CBSE Class 12 Biology Microbes In Human Welfare Notes Set B

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.
• During growth, the LAB produces 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.
• In our stomach, the LAB play very beneficial role in checking disease-causing microbes.
• The dough, which is used for making foods such as dosa and idlis, also fermented by bacteria.
• The puffed-up appearance of dough is due to the production of CO₂ gas.
• The large holes in ‘Swiss cheese’ are due to production of a large amount of CO₂ by a bacterium named Propionibacterium sharmanii.

Microbes in Industrial Products

Fermented Beverages
• Saccharomyces cerevisiae is used for bread-making and commonly called brewer’s yeast.
• Wine and beer are produced without distillation
• Whisky, brandy and rum are produced by distillation of the fermented broth.

Antibiotics
• 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.
• However, its full potential as an effective antibiotic was established much later 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.

Chemicals, Enzymes And Other Bioactive Molecules
• Aspergillus niger (a fungus): Citric acid
• Acetobacter aceti (a bacterium): Acetic acid
• Clostridium butylicum (a bacterium): Butyric acid
• Lactobacillus (a bacterium): Lactic acid
• Saccharomyces cerevisiae (Yeast) is used for commercial production of ethanol
• Lipases are used in detergent formulations and are helpful in removing oil 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 infarction leading to heart attack.
• Bioactive molecule, Cyclosporin – A, 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.
• 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.

Microbes in Sewage Treatment

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 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 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. The effluent from the secondary treatment plant is generally released into natural water bodies like rivers and streams.

Microbes in the Production of Biogas
• 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 commonly found in the anaerobic sludge during sewage treatment.
• In rumen, these bacteria help in the breakdown of cellulose and play an important role in the nutrition of cattle.
• 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 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).
• Biogas: It is an ideal gas made up of 50-70% methane (CH₄), 30-40% CO₂, 1-5% H₂, traces of O₂ and N₂ and H₂S.

Microbes As Biocontrol Agents
• The use of biocontrol measures will greatly reduce our dependence on toxic chemicals and pesticides.
• 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.

Microbes As Biofertilizers
• The main sources of biofertilizer are bacteria, fungi and Cyanobacteria.
• 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.
• Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environments many of which can fix atmospheric nitrogen, e.g. Anabaena, Nostoc, Oscillatoria, etc.
​​​​​​​• In paddy fields, Cyanobacteria serve as an important biofertilizer.

- Those organisms which are not visible with naked eyes and viewed under the microscope are called microorganisms or microbes. These include bacteria, protozoans, yeasts, viruses etc. 

- The microbes are almost omnipresent (i.e., found every where). They are found in snow, inside thermal vents (or inside geysers, high acidic habitats etc.) Some remain viable when cooled upto – 190°C.

- Microbes are both useful and harmful for humans. They cause several diseases, can spoil food and  used in many economical products. Here, we are concerned mainly with beneficial effects of microbes.

MICROBES IN HOUSEHOLD PRODUCTS 
A variety of microbes or products obtained from them are used in our daily life. 

Dairy Products

- Lactic acid bacteria convert lactose sugar of milk into lactic acid.

- Lactic acid causes coagulation of milk protein casein. Milk is changed into curd, yoghurt and cheese.

- Curd is prepared by inoculating cream and skimmed milk with Lactobacillus acidophilus at temperature of about 40°C.

- Yoghurt is produced by curdling milk with the help of Streptococcus thermophilus and Lactobacillus bulgaricus.

- Butter milk is acidulated product which is formed by inoculating skimmed milk with starter culture of Streptococcus cremoris, S. lactis, Lactobacillus acidophilus, Leuconostoc species at 22°C for 18 hours.

- Cheese is the partially degraded concentrate of milk fat and casein manufactured by microorganisms. Swiss cheese is characterised by the characteristic flavour and large holes. The large holes are formed due to amount of CO₂ released by a thermophilic bacteria (Propionibacterium sharmanii). Roquefort cheese is characterised by greenish blue mottling. It is ripened by Penicillium roquefortii. It is probably the best known cheese made from sheep’s milk. Camembert cheese employs Penicillium camemberti for ripening. 

Dough for Making Food Items

- Numerous food items such as ‘dosa’, ‘idli’, ‘jalebi’ and ‘bread’ are prepared by fermentation process in which one or more kinds of microbes are used.

- The ‘dough’ which is used for making dosa and idli is allowed to ferment overnight for 10 to 12 hours. The bacteria, which come from atmosphere (particularly Leuconostoc  mesenteroides, Streptococcus faecalis) cause fermentation so that the dough increases in volume and gets sour. Increase in the volume of dough is due to carbon dioxide gas (CO₂ ) that is released as a result of fermentation

- Bread is made from flour obtained by grinding cereal grain usually wheat. Selected strains of Saccharomyces cerevisiae grown on molasses are used as baker’s yeast. A small quantity of yeast is added to wheat flour and kneaded. The kneaded flour is kept at warm temperature for a few hours. It swells up. The phenomenon is called leavening.

