In secondary treatment of sewage, once the BOD of sewage water is reduced significantly, the effluent is passed into a settling tank where the bacterial "floes" are allowed to sediment. This sediment is calleda as activated slidge. A small part of activated sludge is pumped back into the aeration tank to serve as the inoculum.

Cyclosporin A, an immunosuppressant used in organ transplantation is produced from the fungus Trichoderma polysporum. It is also used for its anti-inflammatory, anti-fungal and antiparasitic properties.

Statins : produced by the yeast Monascus purpureus have been used to lower blood cholesterol levels. It acts by competitively inhibiting the enzyme responsible for the synthesis of cholesterol.

(i) Antibiotics should be used only when prescribed by a certified health professional.
(ii) Narrow spectrum antibiotics are preferable since they effectively and accurately target specific pathogens and are less likely to cause resistance.

Sensitivity test is important before administering penicillin to a person.
(i) Hypersensitivity reaction is a major problem with the use of penicillin, resulting in nausea; vomiting, wheezing and ultimately cardiovascular collapse.
(ii) This can be prevented by checking the sensitivity reaction of the patient before administering the antibiotic

(i) It is an antibiotic produced by the fungus Penicillium notatum and Penicillium chrysogenum.
(ii) It is bactericidal in action and inhibits the synthesis of the bacterial cell wall.
(iii) It is the queen of drugs and was discovered by Alexander Flemming.

Production of microbial products on a large scale requires growing microbes in very large vessels called fermentors. A fermentor (bioreactor) is a closed vessel with adequate arrangement for aeration, agitation, temperature, pH control and drain or overflow vent to remove the waste biomass of cultured microorganisms along-with their products

Single cell protein refers to edible unicellular microorganisms like Spirulina. Protein extracts from pure or mixed cultures of algae, yeasts, fungi or bacteria may be used as ingredient or as a substitute for protein rich foods and is suitable for human consumption or as animal feed.

The dough used in bread making is fermented by Saccharomyces cerevisiae (Baker's Yeast). Fermentation of glucose mainly forms ethyl alcohol and carbon-dioxide which is responsible for leavening of dough. When leavened dough is baked, both carbon-dioxide and ethyl alcohol evaporate making the bread porous and soft

Cheese is a dairy product formed by coagulation of the milk protein, casein. During cheese production, milk is usually acidified and the enzyme rennet is added to cause coagulation. The solids are separated and pressed to form cheese. Most cheese are made with a starter bacteria, Lactococcus, Lactobacillus or Streptococcus.

Yogurt is produced by bacterial fermentation of milk, and lactic acid is produced as a byproduct. Microorganisms such as Streptococcus thermophilus and Lactobacillus bulgaricus coagulate the milk protein and convert the lactose in the milk to lactic acid. The flavour in yogurt is due to acetaldehyde.

Recombinant human insulin has been produced using yeast (Saccharomyces cerevisiae) which is used in diabetes treatment.

(i) Bio-fertilizers are formulation of living microorganisms that enrich the nutrient quality of the soil. They increase physico - chemical properties of soils such as soil structure, texture, water holding capacity, cation exchange capacity and pH by providing several nutrients and sufficient organic matter.
(ii) The main sources of bio-fertilizers are bacteria, fungi and cyanobacteria. Rhizobium is a example for symbiotic nitrogen fixing bacteria. This bacterium infects the root nodules of leguminous plants and fixes atmospheric nitrogen into organic forms. Azospirillum and Azotobacter are free living bacteria that fix atmospheric nitrogen and enrich the nitrogen content of soil.
(iii) A symbiotic association between a fungus and the roots of the plants is called mycorrhiza. The fungal symbiont in these associations absorbs the phosphorus from soil and transfers to the plant. Plants having such association show other benefits such as resistance to root-borne pathogens, tolerance to salinity, drought, enhances plant growth and developments. For example, genus Glomus form mycorrhiza.
(iv) Cyanobacteria (or) blue green algae (BGA) are prokaryotic free-living organisms which can fix nitrogen. Oscillatoria, Nostoc, Anabaena, Tolypothrix are well known nitrogen fixing cyanobacteria. In water logged paddy fields Cyanobacteria multiply and fix molecular nitrogen. Cyanobacteria secrete growth promoting substances like indole-3-acetic acid, indole-3-butyric acid, naphthalene acetic acid, amino acids, proteins, vitamins which promotes plant growth and production.
(v) Biofertilizers are commonly used in organic farming methods.
(vi) This process involves the use of biological materials, avoiding synthetic substances to maintain soil fertility and ecological balance thereby minimizing pollution and wastage.

(i) Protecting soil quality using organic materials and encouraging biological activity.
(ii) Indirect provision of crop nutrients using soil microorganisms.
(iii) Nitrogen fixation in soils using legumes.
(iv) Weed and pest control based on methods like crop rotation, biological diversity, natural predators, organic manures and suitable chemical, thermal and biological interventions.

(i) Bacillus thuringiensis is a soil dwelling bacterium which is commonly used as a biopesticide and contains a toxin called cry toxin. Scientists have introduced this toxin producing genes into plants and have raised genetically engineered insect resistant plants. Eg. Bt-cotton.
(ii) When the insects ingest the toxin crystals their alkaline digestive tract denatures the insoluble crystals making them soluble. The cry toxin then gets inserted into the gut cell membrane and paralyzes the digestive tract. The insect then stops eating and starves to death.