that can be used as fuel (mainly methane, CH4)
n Methanogens, particularly Methanobacterium, anaerobically breaks down cellulosic material to produce CO2 and H2 in
(i) Anaerobic sludge in sewage treatment plants.
(ii) Rumen (a part of stomach) of cattle, thus providing nutrition to cattle.
n Indian Agricultural Research Institute (IARI) and Khadi and Village Industries Commission (KVIC) developed the technology of biogas in India.
Mechanism of Biogas or Gobar Gas Production
n The raw material for biogas production is excreta (dung) of cattle called Gobar which is rich in these bacteria.
n The biogas plant has a concrete tank (10–15 feet deep) in which bio-wastes and slurry of dung is collected.
n The tank has a floating cover which rises on production of gas in the tank.
n Methanobacterium in the dung act on the bio-wastes to produce biogas.
n The gas produced is supplied to nearby houses by an outlet.
n Through another outlet, the spent slurry is removed to be used as fertiliser.
n Biogas is used as fuel for cooking and lighting.
6. Microbes as Biocontrol Agents
n Biocontrol is defined as controlling plant diseases and pests using biological methods.
n Earlier, chemicals like insecticides and pesticides were used for biocontrol.
n Disadvantages of chemical agents:
(i) Chemicals are toxic and harmful to human beings and animals.
(ii) Chemicals pollute the environment and plants.
(iii) Weedicides used to remove weeds also pollute the soil.
n Organic farmers use a holistic approach for following reasons:
(i) Keeping pests at manageable levels by a complex system of checks and balances, within the ecosystem, instead of their complete eradication.
(ii) Complete eradication of pests is undesirable, as without them the beneficial predatory and parasitic insects which depend on them as food or act as host will not be survive. This will disturb the balance of the ecosystem.
(iii) Biocontrol agents reduce dependency on toxic chemicals and fertilizers.
n Following are some of the approaches for biological farming:
(i) Familiarity with various life-forms inhabiting the field.
(ii) Gain knowledge about the life cycles, patterns of feeding and habitat of predators and pests.
Some Examples of Biocontrol
(a) Ladybirds and Dragonflies are used to get rid of aphids and mosquitoes respectively.
(b) The bacteria Bacillus thuringiensis (Bt) are used to control butterfly caterpillars.
l Dried spores of Bt are mixed with water and sprayed on plants such as brassicas and fruit trees.
l Insect larvae, after eating these are killed by the toxin released in their gut.
l B. thuringiensis toxin genes have been introduced into plants to provide resistance to pests. For example, Bt cotton.
(c) Trichoderma sps., free-living fungi, are present in root ecosystems where they act against several plant pathogens.
(d) Baculoviruses are pathogens that attack insects and other arthropods.
l Most of these biocontrol agents belong to the genus Nucleopolyhedrovirus. These are species-specific, narrow spectrum insecticides.
l They do not harm plants, mammals, birds, fish and other non-target insects.
l Baculoviruses are helpful in integrated pest management (IPM) programme, in which beneficial insects are conserved and there is no negative impact on plant mammals, birds, fish or nontarget insects.
7. Microbes as Biofertilisers
n Biofertilisers are the microorganisms which enrich the nutrient (nitrogen, phosphorus, etc.) quality of the soil.
n Bacteria, fungi and cyanobacteria are the three main sources of biofertilisers.
(i) Bacteria as biofertilisers
l Rhizobium is a symbiotic bacterium that lives in the root nodules of legumes and fixes atmospheric nitrogen into organic compounds.
l Azospirillum and Azotobacter are free-living bacteria which absorb free nitrogen from soil, air and convert it into salts of nitrogen and enrich soil nutrients.
(ii) Fungi as biofertilisers
l Fungi form symbiotic association with the roots of higher plants called mycorrhiza, e.g., Glomus.
l The fungal hyphae absorb phosphorus from soil and passes it to the plant.
l Mycorrhiza shows the following benefits to plant:
(a) resistance to root-borne pathogens.
(b) tolerance to salinity and drought.
(c) overall increase in plant growth and development.
(iii) Cyanobacteria as biofertilisers
l They fix atmospheric nitrogen and increase the organic matter of the soil through their photosynthetic activity, e.g., Nostoc, Anabaena, Oscillatoria, etc.
l Blue-green algae increase the soil fertility by adding organic matter to the soil.
l Cyanobacteria are important biofertilisers in paddy fields.
Advantages of biofertilisers
(a) Increase fertility of soil.
(b) Reduce dependency on chemical fertilizers.
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