Microorganisms: Friend and Foe

"Algae by weight represent almost of the biomass of all life on Earth. They produce more than half of all the oxygen we breathe."

1.0Introduction

A microorganism is a living organism that is very minute. It can only be seen with the aid of a microscope. Consider that the largest human cells are about the diameter of human hair. Bacteria cells are one-hundredth the size of a human cell and viruses are much, smaller again. A bacterium next to a human cell is like a tiny boat next to a big ship.

2.0Occurrence of Microorganisms

(i) Microorganisms are present everywhere in air, soil, water, foodstuffs, sewage waste as well as inside animal bodies. (ii) They can survive in all types of environments even in extremely harsh environmental conditions like hot springs, desert soil, saline water, ice-cold water and marshy lands. (iii) They are also present in dead and decaying organic matter. (iv) Some can live alone while others like bacteria and fungi may live in colonies. (v) Some microbes live as parasites either outside or inside the body of other organisms and cause diseases.

3.0Major Groups of Microorganisms

There are five major groups of microorganisms i.e. bacteria, virus, protozoan, algae and fungus.

Bacteria: These are single celled organisms, found in wide range of habitats ranging from glaciers to deserts and hot springs. e.g. Lactobacillus (curd bacteria). They are generally heterotroph, but some bacteria also show autotrophic nutrition.

Bacteria Types on the basis of their Shape

Fungi: These are multicellular, heterotrophic organisms, lack chlorophyll and are generally found in colonies. Yeast is the only exception which is unicellular in nature. e.g. Penicillium, Aspergillus, Breadmould.

Aspergillus

Penicillium

Protozoa: These are unicellular, heterotrophic microorganisms. Usually found in moist & aquatic habitats. e.g. Amoeba, Paramecium

3. Algae: These are unicellular or multicellular eukaryotic autotrophic organisms, contain chlorophyll pigment and carry out photosynthesis. Cell wall of algae is mainly made up of cellulose. e.g. Chlamydomonas, Spirogyra, Chlorella.

4. Viruses: Viruses are acellular structures because they are not built up of cells. They are much smaller than cells. These are ultramicroscopic organisms, which require cells of host organisms to reproduce. e.g. Influenza virus, polio virus, AIDS etc. Structure of virus consist of nucleic acid and a protein coat. Nucleic acid can either be DNA or RNA. Microbes-friend and foe: It is almost impossible to think of any place without microorganisms. Most microorganisms are beneficial, for example, there are micro-organisms in our large intestine that synthesize vitamins. However, a tiny minority are pathogens (disease causing agents). These pathogens, often called germs, are a threat to all life forms.

4.0Microorganisms - As Friends

Microorganisms are used for a number of purposes such as: (1) Preparation of curd, bread, cake, idli, dosa and cheese. (2) In industry - to produce alcohol, wine and acetic acid (vinegar). (3) In agriculture - to increase soil fertility. (4) In medicines - to produce antibiotics and vaccines. (5) Cleaning the environment.

Preparation of Curd, Bread, Cake, Idli, Dosa and Cheese

(i) Formation of curd (dahi): Making of curd is a process in which the lactose (milk sugar) of the milk is converted into lactic acid by the action of certain bacteria (mainly Lactobacillus). This curd is further used in the preparation of idli-dosas and bhaturas.

Q. How does the addition of small amount of curd to milk converts the whole milk into curd?

Explanation Curd contains several microbes. Out of these, Lactobacillus, promotes the formation of curd. When the curd is added to lukewarm milk, the bacteria, multiply faster and results in conversion of whole milk into curd.

Anaerobic respiration in yeast cell: Yeast can survive in the absence of air. They are called anaerobes. They get energy through anaerobic respiration. The glucose breaks down into alcohol and carbon dioxide in the absence of oxygen. The reaction is called anaerobic respiration or fermentation.

Commercial Use of Microorganisms: In Industry

The wine and beer (brewery) industries are important industries which make use of the fungus yeast. Yeast is grown on natural sugars present in crashed fruit juices and grains like barley, wheat and rice. Yeast brings about conversion of sugars into alcohol and carbon dioxide.

Alcoholic beverages are major fermented foods in the diet of humans. The yeast also enriches the beverages with B-vitamins.

Agricultural Use of Microorganisms

All plants and animals need nitrogen, the gas that makes up 78% of the air. Some bacteria and Blue green algae are the only organisms that can take nitrogen directly from air. These microbes convert atmospheric nitrogen into compounds of nitrogen and so called as biological nitrogen fixers. Thus, they are very useful to agriculture, as they enrich the soil with nitrogen.

