Home / Amoebae / Testate / Paulinella
lick on images for larger format
Name derivation:
Classification:
Phylum Certcozoa.
Morphology:
Unicells with an ovoid test made of siliceous scales and having a collared opening through which a cytoplasmic extension (filoplast) protrudes. Cell size ~ 15 μm. Contains two sausage-shaped chromatoplasts with PS pigments resembling those of cyanobacteria, effectively chloroplasts. Endobiosis is relatively new (ca. 60 MYA) compared to those of the archaeoplasts (Glaucophyceae, Rhodophyceae and Chlorophyceae, ~ 1.5 BYA).
Endosymbiont gene loss or transfer to nucleus
Transition from a free-living cyanobacterium such as Synechococcus to an enslaved photosynthetic endobiont has been accompanied by a significant (as much as 67%) loss of genes, rendering it entirely dependent on its host. The rDNA sequence of the endobiont is closely related to that of the cyanobacterium Synechococcus (Marin et al.). In contrast to other plastid genomes, that of the endobiont is ~5 times larger and retains core genes required for photosynthesis (Nakayama and Archibold 2012) suggesting that this is a second known case of primary endosymbiosis of PS plastids. To date 33 nuclear genes are known to be derived from the chromatophore (Ibid.) and some of these produce proteins active in the chromatophore (Nowack at al. 2011). The host regulates division of the endobiont during cell division.
Similar genera:
Habitat:
Freshwater benthos.
References:
Marin, B., E.C. Nowack and M. Melkonian 2005. A plastid in the making: evidence for a second primary endosymbiosis. Protist 156:425-432. Nakayama. T. and J.M. Archibold 2012. Evolving a photosynthetic organelle. BMC Biology 10(35):1-3 Nowack E.C., H. Vogel, M. Groth, A.R. Grossman, M. Melkonian, and G. Glöckner 2011. Endosymbiotic gene transfer and transcriptional regulation of transferred genes in Paulinella chromatophora. Molecular Biological Evolution 2011, 28:407-422.