Microbes in Human Welfare

The One Thing

Microorganisms are biological tools whose metabolic activities can be controlled to produce useful foods, medicines, industrial materials, agricultural inputs, fuels, and environmental services. Their usefulness depends on the organism, the product formed, and the conditions of cultivation.

Reactions, Processes and Experiments

Key Terms

• Microbes: Microscopic organisms such as bacteria, fungi, protozoans, algae, and viruses; many are useful to humans.
• Fermentation: The microbial conversion of organic substances into useful products such as alcohol, acids, gases, or enzymes, usually under controlled conditions.
• Lactic acid bacteria: Bacteria such as Lactobacillus that convert milk into curd and improve its nutritional value by producing lactic acid.
• Yeast: Saccharomyces cerevisiae, a unicellular fungus used in baking and alcohol production.
• Antibiotics: Chemical substances produced by some microorganisms that kill or inhibit disease-causing microbes.
• Penicillin: An antibiotic obtained from Penicillium fungi; it was one of the earliest widely used antibiotics.
• Organic acids: Industrially important acids produced by microbes, including citric acid by Aspergillus niger and acetic acid by Acetobacter aceti.
• Industrial enzymes: Microbial enzymes used in products and processes, such as pectinases for fruit juice clarification and lipases in detergents.
• Bioactive molecules: Microbial substances with medical or industrial value, such as statins, cyclosporin A, and streptokinase.
• Statins: Cholesterol-lowering compounds produced by Monascus purpureus that inhibit cholesterol synthesis.
• Cyclosporin A: An immunosuppressive compound produced by Trichoderma polysporum and used during organ transplantation.
• Streptokinase: An enzyme produced by Streptococcus that helps dissolve blood clots and is used in treating heart attacks.
• Bioreactor: A vessel in which microorganisms or cells are grown under controlled conditions for large-scale production of useful products.
• Biofertilizers: Organisms or microbial preparations that increase soil fertility by fixing nitrogen or making nutrients more available.
• Rhizobium: A symbiotic nitrogen-fixing bacterium found in the root nodules of leguminous plants.
• Frankia: A nitrogen-fixing actinomycete that forms symbiotic associations with the roots of some non-leguminous plants.
• Cyanobacteria: Photosynthetic microbes such as Anabaena and Nostoc that fix atmospheric nitrogen and enrich soil, especially in paddy fields.
• Mycorrhiza: A mutually beneficial association between fungi and plant roots that improves water and mineral absorption.
• Biocontrol: The use of living organisms or their products to control pests and diseases instead of relying mainly on chemical pesticides.
• Bacillus thuringiensis: A bacterium producing insecticidal crystal proteins used to control certain insect larvae.
• Trichoderma: A beneficial fungus used as a biological control agent against several plant pathogens.
• Sewage treatment: The biological and physical removal of pollutants from wastewater before it is released into the environment.
• Biochemical oxygen demand: The amount of dissolved oxygen needed by microorganisms to decompose organic matter in water; high values indicate greater organic pollution.
• Activated sludge: Microbe-rich flocs formed during secondary sewage treatment that help break down organic pollutants.
• Biogas: A fuel-rich gas mainly containing methane, produced by anaerobic microbial decomposition of organic matter.
• Methanogens: Anaerobic archaea such as Methanobacterium that produce methane during the decomposition of biomass and cattle dung.

Easily Confused

• Fermentation and bioreactor: Fermentation is the microbial conversion of substances into useful products; a bioreactor is the controlled vessel in which large-scale microbial growth and production occur.
• Biofertilizers and biocontrol agents: Biofertilizers increase soil fertility or nutrient availability, whereas biocontrol agents control pests and plant diseases.
• Primary and secondary sewage treatment: Primary treatment removes floating and suspended materials by physical methods, whereas secondary treatment uses aerobic microbes to oxidize organic matter and lower biochemical oxygen demand.
• Activated sludge and anaerobic digesters: Activated sludge consists of microbe-rich flocs formed during secondary treatment; anaerobic digesters process remaining sludge using methanogens to produce biogas.
• Lactobacillus and Saccharomyces cerevisiae: Lactobacillus converts lactose into lactic acid and forms curd, whereas Saccharomyces cerevisiae produces ethanol and carbon dioxide during anaerobic fermentation.
• Streptokinase and penicillin: Streptokinase dissolves blood clots, whereas penicillin inhibits or kills disease-causing microbes.
• Statins and cyclosporin A: Statins reduce cholesterol synthesis, whereas cyclosporin A suppresses immune responses during organ transplantation.
• Bacillus thuringiensis and Baculovirus: Bacillus thuringiensis produces insecticidal crystal proteins toxic in the alkaline gut of susceptible larvae, whereas Baculovirus is a narrow-spectrum biological control agent directed against particular insect pests.
• Methanogens and cyanobacteria: Methanogens are anaerobic archaea that produce methane, whereas cyanobacteria are photosynthetic microbes that fix atmospheric nitrogen.

What Gets Asked

• Identify the microorganism and product in industrial fermentation. Marks are lost by confusing producers, such as assigning citric acid to Acetobacter aceti instead of Aspergillus niger, or acetic acid to Aspergillus niger instead of Acetobacter aceti.
• Explain the uses of microbial products in medicine. Questions may require penicillin, streptokinase, cyclosporin A, or statins; the specific product and its medical function must be matched correctly.
• Describe the operation and importance of a bioreactor. Answers should include controlled temperature, pH, oxygen supply, mixing, nutrient availability, contamination control, and downstream processing.
• Compare biofertilizers and biocontrol agents using named examples. Rhizobium, Frankia, Anabaena, Nostoc, and mycorrhiza are associated with nutrient availability, whereas Bacillus thuringiensis, Trichoderma, and Baculovirus are associated with pest or pathogen control.
• Outline primary and secondary sewage treatment. Marks depend on distinguishing screening, grit removal, and sedimentation from aerobic floc formation, organic-matter oxidation, and reduction of biochemical oxygen demand.
• Explain biogas production and its uses. The answer should identify methanogens such as Methanobacterium, anaerobic decomposition, methane-rich biogas, and the use of biogas for cooking, heating, and electricity generation; digested slurry should be identified as nutrient-rich manure.