The Invisible World
We are surrounded by a world that we cannot see. It is a world filled with trillions of tiny living things called microorganisms (or microbes). Microbiology is the scientific study of these microorganisms.
While the word 'germs' often has a negative meaning, the vast majority of microbes are harmless or even essential for life. They are the most abundant organisms on Earth. Let's look at the three main groups.
Bacteria
Bacteria are single-celled organisms that are prokaryotic, meaning their cells do not have a nucleus.
Structure: They are very simple cells, with just a cell wall, cell membrane, cytoplasm, and a loop of DNA.
Reproduction: They reproduce asexually by a process called binary fission, where one cell simply splits into two identical cells. This can happen very rapidly.
Roles:
Beneficial: Bacteria in your intestines help you digest food. Bacteria in the soil are decomposers that recycle nutrients. Some bacteria are used to make foods like yogurt and cheese.
Harmful (Pathogenic): Some bacteria can cause disease by invading tissues or producing toxins. Strep throat, food poisoning, and tetanus are all caused by harmful bacteria. These can often be treated with antibiotics.
Viruses
Viruses are not cells. They are not even truly considered to be alive by many biologists.
Structure: A virus is simply a piece of genetic material (DNA or RNA) enclosed in a protein coat called a capsid. They are much, much smaller than bacteria.
Reproduction: Viruses are parasites. They cannot reproduce on their own. They must infect a host cell and take over the cell's machinery to make more copies of themselves. The new viruses then burst out of the host cell, usually destroying it, and go on to infect other cells.
Roles:
Harmful (Pathogenic): All viruses are harmful to their hosts. They cause a wide range of diseases, including the common cold, the flu, chickenpox, and COVID-19.
Treatment: Antibiotics do not work on viruses. Viral infections are prevented with vaccines or treated with antiviral drugs.
Fungi
Fungi are eukaryotic organisms (their cells have a nucleus). This kingdom includes a wide range of organisms, from mushrooms to molds to single-celled yeasts.
Structure: Multicellular fungi are made of thread-like structures called hyphae. Their cell walls are made of chitin.
Nutrition: Fungi are heterotrophs, specifically decomposers. They release enzymes to break down organic matter externally and then absorb the nutrients.
Roles:
Beneficial: Yeast is a single-celled fungus used to make bread rise and ferment beverages. Molds are the source of some of the first antibiotics, like penicillin. Fungi are essential decomposers in every ecosystem.
Harmful (Pathogenic): Some fungi can cause diseases in humans, like athlete's foot and ringworm. They are also major causes of disease in plants.