Microbes-in Household Products, Industrial Products and in Sewage Treatment and Biogas
Microbes in Daily Life
• Microbes are the major components of the biological system on the earth.
• They are very minute organisms that can not be seen with the naked eyes but are viewed under the
microscope.
• Microbes are present everywhere such as in soil, water, air, inside our body and bodies of animals and plants.
• They are also present where no other life-form could exist such as deep inside the geysers (thermal vents)
where the temperature may be as high as 100°C, deep in the soil, under the layers of snow several metres
thick and in highly acidic environments.
• Microbes are diverse–protozoa, bacteria, fungi and microscopic plants.
• Viruses, viroids and also prions are not considered as living entities, even though, they are considered as
infectious agents.
• Microbes like bacteria and many fungi can be grown on nutritive media to form colonies, that can be seen
with the naked eyes. Such cultures are useful in studies on micro-organisms.
• Some microbes are harmful to mankind, causing several infectious diseases but some are important in many
ways for human welfare.
Microbes in household products.
1. Lactobacillus or Lactic Acid Bacteria (LAB)
• It converts milk into curd.
• It produces lactic acid that coagulates and partially digests the milk protein casein.
• A small amount of curd containing LAB converts fresh milk into curd.
• It also increases vitamin B12.
• In the stomach, it inhibits the growth of pathogens.
2. Bacterial Fermentation (Anaerobic Respiration)
• The dough which is formed by the fermentative activity of bacteria is used to make foods such as dosa, idli etc.
• The puffed-up appearance of dough is due to the production of CO2 gas.
• ‘Toddy’ is an alcoholic drink, made by fermenting flower sap from palms by bacteria.
• Microbes are used to ferment fish, soyabean and bamboo-shoots to make foods.
• Microbes are used to produce cheeses differing in flavour, taste and texture e.g., Large holes in ‘Swiss cheese’ are due to the production of a large amount of CO2 by Propionibacterium shermanii (a bacterium).
• ‘Roquefort cheese’ is ripened by growing a specific fungus (Penicillium roqueforti) on them that gives them a particular flavour.
3. Baker’s Yeast (Saccharomyces cerevisiae) :
• It is used to make bread by fermenting dough.
Microbes in Industrial Products
• The large scale production of beverages, antibiotics etc., on an industrial scale, requires growing microbes in
very large vessels called fermentors or bioreactors.
1. Fermented Beverages
• Saccharomyces cerevisiae (Brewer’s yeast) is used in the production of beverages by fermenting malted cereals
and fruit juices to produce ethanol.
• Wine and Beer are produced without distillation.
• Whisky, Brandy and Rum are produced by distillation of the fermented broth.
2. Antibiotics
• The chemical substances produced by some microbes that can kill or inhibit the growth of other disease-
causing microbes.
• They are used to treat plague, whooping cough, diphtheria, leprosy and many other infectious diseases.
Penicillin
• First antibiotic discovered by Alexander Fleming in 1929.
• He observedthat a mould (Penicillium notatum) growing in unwashed culture plates around which Staphylococci could not grow.
• He extracted penicillin from it.
• Ernest Chain and Howard Florey established its full potential as an effective antibiotic.
• Fleming, Chain and Florey were awarded Nobel Prize (1945).
3. Chemicals, enzymes and other bioactive molecules
(a) Organic Acids : e.g.,
• Aspergillus niger (a fungus) : Citric acid
• Acetobacter aceti (a bacterium) : Acetic acid
• Clostridium butylicum (a bacterium) : Butyric acid
• Lactobacillus (a bacterium) : Lactic acid
(b) Alcohol :
• Yeast (Saccharomyces cerevisiae) is used to produce ethanol.
(c) Enzymes :
• Lipases : Used in detergent formulations. Help to remove oily stains from the laundry.
• Pectinases and Proteases : To clarify bottled juices.
• Streptokinase : Produced by Streptococcus. Used as a ‘clot buster’ to remove clots from the blood vessels of
patients who have a myocardial infarction.
(d) Cyclosporin A :
• It is produced by Trichoderma polysporum (fungus).
• It is used as an immunosuppressive agent in organ-transplant patients.
(e) Statins :
• It is produced by Monascus purpureus (a yeast).
• It is used as a blood-cholesterol lowering agent.
• It inhibits the enzymes responsible for the synthesis of cholesterol.
Microbes in Sewage Treatment
• Sewage (municipal waste-water) contains a large amount of human excreta, organic matter and microbes.
• Sewage is treated in Sewage Treatment Plants (STPs) to make it less polluting. It includes stages namely :
Primary treatment and secondary treatment.
(a) Primary Treatment
• It is a physical treatment.
• It is the physical removal of large and small particles from sewage. It includes :
1. Removal of floating debris by sequential filtration.
2. Removal of the grit (soil and pebbles) by sedimentation.
3. All solids that settle form the primary sludge and the supernatant forms the primary effluent.
4. The effluent is taken for secondary treatments.
(b) Secondary treatment (Biological treatment)
• Primary effluent is passed into large aeration tanks and constantly agitated.
• This allows vigorous growth of useful aerobic microbes into flocs (masses of bacteria associated with fungal
filaments to form mesh-like structures).
• These microbes consume the major part of the organic matter in the effluent.
• This reduces the BOD (Biochemical Oxygen Demand) of the effluent.
• The effluent is then passed into a settling tank where the bacterial ‘flocs’ are allowed to
sediment. This sediment is called ‘activated sludge’.
