Introduction
Q. What are Microorganisms?
Ans: Microorganisms [microbes] include bacteria, fungi, protozoa, some algae, viruses, viroids and also prions that are proteinacious infectious agents. Viruses reproduce only inside the cells of the host organism, which may be a bacterium, plant or animal.
Microorganisms may be single-celled like bacteria, some algae, and protozoa, or multicellular, such as algae and fungi. They can survive under all types of environment, ranging from ice cold climate to hot springs and deserts to marshy lands.
Microorganisms like amoeba can live alone, while fungi and bacteria may live in colonies.
Image: Microorganisms
Source: NCERT Text Books
Microbes
| Diseases Caused By Bacteria | ||||
|---|---|---|---|---|
| Disease | Causative Agent | Mode Of Transmission | Type Of Organism Affected | Details |
| Acne vulgaris (or simply acne or pimples) | Propionibacterium acnes | Direct contact/close contact | Humans/ Adolescents | Skin disease that occurs when hair follicles become clogged with dead skin cells and oil from the skin. Causes = Genetics + Excessive growth of the bacteria Propionibacterium acnes. |
| Anthrax | Bacillus anthraces | Contact with infected meat | Most animals including humans | Causes skin infections and Gastrointestinal (GI) infection that are fatal. French scientist Louis Pasteur developed the first effective vaccine in 1881. |
| Cholera | Vibrio cholerae | Water/food | Humans | Effects small intestine. The classic symptom is large amounts of watery diarrhea that lasts a few days. Vomiting and muscle cramps may also occur. Diarrhea can be so severe that it leads within hours to severe dehydration and electrolyte imbalance. |
| Citrus Canker | Xanthomonas axonopodis | Air | Citrus fruit plants | Infection causes lesions on the leaves, stems, and fruit of citrus trees. |
| Diptheria | Corynebacterium diphtheriae | Air/direct contact | Humans | Symptoms: sore throat and fever. The neck may swell in part due to large lymph nodes. Complications may include myocarditis, inflammation of nerves, kidney problems, and bleeding problems due to low blood platelets. Myocarditis may result in an abnormal heart rate and inflammation of the nerves may result in paralysis. |
| Pneumonia [caused by bacteria or viruses] | Streptococcus pneumoniae and Haemophilus influenzae | Air borne droplets of sneeze | Humans | Pneumonia is an inflammatory condition of the lung affecting primarily the microscopic air sacs known as alveoli.
 |
| Peptic ulcers | Helicobacter pylori | - | Humans | Ulcers in the lining of stomach and starting part of small intestine |
| Plague | Yersinia pestis | Air/ direct contact | Humans | Unhygienic conditions is the main cause. [You know why Surat is one of the cleanest cities in India?] The symptoms of plague depend on the concentrated areas of infection in each person: bubonic plague in lymph nodes, septicemic plague in blood vessels, pneumonic plague in lungs. |
| Tuberculosis | Mycobacterium tuberculosis | Air | Humans | Tuberculosis generally affects the lungs, but can also affect other parts of the body. Most infections do not have symptoms, known as latent tuberculosis. About 10% of latent infections eventually progresses to active disease which, if left untreated, kills about half of those infected. The classic symptoms of active TB are a chronic cough with blood-tinged sputum, fever, night sweats, and weight loss. |
| Typhoid | Salmonella typhi | Water | Humans | Often there is a gradual onset of a high fever over several days. Weakness, abdominal pain, constipation, and headaches also commonly occur. |
| Diseases Caused By Viruses | ||||
|---|---|---|---|---|
| Disease | Causative Agent | Mode Of Transmission | Type Of Organism Affected | Details |
| AIDS | Human Immunodeficiency Virus (HIV) | Blood exchange | Humans and primates | Severely weakens immunity and makes way for a number of other pathogens |
| Chicken Pox | varicella zoster virus (VZV) | Air/contact | Humans | Chickenpox, also known as varicella, is a highly contagious disease. The disease results in a characteristic skin rash that forms small, itchy blisters. Less severe than small pox. Almost eradicated after the invention of vaccination. |
| Small Pox | Variola major and Variola minor | Air/contact/water | Humans | One of the highly dreaded diseases that is highly contagious. Almost eradicated after the invention of vaccination. |
