Microbes in Household Products
- Lactic Acid Bacteria (LAB): E.g., Lactobacillus. Grow in milk and convert it to curd.
- Core Mechanism: LAB produce acids that coagulate and partially digest milk proteins.
- Benefits: Improves nutritional quality by increasing Vitamin B12 NEET 2018 2018. In the stomach, LAB play a beneficial role in checking disease-causing microbes.
- Fermentation of Dough: Used for dosa, idli, and bread.
- The puffed-up appearance of dough is due to the production of CO2 gas 2002.
- Bread dough is fermented using baker's yeast, Saccharomyces cerevisiae.
- Cheese Production:
- 'Swiss cheese': Large holes are due to the production of a large amount of CO2 by a bacterium named Propionibacterium sharmanii 2015.
- 'Roquefort cheese': Ripened by growing a specific fungi (Penicillium roqueforti) on them, giving a particular flavour.
Microbes in Industrial Products
Production on an industrial scale requires growing microbes in very large vessels called fermenters.
Fermented Beverages
- Brewer's yeast (Saccharomyces cerevisiae) ferments malted cereals and fruit juices to produce ethanol 1998 2000 2012 2017 NEET 2019.
- Wine and beer are produced without distillation. Whisky, brandy, and rum are produced with distillation.
Antibiotics
- Definition: Chemical substances produced by some microbes that kill/retard the growth of other (disease-causing) microbes.
- Penicillin: First antibiotic discovered by Alexander Fleming from the mould Penicillium notatum. Its full potential was established by Ernest Chain and Howard Florey (awarded Nobel Prize in 1945).
Chemicals, Enzymes, and Bioactive Molecules
| Microbe | Type | Product | Application / High-Yield Note |
|---|---|---|---|
| Aspergillus niger | Fungus | Citric acid | Good commercial producer 1995 1998 2013 2020 2024 Re. |
| Acetobacter aceti | Bacteria | Acetic acid | Produces vinegar 2011. |
| Clostridium butylicum | Bacteria | Butyric acid | 2016 2020 2024 Re |
| Lactobacillus | Bacteria | Lactic acid | - |
| Microbes (general) | - | Lipases | Used in detergent formulations to remove oily stains from laundry 2016. |
| Microbes (general) | - | Pectinases & Proteases | Used to clarify bottled fruit juices. |
| Streptococcus | Bacteria | Streptokinase | Modified by genetic engineering; used as a 'clot buster' for patients with myocardial infarction (heart attack) 2012 2016 2024 Re. |
| Trichoderma polysporum | Fungus | Cyclosporin A | Used as an immunosuppressive agent in organ-transplant patients 2016 2019 2020 2024 Re. |
| Monascus purpureus | Yeast | Statins | Blood-cholesterol lowering agent 2012 2016 2019 2024 Re. Acts by competitively inhibiting the enzyme responsible for cholesterol synthesis. |
Microbes in Sewage Treatment
Sewage: Municipal waste-water containing large amounts of organic matter and pathogenic microbes. Treated in Sewage Treatment Plants (STPs) by heterotrophic microbes naturally present in sewage.
Primary Treatment (Physical)
- Physical removal of large and small particles through filtration and sedimentation 2017.
- Sequential filtration removes floating debris. Sedimentation removes grit (soil and pebbles).
- Settled solids form the primary sludge, and the supernatant forms the effluent.
Secondary / Biological Treatment
- Step 1: Aeration. Primary effluent is agitated and aerated. Allows vigorous growth of useful aerobic microbes into flocs (masses of bacteria associated with fungal filaments).
- Flocs consume major organic matter, significantly reducing BOD (Biochemical Oxygen Demand) 1998.
- Crucial detail: Greater BOD = more organic matter = higher polluting potential.
- Step 2: Settling. Effluent passed into a settling tank where bacterial flocs sediment. This sediment is activated sludge.
- A small part is pumped back as inoculum.
- Step 3: Anaerobic Sludge Digesters. The major part of activated sludge is pumped into large tanks. Anaerobic bacteria digest the bacteria and fungi in the sludge 2020.
- Core Mechanism: During digestion, anaerobic bacteria produce a mixture of gases (Methane, Hydrogen sulphide, Carbon dioxide) collectively called biogas 2011 2013 2014.
Microbes in Production of Biogas
- Biogas: A mixture of gases containing predominantly methane 2004 2012, produced by microbial activity, used as fuel.
- Methanogens: Anaerobic bacteria (e.g., Methanobacterium) that grow on cellulosic material and produce large amounts of methane along with CO2 and H2.
- Found in anaerobic sludge during sewage treatment.
- Present in the rumen of cattle, helping in the breakdown of cellulose.
- Gobar Gas Plant: Cattle dung (gobar) is fed into a concrete tank. A floating cover rises as gas is produced. Outlet supplies biogas for cooking/lighting. Spent slurry is used as fertiliser. Technology developed in India by IARI and KVIC.
Microbes as Biocontrol Agents
Biocontrol: Use of biological methods for controlling plant diseases and pests, reducing dependence on toxic chemicals and pesticides. Focuses on natural predation (checks and balances).
| Biocontrol Agent | Target Pest / Pathogen | High-Yield Notes |
|---|---|---|
| Ladybird (beetle) | Aphids | Familiar beetle with red/black markings. |
| Dragonflies | Mosquitoes | - |
| Bacillus thuringiensis (Bt) | Butterfly caterpillars | Available as dried spores. Toxin released in the larva's gut kills the caterpillar but leaves other insects unharmed 2010. Introduced into crops (Bt cotton) via genetic engineering 2019. |
| Trichoderma species | Plant pathogens | Free-living fungi, very common in root ecosystems. Effective against soil-borne plant pathogens 2008 2010 2012 2019. |
| Baculoviruses (Nucleopolyhedrovirus) | Insects and arthropods | Excellent for species-specific, narrow spectrum insecticidal applications 2019. No negative impacts on plants, mammals, birds, fish, or non-target insects. Ideal for Integrated Pest Management (IPM). |
Microbes as Biofertilisers
Biofertilisers: Organisms that enrich the nutrient quality of the soil. Main sources are bacteria, fungi, and cyanobacteria. Organic farming relies heavily on biofertilisers instead of chemical fertilisers.
| Microbe Group | Examples & Mechanisms | High-Yield Notes |
|---|---|---|
| Symbiotic Bacteria | Rhizobium forms nodules on roots of leguminous plants, fixing atmospheric nitrogen. | - |
| Free-living Bacteria | Azospirillum and Azotobacter fix atmospheric N2 while free-living in the soil 2010. | - |
| Fungi (Mycorrhiza) | Members of the genus Glomus form endomycorrhizal associations 2010. | Fungal symbiont absorbs phosphorus from soil and passes it to the plant 2011. Provides resistance to root-borne pathogens and tolerance to salinity/drought. |
| Cyanobacteria | Autotrophic microbes that fix atmospheric N2 (e.g., Anabaena, Nostoc, Oscillatoria) 1994 2010. | Serve as important biofertilisers in paddy (rice) fields 1999 2010. Add organic matter to soil. Anabaena forms a symbiotic association with the water fern Azolla to increase rice yield 1998 2000 2001 2004 2012. |