7. Introduction to Microbiology

Explanation: Lactobacilli convert the lactose sugar of milk into lactic acid. Lactic acid makes the milk proteins coagulate (gel out). This gives curd and yoghurt their thick texture.

Explanation: Probiotics contain useful live bacteria like Lactobacillus and Bifidobacterium. They increase the useful microbes in the intestine and reduce harmful microbes like Clostridium.

Explanation: Vinegar is 4% acetic acid (CH₃COOH). It is made by the microbial degradation of ethanol with bacteria like Acetobacter.

Explanation: Aspergillus niger ferments glucose and corn steep liquor to form gluconic acid. Its salts are used as supplements for calcium and iron.

Fuels:

1. Methane (biogas): by anaerobic decomposition of urban, agricultural and industrial waste by microbes.
2. Ethanol: by fermentation of molasses by the yeast Saccharomyces.
3. Hydrogen: released during bio-photolysis of water by bacteria.

Why their use should increase:

• Fossil fuels are limited and will get used up. Microbial fuels can be made again and again from waste and crops.
• Ethanol and hydrogen are clean (smokeless) fuels, so they cause less pollution.
• Waste is disposed of usefully while fuel is produced.

• An oil layer on water is hard to remove by mechanical methods.
• Bacteria like Pseudomonas and Alcanivorax borkumensis can break down the hydrocarbons in oil. They are called hydrocarbonoclastic bacteria (HCB).
• These bacteria are spread on the oil spill. They convert the hydrocarbons into carbon dioxide and water, and the water becomes clean.

• Acid rain contains sulphuric acid, which pollutes the soil.
• Bacteria like Acidiphilium and Acidithiobacillus ferrooxidans use sulphuric acid as their source of energy. So they reduce the acidity of the soil.
• Microbial inoculants like Azotobacter then add nutrients such as nitrogen, and the soil becomes fertile again.

• Bio-pesticides are bacteria, fungi or viruses, or their toxins, that destroy pests and pathogens.
• These toxins can be put into plants using biotechnology, so insects do not eat those plants.
• Unlike chemical pesticides, they do not harm other plants, animals or humans, and leave no harmful residues in soil.
• So crops are grown without chemicals, which is the aim of organic farming. Spinosad is an example of a bio-pesticide.

• Probiotics form colonies of useful microbes in the alimentary canal and control harmful microbes.
• They help digestion and improve resistance (immunity).
• They reduce the ill-effects of harmful substances formed during metabolism.
• They make useful microbes active again after they are harmed by antibiotics.
• They are used to treat diarrhoea and in poultry.

Yeast produced for commercial use contains carbohydrates, fats, proteins, various vitamins and minerals. When this yeast is used to make bread and other products, these nutrients are added to them. So products made with baker’s yeast are nutritious.

• Segregate wet (biodegradable) and dry waste at home.
• Do not mix plastic, glass, metal, batteries, medicines or chemicals with wet waste.
• Keep the waste moist and allow air, so that microbes can act properly.
• Cover the waste with a layer of soil or leaves to avoid bad smell and flies.

• Plastic bags are non-biodegradable. They do not decompose for hundreds of years.
• They block drains and cause flooding in cities.
• Animals eat them and die. They also harm aquatic life.
• Burning plastic releases toxic gases, and plastic pollutes soil and water.

So the use of plastic bags must be banned. Biodegradable (polylactic acid) bags or cloth bags should be used instead.

• During industrial production, for example of milk products, the useful bacteria can be attacked by viruses.
• Mutant strains are developed that resist viruses and work better.
• Some strains are developed artificially to avoid unnecessary steps and materials in production.

So production is faster, cheaper and safer, and the use of mutant strains has increased.

• Microbial enzymes break down dirt, stains, oil and proteins.
• With enzymes, dirt is removed even at low temperature, so hot water is not needed and energy is saved.
• Enzymes are eco-friendly and biodegradable.

• Microbial enzymes are active at low temperature, pH and pressure, so energy is saved.
• Corrosion-proof instruments are not needed.
• Enzymes carry out specific reactions, so unwanted by-products are not formed and less is spent on purification.
• They can be reused, and they are eco-friendly.

• Microbes (bacteria and fungi) in soil decompose biodegradable waste like leaves, vegetable peels and dung.
• They break down complex organic substances into simple substances.
• This forms compost, a good natural manure that makes soil fertile.
• At landfill sites too, microbes decompose waste covered with soil, and good quality compost is formed.

• Ethanol is a clean (smokeless) fuel, so the mixture causes less air pollution.
• Less petrol and diesel is used, so limited fossil fuels are saved.
• Ethanol is made by fermenting molasses from sugarcane, so it is renewable.
• It reduces the import of crude oil and helps farmers.

Sugarcane and sugar beet (molasses for ethanol), maize and sweet sorghum (starch and sugar for ethanol), and jatropha and karanj (seed oil for biodiesel).

• Solid: dung cakes, crop residue, wood
• Liquid: ethanol (alcohol), vegetable oils (biodiesel)
• Gaseous: biogas (gobar gas, methane)

Dough is made by mixing flour with baker’s yeast (Saccharomyces cerevisiae), water and salt. The yeast ferments the sugar in the dough into carbon dioxide and ethanol. Bubbles of CO₂ make the dough rise, so the bread becomes soft and spongy.

• Segregate wet and dry waste in separate bins.
• Make compost at home from wet waste (vegetable peels, leftover food, leaves) in a pot or pit.
• Give dry waste like paper, plastic, metal and glass for recycling.
• Refuse and reduce: avoid plastic bags and use-and-throw items; carry cloth bags and steel bottles.
• Reuse jars, boxes and old clothes.
• Give e-waste, batteries and medicines only to authorized collectors.

Many soil microbes break down chemical pesticides into harmless substances. For example:

• Bacteria: Pseudomonas, Bacillus, Arthrobacter and Flavobacterium.
• Fungi: Trichoderma and Aspergillus.

Using microbes to clean a polluted environment is called bioremediation.

• They kill useful insects like honey bees, earthworms and natural predators of pests.
• They remain in soil and water for a long time and pollute them.
• Their residues enter food chains and harm birds, animals and humans.
• They cause skin diseases and other health problems in farmers.
• Pests slowly become resistant, so more and stronger pesticides are needed.

So bio-pesticides and organic farming are better choices.