Anabaena

Nostoc

Nitrogen Fixation: Refers to the conversion of atmospheric nitrogen gas ( ) into a form usable by plants and other organisms.

It is conducted by a variety of bacteria, both as free-living organisms and in symbiotic association with plants. e.g. The roots of leguminous plants like beans and pea, bear certain swollen structures called root nodules. The bacterium Rhizobium lives in the root nodules. Bacteria fix nitrogen for the plants, while the plants give food and shelter to the bacteria. This type of relationship is called as symbiotic association.

Symbiotic relationship: Mutually beneficial association in which two organisms live together and share shelter and nutrients. This is called symbiotic relationship. For example, Mycorrhiza and Lichen.

Nitrogen cycle:

Nitrogen is an essential element for all living organisms because it is a principle component of proteins, chlorophyll, vitamin and nucleic acids. The circulation of nitrogen through the living and non-living components of the biosphere (air, soil, water, plants and animals) is called nitrogen cycle.

Nitrogen cycle maintain the percentage of nitrogen in the atmosphere more or less at a constant.

The bacterium called Rhizobium can fix atmospheric nitrogen and convert it into a soluble form. But Rhizobium cannot make its own food. So, it lives in the roots of gram, peas, moong, beans and other legumes and provides them with nitrogen.

Pulses (dals) are obtained from leguminous plants. In return, the plants provide food and shelter to the bacteria. They have a symbiotic relationship. This association is of great significance for the farmers. They do not need to add nitrogen fertilizers to the soil in which leguminous plants are grown.

Steps involved in nitrogen cycle: (1) Atmospheric nitrogen is fixed into nitrogen compounds by Rhizobium bacteria, Blue green algae. This is called as nitrogen fixation. (2) The plants absorb nitrogen compounds from the soil and convert them into plant proteins. (3) The plants are eaten up by animals and thus plant proteins are used for making animal proteins. (4) When the plants and animals die, putrefying bacteria and fungi present in the soil decompose the proteins of dead plants and animals into ammonia. This process is called ammonification. (5) Ammonia thus formed is converted first into nitrites and then to nitrates by the action of Nitrosomonas and Nitrobacter bacteria respectively. The process is called nitrification. These nitrates are absorbed by plants. (6) The soil contains denitrifying bacteria called Pseudomonas which convert nitrate form of nitrogen into free nitrogen which goes back into the atmosphere. The process is called denitrification.

Medicinal Use of Microorganisms

Microbes are being employed for the production of both antibiotics and vaccines. Antibiotics: Antibiotics are produced by a number of microorganisms and inhibit the growth of other microorganisms even at very low concentrations. Fungi and bacteria are important microbes producing a variety of antibiotics.

Antibiotics obtained from bacteria: Streptomycin, aureomycin and chloromycetin, tetracycline, erythromycin.
Antibiotics obtained from fungi: Penicillin and Griseofulvin. These antibiotics are used to cure a variety of diseases in humans, plants and animals. In 1929, Alexander Fleming was working on a culture of disease-causing bacteria. Suddenly he found the spores of a little green mould in one of his culture plates. He observed that the presence of mould prevented the growth of bacteria. In fact, it also killed many of these bacteria. From this the mould penicillin was prepared. Antibiotics are not effective against cold and flu as these are caused by viruses.
Precautions to be taken while using antibiotics :

It should be taken only on the advice of a qualified doctor.
Patient must complete the entire course as prescribed by the doctor.
Excess dose must not be taken.
If you take antibiotics when not needed or in wrong doses, it may make the drug less effective when you might need it in future. Also, antibiotic taken unnecessarily may kill the beneficial bacteria in the body.

Even if your symptoms go away, the bacteria may still be present in your body. If you stop treatment before the antibiotic cycle is over, the remaining bacteria can continue to multiply. If these bacteria become resistant to the antibiotics, they can potentially do even more harm.
Vaccines: A vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a diseasecausing microorganism and is often made from weakened or killed forms of the microbe or its toxins. When a disease-causing microbe enters our body, the body produces antibodies to fight the invader.

The body also remembers how to fight the microbe if it enters again. If dead or weakened microbes are introduced into a healthy body, the body fights and kills the invading bacteria by producing suitable antibodies. The antibodies remain in the body and we are protected from the disease-causing microbes for ever. This is how a vaccine works. At present, vaccines against several diseases have been produced such as diphtheria, measles, mumps, rubella and polio. Polio drops given to the children under pulse polio program is actually a vaccine. Edward Jenner discovered the first vaccine against smallpox (1798).

