Notes-Class 9-Science-Chapter-8-Useful and Harmful Microbes-Maharashtra Board

Topics to be learn :

Useful micro-organisms :

Lactobacilli
Rhizobium
Yeast

Harmful microorganisms :

Clostridium
pathogenic bacteria,
viruses.
fungi

Microbes : The living organisms which cannot be seen with naked eyes but those that are all around us are called microbes.

Characteristics of microbes :

All microbes are prokaryotic cells
Microbes can be seen only under high power microscope. Microbes can be seen under compound microscope.

If drops of fresh buttermilk are added on the slide and stained with appropriate stain, Lactobacilli bacteria can be seen. Fungus growing on stale food can also be observed under microscope.

Microbes related to our everyday life : Many microbes are useful to us. We use them for our beneﬁts such as making yoghurt from milk is done by Lactobacilli bacteria. Yeast which is a type of fungus is used for baking processes.

Some microbes are harmful. They cause various diseases and affect our health.

Useful Micro-organisms :

Lactobacilli :

Lactobacillus is a minute, rectangular shaped anaerobic bacteria.
They convert lactose sugar present in the milk into lactic acid and thus produce yoghurt from the milk.
They are also used in the fermentation process.

Uses of Lactobacilli bacteria :

Uses of Lactobacilli :

By fermentation of milk, many milk products like yoghurt. Buttermilk, ghee, cheese, shrikhand, etc. can be obtained.
Large scale production of cider, cocoa, pickles of vegetables, etc. can be produced by fermentation process using lactobacilli.
Lactobacilli and some other useful microbes taken together are used to treat abdominal discomfort and helping in the digestion process.
Leavened fodder fed to domestic cattle like cows and buffalos, is fodder fermented with the help of Lactobacilli.
The Lactobacilli and yeast fermentation process is used to make wine and some types of bread.

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Industries depend upon use of Lactobacilli bacteria :

Industries depend upon use of Lactobacilli bacteria :

Production of milk products : Cheese, butter, buttermilk, ghee, shrikhand, condensed milk, milk powder, etc.
Food products such as cider, cocoa, pickles of different vegetables.
Probiotic medicines and other food stuffs.
Cattle feed.
Preparation of alcohol and in winery.
Bakery products (bread, biscuits, cakes, etc.).

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Process of making of yoghurt from milk :

Process of making of yoghurt from milk :

The culture of previous yoghurt containing lactobacilli is added to the lukewarm milk.
These bacteria bring about chemical change in the milk.
The lactose sugar in the milk is changed to lactic acid.
The pH of the milk is reduced due to lactic acid.
Milk proteins get separated from the other constituents and coagulation of milk occurs.
Thus fermentation and coagulation processes change the milk into yoghurt.

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Probiotic : Eatables which are made healthy by adding useful bacteria like lactobacilli are called probiotics.

They kill the harmful bacteria like Clostridium in the alimentary canal and help to improve our immunity.

Rhizobium : Symbiotic Bacteria

Rhizobium is symbiotically living bacteria with the leguminous plants like beans, sweet pea, soyabean, etc.
Rhizobia living in root nodules supply nitrates, nitrites and amino acids to that plant and in exchange get energy in the form of carbohydrates and space to stay in the root nodules.
Thus their mutually beneﬁcial relationship is called symbiosis.
Due to the nitrogenous compounds made available by Rhizobia through nitrogen ﬁxation process, the beans and pulses become rich in proteins.
The use of Rhizobium reduces adverse effects caused due to the use of chemical fertilizers. As per modern methods ‘Rhizobial inoculation’ is done to supply nitrogen to the cereal crops.

Lichens :

Lichens :

Lichen is co-existence of algae and fungi for mutual benefit.
It is the best example of symbiosis or mutualism.
They are found in extreme environments like snow clad poles.
Algae prepares the food and supplies it to the fungal component, while fungal component provides shelter to algae and also absorbs water and minerals for algae.
The association is intense and it is difﬁcult to identify them as separate living beings.
They are very sensitive to pollutions, hence not found in polluted areas.
They are used as pollution indicators.
They play an important role in soil formation by using speciﬁc acid productions.
Lichens have been used in making dyes, perfumes and in traditional medicines.
Some species of lichens are used for making litmus paper.
A few lichen species are eaten by insects or larger animals, such as reindeer.

