Paulinella

A genus of amoeboid cercozoans

Paulinella is a genus of amoeboid cercozoans within the family Paulinellidae. This genus is notable for its unique photosynthetic species, Paulinella chromatophora, which contains a photosynthetic organelle derived from a cyanobacterium.

Description

Paulinella species are characterized by their amoeboid shape and the presence of a shell or test. The test is typically composed of siliceous scales and plates, which are secreted by the cell. These organisms are found in freshwater environments and are known for their distinctive morphology and cellular structures.

Photosynthetic Organelles

Paulinella chromatophora

One of the most remarkable features of Paulinella chromatophora is its photosynthetic organelle, known as a chromatophore. Unlike the chloroplasts found in most photosynthetic eukaryotes, which originated from a single endosymbiotic event involving a cyanobacterium, the chromatophore of Paulinella chromatophora is the result of a more recent and independent endosymbiotic event. This organelle retains many features of its cyanobacterial ancestor, including a genome that is more similar to that of free-living cyanobacteria than to typical chloroplasts.

Evolutionary Significance

The study of Paulinella provides valuable insights into the process of endosymbiosis and the evolution of photosynthetic organelles. The independent acquisition of a photosynthetic organelle in Paulinella chromatophora represents a rare example of primary endosymbiosis, offering a unique opportunity to study the early stages of organelle evolution and integration into the host cell.

Species

The genus Paulinella includes several species, with Paulinella chromatophora being the most studied due to its photosynthetic capabilities. Other species within the genus are primarily heterotrophic and do not possess photosynthetic organelles.

Related pages

• Endosymbiotic theory
• Chloroplast
• Cyanobacteria
• Cercozoa