Ultramicrobacteria
Encyclopedia
Ultramicrobacteria are bacteria
that are considerably smaller than normal bacterial cells and are 0.3 to 0.2 micrometre
s in diameter. This term was first used in 1981, to refer to cocci
in seawater that were less than 0.3 μm in diameter. These cells have also been recovered from soil and appeared to be a mixture of Gram-positive and negative species. Many, if not all, of these small bacteria are dormant
forms of larger cells that allow survival under starvation conditions. In this process, cells downregulate their metabolism, stop growing and stabilize their DNA, creating dormant non-growing cells that can remain viable for many years. These starvation forms may be the most common type of ultramicrobacteria in seawater.
These small living bacterial cells are distinct from the purported "nanobacteria" or "calcifying nanoparticles", which were proposed to be living organisms that were 0.1 μm in diameter. These structures are now thought to be non-living, and are probably precipitated particles of inorganic material.
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
that are considerably smaller than normal bacterial cells and are 0.3 to 0.2 micrometre
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
s in diameter. This term was first used in 1981, to refer to cocci
Coccus
Coccus can be used to describe any bacterium that has a spherical shape. It is one of the three distinct types of bacteria shapes, the other two being bacillus and spirillum cells...
in seawater that were less than 0.3 μm in diameter. These cells have also been recovered from soil and appeared to be a mixture of Gram-positive and negative species. Many, if not all, of these small bacteria are dormant
Dormancy
Dormancy is a period in an organism's life cycle when growth, development, and physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be closely associated with environmental conditions...
forms of larger cells that allow survival under starvation conditions. In this process, cells downregulate their metabolism, stop growing and stabilize their DNA, creating dormant non-growing cells that can remain viable for many years. These starvation forms may be the most common type of ultramicrobacteria in seawater.
These small living bacterial cells are distinct from the purported "nanobacteria" or "calcifying nanoparticles", which were proposed to be living organisms that were 0.1 μm in diameter. These structures are now thought to be non-living, and are probably precipitated particles of inorganic material.