CHAPTER 10 MICROBES IN HUMAN WELFARE - PowerPoint Presentation

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CHAPTER 10

MICROBES IN HUMAN WELFARE

Besides macroscopic plants and animals, microbes are the major components of biological systems on this earth. Microbes are present everywhere – in soil, water, air, inside our bodies and that of other animals and plants. 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 of the most important contributions of microbes to human welfare are as follows.

MICROBES IN HOUSEHOLD PRODUCTS:

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. In our stomach too, the LAB play very beneficial role in checking disease causing microbes.

The dough, which is used for making foods such as

dosa

and

idli

is also fermented by bacteria. The puffed-up appearance of dough is due to the production of CO2 gas.

Similarly the dough, which is used for making bread, is fermented using baker’s yeast (

Saccharomyces

cerevisiae

).

‘Toddy’, a traditional drink of some parts of southern India is made by fermenting sap from palms. 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

.

MICROBES IN INDUSTRIAL PRODUCTS:

In industry, microbes are used to synthesise a number of products

e.g.,

beverages and antibiotics. Production on an industrial scale, requires growing microbes in very large vessels called

fermentors

.

Fermented Beverages

Microbes especially yeasts are used for the production of beverages like wine, beer, whisky, brandy or rum.

Saccharomyces

cerevisiae

used for bread-making and commonly called brewer’s yeast, is used for fermenting malted cereals and fruit juices, to produce ethanol. Wine and beer are produced without distillation whereas whisky brandy and rum are produced by distillation of the fermented broth.

Antibiotics

Antibiotics are chemical substances, which are produced by some microbes and can kill or retard the growth of other (disease-causing) microbes. Penicillin was the first antibiotic to be discovered, and it was a chance discovery. Alexander Fleming while working on Staphylococci bacteria, once observed a mould growing in one of his unwashed culture 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.

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,

sAcetobacter

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 .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. 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.

Microbes in Sewage Treatment

Sewage

is the municipal waste water, containing large quantities of human excreta.

Need for sewage treatment:

Sewage contains large. amount of organic matter and pathogenic microbes, Before discharging into natural bodies sewage is made less polluting.

Sewage is treated in sewage treatment plants (STPs).

Ganga

Action plan and

Yumuna

Action Plan

have been initiated by Ministry of Environment and Forest, under which large number of STPs will be build to treat sewage before their discharge in rivers to reduce their pollution.

Sewage treatment is carried out in two stages:

Primary treatment or physical treatment

It is the physical removal of large and small particles from sewage.

First, the floating debris is removed by sequential filtration by passing through wire mesh screens.

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.

The effluent is taken for secondary treatment.

Secondary treatment or biological treatment

.

Primary effluent is passed into large

aeration tanks

with constant mechanical agitation

and air

supply.

Useful aerobic microbes grow rapidly and form

flocs

.

Flocs

are masses of bacteria associated with fungal filaments to form mesh-like structures.

The growing microbes consume organic matter and thus reduce the biochemical oxygen demand (BOD).

When BOD of sewage has reduced, the effluent is passed into

settling tank

.

Here, the bacterial

flocs

settle and the sediment is called

activated sludge.

A small part of the sludge is used as an inoculums in the aeration tank and the remaining parts passed into large tanks called

anaerobic sludge digesters.

In the digesters,

heterotrophic microbes

anaerobically

digest bacteria and fungi in sludge producing mixture of gases as methane, hydrogen sulphide and CO

2

which form the

biogas.

Biological Oxygen Demand (BOD)

BOD refers to the amount of oxygen consumed if all the organic matter in one litre of water oxidised by bacteria.

BOD measures the amount of organic matter in water by measuring the rate of oxygen uptake is microbes.

Higher BOD indicates higher polluting potential.

Microbes in Production of Biogas

Biogas is mixture of inflammable gases (methane, SO

2,

CO

2,

etc) produced by microbial activity that can be used as fuel.

Methanogens

,

Particularly

Methanobacterium

,

anaerobically

breaks down cellulosic material to produce CO

2

and H

2.

These bacteria are found in anaerobic sludge during sewage

treatment.These

bacteria are also present in Rumen (a part of stomach) of

cattle.The

excreta(Dung) of cattle is rich in these bacteria.

Dung can be used for generation of biogas.

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

The raw material for biogas production is excreta (dung) of cattle.

The biogas plant has a concrete tank (10-15) feet deep in which bio-waster and slurry of dung is collected.

The tank has a floating cover which rises on production of gas in the tank.

Methanobacterium

in the dung act on the bio wastes to produce biogas.

The gas produced is supplied to nearbby houses by an outlet.

Through another outlet, the spent slurry is removed to be used as fertiliser.

Biogas is used for fuel for cooking and lighting.

Fig. A typical biogas plant

Microbes as

Biocontrol

Agents

Biocontrol

is defined as controlling plant disease and pests using biological methods.

Earlier, chemical like insecticides and pesticides were used for

biocontrol

.

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.

Organic farmers

use a holistic approach and keep pests at manageable levels by complex system of checks and balances within the ecosystem, instead of their complete eradication.

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.

(b). The bacteria

Bacillus

thuringiensis

(Bt) are used to control butterfly caterpillars.

Dried spores of Bt are mixed with water and sprayed on plants such as

brassicas

and fruit trees.

Insect larvae, after eating these are killed by the toxic released in their gut.

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 plants pathogens.

(d).

Baculoviruses

are pathogens that attack insects and other arthropods.

Most of these

biocontrol

agents belong to the genus

Nucleopolyhedrovirus

.

These are species specific, narrow spectrum insecticides.

They do not harm plants, mammals, birds fish and other non-target insects.

Baculoviruses

are helpful in

integrated pest management

(IPM) programme, in which beneficial insects are conserved.

Microbes as

Biofertilisers

Biofertilisers

are the microorganisms which enrich the nutrient (nitrogen, phosphorus, etc.) quality of the soil.

Bacteria, fungi and

cynobacteria

are the three main sources of

biofertilisers

.

Bacteria as biofertiliser

Rhizobium

is a symbiotic bacterium that lives in the root nodules of legumes and fixes atmospheric nitrogen into organic compounds.

Azospirillum

and

Azotobacter

are free-living bacteria which absorb free nitrogen from soil, air and convert it into salts of nitrogen like amino acids and enrich soil nutrients.

Fungi as

biofertilisers

Fungi form symbiotic association with the roots of higher plants called

mycorrhiza

,

e.g.,

Glomus

.

The fungal

hyphae

absorb phosphorus from soil and passes it to the plant

.

Mycorrhiza

shows the following benefits:

Resistance to root-borne pathogens.

Tolerance to salinity and drought.

Overall increase in plant growth and development.

Cyanobacteria

as

biofertilisers

They fix atmospheric nitrogen and increase the organic matter of the soil through their photosynthetic activity, e.g.,

Nostoc

, Anabaena,

Oscillatoria

,

etc

.

Blue-green algae increase the soil fertility adding organic matter to the soil.

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