| Chikungunya | Chikungunya virus | Aedes mosquitoes, such as A. aegypti and A. albopictus | - | Causes severe joint pains. Animal reservoirs of the virus include monkeys, birds, cattle, and rodents. This is in contrast to dengue, for which primates are the only hosts |
| Cold, influenza (flu) and most coughs | Rhino viruses | Air borne droplets of sneeze | Humans | Summer are hostile for the virus. Most common during winter months. |
| Dengue fever | Flavivirus | Female Aedes mosquito | Humans | High fever, headache, vomiting, muscle and joint pains, and a characteristic skin rash. In a small proportion of cases, the disease develops into the life-threatening dengue hemorrhagic fever, resulting in bleeding, low levels of blood platelets and blood plasma leakage, or into dengue shock syndrome, where dangerously low blood pressure occurs. |
| Ebola | Ebola virus | Animal to man | Humans and Some Animals | Ebola infection shows a sudden onset of the disease resulting initially in flu-like symptoms: fever, chills and malaise. As the disease progresses, it results in multi-system involvements indicated by the person experiencing lethargy, nausea, vomiting, diarrhoea and headache. |
| Foot and Mouth Disease | Picornavirus[genus Aphthovirus] | Close-contact animal-to-animal spread | Animals | Serious problem to animal farming in India. |
| Hepatitis B | hepatitis B virus (HBV) | Blood Exchange, STD [Sexually transmitted disease] | Humans | Affects the liver. Acute as well as chronic. |
| Measles | measles virus | Air | Humans | Complications occur in about 30% and may include diarrhea, blindness, inflammation of the brain, and pneumonia among others |
| Polio or Poliomyelitis | Poliovirus | Water/faecal-mouth | Humans | Weak muscles leading to deformations. |
| Zika | Zika virus | Aedes mosquitoes, such as A. aegypti and A. albopictus | Humans |  |
| Diseases Caused By Protozoans | ||||
|---|---|---|---|---|
| Disease | Causative Agent | Mode Of Transmission | Type Of Organism Affected | Details |
| Amoebiasis (amoebic dysentery) | Entamoeba histolytica | Contaminated Water/food | Humans | Symptoms may include abdominal pain, mild diarrhoea, bloody diarrhea or severe colitis with tissue death and perforation. This last complication may cause peritonitis. People affected may develop anemia due to loss of blood. |
| Dysentery | Leishmania | - | - | - |
| Kala-Azar or Visceral leishmaniasis | Leishmania genus | Sandflies | Humans | This disease is the second-largest parasitic killer in the world (after malaria). The parasite migrates to the internal organs such as the liver, spleen (hence "visceral"), and bone marrow, and, if left untreated, will almost always result in the death of the host. Signs and symptoms include fever, weight loss, fatigue, anemia, and substantial swelling of the liver and spleen. |
| Malaria | Different species of Plasmodium (P. vivax, P. malaria and P. falciparum | Female Anopheles mosquito | Humans | Malaria causes symptoms that typically include fever, fatigue, vomiting, and headaches. In severe cases it can cause yellow skin, seizures, coma, or death. |
| Sleeping Sickness | Trypanosoma | Infected tsetse fly | Humans | Initially, in the first stage of the disease, there are fevers, headaches, itchiness, and joint pains. This begins one to three weeks after the bite. Weeks to months later the second stage begins with confusion, poor coordination, numbness and trouble sleeping. |
| Yellow Vein Mosaic of Okra [Ladies finger] | Bhendi yellow vein mosaic virus | Insect | Okra plant | Okra are dwarfed, malformed. |
| Diseases Caused By Fungi | ||||
|---|---|---|---|---|
| Disease | Causative Agent | Mode Of Transmission | Type Of Organism Affected | Details |
| Ringworms | Fungi belonging to the genera Micr Trichophyton and Epidermophyton | Skin-skin contact | Humans | The fungi that cause parasitic infection, collectively dermatophytes, feed on keratin, the material found in the outer layer of skin, hair, and nails. |
| Rust of wheat | Puccinia rust fungus | Air/seeds | Wheat and other crops | Wheat leaf rust is a fungal disease that affects wheat, barley and rye stems, leaves and grains. In temperate zones it is destructive on winter wheat because the pathogen. overwinters. Infections can lead up to 20% yield loss exacerbated by dying leaves which fertilize the fungus. |
- Microorganisms include bacteria, fungi, protozoa, some algae, viruses, viroids and also prions. Microorganisms may be single-celled like bacteria, some algae, and protozoa, or multicellular, such as algae and fungi.
