Bacteria are microscopic single-celled organisms that constitute one of life’s fundamental domains. These prokaryotic microorganisms exist in virtually every habitat on Earth and play vital roles in global ecosystems.
Structure and Composition
Cell Architecture
A bacterial cell contains a cell membrane, cell wall, and cytoplasm. The genetic material floats freely in the cytoplasm since bacteria lack a membrane-bound nucleus. The cell wall contains peptidoglycan, giving bacteria their shape and protection.
Size and Morphology
Bacterial cells measure 0.5-5.0 micrometers in length, roughly one-tenth the size of eukaryotic cells. They come in three main shapes:
- Cocci (spherical)
- Bacilli (rod-shaped)
- Spirilla (spiral)
Ecological Impact
Environmental Roles
Bacteria drive crucial ecological processes:
- Decomposition of organic matter
- Nitrogen fixation
- Nutrient cycling
- Photosynthesis in cyanobacteria
Human Microbiome
The human body hosts trillions (10^13 to 10^14) of bacterial cells. Most reside in the gut and on skin, where they:
- Aid digestion
- Produce vitamins
- Support immune function
- Protect against pathogens
Medical Significance
Bacterial Infections
Some species cause diseases like:
- Tuberculosis
- Tetanus
- Cholera
- Pneumonia
Antibiotic Resistance
The widespread use of antibiotics in medicine and agriculture has led to increasing bacterial resistance, creating a significant public health challenge.
Industrial Applications
Bacteria serve various industrial purposes:
- Food production (yogurt, cheese)
- Waste treatment
- Biofuel generation
- Mining operations
- Antibiotic manufacture
Evolution and Diversity
Bacteria emerged approximately 4 billion years ago as Earth’s first life forms. Through evolution, they’ve developed remarkable adaptability, allowing them to thrive in extreme environments from hot springs to radioactive waste. Scientists estimate the existence of 10^7 to 10^9 bacterial species, though only a small fraction have been identified and studied.
The drawback in bacterial research lies in the difficulty of culturing many species in laboratory conditions, limiting our understanding of their full diversity and potential.
Bacteria (/bækˈtɪəriə/ ; sg.: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit the air, soil, water, acidic hot springs, radioactive waste, and the deep biosphere of Earth's crust. Bacteria play a vital role in many stages of the nutrient cycle by recycling nutrients and the fixation of nitrogen from the atmosphere. The nutrient cycle includes the decomposition of dead bodies; bacteria are responsible for the putrefaction stage in this process. In the biological communities surrounding hydrothermal vents and cold seeps, extremophile bacteria provide the nutrients needed to sustain life by converting dissolved compounds, such as hydrogen sulphide and methane, to energy. Bacteria also live in mutualistic, commensal and parasitic relationships with plants and animals. Most bacteria have not been characterised and there are many species that cannot be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology.
| Bacteria | |
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| Scanning electron micrograph of Escherichia coli rods | |
Scientific classification  | |
| Domain: | Bacteria Woese et al. 2024 |
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See § Phyla | |
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Like all animals, humans carry vast numbers (approximately 1013 to 1014) of bacteria. Most are in the gut, though there are many on the skin. Most of the bacteria in and on the body are harmless or rendered so by the protective effects of the immune system, and many are beneficial, particularly the ones in the gut. However, several species of bacteria are pathogenic and cause infectious diseases, including cholera, syphilis, anthrax, leprosy, tuberculosis, tetanus and bubonic plague. The most common fatal bacterial diseases are respiratory infections. Antibiotics are used to treat bacterial infections and are also used in farming, making antibiotic resistance a growing problem. Bacteria are important in sewage treatment and the breakdown of oil spills, the production of cheese and yogurt through fermentation, the recovery of gold, palladium, copper and other metals in the mining sector (biomining, bioleaching), as well as in biotechnology, and the manufacture of antibiotics and other chemicals.
Once regarded as plants constituting the class Schizomycetes ("fission fungi"), bacteria are now classified as prokaryotes. Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and rarely harbour membrane-bound organelles. Although the term bacteria traditionally included all prokaryotes, the scientific classification changed after the discovery in the 1990s that prokaryotes consist of two very different groups of organisms that evolved from an ancient common ancestor. These evolutionary domains are called Bacteria and Archaea.
English
Pronunciation
- (Received Pronunciation) IPA(key): /bakˈtɪə̯.ri.ə/
- (General American