Key Points

Lactic Acid Bacteria (LAB) like Lactobacillus convert milk to curd by producing acids that coagulate milk proteins. This process also improves nutritional quality by increasing vitamin $\text{B}_{12}$.

Yeast (Saccharomyces cerevisiae) is used to ferment dough for bread, while bacteria ferment dough for dosa and idli. The puffed-up appearance is due to the production of $\text{CO}_2$ gas.

Specific microbes create unique cheese varieties. 'Swiss cheese' holes are from $\text{CO}_2$ produced by Propionibacterium sharmanii, while 'Roquefort cheese' is ripened by specific fungi.

Brewer's yeast (Saccharomyces cerevisiae) ferments malted cereals and fruit juices to produce ethanol. Wine and beer are made without distillation, while whisky, brandy, and rum require distillation.

Antibiotics are chemical substances produced by microbes that kill or inhibit other disease-causing microbes. Penicillin was the first antibiotic, discovered from the fungus Penicillium notatum.

Microbes produce organic acids like citric acid (Aspergillus niger) and enzymes like lipases for detergents and pectinases for clarifying bottled juices.

Streptokinase is a 'clot buster', Cyclosporin A is an immunosuppressive agent for organ transplants, and Statins produced by yeast Monascus purpureus lower blood cholesterol.

This is a physical process that removes large and small particles from sewage through sequential filtration and sedimentation. The settled solids form primary sludge.

This is a biological process where aerobic microbes grow into flocs, consuming organic matter and reducing the Biochemical Oxygen Demand (BOD) of the effluent.

BOD measures the amount of oxygen consumed by bacteria to oxidize organic matter in water. A higher BOD indicates a greater polluting potential of the wastewater.

In anaerobic sludge digesters, bacteria digest the organic matter in the sludge, producing a mixture of gases called biogas, which contains methane ($\text{CH}_4$), hydrogen sulphide ($\text{H}_2\text{S}$), and carbon dioxide ($\text{CO}_2$).

Methanogens, like Methanobacterium found in cattle rumen, break down cellulosic material. Cattle dung (gobar) is used in biogas plants to produce methane ($\text{CH}_4$) for fuel.

Biocontrol uses biological methods to control pests. The bacterium Bacillus thuringiensis (Bt) produces a toxin that kills insect larvae like butterfly caterpillars.

The fungus Trichoderma is a biocontrol agent for several plant pathogens. Baculoviruses are pathogens that attack insects and are used as species-specific, narrow-spectrum insecticides.

Biofertilisers are organisms that enrich soil nutrients. Rhizobium bacteria fix nitrogen symbiotically in legume roots, while Azospirillum and Azotobacter fix nitrogen as free-living organisms in the soil.

Mycorrhiza is a symbiotic association between fungi (e.g., Glomus) and plant roots, where the fungus helps absorb phosphorus. Cyanobacteria (e.g., Anabaena, Nostoc) fix nitrogen and are important in paddy fields.