Role of Microbes in Human Welfare

1. Microbes in Household Products-

Micro-organisms such as Lactobacillus and others commonly called lactic acid bacteria (LAB) grow in milk and convert it to curd. LAB produce acids that coagulate and partially digest the milk proteins. It also improves its nutritional quality by increasing vitamin B12. In our stomach too, the LAB play very beneficial role in checking disease causing microbes.

The dosa and idli is also fermented by bacteria. 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. The 'Roquefort cheese' are ripened by growing a specific fungi on them, which gives them a particular flavour.

2. Microbes in Industrial Products-

In industry, microbes are used to synthesize a number of products valuable to human beings. Beverages and antibiotics are some examples. Production on an industrial scale requires growing microbes in very large vessels called fermentors.

A) Fermented Beverages-

Microbes like yeast are used for the production of beverages like wine, beer, whisky, brandy or rum. 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. Wine and beer are produced without distillation whereas whisky, brandy and rum are produced by distillation of the fermented broth.

B) Antibiotics-

Anti is a Greek word that means 'against', and bio means 'life', together they mean 'against life' (in the context of disease causing organisms); whereas with reference to human beings, they are 'pro life' and not against. Antibiotics are chemical substances, which are produced by some microbes and can kill or retard the growth of other (disease-causing) microbes.

Alexander Fleming while working on Staphylococci bacteria, once observed a mould growing in one of his unwashed culture plates around which Staphylococci could not grow. He found out that it was due to a chemical produced by the mould and he named it Penicillin after the mould Penicillium notatum. Its full potential as an effective antibiotic was established by Ernest Chain and Howard Florey. This antibiotic was extensively used to treat American soldiers wounded in World War II. Fleming, Chain and Florey were awarded the Nobel Prize in 1945, for this discovery.

Antibiotics have greatly improved our capacity to treat deadly diseases such as plague, whooping cough (kali khansi), diphtheria (gal ghotu) and leprosy (kusht rog), which used to kill millions all over the globe. Today, we can not imagine a world without antibiotics.

C) Chemicals, Enzymes and other Bioactive Molecules-

  • Aspergillus niger (a fungus) produces citric acid,
  • Acetobacter aceti (a bacterium) produces acetic acid
  • Clostridium butylicum (a bacterium) produces butyric acid
  • Lactobacillus (a bacterium) produces lactic acid.
  • Yeast (Saccharomyces cerevisiae) is used for commercial production of ethanol.
  • Enzymes like Lipases are used in detergent formulations and are helpful in removing oily stains from the laundry. 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.
  • Cyclosporin A, which is used as an immunosuppressive agent in organ-transplant patients, is produced by the fungus Trichoderma 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.

3. M icrobes in Sewage Treatment –

The municipal waste-water including human excreta is also called sewage. It contains large amounts of organic matter and microbes. Many of which are pathogenic. This can not be discharged into natural water bodies like rivers and streams directly.Before disposal, hence, sewage is treated in sewage treatment plants (STPs) to make it less polluting. Treatment of waste water is done by the heterotrophic microbes naturally present in the sewage. This treatment is carried out in two stages:

Primary treatment: These treatment steps basically involve physical removal of particles – large and small – from the sewage through filtration and sedimentation. These are removed in stages; initially, floating debris is removed by sequential filtration. Then the grit (soil and small pebbles) are removed by sedimentation. All solids that settle form the primary sludge, and the supernatant forms the effluent. The effluent from the primary settling tank is taken for secondary treatment.

Secondary treatment or Biological 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. The BOD test measures the rate of uptake of oxygen by micro-organisms in a sample of water and thus, indirectly, 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. 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.

4. M icrobes in Production of Biogas –

Biogas is a mixture of gases (containing predominantly methane) produced by the microbes and which may be used as fuel. Certain bacteria, which grow anaerobically on cellulosic material, produce large amount of methane along with CO2 and H2. These bacteria are collectively called methanogens, and one such common bacterium is Methanobacterium. These bacteria are 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.