Q. Why are children/infants given vaccination?

Explanation Vaccination is given to children/infants to strengthen or activate the defence mechanism of the body against a disease and to protect the body from the disease-causing microbes, because the immunity of an infant is low and so is more susceptible to any infection.

Cleaning in The Environment

(i) Microbes, like bacteria and fungi, bring about the decay of dead plants and animals, both on land and in water. (ii) They act on dead plants and animals and convert various complex organic compounds into simple inorganic substances. Thus, microbes also help in recycling of nutrients. decompose polythene bags. (iii) They also help in sewage disposal by putrefaction (incomplete decomposition of dead organic matter).

5.0Microorganisms - As Foe

Microorganisms can cause harm in many ways. Many microbes are the causative agents of various diseases that affect plants and animals. Such disease-causing microorganisms are called pathogens. They also cause damage of clothes, leather and spoilage of food.

Disease Causing Microorganisms

(a) In human: Pathogens enter our body through various sources like air, water, food and infected person. The microbial diseases that can spread from an infected person to a healthy person through air, water, food, insects and physical contact are known as Communicable/Infectious diseases. e.g. Cholera, Common cold, Chicken pox, tuberculosis.

Q. Sneezing can cause infection to a healthy person. Explain?

Explanation When a person suffering from common cold sneezes, fine droplets of moisture carrying thousands of viruses are spread in the air. The virus may enter the body of healthy person while breathing.
Vectors: Those organisms which help the microbes in the transmission of disease, are known as vectors e.g. houseflies, mosquitoes, cockroaches, rats. Cholera and typhoid are spread through houseflies.

Another example of a vector is mosquito, Female Anopheles mosquito, which is the vector for the parasite (Plasmodium), that is the causative agent of malaria. Similarly, Female Aedes mosquito is the vector of dengue virus which causes dengue fever.

Control measures of houseflies and mosquitoes (i) Food must be kept covered. (ii) Proper sanitation. (iii) Garbage should be disposed properly. (iv) Mosquitoes breed in water. So, water must not be allowed to collect anywhere. (v) Spraying of kerosene on the surface of water to form a thin film (this blocks oxygen and kills larvae of mosquitoes). Some common human diseases caused by microbes:

Human disease	Causative microorganism	Mode of transmission	Preventive measures (General)
Tuberculosis	Bacteria	Air	Keep the patient in complete isolation. Keep the personal belongings of the patient away from those of the others. Vaccination to be given at a suitable age.
Measles	Virus	Air	Keep the patient in complete isolation. Keep the personal belongings of the patient away from those of the others. Vaccination to be given at a suitable age.
Chicken pox	Virus	Air/Contact	Keep the patient in complete isolation. Keep the personal belongings of the patient away from those of the others. Vaccination to be given at a suitable age.
Polio	Virus	Air/Water	Keep the patient in complete isolation. Keep the personal belongings of the patient away from those of the others. Vaccination to be given at a suitable age.
Cholera	Bacteria	Water/Food	Maintain personal hygiene and good sanitary habits. Consume properly cooked food and boiled drinking water. Vaccination.
Typhoid	Bacteria	Water	Maintain personal hygiene and good sanitary habits. Consume properly cooked food and boiled drinking water. Vaccination.
Hepatitis A	Virus	Water	Drink boiled water. Vaccination.
Malaria	Protozoa	Mosquito	Use mosquito net and repellents. Spray insecticides and control breeding of mosquitoes by not allowing water to collect in the surroundings.

(b) In animals: Microbes not only cause disease in humans but also in other animals. The following table shows the list of microorganisms affecting various animals.

Common animal diseases

Microorganism	Name of animal diseases
Virus	Foot and mouth disease of cattle, Ranikhet of birds
Bacteria	Anthrax disease of cattle
Protozoa	Sleeping sickness (in cattle, pigs and horses)

(c) In plants: There are several microbes causing diseases in plants. The list of microorganisms affecting plants is shown below in the table.

Common plant diseases

Plant Diseases	Micro-organism	Mode of Transmission
Citrus canker	Bacteria	Air
Rust of wheat	Fungi	Air, seeds
Yellow vein mosaic of bhindi (Okra)	Virus	Insect

The diseases in plants result in decrease in crop yield. Therefore, the plants have to be treated by chemicals to protect them from disease causing microorganisms.

