7. Introduction to Microbiology
Chapter focus: Applied Microbiology Industrial Microbiology Products & Processes
Can you recall? (i) Which microbes are useful to us? (ii) Which products can microbes help us make?
Applied Microbiology
Definition: A branch of biology that studies microbial enzymes (prokaryotic & eukaryotic), proteins, applied genetics and molecular biology to apply this knowledge for society—producing foods, medicines and other products on a large scale.
- Tools: Fermentation, enzyme technology, strain improvement, downstream processing.
- Outcomes: Nutritious foods, antibiotics, organic acids, biofuels, eco-friendly waste treatment.
Industrial Microbiology
Definition: Commercial use of microbes for economical, social and environmental benefits.
Main Features
- (A) Fermentation-based production: bread, cheese, yoghurt, kefir, vinegar, soy sauce, beverages; raw materials for chemicals, enzymes, nutrients, medicines.
- (B) Microbes for waste & pollution management: composting, biogas, sewage treatment, bioremediation, oil-spill cleanup.
Products (Food & Beverages)
A. Dairy Products
Key principles: Pasteurize milk → inoculate with starter cultures → lactose fermentation → lactic acid \(\\rightarrow\) protein coagulation & flavour development (e.g., diacetyl).
1) Yoghurt (Curd/Dahi)
- Starters: Streptococcus thermophilus (lactic acid; gel structure) + Lactobacillus delbrueckii subsp. bulgaricus (acetaldehyde; flavour) in ~1:1.
- Process: Boil milk \(\rightarrow\) cool to warm \(\rightarrow\) inoculate \(\rightarrow\) incubate \(\rightarrow\) chill. For thicker yoghurt, add milk powder (protein boost).
- Variants: Fruit yoghurts (strawberry, banana, etc.). Probiotic versions (see below). Pasteurization can improve shelf life.
2) Butter
- Types: Sweet cream butter (no microbes) and cultured butter (starter microbes develop flavour).
3) Cheese
- Starters: Lactococcus lactis, Lactococcus cremoris, Streptococcus thermophilus.
- Coagulation: Traditionally animal rennet; vegetarian cheeses use fungal protease (e.g., from Rhizomucor/Aspergillus spp.).
- Steps: Test milk → pasteurize → add starter & colour → coagulate → cut curd → drain whey → wash/rub/salt → add adjunct cultures/pigments → press → cut → ripen.
- Textures: Fresh (paneer/cottage, cream, mozzarella) → Semi-hard (cheddar, ~3–12 months) → Hard (parmesan, ~12–18 months).
- Industrial note: Virus-resistant starter strains & mutants are used to avoid bacteriophage losses and to simplify processing.
Probiotics
What: Foods containing live beneficial microbes (e.g., Lactobacillus acidophilus, L. casei, Bifidobacterium bifidum) that improve gut microbial balance.
- Benefits: Support digestion, suppress harmful microbes (e.g., Clostridium), enhance immunity, help recovery after antibiotics; used in diarrhoea management and poultry.
- Examples: Probiotic yoghurt/kefir, sauerkraut, miso, pickles, dark chocolate; microalgae foods (e.g., Spirulina, Chlorella).
B. Bakery & Fermented Foods
1) Bread
Organism: Baker’s yeast Saccharomyces cerevisiae. Sugars ferment to produce \(\\text{CO}_2\) (leavening) & ethanol.
Reaction (simplified): \(\displaystyle \\text{Glucose}\\ (C_6H_{12}O_6) \\rightarrow 2\\,\\text{C}_2H_5\\text{OH} + 2\\,\\text{CO}_2\\uparrow\)
Compressed or dry yeast is used. Yeast adds nutrients (B-vitamins, protein, minerals) improving product value.
2) Vinegar (Acetic Acid ~4%)
- Step 1 (alcoholic fermentation): Yeast converts sugars (molasses/fruit juice) to ethanol.
- Step 2 (acetic fermentation): Acetobacter/Gluconobacter oxidize ethanol to acetic acid.
\(\displaystyle \\text{C}_2H_5\\text{OH} + O_2 \\rightarrow \\text{CH}_3\\text{COOH} + H_2O\) - Polish & Pack: Clarify (e.g., by rarefaction), bleach (e.g., with allowed agents), pasteurize; trace \(\\text{SO}_2\) may be added.
3) Soy Sauce (overview)
Ferment wheat/rice flour + soybean using fungus Aspergillus oryzae (koji), followed by brine fermentation to develop deep umami flavours.