The biogas plant consists of a concrete tank (10-15 feet deep) in which bio-wastes are collected and a 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 due to the microbial activity. The biogas plant has an outlet, which is connected to a pipe to supply biogas to nearby houses. The spent slurry is removed through another outlet and may be used as fertilizer. Cattle dung is available in large quantities in rural areas where cattle are used for a variety of purposes. So biogas plants are more after build in rural areas. The biogas thus produced is used for cooking and lighting.

The technology of biogas production was developed in India mainly due to the efforts of Indian Agricultural Research Institute (IARI) and Khadi and Village Industries Commission (KVIC).

5. M icrobes as Biocontrol Agent –

Biocontrol refers to the use of biological methods for controlling plant diseases and pests. Use of chemicals like insecticides and pesticides causes great harm. These chemicals are toxic and extremely harmful, to human beings and animals alike, and have been polluting our environment (soil, ground water), fruits, vegetables and crop plants. Our soil is also polluted through use of weedicides to remove weeds.

Biological control of pests and diseases: It 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 organic farmer 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. 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 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 brassica 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.

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. Baculoviruses (genus Nucleopolyhedrovirus) are pathogens that attack insects and other arthropods. These viruses are excellent candidates for species-specific, narrow spectrum insecticidal applications. The beneficial insects are being conserved to aid in an overall integrated pest management (IPM) programme, or when an ecologically sensitive area is being treated.

6. Microbes as Biofertilizers-

Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilisers are bacteria, fungi and cyanobacteria.

  • 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, eg Anabaena, Nostoc, Oscillatoria, etc. In paddy fields, cyanobacteria serve as an important biofertiliser. Blue green algae also add organic matter to the soil and increase its fertility. Currently, in our country, a number of biofertilisers are available commercially in the market and farmers use these regularly in their fields to replenish soil nutrients and to reduce dependence on chemical fertilisers.

Important terminology-

Fermentors – Production of beverages and antibiotics on an industrial scale, requires growing microbes in very large vessels called fermentors.

Antibiotics – Antibiotics are chemical substances, which are produced by some microbes and can kill or retard the growth of other (disease-causing) microbes.

Primary treatment: The treatment step of sewage for physical removal of particles – large and small – from the sewage through filtration and sedimentation is called Primary treatment.

Secondary treatment or Biological treatment: After primary treatment.the primary effluent is passed into large aeration tanks where it is constantly agitated mechanically and air is pumped associated with fungal filaments to form mesh like structures).

BOD (biochemical oxygen demand) -BOD refers to the amount of the oxygen that would be consumed if all the organic matter in one liter of water were oxidised by bacteria.

Activated sludge – 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.

Anaerobic sludge digesters – A small part of the activated sludge is pumped back into the aeration tank to serve as the inoculum. The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters.where anaerobica bacteria and the fungi digest the sludge.

Methanogens – Certain bacteria, which grow anaerobically on cellulosic material, produce large amount of methane along with CO2 and H2. These bacteria are collectively called methanogens.

Biocontrol refers to the use of biological methods (using biological agents for natural predation) for controlling plant diseases and pests, rather than using chemicals.

Biofertilisers – In agriculture Biofertilisers are organisms that enrich the nutrient quality of the soil.

Organic farming -Agriculture by using only biofertilisers is called organic farming because there are problems of pollution, associated with the overuse of chemical fertilizers. The main sources of biofertilisers are bacteria, fungi and cyanobacteria.

Mycorrhiza – Fungal symbiotic association with plants which helps plants to absorb phosphorus from soil, is called mycorrhiza. Many members of the genus Glomus form mycorrhiza.

Cyanobacteria -Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environments many of which can fix atmospheric nitrogen, eg Anabaena, Nostoc, Oscillatoria, etc.

Anup Singh Yadav M.Sc. M.Ed. M.Phil. NET Lecturer in Biology