Bacterium
Say it: bak-TEER-ee-um
A bacterium is a single-celled prokaryote with no nucleus, found in almost every habitat on Earth, including in and on the human body.
Also: bacteria, eubacteria
Definition
What is a bacterium?
A bacterium is a microscopic, single-celled organism in the domain Bacteria, one of the three domains of life. Like archaea, bacteria are prokaryotes: their DNA, usually a single circular chromosome, lies in a region called the nucleoid rather than inside a nucleus, and they have no membrane-bound organelles such as mitochondria. Many also carry small extra rings of DNA called plasmids, and they build proteins on 70S ribosomes, which differ from the ribosomes in human cells.
Most bacteria are enclosed by a cell wall made of peptidoglycan, and the structure of that wall splits them into Gram-positive and Gram-negative groups. Common shapes are spheres (cocci), rods (bacilli) and spirals. Bacteria usually reproduce by binary fission, and under good conditions some can double their numbers in well under an hour.
Bacteria live almost everywhere, from soil and oceans to hot springs and the human gut. Only a small share of species cause disease; many are harmless or helpful, recycling nutrients, aiding digestion and making antibiotics and other useful compounds. Differences between bacterial and human cells, such as the cell wall and the ribosomes, are what many antibiotics exploit.
Word parts
Where does the word “bacterium” come from?
- bacter-
- small staff, rodGreek bakterion, diminutive of bakteria, staff
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Terms that go with it
- ProkaryoteA prokaryote is a usually single-celled organism, a bacterium or an archaeon, whose cell has no nucleus or other membrane-bound organelles.
- PeptidoglycanPeptidoglycan is the mesh-like polymer of sugars and short peptides that forms the bacterial cell wall and gives bacteria their shape and strength.
- Gram stainThe Gram stain is a lab staining method that sorts bacteria into Gram-positive (purple) and Gram-negative (pink) groups based on their cell walls.
- Binary fissionBinary fission is how bacteria and archaea reproduce: a cell copies its DNA, grows, and splits in the middle into two identical daughter cells.
- PlasmidA plasmid is a small, usually circular DNA molecule that copies itself independently of the main chromosome, found mostly in bacteria.
- AntibioticAn antibiotic is a drug that kills bacteria or stops them from growing, used to treat or prevent bacterial infections; it has no effect on viruses.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Microbiology, 3.3 Unique Characteristics of Prokaryotic Cells
- NHGRI Talking Glossary: Bacteria
- OpenStax Microbiology, 9.1 How Microbes Grow
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