Microbes in Human Welfare Biology Notes - Household, Industrial, Sewage Treatment, Biogas, Biocontrol and Biofertilizers

Microbes in Household Products

• Lactobacillus or Lactic acid bacteria (LAB):
  • It converts milk to curd by producing acids that coagulate and partially digest the milk proteins.
  • Fresh milk can be converted to curd by adding some curd containing LAB. It also increases vitamin B₁₂ in curd.
  • In stomach, LAB helps to check pathogens.
• Bacterial fermentation (anaerobic respiration) in dough is used to make foods such as dosa, idli, etc. The puffed-up appearance of dough is due to the production of CO₂.
• Baker’s Yeast (Saccharomyces cerevisiae): It is used to make bread by fermenting dough.
• Toddy is made by fermenting sap from palms.
• Microbes are used to ferment fish, soya bean, and bamboo-shoots and to produce cheeses.
• Swiss cheese has large holes due to production of CO₂ by Propionibacterium sharmanii (a bacterium).
• Roquefort cheese is ripened by growing a fungus (Penicillium roqueforti) on them.

Microbes in Industrial Products

Production of beverages, antibiotics, etc., on an industrial scale requires growing microbes in very large vessels (fermentors).

Fermented Beverages

• Saccharomyces cerevisiae (Brewer’s yeast) is used in the production of beverages by fermenting malted cereals and fruit juices to produce ethanol.
• Wine and beer are produced without distillation.
• Whisky, brandy, rum, gin, arrack, etc., are produced by distillation of fermented broth.

Antibiotics

• Chemical substances produced by some microbes that can kill or retard the growth of pathogens.
• They are used to treat plague, whooping cough, diphtheria, leprosy, etc.
• Penicillin: First antibiotic discovered by Alexander Fleming. He observed that Staphylococci could not grow around a mould (Penicillium notatum) growing in unwashed culture plates. He extracted penicillin from it.
• Earnest Chain and Howard Florey established its full potential as an effective antibiotic.
• Fleming, Chain, and Florey were awarded the Nobel Prize (1945).

Chemicals, Enzymes, and Other Bioactive Molecules

• Organic acids: Acid producer microbes include:
  • Aspergillus niger (a fungus): Citric acid.
  • Acetobacter aceti (a bacterium): Acetic acid.
  • Clostridium butylicum (a bacterium): Butyric acid.
  • Lactobacillus (a bacterium): Lactic acid.
• Alcohol: Yeast (S. cerevisiae) is used to produce ethanol.
• Enzymes:
  • Lipases: Used in detergent formulations. Help to remove oily stains from the laundry.
  • Pectinases and Proteases: To clarify bottled juices.
  • Streptokinase: Produced by Streptococcus. Used as a ‘clot buster’ to remove clots from the blood vessels of patients who have myocardial infarction.
• Cyclosporine A: Produced by Trichoderma polysporum (fungus). Used as an immunosuppressive agent in organ transplant patients.
• Statins: Produced by Monascus purpureus (a yeast). Used as blood-cholesterol lowering agents. It inhibits the enzymes responsible for synthesis of cholesterol.

Microbes in Sewage Treatment

Sewage (municipal wastewater) contains large amounts of organic matter and microbes. Sewage is treated in Sewage Treatment Plants (STPs) to make it less polluting. It includes two stages.

Primary Treatment

It is the physical removal of particles. It includes:

• Removal of floating debris by sequential filtration.
• Removal of the grit (soil and pebbles) by sedimentation.

The settled solids form the primary sludge, and the supernatant forms the primary effluent.

Secondary Treatment (Biological Treatment)

• Primary effluent is passed into large aeration tanks and constantly agitated. This allows vigorous growth of useful aerobic microbes into flocs (bacteria associated with fungal filaments to form mesh-like structures). These microbes consume the organic matter in the effluent, reducing the Biochemical Oxygen Demand (BOD).

• The effluent is then passed into a settling tank where the bacterial flocs are sedimented. 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 sludge is pumped into large tanks called anaerobic sludge digesters, where anaerobic bacteria digest the bacteria and fungi in the sludge, producing gases like CH₄, H₂S, and CO₂. These gases form biogas.
• The effluent is released into natural water bodies like rivers and streams.
• The Ministry of Environment and Forests initiated the Ganga Action Plan and Yamuna Action Plan to save rivers from water pollution.

Microbes in Biogas Production

• Biogas is a mixture of gases (mainly CH₄) produced by microbial activity. It is used for cooking and lighting.
• Methanogens grow anaerobically on cellulosic material and produce CH₄. E.g., Methanobacterium.
• Methanobacterium is found in anaerobic sludge and the rumen of cattle (for cellulose digestion).
• The cattle dung (gobar) is rich in these bacteria. Dung can be used for generation of biogas (gobar gas).
• The Biogas plant consists of:
  • A concrete tank (10–15 feet deep) to collect bio-wastes and slurry of dung. A floating cover is placed over the slurry, which rises as biogas is produced.
  • An outlet connected to a pipe to supply biogas.
  • An outlet to remove spent slurry (used as fertilizer).

Indian Agricultural Research Institute (IARI) and Khadi and Village Industries Commission (KVIC) developed the technology of biogas production in India.

Microbes as Biocontrol Agents

• Biocontrol is the use of biological methods for controlling plant diseases and pests. For example, ladybird beetles control aphids, and dragonflies control mosquitoes.
• Chemical pesticides and insecticides kill both useful and harmful organisms and cause pollution. Biocontrol methods have no such problems.

Microbial Biocontrol Agents

• Bacillus thuringiensis (Bt): Used to control butterfly caterpillars.
  • Dried spores of Bt are mixed with water and sprayed onto vulnerable plants such as brassicas and fruit trees. These are eaten by caterpillars, releasing toxin in their gut, which kills the larvae.
  • Scientists have introduced B. thuringiensis toxin genes into plants, such as Bt cotton.
• Trichoderma sp. (fungus): Free-living fungi present in root ecosystems that control several plant pathogens.
• Baculoviruses (especially genus Nucleopolyhedrovirus): Attack insects and other arthropods. Suitable for species-specific, narrow-spectrum insecticidal applications and desirable in Integrated Pest Management (IPM) programs to conserve beneficial insects.

Microbes as Biofertilizers

• Biofertilizers are organisms that enrich the nutrient quality of the soil, such as bacteria, fungi, and cyanobacteria.
• Rhizobium (symbiotic bacteria in root nodules of leguminous plants) fix atmospheric N₂.
• Free-living bacteria in the soil, such as Azospirillum and Azotobacter, enrich the nitrogen content of the soil.
• Mycorrhiza: Symbiotic association of fungi (e.g., genus Glomus) with plants. The fungus gets food from the plant, and the fungal symbiont performs the following:
  • Absorbs phosphorus from soil and passes it to the plant.
  • Provides resistance to root-borne pathogens and tolerance to salinity and drought.
  • Contributes to overall increase in plant growth and development.
• Cyanobacteria (blue-green algae): Autotrophic microbes that fix atmospheric nitrogen, such as Anabaena, Nostoc, and Oscillatoria. In paddy fields, cyanobacteria serve as important biofertilizers, adding organic matter to the soil and increasing its fertility.