Microbes in Human Welfare

• Household Products

  • Curd
    • Microbe: Lactobacillus (LAB - Lactic Acid Bacteria)
    • Process: Converts milk to curd, coagulates and digests milk proteins (casein)
    • Benefit: Improves nutritional quality, increases Vitamin B12
  • Dough (Idli & Dosa)
    • Process: Fermentation by bacteria
    • Result: Production of $CO_2$ gas causes puffing-up appearance
  • Bread
    • Microbe: Baker's yeast (Saccharomyces cerevisiae)
    • Process: Fermentation of dough
  • Traditional Drinks
    • Toddy: Made by fermenting sap from palms

• Industrial Products

  • Fermentors
    • Large vessels used for growing microbes on an industrial scale
  • Beverages
    • Microbe: Brewer's yeast (Saccharomyces cerevisiae)
    • Substrate: Malted cereals and fruit juices
    • Products: Wine, beer (produced without distillation); Whisky, brandy, rum (produced with distillation)
  • Antibiotics
    • Definition: Chemical substances produced by microbes to kill/growth-inhibit other disease-causing microbes
    • Discovery: Alexander Fleming discovered Penicillin from Penicillium notatum
    • Uses: Treat deadly diseases like plague, whooping cough, diphtheria, and leprosy
  • Chemicals, Enzymes, and Bioactive Molecules
    • Organic Acids
      • Aspergillus niger $\rightarrow$ Citric acid
      • Acetobacter acetic $\rightarrow$ Acetic acid
      • Clostridium butylicum $\rightarrow$ Butyric acid
      • Lactobacillus $\rightarrow$ Lactic acid
    • Alcohols
      • Saccharomyces cerevisiae $\rightarrow$ Ethanol
    • Enzymes
      • Lipases: Used in detergent formulations to remove oil stains
      • Pectinases & Proteases: Used to clarify bottled fruit juices
      • Streptokinase: Produced by bacterium Streptococcus, acts as a 'clot buster' for myocardial infarction patients
    • Bioactive Molecules
      • Cyclosporin A: Produced by fungus Trichoderma polysporum; acts as an immunosuppressive agent in organ-transplant patients
      • Statins: Produced by yeast Monascus purpureus; acts as blood-cholesterol lowering agents by competitively inhibiting the enzyme responsible for cholesterol synthesis

• Sewage Treatment

  • Definition: Municipal wastewater treatment to make it less polluting
  • Primary Treatment
    • Physical removal of particles through filtration and sedimentation
    • Floating debris removed by sequential filtration
    • Grit (soil and small pebbles) removed by sedimentation
    • Solids form the primary sludge; effluent forms the primary effluent
  • Secondary Treatment (Biological Treatment)
    • Aeration Tanks: Primary effluent passed; vigorous growth of useful aerobic microbes into flocs (masses of bacteria associated with fungal filaments)
    • Microbes consume major part of organic matter, significantly reducing BOD (Biochemical Oxygen Demand)
    • Settling Tank: Bacterial flocs are sedimented, forming activated sludge
    • Anaerobic Sludge Digesters:
      • A small part of activated sludge is pumped back into aeration tank; remaining is fed into anaerobic digesters
      • Anaerobic bacteria digest bacteria and fungi, producing gases like methane, hydrogen sulfide, and $CO_2$ (Biogas)
    • Effluent is released into natural water bodies like rivers and streams

• Production of Biogas

  • Definition: Gas mixture (mainly methane) produced by microbial activity for cooking and lighting
  • Methanogens
    • Anaerobic bacteria (e.g., Methanobacterium)
    • Grow anaerobically on cellulosic material in cattle dung (gobar)
  • Biogas Plant Structure
    • Concrete tank (10-15 feet deep) for slurry input
    • Floating cover or gas holder which rises as biogas is produced
    • Outlet pipe to supply biogas and connection for spent slurry use as fertilizer

• Microbes as Biocontrol Agents

  • Definition: Biological method of controlling plant diseases and pests
  • Advantages: Chemical-free, eco-friendly, species-specific
  • Examples
    • Ladybird: Controls aphids
    • Dragonflies: Controls mosquitoes
    • Bacillus thuringiensis (Bt): Bacteria used to control butterfly caterpillars; available as dried spores mixed with water and sprayed onto vulnerable plants
    • Nucleopolyhedrovirus (NPV): Attack insects and other arthropods; excellent for species-specific, narrow-spectrum insecticidal applications (ideal for Integrated Pest Management - IPM)

• Microbes as Biofertilisers

  • Definition: Organisms that enrich the nutrient quality of the soil
  • Main Sources
    • Bacteria
      • Rhizobium: Symbiotic association in root nodules of legumes, fixes atmospheric nitrogen
      • Azospirillum & Azotobacter: Free-living bacteria that fix atmospheric nitrogen in soil
    • Fungi (Mycorrhiza)
      • Symbiotic association between fungi and roots of higher plants (e.g., Glomus genus)
      • Fungal symbiont absorbs phosphorus from soil and passes it to the plant
      • Plant benefits: Resistance to root-borne pathogens, tolerance to salinity and drought, overall an increase in plant growth and development
    • Cyanobacteria
      • Autotrophic, aquatic/terrestrial microbes capable of fixing atmospheric nitrogen
      • Examples: Anabaena, Nostoc, Oscillatoria
      • Major biofertiliser in paddy fields; blue-green algae also add organic matter to the soil and increase its fertility