Profiles of Bacterial Groups

Five major bacterial groups


Bacteria are microorganisms made up of a single cell. A single teaspoon of soil can contain up to a billion bacterial cells. Unsurprisingly, the bacteria population of a jar of soil can probably easily outnumber the human population. While a single bacteria cell is invisible to the naked eye and can only be seen under a powerful microscope, we can see bacteria when they live together in colonies.

Scientists attempt to categorise bacteria into smaller, discrete groups based on how similar their DNA is. These groups are known as phyla (singular: phylum). The DNA of bacteria within the same phylum are more similar, compared to those from another phylum. However, even within a phylum, bacteria remain incredibly diverse and like every living organism, bacteria come in all shapes and sizes.

Although there are around thirty phyla in the bacterial kingdom, the following five are the most abundant and are renowned for their diversity in appearance and function: