Microbes in Human Welfare

We often think of microbes (microorganisms) — bacteria, fungi and others — only as germs that cause disease. But most microbes are harmless or useful, and many work for human welfare every day. They are used in our homes, in industry, in farming and in cleaning up the environment.

In the household, microbes help make many familiar foods:

• Curd (yoghurt) — made from milk by lactic acid bacteria (LAB), which also add vitamins and improve nutrition.
• Bread and dosa/idli batter — made to rise by yeast or bacteria, which produce carbon dioxide that puffs up the dough.
• Cheese — made using bacteria and fungi; the holes and flavour of some cheeses come from particular microbes.

In industry, microbes are grown on a large scale to make valuable products:

• Alcohol and beverages — produced by yeast through fermentation of sugars.
• Antibiotics — medicines that kill or stop bacteria; the first, penicillin, was discovered by Alexander Fleming from the fungus Penicillium. Antibiotics have saved countless lives.
• Other products — organic acids (like citric acid), enzymes and vitamins are also produced using microbes.

Microbes are also nature's recyclers and cleaners. Two important uses are treating sewage and making biogas.

Sewage treatment: the dirty water from homes and cities (sewage) contains a lot of human waste and harmful germs, so it cannot be released directly into rivers. In a sewage treatment plant, helpful microbes break down the organic matter in the sewage, cleaning the water. The process has two main stages: primary treatment (physical removal of solids by settling and filtering) and secondary (biological) treatment, in which large numbers of aerobic microbes digest the remaining organic matter, greatly reducing the pollution. The cleaned water can then be released safely or reused.

Biogas: certain microbes (called methanogens) live without oxygen and produce a gas mixture rich in methane while breaking down organic waste — this is biogas. In a biogas plant (gobar gas plant), animal dung and other waste are digested by these microbes, and the biogas produced is used as a clean fuel for cooking and lighting, especially in villages. The leftover slurry is a good manure. So biogas turns waste into useful energy and helps the environment. (Methanogens are also found in the gut of cattle, which is why cattle dung is used to start biogas plants.)

Modern farming tries to reduce harmful chemical fertilisers and pesticides by using microbes instead — a more eco-friendly approach.

Biofertilisers are living microbes that enrich the soil with nutrients, especially nitrogen, naturally. Important examples:

• Rhizobium — a bacterium that lives in the root nodules of legumes and fixes nitrogen from the air into the soil.
• Azotobacter and Azospirillum — free-living soil bacteria that also fix nitrogen.
• Cyanobacteria (blue-green algae) like Anabaena — fix nitrogen, useful especially in paddy (rice) fields.
• Mycorrhiza — a partnership between a fungus and plant roots that helps the plant absorb phosphorus and water.

Biofertilisers improve soil fertility without polluting it, unlike chemical fertilisers.

Biocontrol means controlling pests and plant diseases using living organisms instead of chemical pesticides. Examples include the bacterium Bacillus thuringiensis (Bt), which is sprayed to kill certain insect larvae but is harmless to other animals, and the fungus Trichoderma, which protects plants from disease-causing microbes. The ladybird beetle and dragonflies are natural predators used to control aphids and mosquitoes. Biocontrol is safer for human health and the environment because it avoids toxic chemicals. Together, biofertilisers and biocontrol agents show how microbes (and other organisms) can make agriculture more sustainable.