C. Beverages (selected)
| Raw material | Microbe(s) | Role | Beverage |
|---|---|---|---|
| Coffea arabica (coffee fruit) | Lactobacillus brevis (and others) | Pulp/seed separation & flavour development | Coffee |
| Theobroma cacao (cocoa) | Mixed (yeast/lactic/acetic flora) | Fermentation of beans; chocolate precursors | Cocoa |
| Grapes | Saccharomyces cerevisiae (+ wild yeasts: Candida, Pichia, Hansenula) | Alcoholic fermentation of must | Wine |
| Apple | Saccharomyces cerevisiae | Fermentation of juice | Cider |
Microbial Enzymes
Why enzymes from microbes? Highly specific, active at lower temperature/pH/pressure ⇒ energy saving, fewer by-products, reusable, eco-friendly.
Major classes: Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerases, Ligases.
- Everyday uses: Detergent enzymes remove stains even at low temperature.
- Sweeteners/syrups: From corn starch via enzymes from Bacillus/Streptomyces.
- Industries: Cheese, plant extracts, textile, leather, paper, beverages.
Selected Organic Acids (Industrial) & Their Microbes
| Feed / Source | Microbe | Product | Uses |
|---|---|---|---|
| Sugar/beet molasses + ammonia salts | Brevibacterium, Corynebacterium | L-Glutamic Acid | Monosodium glutamate (flavour enhancer) |
| Molasses / sugars | Aspergillus niger | Citric Acid | Drinks, confectionery, acidity regulator |
| Glucose, corn steep liquor | Aspergillus niger | Gluconic Acid | Mineral supplements (Ca/Fe salts) |
| Molasses, corn steep liquor | Lactobacillus delbrueckii | Lactic Acid | Food acidulant; vitamin production |
| Molasses, corn steep liquor | Aspergillus itaconicus | Itaconic Acid | Paper, textile, plastics, gums |
Substances via Microbial Processing & Their Roles
| Substance | Role |
|---|---|
| Citric, Malic, Lactic acids | Impart acidity; preservation |
| Glutamic acid, Lysine, Tryptophan | Flavour & protein fortification |
| Nisin, Natamycin | Natural antimicrobials (preservation) |
| Vitamins: \(\\mathrm{C}, B_{12}, B_{2}\) | Nutrition; antioxidants |
| Carotenoids (β-carotene), lycopene, xanthins, lutein | Edible colours & nutraceuticals |
| Polysaccharides, glycolipids | Emulsifiers/thickeners |
| Flavours: Vanillin, Ethyl butyrate, peppermint essence | Food flavouring & fragrance |
| Xylitol, Aspartame | Low-calorie sweeteners |
Xanthan gum (from Xanthomonas via starch/molasses fermentation) gives thickness/creaminess to ice-creams, puddings, soups, chocolates; also used in pigments, fertilizers, toothpaste, specialty papers.
Antibiotics (Microbes against Microbes)
Microbially derived drugs control many bacterial diseases in humans & animals. Use responsibly (doctor’s advice, full course).
Examples: Penicillins, Cephalosporins, Monobactams, Bacitracin, Erythromycin, Gentamicin, Neomycin, Streptomycin, Tetracyclines, Vancomycin; Rifamycin (notably for tuberculosis).
Microbes & Fuels
- Biogas (Methane): From anaerobic digestion of urban/agricultural/industrial organic waste by methanogens.
- Ethanol (bio-alcohol): From molasses/sugars via Saccharomyces—a cleaner, smokeless fuel; blended with petrol.
- Bio-Hydrogen (fuel of the future): Produced during microbial bio-photolysis/photoreduction of water under specific conditions.
- Platform chemicals: Microbes also make alcohols, acetone, organic acids, fatty acids, and polysaccharides—raw materials for plastics/food industries.
Fermentation equation (ethanol): \(\displaystyle C_6H_{12}O_6 \\rightarrow 2\\,C_2H_5OH + 2\\,CO_2\)
Biofuel loop (concept): Biomass \(\\xrightarrow{\\text{hydrolysis}}\\) sugars \(\\xrightarrow{\\text{fermentation}}\\) liquid fuels; carbon cycles back as \(\\text{CO}_2\) to plants via photosynthesis.
Microbial Pollution Control
1) Modern Landfill (Bioreactor) Sites
- Large pits lined with plastic sheets prevent toxic leachate from polluting soil/groundwater.
- Compressed biodegradable waste is layered with soil/sawdust/leaf waste and bio-reactors (microbes) to speed decomposition.
- After stabilization: seal with soil slurry → harvest high-quality compost; site can be reused.
- Why segregate waste? Wet (biodegradable) → compost/biogas; Dry (recyclables) → recycling; reduces load on landfills.
2) Sewage Management
- In cities, sewage is piped to treatment plants where microbes decompose organics and kill pathogens (cholera, typhoid, etc.).
- Methane & \(\\text{CO}_2\) are released during decomposition; phenol-oxidizing bacteria degrade xenobiotics.