Other Household Products

- Toddy, a traditional drink of South India is made by fermenting latex obtained from toddy palm and coconut water. It undergoes fermentation with the help of naturally occurring yeast. It is a refreshing drink which can be heated to produce palm sugar (Jaggery).

- Other foods like tempeh (Indonesia), tofu (Japanese) and sufu (Chinese) are fermented foods  obtained from soyabean.

- Soy sauce is brown flavoured salty sauce fermented from soyabean and wheat.

- Several types of sausages are prepared by fermentation and curing of fish and meat is also done with the help of microbes.

MICROBES IN INDUSTRIAL PRODUCTS
A variety of products in enormous amounts are produced by microbes such as – beverages (alcoholic and non alcoholic ),antibiotics, organic acids, enzymes, vitamins, hormones, amino acids, vaccines and steroids.

Alcoholic fermentation

- Yeast species used in alcoholic fermentation are Saccharomyces cerevisiae, S. ellipsoideus, S. sake, etc.

- Fermented nutrient medium used differs based on products.

- The yeasts which are used in the brewing industry for the preparation of alcoholic drinks are collectively called brewer’s yeast.

different types of alcoholic beverages are produced by using different brewer’s yeast.

Products (Source)     Method                         Brewer’s yeast
Beer (Grain)              Non distillation        Saccharomyces cerevisiae and S. carisbergensis
Wine (Fruit juice)       Non distillation        S. ellipsoideus

- Whisky, rum, gin, brandy, vodka and fenny are distilled beverages, so called hard liquors (Higher % of alcohol). 

- By products of alcoholic fermentation are CO₂ and ethanol.

Antibiotics

- Antibiotics are the chemical substances produced by microorganisms that in low concentration inhibits the growth or kill the pathogenic organisms without harming the host. The term “antibiotic“ (means against life) was coined by Waksman (1942).

- Alexander Fleming (1928) discovered first antibiotic penicillin from Penicillium notatum in 1928.

- It was commercially extracted by efforts of Chain and Florey.

- This antibiotic was extensively used in treating wounded American soldiers in world war II.

- Fleming, Chain and Florey were awarded with Nobel prize in 1945.

- Over 7000 antibiotics are known. Streptomyces griseus produces more than 41 antibiotics while Bacillus subtilis can give about 60 antibiotics. 

Antibiotics are obtained from lichens, eubacteria, fungi and actinomycetes.

Antibiotics               Source                            Action
Chloramphenicol    S. venezuelae               Typhoid, whooping cough (Kali Khansi)
Erythromycin          S. erythreus                  Diphtheria (gal ghotu)
Chloromycetin        S. lavendulae                Pneumonia
Streptomycin          S. griseus                      Meningitis, Pneumonia, TB
Bacitracin               Bacillus licheniformis     Syphilis

Antibiotics are medicines used for treatment of a number of pathogenic or infectious diseases.

Single Cell Protein

- Single cell protein (SCP) is the production of microbial biomass for consumption as human food or animal feed. The common SCP are Spirulina, yeast and Fusarium graminearum.

- SCP is rich in high quality proteins but poor in fat.

- SCP is useful in reducing environmental pollution by managing industrial and agricultural wastes.

Chemicals, Enzymes and other Bioactive Molecules

- A number of organic acids are manufactured with the help of microbes e.g., acetic acid, citric acid, lactic acid, gluconic acid, cyclosporin A, statins.

- Acetic acid is produced from fermented alcohol with the help of bacteria, Acetobacter aceti.

- Citric acid is obtained through the fermentation carried out by Aspergillus niger and Mucor species on sugary syrup.

- Gluconic acid is prepared by the activity of Aspergillus niger and Penicillium species.

- Cyclosporin A is an important bioactive chemical produced by the fungus Trichoderma polysporum. It is used as an immunosuppressive agent in organ transplantation.

- Statins are produced by yeast Monascus purpureus. It acts as competitive inhibitor of enzyme for cholesterol synthesis. So, it is used as blood cholesterol lowering agent.

- Enzymes are proteinaceous substances of biological origin which are capable of catalysing biochemical reactions without themselves undergoing any change. 

- Pectinases are enzymes obtained commercially from Byssochlamys fulva. Alongwith proteases they are used in clearing of fruit juices and also in retting of fibres and preparation of green coffee.

- Lipases are lipid dissolving enzymes that are obtained from Candida lipolytica and Geotrichum candidum. Lipases are added in detergents for removing oily stains from laundry and also used in flavouring cheese.

- Streptokinase (Tissue Plasminogen Activator or TPA) is an enzyme obtained from the cultures of some haemolytic streptococci. It has fibrinolytic effect, therefore it helps in clearing blood clots inside the blood vessels.

- Yeast (Saccharomyces cerevisiae) is used for commercial production of ethanol.