Introduction to Bacteria
– Etymology: The word ‘bacteria’ is the plural of the Neo-Latin ‘bacterium’, which is the Latinisation of the Ancient Greek βακτήριον (baktḗrion), meaning staff, cane.
– Origin and early evolution: Bacteria were the first forms of life to appear on Earth, about 4 billion years ago. For about 3 billion years, bacteria and archaea were the dominant forms of life.
– Habitat: Bacteria are ubiquitous and can be found in every possible habitat on Earth. They inhabit soil, water, acidic hot springs, radioactive waste, and the deep biosphere of Earth’s crust.

Morphology and Structure of Bacteria
– Morphology: Bacteria display a wide diversity of shapes and sizes. Bacterial cells are typically 0.5–5.0 micrometers in length, one-tenth the size of eukaryotic cells.
– Cellular Structure: Bacterial cells are surrounded by a cell membrane and lack large membrane-bound structures like a nucleus or mitochondria. Bacteria have a multi-component cytoskeleton to control localization and cell division.
– Intracellular and Extracellular Structures: Bacterial cells have a single circular chromosome located in the nucleoid and contain ribosomes for protein production. Bacteria have cell walls made of peptidoglycan, distinct from plants and fungi.

Importance and Applications of Bacteria
– Nutrient Cycle and Ecological Role: Bacteria play a vital role in the nutrient cycle, decomposing dead bodies and fixing nitrogen from the atmosphere. They are involved in processes such as sewage treatment, breakdown of oil spills, and production of cheese and yogurt through fermentation.
– Biotechnology and Industrial Applications: Bacteria are used in biotechnology, antibiotic production, and the recovery of metals in the mining sector. Antibiotics are used to treat bacterial infections, but antibiotic resistance is a growing problem.
– Potential for Future Discoveries: Only around 2% of bacterial species have been fully studied, highlighting the vast potential for future discoveries.

Bacterial Behavior and Survival Strategies
– Bacterial Growth and Reproduction: Bacteria reproduce through binary fission, a form of asexual reproduction. Bacterial growth and cell division are tightly linked, with cells growing to a fixed size before dividing.
– Bacterial Genetics: Most bacteria have a single circular chromosome, and genetic changes can emerge from random or stress-directed mutation. Bacteria can transfer genetic material between cells through transformation, transduction, and conjugation.
– Bacterial Behavior: Bacteria can communicate through chemical signals, transfer DNA between different bacterial species, and exhibit adaptations to harsh environments. Bacterial growth follows four phases: lag phase, logarithmic phase, stationary phase, and death phase.

Bacterial Impact and Survival Strategies
– Impact on Ecology and Human Society: Bacterial processes are important drivers in biological responses to pollution. Bacteria play roles in ecological processes such as denitrification and acetogenesis. Bacterial infections can cause diseases in humans and animals.
– Endospores: Endospores are highly resistant, dormant structures formed by certain Gram-positive bacteria. They allow bacteria to survive in harsh environments, including outer space.
– Bacterial Movement and Communication: Bacteria can use flagella for movement and communicate through chemical signals, allowing coordinated behavior. Transfer of DNA between different bacterial species can have significant consequences.

Note: The subtopics “Bacterial Shapes,” “Multicellularity,” “Biofilms,” “Bacterial Structures,” “Bacterial Growth,” and “Bacterial Behavior” have been incorporated into the relevant comprehensive groups.

Merriam-Webster Online Dictionary
bacteria (noun)
- bacterium not usually used technically
Bacteria (Wikipedia)

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 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.

Temporal range: ArcheanPresent
Scanning electron micrograph of Escherichia coli rods
Scientific classification Edit this classification
Domain: Bacteria
Woese et al. 1990

See § Phyla

  • "Bacteria" (Cohn 1872) Cavalier-Smith 1983
  • "Bacteria" Haeckel 1894
  • "Bacteria" Cavalier-Smith 2002
  • "Bacteriaceae" Cohn 1872a
  • "Bacteriobionta" Möhn 1984
  • "Bacteriophyta" Schussnig 1925
  • "Eubacteria" Woese and Fox 1977
  • "Neobacteria" Möhn 1984
  • "Schizomycetaceae" de Toni and Trevisan 1889
  • "Schizomycetes" Nägeli 1857

Humans and most other animals 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, 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.

Bacteria (Wiktionary)



Etymology 1

Irregular plural of bacterium from New Latin bactēria.



  1. plural of
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