Microbes in Human Welfare and Applied Microbiology
This domain tests beneficial microbes in food, industrial products, sewage treatment, biogas, biocontrol and biofertilisers.
Core rules
- Lactobacillus converts milk to curd; Saccharomyces cerevisiae is used in bread and ethanol fermentation.
- Aspergillus niger produces citric acid; Penicillium notatum produces penicillin; Streptomyces griseus produces streptomycin.
- Sewage treatment uses aerobic microbes to reduce BOD, then anaerobic sludge digestion produces biogas.
- Methanogens produce methane-rich biogas; Rhizobium fixes nitrogen symbiotically, Azotobacter is free-living, and cyanobacteria can enrich paddy soils.
- Biocontrol agents include Trichoderma and Baculovirus; Bt cotton uses Bacillus thuringiensis toxin.
Worked example
A sewage sample has high BOD, meaning heavy organic pollution. Aerobic bacteria oxidise organic matter, so BOD falls as treatment proceeds. The reasoning is that BOD measures oxygen demand by microbes; a high value means more biodegradable organic matter. After aerobic treatment, anaerobic digestion of sludge produces biogas, mainly methane and carbon dioxide, plus nutrient-rich manure.
Traps
- Biogas is mainly methane, not mainly carbon dioxide.
- Yeast makes ethanol under anaerobic conditions but CO2 under aerobic respiration.
- Antibiotics do not treat viral infections.
- Biofertilisers add living nitrogen-fixing or phosphate-solubilising microbes, not just chemical nutrients.