Microbes Are Everywhere

Microbes are the major components of the living world, far more numerous and widespread than the plants and animals we notice. They turn up in soil, water and air, inside our own bodies and those of other animals and plants. What is remarkable is how far their range extends: they thrive even where no other life-form could survive — deep inside geysers and thermal vents where the temperature can reach 100 degrees Celsius, several metres down in the soil, under thick layers of snow, and in strongly acidic surroundings.

This toughness is worth remembering. It is the reason microbes can be put to work in so many different processes, from fermenting food to treating sewage, and it hints at why they are such a central part of life on earth.

The Many Kinds of Microbes

"Microbe" is an umbrella term rather than a single group. It includes protozoa, bacteria, fungi and microscopic plants, the viruses, the even simpler viroids, and the prions — proteinaceous infectious agents. Some of these are cellular organisms with their own metabolism; others, like viruses and viroids, are non-cellular and depend entirely on a host.

So when we talk about the uses of microbes in this chapter, we are drawing on a very varied cast — bacteria and fungi do most of the useful work, but the diversity of the microbial world is what makes their applications so wide-ranging.

Growing Microbes as Colonies

Individual microbes are invisible to the naked eye, but they do not have to stay that way. Bacteria and many fungi can be grown on nutritive media, where a single cell multiplies again and again until it forms a colony — a visible mass of millions of cells that we can see without a microscope. A petri dish streaked with bacteria soon shows distinct colonies; a fungal culture spreads as a fuzzy patch.

These cultures are the working tools of microbiology. Being able to grow, isolate and study microbes in the laboratory is what allows us to identify the useful ones and harness them.

Not All Microbes Are Harmful

It is easy to think of microbes only as germs, because so many diseases in humans, animals and plants are caused by them. But that is only one side of the story. A great many microbes are genuinely useful, and we rely on their products almost every day — in the curd on our plate, the bread we eat, the antibiotics that cure us, and the treatment of the sewage our cities produce.

The rest of this chapter looks at these contributions in turn: microbes in household products, in industrial products (beverages, antibiotics and a range of chemicals and enzymes), in sewage treatment, in the production of biogas, as biocontrol agents against pests, and as biofertilisers that enrich the soil.

Quick Recap

  • Microbes are the major components of life on earth, found in soil, water, air, inside bodies, and even in extreme places like thermal vents, deep soil, under snow and in acidic environments.
  • The microbial world includes protozoa, bacteria, fungi, microscopic plants, viruses, viroids and prions (proteinaceous infectious agents).
  • Bacteria and fungi can be grown on nutritive media to form colonies visible to the naked eye; such cultures are the basis of microbiological study.
  • Not all microbes cause disease — many are useful, and we use microbes or their products daily.
  • The chapter covers microbes in household products, industrial products, sewage treatment, biogas, biocontrol and biofertilisers.

Solved Examples — Section 1

Q1. Give two examples of extreme habitats where microbes are found.

Answer: Thermal vents or geysers where the temperature may reach about 100 degrees Celsius, and highly acidic environments; they also live deep in soil and under thick snow.

Q2. Name the groups of organisms covered by the term "microbe".

Answer: Protozoa, bacteria, fungi and microscopic plants, viruses, viroids, and prions (proteinaceous infectious agents).

Q3. What is a colony, and why is it useful?

Answer: A colony is a visible mass of millions of cells arising from a single microbe multiplying on nutritive media. It lets us see, isolate and study microbes that are otherwise invisible.

Q4. What are prions?

Answer: Prions are proteinaceous infectious agents — infectious particles made essentially of protein, counted among the microbes.

Q5. Correct the statement: "All microbes are harmful."

Answer: Not all microbes are harmful. Although some cause disease, many are useful to humans — in food, medicine, sewage treatment, biogas, biocontrol and as biofertilisers.

Q6. On what are microbes grown in the laboratory to form colonies?

Answer: On nutritive media, where a single cell divides repeatedly to produce a colony visible to the naked eye.