- Settled sludge is used as fertilizer; treated water is environmentally safe.
- Bioremediation: Intentional use of microbes to detoxify polluted environments.
3) Clean Technology via Microbes
- Desulphurization: Selected microbes remove sulphur from fuels—reduces SOx emissions.
- Bio-leaching control: Thiobacilli/Sulphobacilli manage metals (Cu, Fe, U, Zn) from low-grade ores; convert to less mobile forms.
- Oil-spill bioremediation: Hydrocarbonoclastic bacteria (HCB) such as Pseudomonas, Alcanivorax borkumensis degrade oil (hydrocarbons) to \(\\text{CO}_2 + H_2O\).
- Plastic & Rubber degradation: PET-degrading species (e.g., Ideonella sakaiensis, some Vibrio) and actinomycetes (Streptomyces, Nocardia, Actinoplanes) aid waste reduction.
- Acid rain/acid mine drainage: Acidophilium, Acidithiobacillus ferrooxidans (formerly Acidobacillus) utilize sulphuric acid—help mitigate soil/metal corrosion impacts.
- Uranium immobilization: Geobacter reduces soluble uranium to insoluble forms—prevents groundwater contamination.
Microbes & Farming
Microbial Inoculants (Biofertilizers)
- Seed/soil inoculation: Cultures (e.g., Rhizobium for legumes; Azotobacter) supply bio-available nitrogen; improve plant growth and food quality.
- Benefits: Lower chemical fertilizer use, reduce soil pollution; solutions with Azotobacter or even artificial nitrogenase concepts aid organic farming.
- Pesticide detox: Microbes can degrade soil-residual chemicals (e.g., fluoroacetamide), reducing ecological & health hazards.
Bio-insecticides / Bio-pesticides
- Toxin genes in plants: Using biotechnology, bacterial/fungal toxins expressed in crops deter insect feeding.
- Microbial agents: Bacteria, fungi, and viruses can be used directly against pests (eco-friendly specificity).
- Example: Spinosad — a fermentation by-product used as a biopesticide.
Always remember: Use biodegradable garbage bags (e.g., polylactic acid) responsibly; reduce single-use plastics to protect the environment.
Key Equations (with MathJax)
- Lactic fermentation (yoghurt): \(\displaystyle \\text{Lactose} \\rightarrow 2\\,\\text{Lactic Acid}\\)
- Alcoholic fermentation (bread, beverages): \(\displaystyle C_6H_{12}O_6 \\rightarrow 2\\,C_2H_5OH + 2\\,CO_2\\)
- Acetic fermentation (vinegar): \(\displaystyle C_2H_5OH + O_2 \\rightarrow CH_3COOH + H_2O\)
Chapter 7 — Exercise: Perfect Solutions
1) Rewrite using the correct options & explain
Options: gluconic acid, coagulation, amino acid, acetic acid, clostridium, lactobacilli
- a) Process of coagulation of milk proteins occurs due to lactic acid.
Why? Lactic acid (from starter bacteria) lowers pH so casein proteins gel/curdle → curd/yoghurt structure. - b) Harmful bacteria like Clostridium in the intestine are destroyed (suppressed) due to probiotics.
Why? Probiotics (e.g., Lactobacillus, Bifidobacterium) outcompete pathogens and produce acids/bacteriocins. - c) Chemically, vinegar is acetic acid (~4% solution).
Why? Ethanol is oxidized by Acetobacter/Gluconobacter to acetic acid. - d) Salts used as supplements of calcium and iron are obtained from gluconic acid (e.g., calcium/ferrous gluconate).
Why? Gluconate salts are bioavailable and gentle mineral supplements.
2) Match the pairs
| ‘A’ group | ‘B’ group |
|---|---|
| a. Xylitol | 2. To impart sweetness ✅ |
| b. Citric acid | 5. To impart acidity ✅ |
| c. Lycopene | 1. Pigment ✅ (natural red colour) |
| d. Nycin (Nisin) | 3. Microbial restrictor ✅ (natural preservative) |
Note: Option “4. Protein binding emulsifier” doesn’t match the given items; emulsifiers are typically polysaccharides/lecithins, not the four items in group A.
