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Science & Nature • Microbiology

Bacteria

Bacteria are a domain of microscopic, usually single-celled prokaryotic organisms found in nearly all environments on Earth.

By Ethan Anderson| Reviewed by Olivia Bennett, Standards & Fact-Checking Lead| Updated July 27, 2026|2 min read| Fact-checked

Bacteria are a domain of microscopic, usually single-celled prokaryotic organisms found in nearly all environments on Earth. They are structurally simple, lack a membrane-bound nucleus, and include species that are beneficial, harmless, or pathogenic to other organisms.

Characteristics

Bacteria are prokaryotic microorganisms with DNA not enclosed in a nucleus. They are typically small and may have spherical, rod-like, or spiral forms.

Habitat and diversity

Bacteria occur in almost every habitat on Earth, including extreme environments such as deep-sea and subsurface settings. Their metabolic diversity allows them to use a wide range of chemical sources for energy and growth.

Relationship with humans

Many bacteria live harmlessly on or in the human body, especially in the digestive tract and on the skin. A smaller number are pathogenic and can cause disease.

Scientific study and uses

The study of bacteria is called bacteriology, a branch of microbiology. Bacteria are used in food production, biotechnology, and other industrial applications.

Key facts

  • Bacteria are microscopic single-celled organisms that lack a membrane-bound nucleus.
  • They are found in soil, water, air, extreme environments, and inside the bodies of plants and animals.
  • Bacteria show wide diversity in shape and metabolism.
  • Some bacteria cause disease, but most are harmless or beneficial.
  • Bacteria play important roles in ecosystems and industrial processes.
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Canadian context

Bacteria are relevant to Canadian health, food production, environmental science, and biotechnology, and are studied in Canadian schools, universities, and public health systems.

Frequently asked questions

What are bacteria?
Bacteria are microscopic, usually single-celled prokaryotic organisms found in nearly all environments on Earth.
Do bacteria have a nucleus?
No. Bacteria lack a membrane-bound nucleus and other membrane-bound organelles.
Are all bacteria harmful?
No. Most bacteria are harmless or beneficial, although some species can cause disease.
Where do bacteria live?
Bacteria live in soil, water, air, extreme environments, and inside or on living organisms.
What shapes do bacteria have?
Common bacterial shapes include spherical, rod-shaped, and spiral forms.

References

  1. Britannicahttps://www.britannica.com/science/bacteria
    Supports: Bacteria as microscopic single-celled prokaryotes, habitats, metabolic diversity, beneficial and pathogenic roles.
  2. The Canadian Encyclopediahttps://thecanadianencyclopedia.ca/en/article/bacteria
    Supports: Definition, cell structure, sizes, shapes, and Canadian-relevant encyclopedic treatment.
  3. Wikipediahttps://en.wikipedia.org/wiki/Bacteria
    Supports: General overview of habitats, prokaryotic nature, and early appearance on Earth.
  4. National Human Genome Research Institutehttps://www.genome.gov/genetics-glossary/Bacteria
    Supports: General characteristics, shapes, human microbiome relevance, and biotechnology importance.