Microbes Causing Food Spoilage

The contamination of food by microorganisms results into food spoilage. The consumption of this spoiled food by humans or animals results into food poisoning. Microorganisms like bacteria and fungi are responsible for food poisoning. These microbes when grow on food substances produce toxin. These make the food poisonous causing vomiting, serious illness and even death.

Therefore, there is a need to preserve food from being spoiled.

6.0Food Preservation

The food that we eat is either in raw or cooked form. All types of food can be targets of microbes which result into food spoilage.

Methods of Food Preservation

The process of treating and handling food with an aim to stop or slow down its spoilage while maintaining its nutritional value, texture, and flavour.

(i) Heat and cold treatment: Boiling of milk and liquid food products kills many microorganisms. Similarly, low temperature inhibits the growth of microbes.

Pasteurisation: This method was developed by scientist Louis Pasteur. It is used to store milk and liquid food products. In this the food is heated about for 15 to 30 seconds and then suddenly chilled and stored.

Low temperature Storage: Microorganisms present in food products cannot be destroyed by low temperature, but their metabolic activities can be arrested so that they can't act on food products at to temperature. Fruits, eggs and meat can be stored for long time.

Refrigeration: Fresh fruits, vegetables, fish, meat, eggs, etc. can be stored by keeping the temperature below .

Q. Why does the milk that comes in packet does not require boiling?

Explanation The milk that comes in packet is pasteurized milk, so it can be consumed without boiling as it is free from harmful microbes.

(ii) Chemical Method: Chemicals which are used to check the growth of microbes are called preservatives. Salts and edible oils are commonly used for this. The commonly used preservatives are sodium benzoate, sodium metabisulphite and potassium metabisulphite. This method is employed in the preservation of fruit juices, jams, squashes, fruits, etc.

(iii) Preservation by common salt: Common salt has been used to preserve meat and fish for ages. Concentrated solutions of common salt can kill microorganisms due to dehydration. Salting is also used to preserve amla (Indian gooseberry), tamarind and raw mangoes.

(iv) Preservation by sugar: Sugar reduces the moisture content which inhibits the growth of bacteria. Jams, jellies and squashes are preserved by sugar.

(v) Preservation by oil and vinegar: Use of oil and vinegar prevents spoilage of pickle because bacteria cannot live in this environment. Vegetables, fruits, fish and meat are often preserved by this method.

(vi) Preservation by radiation: In this method air tight packed food substances, are passed through a radiation beam, microorganisms present in food substances get destroyed due to radiation. This method is new and cheaper.

(vii) Storage and Packing: Dry fruits and vegetables are sold in sealed air tight packet to prevent the attack of microbes.

Q. Mango gets spoiled at room temperature within few days, but the mango pickle remains as such for a long time. Explain.

Explanation In pickles, we add some preservatives such as salt or acids that do not allow microbes to grow in such an environment. Therefore, mango pickles can remain fresh and preserved for a long time.

Advantages of food preservation

(i) This prevents the food from being spoiled by the action of microorganisms. (ii) It increases the storage period of food materials. (iii) It helps in obtaining the off-season food materials. (iv) It makes the transportation of food materials easier.

Anti - oxidants are also used to preserve food. They prevent the reaction of food with oxygen. e.g. chilli and pepper.

7.0Chapter At A Glance

8.0Some Basic Terms

Fission: The division of cells into new cells.
Prokaryotic: Unicellular organism that lacks a membrane bound nucleus.
Eukaryotic: Organism whose cells have a nucleus enclosed within membranes.
Ailment: Any illness that is not very serious.
Susceptible: Capable of
Handkerchief: A square piece of cloth or soft thin paper that you use for cleaning your nose.
Inhibit: Stop something or make something happen more slowly.
Dehydration: Loss of water.
Repellent: A chemical substance that is used to keep insects away.
Porous: Allowing liquid or air to pass through slowly.
Dough: A mixture of flour, water etc, used to make bread etc.
Symbiotic: Special type of interaction between species which is beneficial to both.
Isolation: The state of being separate and alone.
Baking: Method of preparing food that uses dry heat.
Immunity: The ability to avoid or not be affected by disease.
Glaciers: Are made up of fallen snow that over many years, compress into large, thickened ice mass.
Harsh: Unpleasantly rough.
Decaying: Decomposing through the action of bacteria and fungi.
Invaders: Attacker.
Conversion: The process of changing.

9.0Also Read

Reaching the Age of Adolescence	Coal and Petroleum	Friction
Reproduction in Animals	Chemical Effects of Electric Current	Sounds
Combustion and Flame	Light	Some Natural Phenomena