- Some microorganisms are harmful [pathogens] as they cause various diseases in humans. A list of common diseases caused by microorganisms are given in the previous post [Diseases Caused by Microorganisms].
- Some other microorganisms are beneficial and contribute to human welfare. This post is about such useful microorganisms [useful microbes].
- Whenever you fall ill the doctor may give you some antibiotic tablets, capsules or injections such as of penicillin. The source of these medicines is microorganisms.
- These medicines kill or stop the growth of the disease-causing microorganisms. Such medicines are called ANTIBIOTICS.
- These days a number of antibiotics are being produced from bacteria and fungi. Streptomycin, tetracycline, and erythromycin are some of the commonly known antibiotics which are made from fungi and bacteria.
- In 1929, Alexander Fleming was working on a culture of disease-causing bacteria [Staphylococci]. Suddenly he found the spores of a little green mold [Penicillium notatum] in one of his culture plates. He observed that the presence of mold prevented the growth of bacteria. In fact, it also killed many of these bacteria. From this, the mold penicillin was prepared.
- Antibiotics have greatly improved our capacity to treat deadly diseases such as plague, whooping cough, diphtheria, and leprosy, which used to kill millions all over the globe. Today, we cannot imagine a world without antibiotics.
- Antibiotics taken unnecessarily may kill the beneficial bacteria in the body.
- Antibiotics, however, are not effective against cold and flu as these are caused by viruses.
- When a disease-carrying 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. So, if dead or weakened microbes are introduced in a healthy body, the body fights and kills them by producing suitable antibodies. The antibodies remain in the body and we are protected from the disease-causing microbes. This is how a vaccine works.
- Several diseases, including cholera, tuberculosis, smallpox, and hepatitis can be prevented by vaccination. Edward Jenner discovered the vaccine for smallpox in 1798.
- Microbes are also used for commercial and industrial production of certain chemicals like organic acids, alcohols, and enzymes. Examples of acid producers are 1. Aspergillus niger (a fungus) of citric acid 2. Acetobacter acetic (a bacterium) of acetic acid 3. Clostridium bretylium (a bacterium) of butyric acid 4. Lactobacillus (a bacterium) of lactic acid.
- Yeast (Saccharomyces cerevisiae) is used for commercial production of ethanol.
- Lipases are used in detergent formulations and are helpful in removing oily stains from the laundry.
- You must have noticed that 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 infraction leading to a heart attack.
- Another bioactive molecule, cyclosporin A, that is used as an immunosuppressive agent in organ-transplant patients, is produced by the fungus Trichoderma polypore.
- Statins produced by the yeast Monascus purpureus have been commercialized as blood-cholesterol lowering agents. It acts by competitively inhibiting the enzyme responsible for the synthesis of cholesterol.
- 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 [helps in the synthesis of DNA and RBC (red blood cells). Vitamin B12 deficiency causes Anemia, severe damage to the nervous system, etc.]
