Prochlorococcus is a
genusIn biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of very small (0.6
µmA 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...
)
marineAn ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
cyanobacteria with an unusual pigmentation (
chlorophyllChlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
b). These bacteria belong to the
photosynthetic picoplanktonPhotosynthetic picoplankton is the fraction of the plankton performing photosynthesis composed by cells between 0.2 and 2 µm . It is especially important in the central oligotrophic regions of the world oceans that have very low concentration of nutrients.- History :* 1952: Description of the...
and are probably the most abundant
photosyntheticPhotosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
organism on Earth.
Discovery and naming
Although there had been several earlier records of very small chlorophyll-
b-containing cyanobacteria in the ocean,
Prochlorococcus was actually discovered in 1986 by
Sallie W. (Penny) ChisholmSallie W. Chisholm is a U.S. biological oceanographer. She attended Skidmore College and received her Ph.D. from the SUNY Albany in 1974. Since 1976, she has been a member of the faculty at the Massachusetts Institute of Technology, where she is the McAfee Professor of Engineering.Chisholm's...
of the
Massachusetts Institute of TechnologyThe Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological education and research.Founded in 1861 in...
, Robert J. Olson of the
Woods Hole Oceanographic InstitutionThe Woods Hole Oceanographic Institution is a private, nonprofit research and higher education facility dedicated to the study of all aspects of marine science and engineering and to the education of marine researchers. Established in 1930, it is the largest independent oceanographic research...
, and other collaborators in the
Sargasso SeaThe Sargasso Sea is a region in the middle of the North Atlantic Ocean, surrounded by ocean currents. It is bounded on the west by the Gulf Stream; on the north, by the North Atlantic Current; on the east, by the Canary Current; and on the south, by the North Atlantic Equatorial Current. This...
using
flow cytometryFlow cytometry is a technique for counting and examining microscopic particles, such as cells and chromosomes, by suspending them in a stream of fluid and passing them by an electronic detection apparatus. It allows simultaneous multiparametric analysis of the physical and/or chemical...
. The first culture of
Prochlorococcus was isolated in the Sargasso Sea in 1988 (
strainIn biology, a strain is a low-level taxonomic rank used in three related ways.-Microbiology and virology:A strain is a genetic variant or subtype of a micro-organism . For example, a "flu strain" is a certain biological form of the influenza or "flu" virus...
SS120) and shortly another strain was obtained from the
Mediterranean SeaThe Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
(strain MED). The name
Prochlorococcus originated from the fact it was originally assumed that
Prochlorococcus was related to
ProchloronProchloron is a unicellular oxygenic photosynthetic prokaryote commonly found as symbionts in coral reefs, particularly in didemnid ascidians...
and other chlorophyll-
b-containing bacteria, called prochlorophytes, but it is now known that prochlorophytes form several separate
phylogeneticA phylogenetic tree or evolutionary tree is a branching diagram or "tree" showing the inferred evolutionary relationships among various biological species or other entities based upon similarities and differences in their physical and/or genetic characteristics...
groups within the cyanobacteria subgroup of the
bacteriaBacteria 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...
kingdom.
The only species of the genus that has been described is
Prochlorococcus marinus.
Description
Marine cyanobacteria are to date the smallest known
photosyntheticPhotosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
organisms;
Prochlorococcus is the smallest at just 0.5 to 0.8 micrometres across. It has a genome of roughly 2,000 genes in contrast to eukaryotic
algaeAlgae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
that have over 10,000 genes. Possibly it is also the most plentiful
speciesIn biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
on Earth: a single millilitre of surface seawater may contain 100,000 cells or more. Worldwide, there are estimated to be several octillion (~10
27) individuals.
Prochlorococcus is ubiquitous between 40°N and 40°S and dominates in the
oligotrophAn oligotroph is an organism that can live in an environment that offers very low levels of nutrients. They may be contrasted with copiotrophs, which prefer nutritionally rich environments...
ic (nutrient poor) regions of the oceans. The bacterium accounts for an estimated 20% of the
oxygenOxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
in the Earth's
atmosphereAn atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
, and forms part of the base of the ocean
food chainA food web depicts feeding connections in an ecological community. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs...
.
The light-harvesting pigment complement of
Prochlorococcus is unique, consisting predominantly of di
vinylA vinyl compound is any organic compound that contains a vinyl group ,which are derivatives of ethene, CH2=CH2, with one hydrogen atom replaced with some other group...
derivatives of chlorophyll a (Chl a2) and b (Chl b2) and lacking monovinyl chlorophylls.
Prochlorococcus occupies two distinct niches, leading to the nomenclature of the low light (LL) and high light (HL) groups, which vary in pigment ratios (LL has a high ratio of chlorophyll b2:a2 and HL has a low ratio of b2:a2), light requirements, nitrogen and phosphorus utilization, copper and virus sensitivity. These "ecotypes" can be differentiated on the basis of the sequence of their
ribosomal RNARibosomal ribonucleic acid is the RNA component of the ribosome, the enzyme that is the site of protein synthesis in all living cells. Ribosomal RNA provides a mechanism for decoding mRNA into amino acids and interacts with tRNAs during translation by providing peptidyl transferase activity...
gene. Recently the genomes of several strains of
Prochlorococcus have been sequenced.
External links
- The Most Important Microbe You've Never Heard Of: NPR
NPR, formerly National Public Radio, is a privately and publicly funded non-profit membership media organization that serves as a national syndicator to a network of 900 public radio stations in the United States. NPR was created in 1970, following congressional passage of the Public Broadcasting...
Story on Prochlorococcus
- The Habitable Planet Video