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Yeast :

Yeast is a heterotrophic unicellular fungus having eukaryotic cell. It grows on the carbon compounds.
Yeast cells are colourless and oval. Some of the cells show small round buds attached to it. Yeast reproduces asexually by budding.
Yeast cells carry out fermentation during process of obtaining its nutrition. It converts carbohydrates into alcohol and carbon dioxide.
During the baking of the bread, the same fermentation process of the yeast is used.
Many other processes involving fermentation also involve use of yeast.

Q. Chapattis made from wheat only swell up but bread becomes spongy, soft and easy to digest. Why is it so?

Answer

Yeast is added to the flour of bread. This yeast carries out fermentation and releases carbon dioxide in the process. Therefore the bread becomes spongy and soft. Due to yeast some nutrients are also produced in the ﬂour. So it becomes more tasty, nutritious and easy to digest.

Flour of chapattis does not contain yeast. While roasting these, only the gas present in the ﬂour expands, making them to swell.

Bio-remediation :

Yarrowia lipolytica is also a yeast species which is used to absorb the toxins released during production of palm oil. It is also used to absorb heavy metals and minerals released in industrial processes.
Saccharomyces cereviceae is also a yeast species used to absorb arsenic which is one of the harmful pollutants.
Alcanivorax is the bacterial species used to clean up marine oil spills.

Production of alcohol :

Production of alcohol :

Alcohol is produced along with sugar in sugar factories. Molasses are rich in carbohydrates. They are fermented with yeast called Saccharomyces. By this process ethanol (C₂H₅OH) is obtained as a main product and esters and other alcohols are obtained as secondary products.
Ethanol is a smokeless and high quality fuel
Spirit and other alcohols can be obtained from ethanol.
Besides molasses, maize, barley and other grains are also used for industrial production of ethanol.
The grape juice contains sugars such as glucose and fructose. This juice can be fermented with the help of yeast to produce the alcohol which is later converted to wines.

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Give reasons: Recently, it has been made compulsory in India and some other countries to mix 10% ethanol with fuels like petrol and diesel.

Ethanol is produced from molasses of sugar cane and other grains. The ethanol is less polluting if used as a fuel.
Petrol and diesel are fossil fuels. They are obtained from deep interiors of the earth, but they are limited sources of energy. They cannot be produced again if exhausted.
Due to limited fossil fuels mankind is facing energy crisis. The remedial measure of this problem is using 10% ethanol in the fuels.
This mixture saves fuels quantity.
It also emits less carbon monoxide and thus creates less air pollution.

Therefore recently, it has been made compulsory in India and some other countries to mix 10% ethanol with fuels like petrol and diesel.

Antibiotics :

Some bacteria and fungi produce carbon compounds which can destroy or prevent the growth of harmful micro-organisms. Such compounds are called antibiotics.
Antibiotics have controlled many bacterial diseases such as tuberculosis and typhoid and thus have created a revolution in the medical field.
Broad spectrum antibiotics : The antibiotics that are useful against a wide variety of bacteria are called broad spectrum antibiotics. E.g. ampicillin, amoxicillin, tetracycline, etc.
Narrow spectrum antibiotics : The antibiotic used to destroy a definite and known micro-organisms, is called narrow spectrum antibiotic. E.g. penicillin, gentamycin, erythromycin, etc.

Q. Which cautions should be followed while using antibiotics?

Answer

Antibiotics should be taken only when doctor prescribes to take those.
One should not purchase any antibiotic from medical stores without a prescription from a doctor.
One should not use antibiotics according to own will to treat common diseases like a throat infection, common cold or inﬂuenza.
The dosage of the antibiotics as told by doctor, should be completed and should not be left half way even if one feels well.
Even if we find antibiotic very effective, we should not suggest these to other people.
Antibiotics whose expiry date is over, should never be used.

