Table of Contents
Useful Microbes – Microbes In Human Welfare: Microbes in the production of Antibiotics, Vaccines, Curd, Fermented beverages, Biogas, Biofertilisers etc.
Useful Microbes – Microbes In Human Welfare
- 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].
Antibiotics and Vaccination
- 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 mould [Penicillium notatum] 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 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.
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
- Acetobacter aceti (a bacterium) of acetic acid
- Clostridium butylicum (a bacterium) of butyric acid
- 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 heart attack.
- Another bioactive molecule, cyclosporin A, that is used as an immunosuppressive agent in organ-transplant patients, is produced by the fungus Tnchoderma polysporum.
- Statins produced by the yeast Monascus purpureus have been commercialized as blood-cholesterol lowering agents. It acts by competitively inhibiting the enzyme responsible for synthesis of cholesterol.
Milk to Curd
- 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 nervous system etc.].
- In our stomach too, the LAB play very beneficial role in checking disease-causing microbes.
Microbes and Fermentation
- 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, soyabean 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, whisky, 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 whisky, brandy and rum are produced by distillation of the fermented broth.
Microbes in sewage treatment
- Sewage contains large amounts of organic matter and microbes. Many of which are pathogenic.
- Treatment of waste water 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 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 waste water, more is its polluting potential.
- Once the BOD of sewage or waste water 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 sulphide and carbon dioxide. These gases form biogas and can be used as 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.
Microbes in production of biogas
- 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 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 generation of biogas, commonly called gobar gas. [Humans cannot digest cellulose. Hence their faecal waste cannot produce methane].
Microbes as biocontrol agents
- 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, the 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.
Microbes as biofertilisers
- Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilisers 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.
- Microbes are a very important component of life on earth. Not all microbes are pathogenic. Many microbes are very useful to human beings.
- We use microbes and microbially derived products almost every day.
- Bacteria called lactic acid bacteria (LAB) grow in milk to convert it into curd.
- The dough, which is used to make bread, is fermented by yeast called Saccharomyces cerevisiae.
- Certain dishes such as idli and dosa, are made from dough fermented by microbes.
- Bacteria and fungi are used to impart particular texture, taste and flavor to cheese.
- Microbes are used to produce industrial products like lactic acid, acetic acid and alcohol, which are used in a variety of processes in the industry.
- Antibiotics like penicillins produced by useful microbes are used to kill disease-causing harmful microbes.
- Antibiotics have played a major role in controlling infectious diseases like diphtheria, whooping cough and pneumonia.
- For more than a hundred years, microbes are being used to treat sewage (waste water) by the process of activated sludge formation and this helps in recycling of water in nature.
- Methanogens produce methane (biogas) while degrading plant waste.
- Biogas produced by microbes is used as a source of energy in rural areas.
- Microbes can also be used to kill harmful pests, a process called as biocontrol.
- The biocontrol measures help us to avoid heavy use of toxic pesticides for controlling pests.