MICROBES IN HUMAN WELFARE

Microbes are used to prepare food and beverages, manufacture medicines and industrial products, treat sewage, control pests and enrich soil fertility.

Lactic acid bacteria (LAB), especially Lactobacillus, convert milk to curd. Lactic acid coagulates and partially digests milk proteins; LAB also increase vitamin B₁₂ content and inhibit disease-causing microbes in the stomach.

• Baker's yeast, Saccharomyces cerevisiae, makes bread dough rise by producing carbon dioxide.
• Toddy is fermented sap from palms. Yeast is also used in fermented beverages.
• Swiss cheese gets its large holes from CO₂ released by Propionibacterium shermanii; Roquefort cheese is ripened with Penicillium roqueforti.

Large-scale production uses fermenters: vessels in which microbes are grown under controlled temperature, pH, aeration, foam and nutrient conditions.

• Yeast ferments malted cereals and fruit juices to make wine and beer. Distillation produces spirits such as whisky, brandy and rum.
• Microbes produce organic acids: Aspergillus niger - citric acid; Acetobacter aceti - acetic acid; Clostridium butylicum - butyric acid; Lactobacillus - lactic acid.
• They also produce enzymes. Lipases are used in detergent formulations; pectinases and proteases clarify fruit juices.

• Streptokinase, produced by Streptococcus, is a clot buster. It modifies plasminogen to dissolve blood clots in affected vessels.
• Cyclosporin A, from Trichoderma polysporum, is an immunosuppressive agent used in organ transplantation.
• Statins are produced by the yeast Monascus purpureus. They competitively inhibit enzymes involved in cholesterol synthesis and lower blood cholesterol.

Sewage contains large amounts of organic matter and pathogenic microbes. Treatment plants remove pollutants before effluent is released into water bodies.

• Primary treatment physically removes floating debris, grit and sediment. It yields primary sludge and primary effluent.
• Secondary treatment is biological. Air is pumped through the aeration tank, where bacterial flocs with fungal filaments consume organic matter and lower BOD.
• Activated sludge is partly returned as inoculum; the rest enters anaerobic sludge digesters. Methanogens digest it and produce biogas - methane, hydrogen sulphide and carbon dioxide.

Biocontrol uses natural enemies and microbial pathogens instead of relying only on chemicals. It is central to integrated pest management.

• Bacillus thuringiensis (Bt) forms protein crystals. When susceptible insect larvae ingest them, the alkaline gut activates the toxin, which damages gut cells and kills the larvae.
• Baculoviruses, especially genus Nucleopolyhedrovirus, are highly host-specific and are useful where beneficial insects must be conserved.
• Ladybird beetles control aphids; dragonflies control mosquitoes. The fungus Trichoderma helps control several plant pathogens.

Biofertilisers are organisms that enrich nutrient quality and availability in soil, reducing dependence on chemical fertilisers.

• Rhizobium forms root nodules of legumes and fixes atmospheric nitrogen. Free-living nitrogen fixers include Azotobacter and Azospirillum.
• Cyanobacteria such as Anabaena and Nostoc are important in paddy fields. Anabaena also forms an association with the water fern Azolla.
• Mycorrhiza is a fungal-root association, commonly involving Glomus. It increases phosphate uptake and gives resistance to drought, salinity, root pathogens and pests.

• LAB turn milk into curd; yeast makes dough rise and ferments beverages.
• Microbes yield antibiotics, organic acids, enzymes and bioactive molecules.
• Secondary sewage treatment uses aerobic flocs to lower BOD; anaerobic digesters generate biogas.
• Bt, baculoviruses and natural predators are biocontrol tools.
• Nitrogen-fixers, cyanobacteria and mycorrhiza are key biofertilisers.