Prochlorobacteriae The Prochlorobacteria

In 1976, Ralph A. Lewin of the Scripps Institute of Oceanography announced the discovery of unicellular, prokaryotic organisms with bright green cells that were living on marine animals called sea squirts found in shallow marine waters of Baja California. These organisms, which were given the name Prochloron, have the chlorophylls a and b of higher plants but no trace of the phycobilin accessory pigments associated with cyanobacteria. Instead, their accessory pigments were confined to the carotenoid pigments found in higher plants. Also, unlike the single membrane thylakoids of cyanobacteria, those of the new organisms are double.

Lewin considered the pigment differences between cyanobacteria and the bright green cells of Prochloron to be basic enough to warrant recognition at the division level, and he proposed a new division to be known as the Prochlorophyta. Many microbiologists are reluctant to recognize these organisms as belonging to a separate bacterial division because the prokaryotic cell structure and chemistry is similar to that of cyanobacteria and other true bacteria (Fig. 17.13), but others

Prochloron

Figure 17.13 A section through a cell of the prochlorobac-terium Prochloron, which lives on the surface of sea squirts (marine animals). Note the absence of a nucleus and other organelles, and the concentric layers of membranes that perform some of the functions of organelles, x15,750. (Electron micrograph courtesy Jean Whatley)

Figure 17.13 A section through a cell of the prochlorobac-terium Prochloron, which lives on the surface of sea squirts (marine animals). Note the absence of a nucleus and other organelles, and the concentric layers of membranes that perform some of the functions of organelles, x15,750. (Electron micrograph courtesy Jean Whatley)

Kingd om Bacteria, Kingdom Archaea, and Viruses 315

agree with Lewin's assessment of the significance of the pigment system. While the pigment system is, indeed, significant, they are treated here as a class of true bacteria because their remaining structure and features are essentially indistinguishable from those of other true bacteria.

In 1984, Dutch biologists discovered a similar organism, which they named Prochlorothrix, in shallow lakes in the Netherlands. It differs from Prochloron in being free-living and filamentous. In the late 1980s, Sally Chisholm of the Massachusetts Institute of Technology identified yet another marine prochlorobacterium that flourishes in dim light at a depth of about 100 meters (328 feet). This organism now appears to be one of the two most numerous bacteria living in ocean waters.

The discovery of prochlorobacteria adds weight to the theory that chloroplasts may have originated from such cells living within the cells of other organisms, especially since the pigments involved are identical with those of higher plants.

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Responses

  • katharina busch
    Where prochlorobacteria is found?
    8 years ago
  • sarah
    Why sea squirts need prochloron?
    8 years ago
  • bisrat
    Why are prochlorobacteria sometimes called prochlorophyta?
    8 years ago
  • uwe
    What are the classes of the prochlorobacteria?
    8 years ago
  • mary
    What are the characteristics of a prochlorobacteria?
    8 years ago
  • cerdic
    What are plant features for prochlorobacteriae?
    4 years ago
  • wilmer
    What are prochlorobacterial?
    3 years ago
  • Rio
    What is true about prochlorobacteria?
    3 years ago

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