If a single bacterium isn't visible to the naked eye, how can we know so much about it?
Scientists have developed powerful microscopes to magnify bacteria — usually ranging from one to a handful of microns (one millionth of a meter) in length, giving us a glimpse into their inner workings and how they compare to other forms of life such as plants, animals, viruses and fungi.
As you might already know, cells act as the building blocks of life, whether they compose our own tissues or a tree branch outside of your window. Humans, animals and plants have cells with genetic information contained in a type of membrane called a nucleus. These types of cells, called eukaryotic cells, have specialized organelles, each with a unique job to keep the cell working and healthy.
Bacteria, however, lack a nucleus, and their genetic material, or DNA, floats freely within the cell. These microscopic cells don't have organelles and possess different methods to reproduce and swap genetic material. Bacteria are classified as prokaryotic cells.
Basic categories aside, scientists also place bacteria in different camps based on:
- Whether bacteria survive and thrive in environments with or without oxygen
- Their shape, including rods (bacillus), circles (cocci) or spirals (spirillum)
- Whether bacteria are gram-negative or gram-positive, which are stain tests that provide insight into the composition of the cell's outer protective wall
- How bacteria get around and navigate their environments (Many bacteria have flagella, tiny whip-like structures that propel them in their environment.)
Microbiology — the study of all different types of microbes including bacteria, archaea, fungi, viruses and protozoa — has leveraged a growing wealth of knowledge to further distinguish bacteria from their microbial brethren.
Similar prokaryotic organisms now classified in the domain archaea were previously clumped together with bacteria, but after researchers learned more about them, they gave microbes in archaea their own category for their similarities to eukaryotic cells.