Microbes are tiny living things that are found all around us and are too small to be seen by the naked eye. They live in water, soil, and in the air. The human body is home to millions of these microbes too, also called microorganisms. Some microbes make us sick, others are important for our health.

1. : Microbes in Human Welfare:
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Rahul Pals | BIOLOGY NOTES
Microbes in Human Welfare:
Microbes are the major components of biological systems on this earth, which mainly present
everywhere like soil, water, air, inside our bodies, other animals & plants.
❑ Microbes are diverse- protozoa, bacteria, fungi and microscopic plants viruses,
viroids and prions are proteinaceous infectious agents.
Microbes like bacteria & many fungi can be grown on nutritive media to form colonies that can
be seen with the naked eyes.
Microbes in Household Products: -
There are several examples in our daily life in which the microbes are involved-
01. Production of curd from milk:
Microorganism like lactobacillus & other called as Lactic acid Bacteria (LAB), added to milk
produce acids. These acids coagulate & partially digest the milk proteins.
- A starter is added to the milk in form of small amount of curd, it possesses millions of
LAB in it which multiply at favorable temperature & convert milk in curd.
02. The dough is used for making foods such as dossa and idli is fermented by bacteria. The
puffed-up appearance of dough is due to the production of CO2 gas. The dough, which is
used for making bread, is fermented by using baker’s yeast (Saccharomyces
Cerevisiae).
03. “Toddy”, a traditional drink of some parts of southern India is made by fermenting sap
from palms.
04. Cheese, one of the oldest foods in which microbes were used. The large holes in ‘Swiss
cheese’ are due to production of a large amount of CO2 by a bacterium named
Propionibacterium sharmanii.
The ‘Roquefort cheese’ is ripened by growing a specific fungus on them for a particular
flavor.

2. : Microbes in Human Welfare:
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Rahul Pals | BIOLOGY NOTES
Microbes in Industrial Production:
“Production on an industrial scale requires growing microbes in very large vessels called
Fermentors.”
- There are valuable products like beverages, antibiotics are produced in industrial on
a large scale.
01). Fermented Beverages: - Various beverages prepared by the action of microbes specially
yeast. Example: Wine, beer, rum, brandy & whisky etc.
Wine and beer are prepared without distillation, rum, brandy & whisky are produced with
distillation.
- Brewer’s yeast (Saccharomyces Cerevisiae)- Same that used for making bread
ferment malted cereals & fruits juices to produced ethanol.
02). Antibiotics: - The chemicals produced by microbes & kill the growth of other pathogens.
Penicillin: discovered by ‘Alexander Fleming’, it was the 1st
antibiotics to be discovered.
❑. Discovery of Penicillin: -
Alexander Fleming observed that Staphylococci Bacteria was unable to grow around the
should that has grown in one of his unwashed culture plates. He later on found that it was
because of chemical produced by the fungus. He gave the term penicillin to the chemical after
the mould Penicillin Notatum.
- In World war II penicillin was extensively used to treat the wounded American
soldiers.
- In 1945, Fleming, Chain & Florey was awarded Nobel Prize for their contribution.
Microbes also used for the production of enzymes: -
01). Lipase: commercially used in detergents laundry to remove oily stains from the clothes.
02). Pectinase & Proteases: These enzymes are utilized for making the bottles fruits juices
clearer in comparison to homemade fruit juices.
Microbes Product Use of Product
Aspergillus Niger (Fungus) Citric Acid Industrial use
Acetobacter aceti (bacterium) Acetic acid Industrial use
Clostridium butylicum (bacterium) Butyric acid Industrial use
Lactobacillus (bacterium) Lactic acid Industrial use
Streptococcus (bacterium) Streptokinase Used as clot buster for removal of blood
clots.
Saccharomyces cerevisiae (yeast fungus) alcohol Alcoholic beverages

