In this article we will discuss about the economic importance of microbes.
Microbes in Household Products:
Microbes and their products are used in everyday life like production of curd, formation of dough, cheese, etc.
Production of Curd:
Microorganisms like Lactobacillus and other Lactic Acid Bacteria (LAB) grow in milk, which convert it into curd. We have seen at home that a starter is added to milk which turn it into curd. This starter is known as inoculum, which contains millions of LAB.
During growth, LAB produce acids that coagulate and partially digest the milk proteins. Thus, converting milk to curd. These also improve nutritional quality by increasing vitamin-B12 content of the curd. LAB also play very beneficial role in checking disease causing microbes in our stomach.
Fermentation by Microbes:
(i) Dough:
It is fermented by bacteria in making foods such as dosa and idli. The puffed up appearance of dough is due to the production of CO2 during fermentation. In bread making, dough is fermented using baker’s yeast, i.e., Saccharomyces cerevisiae.
(ii) Toddy:
It is a traditional drink of some parts of Southern India. It is made by yeast fermentation sap from palms trees, coconut, etc. Microbes are also used to ferment fish, soya bean, bamboo shoots, etc.
(iii) Cheese:
It is known to be the oldest food item in which microbes are used. It is formed by partial degradation of milk by different microorganisms. Different varieties of cheese are known by their texture, flavour and taste.
Swiss cheese with large holes is produced by Propionibacterium sharmanii. Holes are created due to the production of large amount of CO2 produced by this bacterium. Roquefort cheese is ripened by growing a specific fungi on them, which give them a particular flavour.
Microbes in Industrial Products:
Microbes are used to synthesise a number of products valuable to human beings in industries also e.g., beverages and antibiotic. For industrial production, microbes are grown in very large vessels called fermenters.
1. Fermented Beverages:
Yeasts have been used from ancient time for the production of beverages like wine, beer, whisky, brandy and rum. Saccharomyces cerevisiae commonly called brewer’s yeast is used for bread making, fermenting malted cereals and fruit juices to ethanol.
Depending upon the type of raw material and processes, different types of alcoholic drinks are prepared. Wine and beer are filtered, pasteurized and bottled without further distillation, whereas whisky, brandy and rum are produced by the distillation of fermented broth. Beer has an alcoholic content of 3-6%, while in wines; the alcoholic content is around 9-12%.
2. Antibiotics:
The term ‘antibiotics’ was coined by Waksman (1942). The name antibiotic is derived from the Greek words against and bios—life, together they mean ‘against life’ (with reference to disease causing organisms). These are the chemical substances, produced by some microbes and can kill or retard the growth of other disease causing microbes.
The first antibiotic discovered was Penicillin. Alexander Fleming, while working on Staphylococci bacteria, found a chemical, which inhibits the bacterial growth. It was named as penicillin after the mould Penicillium notatum. The potential use of Penicillium as antibiotic was established by Ernest Chain and Howard Florey.
Penicillium was extensively used in treating American soldiers wounded in World War II. Chain and Florey were awarded the Nobel Prize in 1945, for this discovery. Some other antibiotics were also purified after the successful discovery of Penicillium.
They greatly improved the capacity to treat deadly diseases like plaque, whooping cough (kali khansi), diphtheria (gal ghotu), leprosy (kusht rog), which use to kill millions of people all over the world, etc.
As pathogens often develop resistance to existing antibiotics, so, the newer antibiotics are required to be produced.
The good antibiotics should be harmless to host with no side effects and should have the ability to destroy pathogens. Antibiotics are mainly obtained from Actinomycetes, eubacteria and fungi, etc.
3. Chemicals, Enzymes and other Bioactive Molecules:
Microbes are being used for the commercial and industrial production of certain chemicals like alcohols, organic acids and enzymes. The other molecules, which are functional in living systems or can interact with their components are called bioactive molecules. Enzymes are very well established in biotechnology and the microbes are also used in their production.
Microbes in Sewage Treatment:
Sewage refers to the municipal wastewater generated every day in cities and towns.
Human excreta is a major component of it. It contains large amount of organic matter, microbes and pathogens out of which many are pathogenic.
It cannot be discharged into natural water-bodies like rivers, streams, etc., because it not only contains human excreta and other organic wastes but a number of pathogenic microorganisms too.
Before disposal, sewage has to be treated in a Sewage Treatment Plants (STPs) in order to make it less polluting. The treatment of wastewater is done by the heterotrophic microbes, naturally present in the sewage.
This treatment is carried out in two stages:
1. Primary Treatment:
It is also known as physical treatment because it basically involves physical removal of small and large, floating and suspended solids from sewage.
Primary treatment involves various stages like filtration and sedimentation. Initially, floating debris are removed by sequential filtration with progressively small pore filter.
Then, the grit (soil and small pebbles) are removed by sedimentation in settling tanks. Aluminium or iron sulphate is added in certain places for flocculation. All the solids that settle forms the primary sludge.
It traps lots of microbes and debris. The supernatant forms the effluent. The effluent from primary tank goes for secondary treatment.
2. Secondary Treatment:
This treatment is also known as biological treatment because it involves the use of microbes or biota for the treatment of sewage.
The effluent from primary treatment is passed into a large aeration tank, where it is constantly mechanically agitated and air is pumped into it.
This air helps in the growth of useful aerobic, microbes into floes (masses of bacteria associated with fungal filament to form mesh likes structures).
While growing, these microbes consume the major part of the organic matter converting into microbial biomass and releasing a lot of minerals. This significantly reduces the BOD (Biochemical Oxygen Demand).
Biochemical Oxygen Demand (BOD):
BOD refers to the amount of the oxygen that would be consumed if all the organic matter in one liter of water was oxidised by bacteria.
(a) The greater the BOD, more polluting water will result. So, the sewage water is treated till the BOD is reduced.
(b) When the BOD of effluent is reduced significantly, the effluent is then passed into a settling tank, where the bacterial ‘floes’ are allowed to sediment called activated sludge.
(c) A small part of the activated sludge is then pumped back into the aeration tank to serve as the inoculum. Then the remaining part of the sludge is pumped into large tanks called anaerobic sludge digesters, in which other anaerobic bacteria are also present.
(d) They digest the organic mass as well as aerobic microbes bacteria and fungi of the sludge. During the digestion, gases like methane, hydrogen sulphide (H2S), carbon dioxide (CO2) etc., are produced.
(e) These gases form biogas that are used as a source of energy because these are inflammable.
(f) The effluent from secondary treatment plant is released into natural water-bodies like rivers and streams.
Microbes in Production of Biogas:
Biogas is a mixture of gases, but the major content is methane gas. It is produced by the microbial activity in digestion of biomass with the help of certain bacteria. Biogas is used as fuel.
The type of gas produced depends upon the microbes and the organic substrates they utilise. Certain bacteria, which grow anaerobically on cellulosic material, produce large amount of methane along with CO2 and H2.
These bacteria are called methanogens. Methanogens produce large amount of methane (50-70%), CO2 (30-40%) and H2. Methanogens, are also present in anaerobic sludge during sewage treatment. They are also present in rumen (a part of stomach) of cattle, where they help in breakdown of cellulosic material in the food and thus, play important role in nutrition of cattle.
Biogas (Gobar Gas) Plant:
These plants are mostly functional in rural areas, where dung can be used for the generation of biogas. The excreta of cattle commonly called gobar is rich in methanogenic bacteria.
Cattle dung is available in large quantities in rural areas hence; it is a good choice for the production of biogas. Biogas plant consists of a concrete tank (10-15 feet deep) in which bio-wastes are collected and slurry of dung is fed. A floating cover is placed over the slurry, which keeps on rising as the gas is produced in the tank.
