Why this chapter matters for UPSC: Microorganisms underpin multiple GS3 themes — biotechnology (GMOs, recombinant insulin, Bt crops), agriculture (biofertilizers, biopesticides), environment (bioremediation, biogas), and public health (AMR, vaccines, disease control). Antimicrobial resistance (AMR) is a recurring Mains topic.

PART 1 — Quick Reference Tables

Types of Microorganisms

Type Structure Key Examples UPSC Relevance
Bacteria Prokaryote; single-celled Lactobacillus, Rhizobium, E. coli, Bt Biofertilizers, curd, biotech
Viruses Not cells; protein coat + nucleic acid COVID-19, Influenza, Dengue, Polio, HIV Pandemic, vaccine policy
Fungi Eukaryote; can be multicellular Penicillium, Yeast, Aspergillus Antibiotics, fermentation, aflatoxin
Protozoa Single-celled eukaryote Plasmodium, Entamoeba, Leishmania Malaria, kala-azar (VL)
Algae Photosynthetic; aquatic Chlorella, Spirulina Biofuel, superfood, N-fixation

Common Diseases Caused by Microorganisms

Disease Causative Agent Type Mode of Spread
Tuberculosis (TB) Mycobacterium tuberculosis Bacterium Airborne droplets
Cholera Vibrio cholerae Bacterium Contaminated water/food
Malaria Plasmodium spp. Protozoan Anopheles mosquito
Dengue Dengue virus (DENV) Virus Aedes mosquito
COVID-19 SARS-CoV-2 Virus Airborne/droplet
Kala-azar (VL) Leishmania donovani Protozoan Sandfly bite
Amoebic dysentery Entamoeba histolytica Protozoan Contaminated food/water
Botulism Clostridium botulinum Bacterium Improperly canned food

PART 2 — Detailed Notes

Bacteria — Useful and Harmful

Key Term

Rhizobium: Nitrogen-fixing bacteria found in root nodules of leguminous plants (beans, peas, lentils, soybean). They convert atmospheric nitrogen (N₂) into ammonia (NH₃) usable by plants — a process called biological nitrogen fixation. This reduces the need for nitrogenous chemical fertilizers.

Free-living nitrogen fixers: Azotobacter (aerobic, in soil) and Azospirillum (in rhizosphere). These form the basis of biofertilizer formulations used in organic farming.

UPSC Connect

UPSC GS3 — Biofertilizers: Biofertilizers are preparations containing living microorganisms that promote plant growth by fixing nitrogen, solubilising phosphorus, or producing growth hormones.

  • Rhizobium — for legume crops (pulse cultivation, soybean)
  • Azotobacter / Azospirillum — for cereals, vegetables
  • Blue-Green Algae (BGA) / Cyanobacteria — for paddy fields (e.g., Anabaena, Nostoc)
  • Phosphate Solubilising Bacteria (PSB) — converts insoluble phosphate to plant-available form

Promoted under National Mission on Sustainable Agriculture (NMSA) and PKVY. Reduce chemical fertilizer dependence and improve soil health.

Microorganisms in Food Production

  • Yeast (Saccharomyces cerevisiae): Fermentation — glucose → ethanol + CO₂; used in bread making (CO₂ causes dough to rise), beer, wine
  • Lactobacillus: Converts lactose in milk to lactic acid → curd/yoghurt; also used in cheese, buttermilk, and fermented foods
  • Leuconostoc mesenteroides: Involved in fermentation of idli and dosa batter (along with Lactobacillus)
  • Aspergillus oryzae: Used in soy sauce and sake production
Explainer

Pasteurisation (Louis Pasteur, 1864): Milk is heated to 72°C for 15 seconds, then rapidly cooled to below 5°C. This kills pathogenic bacteria (Salmonella, Listeria, E. coli O157) without completely sterilising the milk. Pasteurisation extends shelf life and makes milk safe for consumption. It is NOT the same as sterilisation (which kills all microorganisms). Ultra-High Temperature (UHT) treatment (135°C for 2–4 seconds) gives longer shelf life at room temperature.

Microorganisms in Medicine

  • Penicillin: Discovered by Alexander Fleming in 1928 from Penicillium notatum fungus — first antibiotic; revolutionised medicine
  • Streptomycin: Discovered by Selman Waksman from Streptomyces griseus — first antibiotic effective against TB
  • Tetracycline, Erythromycin, Ampicillin — other important antibiotics from microorganisms
  • Vaccines: Use killed/attenuated pathogens or their antigens to build immunity (Polio — Salk/Sabin vaccines; BCG for TB; DPT; COVID-19 vaccines: Covaxin, Covishield)
UPSC Connect

UPSC GS3 — Recombinant Insulin (Biotechnology): Insulin was traditionally extracted from pig/cattle pancreas — expensive and limited. In 1982, Eli Lilly (USA) produced the first recombinant human insulin by inserting the human insulin gene into Escherichia coli (E. coli) using recombinant DNA technology — the first commercially approved GMO product in medicine.

India produces recombinant insulin domestically (BIOCON, Hyderabad-based, is among world's largest insulin manufacturers). This is a landmark example of how genetic engineering benefits human health.

