Prochlorococcus marinus

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Prochlorococcus marinus
Systematics
Department : Cyanobacteria ("Cyanobacteria")
Class : Cyanobacteria (Cyanobacteria)
Order : Prochlorales
Family : Prochlorococcaceae
Genre : Prochlorococcus
Type : Prochlorococcus marinus
Scientific name of the  genus
Prochlorococcus
SW Chisholm , SL Frankel , R. Goericke ,
RJ Olson , B. Palenik , JB Waterbury ,
L. West-Johnsrud & ER Zettler
Scientific name of the  species
Prochlorococcus marinus
SW Chisholm , RJ Olson , ER Zettler , JB Waterbury , R. Goericke & N. Welschmeyer

Prochlorococcus marinus is the only known and scientifically described species of the genus Prochlorococcus . It is a photosynthetic , single-celled cyanobacterium that is predominantly distributed in the marine environment . Prochlorococcus is one of the smallest known photoautotrophic organisms. Due to its high concentration in large areas of the oceans, according to the current state of research, it is the living being with the highest number of individuals and at the same time the most widespread living being on earth and plays a particularly important role in the primary production of organic substances.

features

The cells are 0.5 to 0.8 µm in diameter - compared to other cyanobacteria - small. They are among the smallest known photosynthesis-performing organisms and are classified as picoplankton . They have the photosynthetic pigments chlorophyll a2 and chlorophyll b2, which are divinyl derivatives of the chlorophylls a and b occurring in plants.

The genome of Prochlorococcus marinus has been completely sequenced .

distribution

According to current knowledge, Prochlorococcus is numerically the most common and most widespread organism on earth. It occurs mainly in the oceans between latitudes 40 ° N and 40 ° S in the upper 100 to 150 m, especially in nutrient-poor ( oligotrophic ) areas with a water temperature of at least 10 ° C. It reaches concentrations of 1 · 10 5 to 3 · 10 5 per milliliter and 10 11 to 10 14 per square meter and represents a considerable proportion of the bacterioplankton of all oceans.

Way of life and ecology

As a photoautotrophic organism, Prochlorococcus is at the beginning of the food chain and is responsible for a substantial part of primary marine production. Under natural conditions, the cells divide once a day on average. This means that 50 percent of the total Prochlorococcus biomass enters the marine food webs every day .

Prochlorococcus mainly colonizes two ecological niches : In addition to populations living close to the surface, photosynthesis-performing cells can also be found at depths of over 150 meters. Less than 1 percent of the near-surface light intensity is available and the electromagnetic spectrum of the light only contains the blue component. These cells, adapted to weak light, have antenna pigments that can also absorb blue light of low intensity and enable survival. Accordingly, the bacteria are divided into two groups: Members of the low light (LL) group have a higher ratio of chlorophyll b2: a2 than members of the high light (HL) group. The groups also differ in their nitrogen and phosphate requirements and in their sensitivity to copper compounds and viruses.

Systematics

Flow cytometry of a seawater sample in which three picoplankton groups can be identified ( prochlorococcus , synechococcus and pico-eukaryotes)

Prochlorococcus was first discovered, isolated and described in the Sargasso Sea in 1988 by Sallie W. Chisholm ( Massachusetts Institute of Technology ), Robert J. Olson ( Woods Hole Oceanographic Institution ) and other colleagues using flow cytometry .

Originally Prochlorococcus was thought to be a relative of Prochloron and other bacteria containing chlorophyll b, so that the NCBI system used here also classifies the genus as Prochlorophytes ( Prochlorales ). However, based on their rRNA sequences, it was recognized that Prochlorococcus is an independent group among the cyanobacteria . The light-absorbing pigments of the bacteria consist mainly of divinyl derivatives of chlorophyll a (Chl a2) and b (Chl b2), but they do not contain any mono-vinyl chlorophylls.

supporting documents

  1. ^ A b c F. Partensky, WR Hess, D. Vaulot: Prochlorococcus, a marine photosynthetic prokaryote of global significance. In: Microbiology and Molecular Biology Reviews . Vol. 63, No. 1, 1999, pp. 106-127.
  2. ^ A b Thomas M. Smith, Robert L. Smith: Ecology. Pearson Studies, Munich 2009; P. 447. ISBN 978-3-8273-7313-7 .
  3. ↑ SW Chisholm, RJ Olson, ER Zettler, J. Waterbury, R. Goericke, N. Welschmeyer: A novel free-living prochlorophyte occurs at high cell concentrations in the oceanic euphotic zone . In: Nature Vol. 334, 1988, pp. 340-343. doi : 10.1038 / 334340a0 .

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