2.6 How We Are Connected to Microbes

Microbes are not just out there in ponds and soil — they are woven into our daily lives. They rise our bread, set our curd, feed our crops, recycle our waste, and fill the air with oxygen. Let us meet some of these invisible helpers.

Cleaning the environment

Have you seen a lemon or tomato grow a powdery or cottony fuzz after sitting out too long? That fuzz is microbes, which are present in water, soil, air and food everywhere. (Pickles and murabbas resist them because the high salt or sugar acts as a preservative, stopping microbes from growing.)

Activity 2.7 — Make manure Half-fill a container with garden soil, add fruit and vegetable peels, cover with a layer of soil, and leave it. After 2–3 weeks the peels have turned into dark, crumbly manure — material rich in nutrients that makes soil more fertile. The soil’s fungi and bacteria slowly broke the waste down into simple, nutrient-rich substances.

This breakdown of dead plant and animal matter into simpler, nutrient-rich substances is called decomposition, and the microbes that do it are decomposers. The freed nutrients return to the soil and help new plants grow. Microbes even break down dead animals and dung — so they constantly recycle waste and return nutrients to nature. This is why gardeners heap dry leaves and plant waste into pits to make natural manure.

Microbes as Fuel: Biogas Some bacteria live without oxygen and decompose plant, animal and household waste, releasing biogas — a mixture rich in methane (plus carbon dioxide). Biogas is burned for cooking, heating, generating electricity, and even running vehicles. India set up one of its oldest biogas plants back in the 1850s.

Be a Scientist: A. M. Chakrabarty Ananda Mohan Chakrabarty (1938–2020) engineered a special bacterium that could break down oil spills, helping clean polluted water. In 1980 his work received a patent (a legal right that stops others from copying or selling an invention without permission) — a landmark showing how microbes can solve environmental problems like pollution.

Microbes in our food

Activity 2.8 — Yeast and dough Knead two batches of flour with a pinch of sugar and warm water — but add a little yeast to one and none to the other. Keep both warm under a damp cloth for a few hours. The yeast batch rises, turns fluffy, and smells different; the other does not. Yeast is a fungus: it respires, breaking down the sugar and releasing carbon dioxide, whose bubbles puff up the dough. (It also makes a little alcohol, which gives the smell.) This is how bread, cakes — and, with helpful bacteria like Lactobacillus, idli, dosa and bhatura batter — are made.

Activity 2.9 — Setting curd Add a spoon of curd to warm milk (bowl A) and to cold milk (bowl B), and leave both for a few hours. Bowl A sets into curd and turns slightly sour; bowl B mostly does not. Curd contains bacteria such as Lactobacillus, which feed on milk sugar (lactose), multiply, and produce lactic acid — that acid sets the milk into curd and makes it sour. These bacteria need warmth, which is why only the warm bowl works.

Free Fertiliser: Rhizobium The roots of legumes — beans, peas, lentils — carry swollen root nodules that house Rhizobium bacteria. These bacteria trap nitrogen from the air and turn it into a form plants can use, so the crop grows well without chemical fertiliser. This is why farmers grow legumes in rotation with other crops: it naturally restores nitrogen and keeps the soil healthy for the next planting.

Worked Example

Two farmers grow side by side: one adds nitrogen fertiliser to his wheat, the other adds none to her beans — yet both get healthy crops. How?

Wheat has no way of its own to capture nitrogen, so that farmer must add it as fertiliser. Beans are legumes: their root nodules contain Rhizobium, which fixes nitrogen from the air straight into the soil. So the bean farmer gets her nitrogen for free, from the bacteria — no fertiliser needed.

Tiny helpers in water: microalgae

Microalgae are microscopic, plant-like organisms that make their own food using sunlight. In doing so they release oxygen — together producing more than half of all the oxygen on Earth. They feed countless water animals, clean water, and can be made into biofuel.

Ever Heard Of… Spirulina is a microalga called a superfood: over 60% of its weight is protein, and it is rich in vitamin B₁₂. It can be grown in simple tanks of pond water — a real livelihood opportunity. But pollution, climate change and habitat loss threaten microalgae, so conserving them protects both our food security and the oxygen balance of the planet.

Helpful and Harmful Everything in this section shows microbes as friends. But some microbes are foes — they cause diseases in plants, animals and people. That darker side is the subject of the next chapter, Health: The Ultimate Treasure.

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