Microorganisms in Agriculture — Bt and Biopesticides

Key Term

Bacillus thuringiensis (Bt): A soil bacterium that produces crystal proteins (Cry proteins) toxic to specific insect larvae (caterpillars, bollworms, mosquito larvae) but harmless to humans, mammals, birds, and most beneficial insects. Used as:

  1. Biopesticide (spray): Applied to crops as microbial pesticide — organic farming alternative
  2. Bt crops (GMO): Bt toxin genes (Cry1Ac, Cry2Ab) inserted into crop plants so the plant itself produces the toxin — Bt cotton approved in India in 2002 (first GM food/fibre crop in India). Also Bt brinjal (approved 2010, approval suspended same year due to political opposition; Bangladesh commercialised Bt brinjal in 2014).

Microorganisms in Environment

  • Decomposers: Bacteria and fungi break down dead organic matter → release nutrients back into soil (carbon cycling, nitrogen cycling)
  • Biogas production: Anaerobic bacteria (methanogenic archaea) decompose organic waste → methane (CH₄) + CO₂; used for cooking and electricity; Gobardhan scheme promotes biogas from cattle dung
  • Bioremediation: Using microorganisms to clean up environmental pollutants — oil spills (Pseudomonas), heavy metals, industrial effluent (sewage treatment plants use aerobic/anaerobic bacteria)

Harmful Microorganisms — Food Spoilage

  • Aflatoxin: Produced by Aspergillus flavus and Aspergillus parasiticus on stored groundnuts, maize, and spices — carcinogenic (cause liver cancer); major food safety concern in tropical countries including India
  • Botulism: Clostridium botulinum toxin in improperly canned/sealed foods — causes severe neurotoxic illness; most potent biological toxin known
  • Food preservation methods: Pasteurisation, canning, salting, drying, pickling (acid medium), refrigeration, vacuum packing, chemical preservatives (sodium benzoate), irradiation (gamma rays)

Antimicrobial Resistance (AMR)

UPSC Connect

UPSC GS3 — AMR: A Critical Global Threat: Antimicrobial resistance (AMR) occurs when microorganisms evolve mechanisms to survive antibiotic treatment. Causes: overuse and misuse of antibiotics in humans and livestock; incomplete treatment courses; antibiotics in animal feed for growth promotion.

India's AMR burden:

  • India is one of the world's largest consumers of antibiotics (both human and veterinary)
  • NDM-1 (New Delhi Metallo-beta-lactamase 1): A resistance enzyme discovered in bacteria isolated from a patient in India in 2009–2010; makes bacteria resistant to nearly all antibiotics including carbapenems (last-resort drugs). The name "New Delhi" caused diplomatic controversy.
  • ESKAPE pathogens (Enterococcus, Staphylococcus aureus, Klebsiella, Acinetobacter, Pseudomonas, Enterobacter) — most resistant organisms of clinical concern

India's response:

  • National Action Plan on AMR (NAP-AMR) 2017–2021: Five-year plan covering surveillance, stewardship, infection prevention, R&D, and international cooperation
  • Prescription-only policy for antibiotics (Schedule H and H1 under Drugs Rules)
  • Restricting use of colistin (last-resort antibiotic) in poultry feed — banned in 2019

WHO: Declared AMR one of the top 10 global public health threats. Global deaths attributable to AMR: ~1.27 million directly per year (The Lancet, 2022 study).

Exam Strategy

Prelims traps:

  • Smallpox was eradicated globally in 1980 (WHO declaration) — the only human disease eradicated so far; polio is near-eradicated but not yet officially declared
  • Penicillin was discovered in 1928 by Alexander Fleming from the fungus Penicillium — not a bacterium
  • Pasteurisation destroys pathogens but does NOT sterilise — UHT processing is closer to sterilisation
  • Bt cotton was first approved in India in 2002 — not 2001 or 2003
  • NDM-1 makes bacteria resistant — it is a resistance enzyme, not a bacterium itself
  • Biofertilizers contain living microorganisms — not dead or chemical

Mains angles:

  • India's AMR crisis: causes, consequences, National Action Plan
  • Biotechnology in agriculture: Bt crops, GMO debate, biosafety regulations
  • Bioremediation as environmental solution

Previous Year Questions

Prelims:

  1. With reference to Bacillus thuringiensis (Bt), which of the following statements is/are correct?

    1. Bt toxin proteins are toxic to all insects including beneficial ones
    2. Bt cotton was the first genetically modified crop approved for cultivation in India
      Select the correct answer:
      (a) 1 only
      (b) 2 only
      (c) Both 1 and 2
      (d) Neither 1 nor 2

  2. Which of the following is correctly matched?
    (a) Pasteurisation — kills all microorganisms in milk
    (b) Rhizobium — free-living nitrogen-fixing bacterium in soil
    (c) Penicillin — antibiotic derived from a fungus
    (d) NDM-1 — a virus causing drug-resistant infections

Mains:

  1. Antimicrobial resistance (AMR) is emerging as a silent pandemic. Examine the factors driving AMR in India and critically evaluate the National Action Plan on AMR. (CSE Mains 2022, GS Paper 3, 15 marks)

  2. What is bioremediation? Discuss its applications in addressing environmental pollution in India with suitable examples. (CSE Mains 2020, GS Paper 3, 10 marks)