Penicillin :

Penicillin is an antibiotic obtained from a fungus, Penicillium.
It is used for controlling the bacterial infections caused by Staphylococci, Clostridia, Streptococci, etc.
Bacterial infections of the ear, nose, throat, skin and diseases like pneumonia and scarlet fever can be best treated by penicillin containing drugs.
Antibiotics should be taken with precaution and only when prescribed by a doctor.

Uses of fungi to Plants and animals :

Uses of fungi to Plants and animals :

The group of fungi called mycorrhiza are attached to roots of living trees and Plants. They extract sugars that they need from these living plants, but in return they supply the host plant with some of the nutrients and water (symbiotic relationship).
Certain plants, such as orchids, are totally dependent on a fungus associated with their roots in order to grow.
Stinkhorn fungi make use of animals to disperse their spores. Many fungi take advantage of the mobility of animals to carry their spores long distances. In some cases the animal is lured in by a reward such as a sweet substance.
Many animals grow fungi as a source of food. Some fungi live symbiotically with animals. Ants grow fungi in their termitarium (anthill) and obtain food from it.
Some species of wasps and other insects lay their eggs in the fungal bodies growing on trees thus ensuring a food supply for their larvae. The larvae that eat leaf debris gain more weight if their food contains fungi. Possibly fungal protein is more digestible by animals than plant protein.
Fungi growing on fallen leaves detoxify them and make them safe to eat. Otherwise many fallen leaves are toxic for the grazing plants
Mound-building termites also use fungus in the same way as done by ants.
Certain wood wasps and a group of beetles called “ambrosia beetles" burrow into the wood of freshly-fallen trees where they create extensive systems of tunnels. The beetles inoculate these with a speciﬁc fungus, the ambrosia. They then lay eggs in the tunnels and the developing larvae feed exclusively on the ambrosia.
A group of fungi called chytrids live Symbiotically in the rumen of the moose.
Some fungi grow on different parts of arthropod bodies. A number of scale insects live within the so called colony of the fungus and are sheltered from the environment and have their food supply beneath them.

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The National Institute of Virology, established in 1952 in Pune carries out research related to diseases like measles, jaundice, fever and diseases of the lungs. Their work is supported by World Health Organization.

Introduction to scientists :

Introduction to scientists :

Alexander Fleming discovered Penicillium fungus while observing Staphylococci cultures on 3rd September 1928. The penicillin is the ﬁrst antibiotic in the world.

Incurable diseases are controlled due to advent of antibiotics.

Van Ermengem proved that the anaerobic bacterium Clostridium botulinum, is responsible for food poisoning.

Ida Bengston conducted research on the toxin responsible for gas gangrene and the antitoxin useful for treating it. She herself contracted the infection of typhus disease while conducting research on it. Then also she continued the research work. She was honoured with the Typhus medal in 1947.

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Harmful Micro-organisms :

(1) Fungi :

Microscopic spores of fungi are present in the air. After acquiring suitable moisture, they start growing on any kind of organic i.e. carbon matter.
The fungal hyphae which are ﬁbre-like penetrate deep into the supporting material to obtain nutrition and start reproducing by spores.
Various species of fungi grow on food items like pickles, murabba, jam, sauce, chutney, etc.
Such fungi absorb nutrients from the food for growth and reproduction. In the process, they produce mycotoxins.
Mycotoxins are toxic substances that may cause food poisoning. Food contaminated with fungus is thus unﬁt for consumption.

Q. Why do articles not get spoilt during the summer or winter but get spoilt in rainy season?

Answer

In summer the surrounding temperature is high. Due to heat, fungus cannot reproduce. The low temperatures of winter also are unfavourable for the fungal growth. In summer as well as winter the humidity of the air is less. The less humidity too does not support the fungal growth. Thus the above articles do not get spoilt during summer and winter.

In rainy season there is growth of fungal hyphae on the leather articles and gunny bags made up of jute. The spores of fungus cover the surfaces of these articles. These articles do not remain usable. There is tremendous wear and tear of the material and thus they become weak. They do not last long.

Clostridium : Sometimes, cases of food poisoning occur during community feasts. The bacteria which spoil cooked food are Clostridium.

