Chapter at a glance
- Microbes (bacteria, fungi, protozoa, viruses, viroids, prions) are present everywhere, including extreme environments, and are grown as visible colonies on nutritive media.
- In household products, LAB (Lactobacillus and others) convert milk to curd by producing acids that coagulate and partially digest milk proteins while increasing vitamin B₁₂; bacteria ferment dough for dosa/idli (CO₂ production) and Saccharomyces cerevisiae ferments bread dough.
- Industrial products include fermented beverages (wine, beer, whisky) from Saccharomyces cerevisiae, antibiotics such as Penicillin (first discovered from Penicillium notatum by Fleming), organic acids (citric from Aspergillus niger), enzymes (lipases, pectinases, proteases), Streptokinase, Cyclosporin A (Trichoderma polysporum) and Statins (Monascus purpureus).
- Sewage treatment occurs in two stages: primary (physical removal of debris/grit by filtration and sedimentation forming primary sludge and effluent) and secondary (biological treatment in aeration tanks producing flocs that reduce BOD, followed by activated sludge and anaerobic sludge digesters yielding biogas).
- Biogas (predominantly methane) is produced by methanogens such as Methanobacterium acting on cellulosic material; these bacteria occur in anaerobic sludge and cattle rumen, enabling gobar-gas plants.
- Biocontrol agents include Ladybird and Dragonflies, Bacillus thuringiensis (Bt) against caterpillars, Trichoderma against plant pathogens and Nucleopolyhedrovirus (baculoviruses) as species-specific insecticides.
- Biofertilisers (Rhizobium, Azospirillum, Azotobacter, Glomus forming mycorrhiza, cyanobacteria such as Anabaena and Nostoc) enrich soil nutrients by fixing nitrogen or supplying phosphorus, reducing chemical fertiliser use.
Definitions and laws
- Antibiotics: “chemical substances, which are produced by some microbes and can kill or retard the growth of other (disease-causing) microbes.”
- BOD (biochemical oxygen demand): “the amount of the oxygen that would be consumed if all the organic matter in one liter of water were oxidised by bacteria.” (No SI unit specified; measured as mg/L.)
- Biogas: “a mixture of gases (containing predominantly methane) produced by the microbial activity and which may be used as fuel.”
- Biofertilisers: “organisms that enrich the nutrient quality of the soil.”
- Biocontrol: “the use of biological methods for controlling plant diseases and pests.”
- Methanogens: bacteria that “grow anaerobically on cellulosic material, produce large amount of methane along with CO₂ and H₂.”
No mathematical formulas or laws are stated in the chapter.
Important diagrams and activities
- Figure 8.1 (bacteria – rod-shaped, spherical, flagellated): shows morphological diversity of bacteria at given magnifications.
- Figure 8.2 (viruses – bacteriophage, adenovirus, TMV): illustrates structure of different viruses at high magnification.
- Figure 8.3 (bacterial and fungal colonies in petri dish): demonstrates visible colony formation on nutritive media.
- Figure 8.4 (fermentors) and Figure 8.5 (fermentation plant): show large-scale industrial culture vessels for microbial products.
- Figure 8.6 (secondary treatment aeration tank): illustrates mechanical agitation and aeration for floc formation.
- Figure 8.7 (aerial view of sewage plant): shows overall layout of STP.
- Figure 8.8 (typical biogas plant): depicts concrete tank, floating cover, inlet/outlet pipes for gobar-gas production.
- Activities: visit to sewage treatment plant (observe primary/secondary stages) and biogas plant (observe microbial gas production and spent-slurry use).
Common misconceptions and exam pitfalls
- Assuming all microbes are harmful/pathogenic (chapter repeatedly emphasises useful roles in household, industry, sewage and agriculture).
- Confusing primary treatment (purely physical) with secondary treatment (biological, involving flocs and BOD reduction).
- Mixing up gases: CO₂ in fermentation of dough/beverages versus methane-rich biogas from methanogens.
- Believing Bt or baculoviruses kill all insects (text specifies action on caterpillars/arthropods only, sparing beneficial insects).
- Overlooking that activated sludge digesters are anaerobic and produce biogas, or that only a small part of activated sludge is recycled as inoculum.
- Forgetting exact microbial sources (e.g., Propionibacterium shermanii for Swiss cheese holes, Trichoderma polysporum for cyclosporin A).
Formula sheet
No mathematical formulas appear in the chapter.