Methanobacterium in the dung acts on the bio-waste to produce biogas. An outlet is also present which connects to a pipe that supply biogas to the nearby house. There is an another outlet from which spent slurry is being removed that can be used as fertiliser.
The biogas thus produced is used for cooking and lighting. Biogas fuel technology was developed in India mainly by Khadi and Village Industries Commission (KVIC) and Indian Agricultural Research Institute (IARI).
Microbes as Bio-Control Agents:
Bio-control is the use of biological methods for controlling plant diseases and pests. These chemicals are also harmful for human beings and animals. Thus, polluting the environment (soil, groundwater).
(a) Chemical pesticides decrease the growth of weeds, reduce attack from pathogens and drive away or kill insects, worms and birds, which happen to feed on crop plants.
(b) These undesirable species can range from agricultural pests to water contaminants to virulent pathogens. They are undesirable because these species are a detriment to human interests in an ecosystem.
(c) Microbes used for bio-control reduce the target species population through many ecological mechanisms, including pathogenism, competition, production of allelochemicals and other interactions.
(d) Bacteria, fungi and viruses can all act as bio-control agents due to the large diversity of target species and the variety of methods of action. The important examples of microbial bio-control agents include Bacillus thuringiensis, Pseudomonas and Beauveria bassiana.
Biological Control of Pests and Diseases:
Bio-control is a holistic approach that seeks to develop an understanding of the interactions between various organisms and use this knowledge to control pests, weeds, etc.
Bio-controlling requires familiarity with various life forms, their habitat, predators, life style, etc., to use them in bio-control measures and reducing the dependence on chemicals and pesticides. Bio-control microbes control their target species through a web of biological interactions.
Some examples of biological control agents are given as under:
(a) Ladybird and dragonflies are useful to get rid of aphids and mosquitoes respectively.
(b) To control butterfly, caterpillars, bacteria, such as. Bacillus thuringiensis is used in the form of sprays.
(c) Using genetic engineering methods. Bacillus thuringiensis toxin genes are introduced into plants. Such plants are resistant to attack by insect pests. Bt cotton is one such example.
(d) Trichoderma species are free-living fungi that are very common in the root ecosystems. They are effective bio-control agents of several plant pathogens.
(e) Baculoviruses belonging to the genus Nucleo poly hedro virus are viruses used in biological control. These are excellent for species-specific, narrow spectrum insecticidal applications. They are used in integrated pest management programme. They do not have any negative impact on the ecosystem.
Microbes as Bio-Fertilisers:
The chemical fertilisers are being used in increasing amounts in order to increase the output in high yielding varieties of crops. However, due to the excessive pollution because of these chemical fertilisers, there is pressure to shift to organic farming i.e., to use biofertilisers. Biofertilisers are the organisms that bring about nutrient enrichment of soil by enhancing the availability of nutrients to the crops.
The main sources of bio-fertilisers are as follows:
1. Bacteria:
Rhizobium is a symbiotic bacterium that lives in the root nodules of legumes and fixes atmospheric nitrogen into organic compounds. Azotobacter and Azospirillum are free-living bacteria, which absorb free nitrogen from the soil, air and convert it into salts of nitrogen compounds like amino acids and enrich the soil nutrients.
Nitrogen-fixing bacteria fix atmospheric nitrogen into organic form, which is used by the plant as nutrient.
2. Fungi:
It also forms symbiotic association with plants called as mycorrhiza, which absorb phosphorus from soil and pass it on to the plants. Many members of genus Glomus form mycorrhiza.
Plants with mycorrhizal association show other benefits also such as:
(i) Resistance to root borne pathogens.
(ii) Tolerance to salinity and drought.
(iii) Increase in plant growth and development.
3. Cyanobacteria:
These are autotrophic microbes found in aquatic and terrestrial environments. Many of them fix-nitrogen, e.g., Anabaena, Nostoc, Oscillatoria, etc.
In paddy fields, cyanobacteria serve as important bio-fertilisers, so blue-green algae also add organic matter to the soil, thus increasing the fertility.