Bacteria are tiny, one-celled organisms that play an important part in all life on Earth. They come in three basic shapes—rod, sphere, and spiral. This bacterium is a spiral type known as a spirochete.
Parts of a Bacterium
A bacterium is protected by an outer cell wall. Just inside the cell wall is a cell membrane that permits substances to move in and out of the bacterium. DNA, the bacterium’s genetic material, floats around inside the cell. A flagellum helps the bacterium move around in search of food or away from things that could harm it.
Bacteria reproduce by splitting themselves in two. A bacterial cell may divide as often as every six minutes. In this way, one cell can become many cells in a short time.
Anthrax is a serious disease caused by the bacterium Bacillus anthracis. Here, a cluster of anthrax bacteria, in red, is shown inside a blood vessel of a human lung.
A high-powered microscope is used to show Streptococcus bacteria. This type of bacteria is commonly found in the human body. It causes illnesses such as strep throat, scarlet fever, and pneumonia.
Antoni van Leeuwenhoek
Antoni van Leeuwenhoek was a Dutch inventor who developed the first microscope. Leeuwenhoek was the first person to observe bacteria, which he called animalcules.
How the Body Fights Bacteria
Some bacteria can cause infections. The body produces cells that defend against infection by attacking bacteria. One of these types of cells, a macrophage, is shown in yellow in this photograph.