Microbes in human welfare,chapter10, is one of important chapter for many examination like neet,board,afmc.etc,we are providing pdf,video,notes…etc about this chapter


Micro-organisms such as Lactobacillus and others commonly called lactic acid bacteria (LAB) grow in milk and convert it to curd. During growth, the LAB produce acids that coagulate and partially digest the milk proteins. A small amount of curd added to the fresh milk as inoculum or starter contain millions of LAB, which at suitable temperatures multiply, thus converting milk to curd, which also improves its nutritional quality by increasing vitamin B12. In our stomach too, the LAB play very beneficial role in checking diseasecausing microbes.
‘Toddy’, a traditional drink of some parts of southern India is made by fermenting sap from palms. Microbes are also used to ferment fish, soyabean and bambooshoots to make foods. Cheese, is one of the oldest food items in which microbes were used. Different varieties of cheese are known by their characteristic texture, flavour and taste, the specificity coming from the microbes used. For example, 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’ are ripened by growing a specific fungi on them, which gives them a particular flavour.


Even in industry, microbes are used to synthesise a number of products valuable to human beings. Beverages and antibiotics are some examples. Production on an industrial scale, requires growing microbes in very large vessels called fermentors

10.2.1 Fermented Beverages

Microbes especially yeasts have been used from time immemorial for the production of beverages like wine, beer, whisky, brandy or rum. For this
purpose the same yeast Saccharomyces cerevisiae used for bread-making and commonly called brewer’s yeast, is used for fermenting malted cereals and fruit juices, to produce ethanol. Depending on the type of the raw material used for fermentation and the type of processing (with or without distillation) different types of alcoholic drinks are obtained. Wine and beer are produced without distillation whereas whisky, brandy and rum are produced by distillation of the fermented broth.

10.2.2 Antibiotics

Anti is a Greek word that means ‘against’, and bio means ‘life’, together they mean ‘against life’ (in the context of disease causing organisms); whereas with reference to human beings, they are ‘pro life’ and not against. Antibiotics are chemical substances, which are produced by some microbes and can kill or retard the growth of other (disease-causing) microbes. Alexander Fleming while working on Staphylococci bacteria, once observed a mould growing in one of his unwashed culture 182 plates around which Staphylococci could not grow. He found out that it was due to a chemical produced by the mould and he named it Penicillin after the mould Penicillium notatum. However, its full potential as an
effective antibiotic was established much later by Ernest Chain and
Howard Florey. This antibiotic was extensively used to treat American
soldiers wounded in World War II. Fleming, Chain and Florey were awarded the Nobel Prize in 1945, for this discovery.

Antibiotics have greatly improved our capacity to treat deadly diseases such as plague, whooping cough (kali khansi), diphtheria (gal ghotu) and leprosy (kusht rog), which used to kill millions all over the globe.
10.2.3 Chemicals, Enzymes and other Bioactive Molecules
Microbes are also used for commercial and industrial production of certain chemicals like organic acids, alcohols and enzymes. Examples of
acid producers are Aspergillus niger (a fungus) of citric acid, Acetobacter
aceti (a bacterium) of acetic acid; Clostridium butylicum (a bacterium) of butyric acid and Lactobacillus (a bacterium) of lactic acid.
Yeast (Saccharomyces cerevisiae) is used for commercial production
of ethanol. Microbes are also used for production of enzymes. Lipases are used in detergent formulations and are helpful in removing oily stains
from the laundry. bottled fruit juices bought from the market are clearer as compared to those made at home. This is because the bottled juices are clarified by the use of pectinases and proteases. Streptokinase produced by the bacterium Streptococcus and modified by genetic engineering is used as a ‘clot buster’ for removing clots from the blood vessels of patients who have undergone myocardial infarction leading to heart attack.
Another bioactive molecule, cyclosporin A, that is used as an immunosuppressive agent in organ-transplant patients, is produced by
the fungus Trichoderma polysporum. Statins produced by the yeast
Monascus purpureus have been commercialised as blood-cholesterol lowering agents. It acts by competitively inhibiting the enzyme responsible
for synthesis of cholesterol.


