Microbes play an important role in many human activities and products. They are used to produce foods through fermentation like yogurt, cheese and bread. They also produce industrial products like antibiotics, organic acids, enzymes and bioactive molecules. Microbes are essential in sewage treatment where they break down organic waste. They generate biogas from waste and help control pests biologically. As biofertilizers, microbes fix nitrogen and enrich soil nutrients through symbiotic relationships with plants.

1. Microbes in Human Welfare
By
Sujoy Tontubay

2. • Microbes or microorganisms form a big component of the biological systems of
the world. They are ubiquitous, present everywhere – within the soil, around us,
in water, the air we breathe, and both in and on our bodies. Animals and plants
also contain microbes or microorganisms. They are so tiny, microscopic in nature,
varying in shape and size. They can only be seen through the microscope. The
different types of microbes are:
• Algae
• Bacteria
• Fungi
• Protozoa
• Virus

3. Microbes in Human Welfare
• There are several useful microorganisms that are beneficial to humans in various ways apart from harmful
and infectious disease-causing pathogens. Some of the foremost important contributions of microbes to
human welfare are discussed below.
• In Household Products
• Fermentation of milk to prepare yoghurt.
• Milk cuddling to prepare curd, cheese, and paneer.
• Fermentation of dough, which is used for making-idli, and dosa.
• The dough that is used to prepare bread is fermented using Saccharomyces cerevisiae which is also known
as baker's yeast.
• ‘Toddy ‘ a traditional south Indian drink is made by fermenting sap from palms.
• Fish, soybean and bamboo shoots are fermented with the help of microbes to produce food.
• A type of cheese - Swiss cheese has huge holes in its texture. These holes are produced by a large amount of
CO2. This CO2 is produced during the fermentation process because of the bacterium used -
Propionibacterium shamanic.
• Another type of cheese called the Roquefort cheese is ripened by growing specific fungi on them. This gives
the cheese a particular flavour.

4. • In Industrial Products
• Production of beverages like wine, beer, whiskey, brandy or rum.
• Production of antibiotics like Penicillin and other chemical substances to kill or
retard the expansion of disease-causing microbes.
• Few Chemicals, Enzymes and other Bioactive Molecules also are produced by these microbes
for various human uses.

5. Fermented Beverages
• To produce microbes on a large scale for industrial purposes a vessel
named fermenter is used.
• The brewer’s yeast (Saccharomyces cerevisiae) is used to produce
ethanol. Here the yeast ferments malted cereals and fruit juices.
• The alcohol produced using distillation is wine, whereas the ones that
are produced without distillation are whisky, brandy and rum.

6. Antibiotics
• Antibiotic means “against life” in Greek. These are substances that
can kill or destroy the growth of other microbes.
• Penicillin was the first antibiotic discovered from the Staphylococci
bacteria by Alexander Fleming.
• Penicillin was named after the molds Penicillium notatum. It was used
to treat soldiers in the USA during WW2.
• Antibiotics today have been developed to treat many deadly diseases
like whooping cough, leprosy, diphtheria, etc.

7. Name of the antibiotic Source Diseases used for
Bacitracin Bacillus subtilis Syphilis, Lymphonema or
Reticulosis
Streptomycin Streptomyces griseus Meningitis, Pneumonia,
Tuberculosis and Local Infection
Chloromycetin Streptomyces venezuelae Typhoid
Erythromycin Streptomyces erythreus Typhoid, Whooping cough and
Diphtheria
Gentamicin Micromonospora purpurea Effective against Gram (+)
bacteria
Tetracycline Streptomyces aureofaciens Acne, urinary and intestinal
tract infections, conjunctivitis

8. Chemicals, Enzymes and Other Bioactive Molecules
• A fungus named Aspergillus niger produces citric acid.
• A bacterium named Acetobacter aceti produces acetic acid.
• Another bacterium named Clostridium bretylium produces butyric acid and a
bacterium named Lactobacillus produces lactic acid.
• The oily laundry stains are removed using the lipases which are present in
the detergent formulations.
• The bottled juices in shops are clarified using pectinases and proteases.
• Streptococcus which produces the streptokinase is used as a clot-buster in
medical treatments.
• Trichoderma polysporum produces a bioactive molecule named cyclosporin
which helps as an immunosuppressive in organ transplant surgery.
• A yeast named Monascus purpureus produces statins that help lower blood
cholesterol levels.

