Amoeboid - Thierry Karsenti

ods to spirals. Bacteria are ubiquitous in every habitat on Earth, growing in soil,
acidic hot springs, radioactive waste, [1] seawater, and deep in the Earth's crust. There
are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in
a millilitre of fresh water; in all, there are approximately five nonillion (5×10 30 )
bacteria on Earth, [2] forming much of the world's biomass. [3] Bacteria are vital in
recycling nutrients, and many important steps in nutrient cycles depend on bacteria,
such as the fixation of nitrogen from the atmosphere. However, most of these bacteria
have not been characterized, and only about half of the phyla of bacteria have species
that can be cultured in the laboratory. [4] The study of bacteria is known as
bacteriology, a branch of microbiology.
There are approximately ten times as many bacterial cells as human cells in the
human body, with large numbers of bacteria on the skin and in the digestive tract. [5]
Although the vast majority of these bacteria are rendered harmless or beneficial by the
protective effects of the immune system, a few are pathogenic bacteria and cause
infectious diseases, including cholera, syphilis, anthrax, leprosy and bubonic plague.
The most common fatal bacterial diseases are respiratory infections, with tuberculosis
alone killing about 2 million people a year, mostly in sub-Saharan Africa. [6] In
developed countries, antibiotics are used to treat bacterial infections and in various
agricultural processes, so antibiotic resistance is becoming common. In industry,
bacteria are important in processes such as sewage treatment, the production of cheese
and yoghurt, and the manufacture of antibiotics and other chemicals. [7]
Bacteria are 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 prokaryotic life consists of two very
different groups of organisms that evolved independently from an ancient common
ancestor. These evolutionary domains are called Bacteria and Archaea. [8]
Contents
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• 1 History of bacteriology
• 2 Origin and early evolution
• 3 Morphology
• 4 Cellular structure
o 4.1 Intracellular structures
o 4.2 Extracellular structures
o 4.3 Endospores
• 5 Metabolism
• 6 Growth and reproduction
• 7 Genetics
• 8 Movement
• 9 Classification and identification
• 10 Interactions with other organisms
o 10.1 Mutualists
o 10.2 Pathogens