3) Answer the following (Short answers)
- a) Microbial fuels & why increase their use
Fuels: Biogas (methane), Bioethanol, Biohydrogen. Why: renewable, lowers net greenhouse emissions, reduces fossil fuel dependence, often biodegradable/cleaner combustion, supports rural economy. - b) Cleaning river/ocean oil spills
Use hydrocarbonoclastic bacteria (HCB) such as Pseudomonas spp. and Alcanivorax borkumensis to biodegrade hydrocarbons to \(CO_2+H_2O\). Methods: biostimulation (add nutrients), bioaugmentation (add cultures); mechanical booms/skimmers as support. - c) Making acid-rain–polluted soil fertile
Employ acid-utilizing bacteria (Acidophilium, Acidithiobacillus ferrooxidans) to moderate acidity; add compost/biochar; (agronomic practice) apply agricultural lime to correct pH; restore microbes via organic matter. - d) Importance of biopesticides in organic farming
Target-specific, eco-friendly, minimal residues, safer to beneficials, slower resistance development; examples: microbial toxins expressed in plants, fungal/viral biopesticides, and fermentation product Spinosad. - e) Why probiotics are popular
Restore gut flora after antibiotics, suppress pathogens (Clostridium), improve digestion, enhance immunity, helpful in diarrhoea; convenient food formats (yoghurt/kefir, etc.). - f) Nutritional value of yeast-based breads
Baker’s yeast adds proteins, B-vitamins & minerals; fermentation can improve flavour and nutrient bioavailability while \(CO_2\) leavens for better texture. - g) Precautions for proper domestic waste decomposition
Segregate wet/dry; no plastics/metal/glass in compost; chop wet waste; keep moist (not soggy); alternate wet (greens) & dry (browns like dry leaves); ensure aeration; avoid chemical cleaners/oils in compost. - h) Why ban plastic bags
Non-biodegradable, clog drains, harm animals, microplastics; hinder composting/landfill bioprocesses. Prefer reusable or certified biodegradable (e.g., PLA) only when necessary.
4) Complete the conceptual picture — Sewage → Cleaning
Sewage (domestic)
Screening & Grit Removal
Primary Settling (sludge)
Aeration with Microbes (kill pathogens, oxidize organics)
Secondary Settling
Disinfection
Cleaned Effluent ✅
By-products: Sludge → anaerobic digestion → biogas (methane) + manure.
5) Give scientific reasons
- a) Mutant strains are preferred because they offer higher yields, faster rates, inhibitor/acid tolerance, phage resistance, process robustness, and tailored metabolic pathways → better industrial productivity.
- b) Detergent enzymes (microbial) work at low temperature & mild pH, specifically break proteins/starches/fats → superior stain removal, energy saving, biodegradable.
- c) Microbial enzymes vs chemical catalysts: higher specificity & selectivity, milder conditions (less corrosion/energy), fewer by-products (easier purification), reusable/greener → ideal for chemical industry.
6) Complete the conceptual picture — Uses of Xanthan gum
Thickener
Stabilizer
Emulsifier
Suspending agent
Ice-cream & desserts
Sauces & salad dressings
Chocolate drinks & instant soups
Toothpaste
Pigments & textile printing
Fertilizer/weedicide carriers
High-quality paper
Industrial fluids (e.g., drilling muds)
7) Complete the conceptual picture — Environmental Management: Oil Spill & Microbes
Oil Spill (rivers/oceans)
Add nutrients (biostimulation)
Introduce/boost HCB
Pseudomonas, Alcanivorax borkumensis
Hydrocarbon biodegradation
\( \mathrm{Hydrocarbons} \rightarrow CO_2 + H_2O \)
Cleaner Water & Shoreline ✅
Support: booms/skimmers for containment; avoid dispersants that harm biota when possible.
8) Answer the following
- a) Role of microbes in compost production
Decomposer bacteria & fungi mineralize kitchen/garden waste; proper C:N, moisture & aeration speed up humus formation → nutrient-rich compost. - b) Benefits of mixing ethanol with petrol/diesel
Higher octane/cleaner combustion, reduced CO/HC emissions, partial fossil fuel replacement, supports agri-based bioeconomy. - c) Plants cultivated to obtain fuel
Sugarcane, corn (starch crops) for ethanol; oilseeds (e.g., jatropha) for biodiesel feedstock; lignocellulosic crops for advanced biofuels. - d) Fuels obtained from biomass
Biogas (methane), Bioethanol, Biodiesel (via transesterification of oils), Biohydrogen, solid biofuels (pellets/briquettes). - e) Why does bread become spongy?
Yeast (Saccharomyces cerevisiae) ferments sugars → \(CO_2\) gas trapped in gluten network → dough rises; baking sets the porous structure → spongy bread.
Project (Guided pointers)
- Zero-garbage at home: Segregate 100% (wet/dry), home-compost wet, recycle dry, refuse single-use plastics, buy in bulk, repair/reuse.
- Microbes that destroy chemical pesticides in soil: e.g., Pseudomonas, Bacillus, Trichoderma, and other specific degraders depending on pesticide class.
- Why avoid chemical pesticides: residues, resistance, non-target toxicity (pollinators/predators), soil & water contamination, health risks; safer alternatives: IPM, biopesticides, cultural controls.