A major component of this waste water is human excreta.
This municipal waste-water is also called sewage. It contains large amounts of organic matter and microbes. Many of which are pathogenic. Before disposal, hence, sewage is treated in sewage treatment plants (STPs)
to make it less polluting. Treatment of waste water is done by the heterotrophic microbes naturally present in the sewage. This treatment is carried out in two stages:
Primary treatment : These treatment steps basically involve physical removal of particles – large and small – from the sewage through filtration and sedimentation. These are removed in stages; initially, floating debris
is removed by sequential filtration. Then the grit (soil and small pebbles) are removed by sedimentation. All solids that settle form the
primary sludge, and the supernatant forms
Secondary treatment, the effluent. The effluent from the primary
settling tank is taken for secondary treatment.

Secondary treatment or Biological treatment : The primary
effluent is passed into large aeration tanks where it is constantly agitated mechanically and air is pumped into it. This allows vigorous growth of useful aerobic microbes into flocs (masses of bacteria associated with fungal filaments to form mesh like structures). While growing, these microbes consume the major part of the organic matter in the effluent. This significantly reduces the BOD (biochemical oxygen demand) of the effluent. BOD refers to the amount of the oxygen that would be consumed if all the organic matter in one liter of water were oxidised by bacteria. The sewage
water is treated till the BOD is reduced. The BOD test measures the
rate of uptake of oxygen by micro-organisms in a sample of water
and thus, indirectly, BOD is a measure of the organic matter present
in the water. The greater the BOD of waste water, more is its polluting
potential. Once the BOD of sewage or waste water is reduced significantly, 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, other kinds
of bacteria, which grow anaerobically, digest the bacteria and the fungi
in the sludge. During this digestion, bacteria produce a mixture of gases
such as methane, hydrogen sulphide and carbon dioxide. These gases
form biogas and can be used as source of energy as it is inflammable.
The effluent from the secondary treatment plant is generally released
into natural water bodies like rivers and streams.

The Ministry of Environment and Forests has initiated Ganga Action
Plan and Yamuna Action Plan to save these major rivers of our country
from pollution. Under these plans, it is proposed to build a large number
of sewage treatment plants so that only treated sewage may be discharged
in the rivers. A visit to a sewage treatment plant situated in any place
near you would be a very interesting and educating experience.


Biogas is a mixture of gases (containing predominantly methane) produced
by the microbial activity and which may be used as fuel. The type of the gas produced depends upon the microbes and the organic substrates they utilise. In the examples cited in relation to fermentation of dough, cheese making and production of beverages, the main gas produced was CO2.. However, certain bacteria, which grow anaerobically on cellulosic material, produce large amount of methane along with CO2 and H2. These bacteria are collectively called methanogens, and one such common bacterium is Methanobacterium. These bacteria are commonly found in the anaerobic sludge during sewage treatment. These bacteria are also present in the rumen (a part of stomach) of cattle. A lot of cellulosic material present in the food of cattle is also present in the rumen. In rumen, these bacteria help in the breakdown of cellulose and play an important role in the nutrition of cattle. Do you think we, human beings, are able to digest the celluose present in our foods? Thus, the excreta (dung) of cattle, commonly called
gobar, is rich in these bacteria. Dung can be used for generation of biogas, commonly called gobar gas.The biogas plant consists of a concrete tank (10-15 feet deep) in which bio-wastes are collected and a slurry of dung is fed. A floating cover is placed over the slurry, which keeps on rising as the gas is produced in the tank due to the microbial activity. The biogas plant has an outlet, which is connected to a pipe to supply biogas to nearby houses. The
spent slurry is removed through another outlet and may be used
as fertiliser. Cattle dung is available in large quantities in
rural areas where cattle are used for a variety of purposes. So
biogas plants are more often built in rural areas. The biogas
thus produced is used for cooking and lighting. A typical biogas plant technology of biogas production was developed in India mainly
due to the efforts of Indian Agricultural Research Institute (IARI) and
Khadi and Village Industries Commission (KVIC). If your school is situated
in a village or near a village, it would be very interesting to enquire if there
are any biogas plants nearby. Visit the biogas plant and learn more about
it from the people who are actually managing it.