- In our stomach too, the LAB play very beneficial role in checking disease-causing microbes.
- Sugar is converted into alcohol by yeast. This process of conversion of sugar into alcohol is known as fermentation. Louis Pasteur discovered fermentation in 1857.
- The dough, which is used for making foods such as dosa and idli is fermented by bacteria. The puffed-up appearance of dough is due to the production of CO2 gas which is released by the microbes.
- Similarly the dough, which is used for making bread, is fermented using baker’s yeast (Saccharomyces cerevisiae).
- A number of traditional drinks and foods are also made by fermentation by the 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, soybean and bamboo- shoots to make foods.
- Cheese is one of the oldest food items in which microbes were used. The large holes in ‘Swiss cheese’ are due to production of a large amount of CO2 by a bacterium named Propionibacterium sharmanii.
- Microbes especially yeasts have been used from time immemorial for the production of beverages like wine, beer, whiskey, 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 whiskey, brandy, and rum are produced by distillation of the fermented broth.
- Sewage contains large amounts of organic matter and microbes. Many of which are pathogenic.
- Treatment of wastewater is done by the primary sludge, and the supernatant forms the effluent. The effluent from the primary settling tank is taken for secondary treatment.
- The primary effluent is passed into large aeration tanks where it is constantly agitated mechanically and the 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 oxidized by bacteria.
- The sewage water is treated till the BOD is reduced. BOD is a measure of the organic matter present in the water. The greater the BOD of wastewater more is its polluting potential.
- Once the BOD of sewage or wastewater 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 or starter.
- 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 sulfide and carbon dioxide. These gases form biogas and can be used as a 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.
- Biogas is a mixture of gases (containing predominantly methane) produced by the microbial activity and which may be used as fuel.
- Certain bacteria, which grow anaerobically on cellulosic material, produce large amount of methane [greenhouse gas] 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 the rumen, these bacteria help in the breakdown of cellulose and play an important role in the nutrition of cattle. Thus, the excreta (dung) of cattle, commonly called gobar, is rich in these bacteria. Dung can be used for the generation of biogas, commonly called gobar gas. [Humans cannot digest cellulose. Hence their faecal waste cannot produce methane].
- Biocontrol refers to the use of biological methods for controlling plant diseases and pests. Biological agents are a better alternative to weedicides and pesticides. 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 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, scientists have introduced 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. They have been shown to have no negative impacts on plants, mammals, birds, fish or even on non-target insects.
- Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilizers are bacteria, fungi and cyanobacteria.
- You may be knowing about the nodules on the roots of leguminous plants formed by the symbiotic association of Rhizobium. 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, Oscillatona, etc.
- In paddy fields, cyanobacteria serve as an important biofertiliser. Blue-green algae also add organic matter to the soil and increase its fertility.
- Salts and edible oils are the common chemicals generally used to check the growth of microorganisms. Therefore they are called preservatives. We add salt or acid preservatives to pickles to prevent the attack of microbes. Sodium benzoate and sodium metabisulphite are common preservatives. These are also used in the jams and squashes to check their spoilage.
- Common salt has been used to preserve meat and fish for ages. Meat and fish are covered with dry salt to check the growth of bacteria. Salting is also used to preserve amla, raw mangoes, tamarind, etc.
- Jams, jellies, and squashes are preserved by sugar. Sugar reduces the moisture content which inhibits the growth of bacteria which spoil food.
- Use of oil and vinegar prevents spoilage of pickles because bacteria cannot live in such an environment. Vegetables, fruits, fish and meat are often preserved by this method.
- Pasteurized milk can be consumed without boiling as it is free from harmful microbes. The milk is heated to about 700 C for 15 to 30 seconds and then suddenly chilled and stored. By doing so, it prevents the growth of microbes. This process was discovered by Louis Pasteur. It is called pasteurization.