9. • Citric acid- Aspergillus niger
• Acetic acid- Acetobacter aceti
• Lactic acid- Lactobacillus
• Butyric acid- Clostridium butylicum
• Ethanol- Saccharomyces cerevisiae
• Enzymes are also produced by microorganisms and are used commercially for various purposes.
E.g. Streptococcus produces an enzyme called streptokinase, which is genetically modified and
used as a clot-buster for removing clots from the blood vessels.
• Lipases- used in detergents and form removal of oily stains
• Proteases and pectinases- used to clarify bottled juices
• Some bioactive molecules are prepared and are used for various purposes.
• Cyclosporin A- produced by Trichoderma polysporum (fungus). It is a suppressor of the immune
system, used in organ transplant patients
• Statins- produced by Monascus purpureus (yeast). It lowers the blood cholesterol level by
inhibiting cholesterol synthesis
Some of the important organic acids manufactured with the help of microbes are:

10. • In Sewage Treatment
• Sewage is treated in sewage treatment plans (STPs) before disposing of it so as to make it less
polluting which is naturally carried out by heterotrophic microbes present in the sewage. The
treatment is administered in two stages – primary treatment, secondary treatment or biological
treatment.
• Primary treatment
• During primary treatment, physical particles are removed from the sewage using the filtration
and sedimentation method.
• Initially, the floating debris is removed by filtration.
• After filtration, the soil and rocks in the debris are removed by the process of sedimentation.
• Solids from the primary sludge and the supernatant from the effluent.

11. Secondary Treatment
• It is also known as biological treatment.
• The effluent from primary treatment is taken forward for the secondary treatment.
• The large aeration tanks here perform the mechanical work and pump air into the tank so as to agitate the
effluents.
• This process accelerates the growth of large numbers of aerobic bacteria eventually leading to flocs.
• Flocs are the mesh-like structures formed during the treatment of sewage.
• These processes minimize the demand for biochemical oxygen of the effluent significantly. BOD is the
amount of oxygen that might be consumed if all the organic matter in one litre of water were oxidized by the
bacteria. The sewage water is treated to reduce the effect of BOD as the BOD gauges the rate of uptake of
oxygen by microbes in a water sample. Therefore, BOD may be a measure of the organic matter present in
water. The more the demand for biochemical oxygen, the more is its polluting potential.
• The significant decrease in the BOD forces the effluents to pass and settle down in the settling tanks, where
they are allowed to sediment.
• This active sludge is then pumped back to aeration tanks and then to larger tanks for the process of
anaerobic sludge digestion.
• Anaerobically here the other bacteria and fungus digest the sludge.

12. In Biogas Production
• Biogas is used as a fuel and is produced by microbial activity. It is a mixture of
gasses containing high concentrations of methane.
• Methanobacterium, commonly found in anaerobic sludge, is used to facilitate
sewage treatment.
• They are also found in the rumen of ruminants.
• Thus they help in the process of digestion of cellulose and play a vital role in the
nutrition of the cattle.
• The excreta of cattle, also known as Gobar is rich in bacteria and therefore is used
for the generation of biogas commonly termed as fertilizer.

13. Biocontrol of pest and diseases
• Chemical pesticides and insecticides kill both harmful and useful organisms. By
understanding natural predation and interacting webs, an appropriate method of
biocontrol can be developed.
• Dragonflies and ladybugs help in controlling mosquitoes and aphids.
• Bacillus thuringiensis is used to control caterpillars and insect larvae. Some plants
have been genetically modified and the gene coding for the toxin has been
introduced in the plant genome. E.g. Bt-cotton is resistant to pests.
• Trichoderma (a fungus) is used to biocontrol various plant pathogens. The fungus
is commonly present in the roots.
• Baculoviruses of the genus Nucleopolyhedrovirus are excellent biocontrol agents.
They attack arthropods but are not harmful to plants and other animals such as
birds, fish and mammals.

14. Biofertilizers
• Excessive use of chemical fertilizers is linked to pollution and harmful effects. Use of
microorganisms as biofertilizers is highly recommended.
• Fungi, bacteria and cyanobacteria are the main sources of biofertilizers.
• Rhizobium is present in the root nodules of leguminous plants. It fixes atmospheric
nitrogen. Growing leguminous plants alternatively helps in increasing the nitrogen
content of the soil.
• Azotobacter and Azospirillum are free-living nitrogen-fixing bacteria present in the soil.
• Fungal association in mycorrhiza also enriches the nutrient content of the soil. Fungi of
the genus Glomus absorbs phosphorus for the plant.
• These symbiotic associations not only benefit by enriching the nutrient content but also
provide disease resistance and tolerance to drought and salinity.
• Most of the cyanobacteria can fix atmospheric nitrogen, e.g. Nostoc, Anabaena,
Oscillatoria, etc. Cyanobacteria are extensively used in paddy fields as a biofertilizer.
Blue-green algae are autotrophic and present everywhere in aquatic and terrestrial
habitats. They increase soil fertility by adding organic matter.