• A small part of the activated sludge is pumped back into the aeration tank to serve as the
inoculum.
• The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters.
• Here, some anaerobic bacteria digest the bacteria and fungi in the sludge by producing gases like CH4
, H2S
and CO2
. These gases form the biogas.
• The effluent from the secondary treatment plant is released into natural water bodies like rivers and streams.
• The Ministry of Environment and Forests has initiated the Ganga Action Plan and Yamuna Action Plan to
save rivers from water pollution.
Biological Oxygen Demand (BOD)
• BOD represents the amount of dissolved oxygen required for the complete oxidation of all the organic matter
present in one litre of water by bacteria at 20°C.
• BOD measures the amount of organic matter present in water by measuring the rate of O2 taken up by
microbes.
• Higher BOD indicates that the water is highly polluted by organic matter. A lower value of BOD means the
water is less polluted or normal.
Microbes in Production of Biogas
• Biogas is a mixture of inflammable gases (mainly CH4
) produced by the microbial activity.
• Biogas is used for cooking and lighting.
• Methanogens grow anaerobically on cellulosic material and produce CH4 gas e.g., Methanobacterium.
• Methanobacterium is found in the anaerobic sludge and rumen of cattle (for cellulose digestion).
• The dung of cattle (gobar) is rich in these bacteria.
• Dung can be used for the generation of biogas (Gobar gas).
A Biogas plant consists of
(a) A concrete tank (b) Floating cover (c) An outlet
• The concrete tank (10-15 feet deep) collects bio-wastes and slurry of dung.
• A floating cover is placed over the slurry, which keeps on rising as the biogas is produced.
• An outlet which is connected to a pipe to supply biogas.
• An outlet to remove spent slurry (used as fertilizer).
Indian Agricultural Research Institute (IARI), Khadi and Village Industries Commission (KVIC) developed the technology of biogas production in India.
Microbes and their uses
Biocontrol
• It is the use of biological methods for controlling plant diseases and pests.
Chemical Pesticides and Insecticides
• These are toxic and harmful to all organisms including human beings and cause pollution.
• Chemical pesticides kills both useful and harmful life forms.
• Weedicides used to eliminate weeds cause soil pollution.
Microbial biocontrol agents
(a) Bacillus thuringiensis (Bt) :
• This is to control the butterfly caterpillar. These are available in sachets as dried spores which are mixed with
water and sprayed on vulnerable plants such as Brassica and fruit trees, where these are eaten by the insect larvae. In the gut of the larvae, the toxin is released and the larvae get killed. Scientists have introduced B. thuringiensis toxin genes into plants e.g., Bt cotton.
(b) Trichoderma sp. (Fungus) :
• These are free livings species that are seen in the root ecosystems. They are effective biocontrol agents of
several plant pathogens.
(c) Baculoviruses (Especially genus Nucleopolyhedrovirus) :
• It attacks insects and other arthropods. These are suitable for species-specific, narrow spectrum insecticidal
applications. This is desirable in the IPM program to conserve beneficial insects.
Microbes as Biofertilizers
• BioMicrobesfertilizers are the micro-organisms that enrich the nutrient quality of the soil. e.g., Bacteria, fungi, cyanobacteria etc.
Rhizobium
• It is a symbiotic bacteria found in root nodules of leguminous plants that fixes atmospheric N2
.
• Free-living bacteria in the soil such as Azospirillum and Azotobacter enrich the nitrogen content of the soil.
Mycorrhiza
• It is a symbiotic association of fungi (e.g., the genus of Glomus) with the roots of higher plants.
• The fungus gets food for the plant.
• The fungal symbiont help to absorb phosphorous from soil and passes it to the plant, give resistance to root-
borne pathogens, tolerance to salinity and drought and also gives an overall increase in plant growth and development.
Cyanobacteria (Bluegreen algae) :
• They are autotrophic microbes that fixes atmospheric nitrogen e.g., Anabaena, Nostoc, Oscillatoria etc.
• In paddy fields, Cyanobacteria serve as an important biofertilizers.
• It also adds organic matter to the soil and increases its fertility.
Know the Terms
BOD : Biochemical oxygen demand
KVIC : Khadi and Village Industries Commission
GAP : Ganga Action Plan
LAB : Lactic acid Bacteria
YAP : Yamuna Action Plan
STPs : Sewage Treatment Plants
IPM : Integrated Pest Management
Primary sewage treatment : It is a mechanical process involving the removal of coarse solid materials.
Secondary sewage treatment : It is a biological process involving the action of microbes.
Tertiary sewage treatment : The treatment removes remaining inorganic compounds and substances, such as the nitrogen and phosphorous.
Flocs : They are masses of bacteria associated with fungal filaments to form mesh-like structures include, tertiary
sewage treatment.
Biological Oxygen Demand (BOD) : It is the method of determining the amount of oxygen required by
microorganisms to decompose the waste present in the water supply.
Biocontrol : It refers to the use of biological methods for controlling plant diseases and pests.
Biopesticides : The biological agents whichareusedto control weeds, insects andpathogenare calledbiopesticides.
Methanogens : Microorganisms that produce methane along with CO2 and H2 under anaerobic conditions are
called methanogens.
Biofertilisers : These are organisms that enrich the nutrient content of the soil.
Symbiotic : The relationship involving interaction between two different organisms living in close physical
association.