3. : Microbes in Human Welfare:
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Rahul Pals | BIOLOGY NOTES
Microbes in Sewage Treatment:
Sewage: “The municipal waste water that is generated every day in cities & towns is termed
Sewage.”
This treatment is carried out in two stages:
- Primary treatment
- Secondary treatment or biological treatment.
Sewage Treatment Plants (STPs)- Treatment of waste water or sewage is done in sewage
treatment plants before their disposal into the water resources lie rivers.
STPs make the sewage less polluting.
Heterotrophic microbes that are already present in the sewage are utilize for the treatment.
A). Primary Treatment: -
It involves the physical removal of the small & large sized particles from the sewage.
Processes involved:
- Step 01: Floating debris is removed by sequential filtration.
- Step 02: grit (soil & small pebbles) is removed by sedimentation in primary settling
tank. All solids that settles are collectively termed as Primary sludge while the
supernatant is termed as effluent.
B). Secondary Treatment: -
It involves the physical removal of the small & large sized particles from the sewage,
Mechanism:
Step 01. Primary effluent is passed into large serration tanks in which constant agitation &
pumping of air is there  growth of microorganism is promoting  Flocs are formed  these
microbes take oxygen during their growth & decompose or consume major organic part of the
effluent.
Step 02. Once the BOD is significantly decreased, effluent is transferred to a large settling tank
 bacterial flocs settle here, which are termed as Activated sludge.
Step 03. A small part of the activated sludge is transferred back into the aeration tank to act as
inoculum.
Step 04. Major part of the activated sludge is pumped into the anaerobic sludge digester which
the large tanks having anerobic bacteria  These anaerobic bacteria digest the bacteria & fungi

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Rahul Pals | BIOLOGY NOTES
present in the sludge  In this process the digestion, various gases are produced in the form of a
mixture – Methane, hydrogen sulphide & Carbon dioxide, these gases are collectively termed
as Biogas.
BOD* (Biological Oxygen Demand): -
It is the amount of oxygen that would be consumed by bacteria if all organic matter in 1 liter of
water is oxidized. BOD is measure of organic pollution in water.
- More the value of BOD, more is the polluting potential.
- During secondary treatment, sewage is treatment until the BOD is significantly
reduced.
- Microbial treatment of sewage is better than anu man made technology for the
treatment of sewage. For more than 100 years, microbes are being used to treat
sewage.
Ganga action Plan & Yamuna Action Plant:
These plans were initiated by The Ministry of Environmental & Forests to protect the major
rivers of our country from pollution. Their aim is to build a large number of sewage treatment
plants to treat the sewage before their disposal into the rivers.

5. : Microbes in Human Welfare:
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Rahul Pals | BIOLOGY NOTES
Microbes in Production of Biogas:
Various microbes produce different types of gaseous end-products during their growth &
metabolism.
. Example 01. CO2 is produced during fermentation of dough, production of beverages &
cheese making.
. Example 02. Methane is produced along with CO2 & H2 when methanogens (bacteria) grow
om cellulosic material.
Methanogens: - “A group of anaerobically bacteria which grow in cellulosic
material & produce CH4 on large scale along with CO2 & H2.”
Example: Methanobacterium
Methanogens are commonly found in-
01. Anerobic sludge digester tanks during sewage treatment.
02. Rumen (Part of stomach) of cattle in which these digest cellulose & help in
nutrition. This is the reason why the dung of the cattle is rich in bacteria.
As the dung of cattle(gobar) is rich in bacteria (methanogens). It’s used for production of
biogas, also known as Gobar Gas.
Biogas Plant:
These are usually built rural areas as the drug is available in large quantities.
This technology for biogas production was developed by Indian Agriculture Research
Institute (IARI) & Khadi & Village Industries Commission (KVIC).
Step 01. Biowastes & slurry of dung is added in a concrete tank (digester) which is 10-15 ft
deep.
Step 02. A floating cover (gas holder) is placed over the slurry. This cover will rise gradually as
the biogas starts producing due to microbial activity. An outlet is also given to which a pipe is
attached so that the biogas can be supplied to the nearby houses. This biogas is used as fuel for
cooking lighting.
Step 03. Spent or used slurry is removed by another outlet. This is being used as fertilizer for
crops.