Clostridium is the anaerobic bacteria causing spoilage of cooked food.
These rod-shaped bacteria produce bottle shaped endospores in adverse conditions.
There are about 100 different species of this bacterium, some are free living in the soil whereas some live in the alimentary canal of humans and other animals.

Preservatives : Salt and oil are both natural preservatives.

Salt is applied to the inner surface of the pickle jars for well preservation of pickles. Due to salt, the fungal growth is arrested and the pickle is not spoilt.
Pickle is also covered with oil for the same reason. Due to oil, pickle does not come in contact with air making it impossible for the fungal spores to enter inside the pickle.

Preservatives mixed with ready-to-eat foods to keep them from spoiling :

The ready-to-eat foods are treated with chemical preservatives. Some of these are as follows :

BHT (Butylated hydroxytoluene)
BHA ( Butylated hydroxyanisole)
Sodium nitrite
Sulphites
Monosodium glutamate or MSG. This is also called Ajinomoto.
Sodium benzoate.

Other Harmful Micro-organisms : Some pathogenic bacteria, viruses, protozoa and fungi are also responsible for causing many infective diseases of human beings. Some of the important diseases are as follows :

Diseases cause by virus :

Diseases caused by virus (Viral diseases) :

1. AIDS

Mode of infection : Through blood and semen of infected person and milk of mother suffering from AIDS

Preventive measures :

Safe blood transfusion
Avoiding reuse of needles and injections
Safe sexual contact

2. Hepatitis :

Mode of infection : Contaminated water and food

Preventive measures :

Clean and filtered water, proper storage of food

3. Inﬂuenza :

Mode of infection : Contact with infected person

Preventive measures :

Personal hygiene and avoiding contact with infected person

4. Measles and Chicken pox :

Mode of infection : Contact with infected person

Preventive measures :

Vaccination, uncontaminated water, clean food.

5. Bird Flu (H7N9) , Swine Flu (HIN1):

Mode of infection : Contact with infected birds and animals.

Preventive measures :

Personal hygiene, properly cooked meat

6. Dengue :

Mode of infection : Mosquito bite (Aedes egypti)

Preventive measures :

Cleanliness of surroundings preventing stagnation of water, mosquito control

Disease caused by bacteria (Bacterial diseases) :

7. Pneumonia :

Mode of infection : Droplets spread in air by infected person

Preventive measures :

Vaccination, avoiding contact with infected person

8. Leprosy :

Mode of infection : Long term contact with infected person

Preventive measures :

Avoiding contact with infected persons and their belongings

9. Cholera :

Mode of infection : Contaminated food and water

Preventive measures :

Clean food and water.

Diseases caused by fungus (Fungal diseases) :

10. Dandruif, ringworm :

Mode of infection : Contact with infected person or his/ her belongings like clothes

Preventive measures :

Personal hygiene, avoiding contact with infected person

11. Malaria :

Mode of infection : Mosquito bite (Anopheles) unclean surroundings, stagnant water

Preventive measures :

Cleanliness of surroundings, preventing {stagnation of water, controlling mosquitoes.

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Diseases in Plants & Animals

Diseases in plants :

There are different pathogens like fungi, bacteria, viruses that cause diseases in plants.

The common plant diseases are:

Leaf rust disease: It is caused by fungus. It is the most common rust disease of wheat.
Blight disease in rice: It is caused by harmful bacteria. It causes wilting of seedlings and yellowing and drying of leaves
Early blight of potato: It is caused by fungi. It causes ‘bulls eye’ patterned leaf spots and tuber blight on potato.
Crown gall disease: It is caused by Agrobacterium tumefaciens. This pathogen infects the plant and forms rough surfaced galls on stem and roots.

Treatment: Spraying the antibiotics and other medicines, proper nutrition of the plants and crops proper cultivation and agricultural practices.

Diseases in animals :

Fungal diseases : Ringworm, actinomycosis, aspergillosis, candidiosis.
Bacterial diseases : Glanders, anthrax, brucellosis, salmonellosis, campylobacteriosis, tetanus, mastitis.
Viral diseases : Rabies, foot and mouth disease, canine distemper, feline herpes, blue tongue, snoring disease.

Treatment : Vaccination, Immunization against infective diseases. Proper maintenance and nutrition.

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