Biocontrol refers to the use of biological methods for controlling plant
diseases and pests. In modern society, these problems have been tackled increasingly by the use of chemicals – by use of insecticides and pesticides.
These chemicals are toxic and extremely harmful, to human beings and
animals alike, and have been polluting our environment (soil, ground
water), fruits, vegetables and crop plants. Our soil is also polluted through
our use of weedicides to remove weeds.

Biological control of pests and diseases: In agriculture, there is a
method of controlling pests that relies on natural predation rather than
introduced chemicals. A key belief of the organic farmer is that biodiversity
186 furthers health. The more variety a landscape has, the more sustainable
it is. The organic farmer, therefore, works to create a system where the
insects that are sometimes called pests are not eradicated, but instead
are kept at manageable levels by a complex system of checks and balances
within a living and vibrant ecosystem. Contrary to the ‘conventional’
farming practices which often use chemical methods to kill both useful
and harmful life forms indiscriminately, this is a holistic approach that seeks to develop an understanding of the webs of interaction between the myriad of organisms that constitute the field fauna and flora. The organic farmer holds the view that the eradication of the creatures that are often described as pests is not only possible, but also undesirable, for without
them the beneficial predatory and parasitic insects which depend upon
them as food or hosts would not be able to survive. Thus, the use of biocontrol measures will greatly reduce our dependence on toxic chemicals
and pesticides. An important part of the biological farming approach is
to become familiar with the various life forms that inhabit the field, predators as well as pests, and also their life cycles, patterns of feeding
and the habitats that they prefer. This will help develop appropriate means
of biocontrol.

The very familiar beetle with red and black markings – the Ladybird,
and Dragonflies are useful to get rid of aphids and mosquitoes, respectively. An example of microbial biocontrol agents that can be introduced in order to control butterfly caterpillars is the bacteria Bacillus thuringiensis (often written as Bt). These are available in sachets as dried spores which are mixed with water and sprayed onto vulnerable plants such as brassicas 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. The bacterial disease will kill the caterpillars, but leave other insects unharmed. Because of the development of methods of genetic engineering in the last decade or so, the scientists have introduced B. thuringiensis toxin genes into plants. Such plants are resistant to attack by insect pests.
Bt-cotton is one such example, which is being cultivated in some states
of our country.

A biological control being developed for use in the treatment of plant disease is the fungus Trichoderma. Trichoderma species are free-living
fungi that are very common in the root ecosystems. They are effective biocontrol agents of several plant pathogens.
Baculoviruses are pathogens that attack insects and other arthropods.
The majority of baculoviruses used as biological control agents are in the genus Nucleopolyhedrovirus. These viruses are excellent candidates for species-specific, narrow spectrum insecticidal applications. They have been shown to have no negative impacts on plants, mammals, birds, fish
or even on non-target insects. This is especially desirable when beneficial insects are being conserved to aid in an overall integrated pest management (IPM) programme, or when an ecologically sensitive area is being treated.


With our present day life styles environmental pollution is a major cause
of concern. The use of the chemical fertilisers to meet the ever-increasing demand of agricultural produce has contributed significantly to this pollution. Biofertilisers are organisms that enrich the nutrient quality of the soil.
The main sources of biofertilisers are bacteria, fungi and cyanobacteria. These bacteria fix atmospheric nitrogen into organic forms, which is used by the plant as nutrient. Other bacteria can fix atmospheric nitrogen while free-living in the soil (examples Azospirillum and Azotobacter), thus enriching the nitrogen content of the soil.
Fungi are also known to form symbiotic associations with plants
(mycorrhiza). Many members of the genus Glomus form mycorrhiza.
The fungal symbiont in these associations absorbs phosphorus from
soil and passes it to the plant. Plants having such associations show
other benefits also, such as resistance to root-borne pathogens, tolerance
to salinity and drought, and an overall increase in plant growth and development.
Cyanobacteria are autotrophic microbes widely distributed in aquatic
and terrestrial environments many of which can fix atmospheric nitrogen,
e.g. Anabaena, Nostoc, Oscillatoria, etc. In paddy fields, cyanobacteria
serve as an important biofertiliser. Blue green algae also add organic matter to the soil and increase its fertility. Currently, in our country, a number of biofertilisers are available commercially in the market and farmers use these regularly in their fields to replenish soil nutrients and to reduce dependence on chemical fertilisers.


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