About What Are Bacteria?
Bacteria are microscopic single-celled organisms. A bacterial cell is much simpler than a plant or animal cell, but bacteria can sense their surroundings, use energy, grow, reproduce, communicate, and survive in an enormous range of environments.
Single Cells
Each bacterium is a complete living cell.
Learn MoreTiny Size
Many bacteria are only a few micrometers across.
Learn MoreShapes
Bacteria come in several common shapes.
Learn MoreDNA Without a Nucleus
Bacterial DNA is not enclosed inside a membrane-bound nucleus.
Learn MoreBinary Fission
Most bacteria reproduce by dividing one cell into two.
Learn MoreMovement
Some bacteria swim, glide, or move in other ways.
Learn MoreMany Ways to Get Energy
Bacteria use an extraordinary variety of chemical reactions.
Learn MoreEverywhere on Earth
Bacteria live in soil, water, air, rocks, animals, plants, and extreme environments.
Learn MoreSingle Cells
Bacteria do not have a nucleus like animal and plant cells. Their DNA is located in the cell interior, usually in a main circular chromosome plus smaller DNA molecules in some species. The cell membrane controls movement of materials, and most bacteria also have a protective cell wall.
Tiny Size
A micrometer is one thousandth of a millimeter. This means hundreds or thousands of bacterial cells could fit across a small printed dot, depending on their size. Microscopes are necessary to see individual cells clearly.
Shapes
Spherical bacteria are often called cocci, rod-shaped forms are bacilli, and spiral forms have curved or corkscrew shapes. Cells may occur alone, in pairs, chains, clusters, or other arrangements.
DNA Without a Nucleus
Bacteria are prokaryotes. Their genetic information directs cell growth, metabolism, and reproduction. Small DNA rings called plasmids can carry additional genes and can sometimes move between bacterial cells.
Binary Fission
The cell copies its DNA, grows, and separates. Under ideal conditions some species can divide rapidly, but in nature temperature, nutrients, moisture, competition, and other factors often slow growth.
Movement
Flagella can act like tiny rotating propellers. Other bacteria glide across surfaces or remain attached in one place. Movement can help cells reach nutrients or move away from harmful conditions.
Many Ways to Get Energy
Some use oxygen and organic food molecules, while others live without oxygen. Certain bacteria gain energy from sulfur, iron, hydrogen, or sunlight. This metabolic diversity lets bacteria live in places that would be impossible for humans.
Everywhere on Earth
They have been found in hot springs, deep ocean sediments, polar ice, deserts, clouds, and underground rocks. Their small size and flexible chemistry make bacteria some of Earth's most widespread forms of life.