Discovery of an Endosymbiotic Nitrogen-Fixing Cyanobacterium UCYN-A in Braarudosphaera bigelowii PrymnesiophyceaeReport as inadecuate




Discovery of an Endosymbiotic Nitrogen-Fixing Cyanobacterium UCYN-A in Braarudosphaera bigelowii Prymnesiophyceae - Download this document for free, or read online. Document in PDF available to download.

Braarudosphaera bigelowii Prymnesiophyceae is a coastal coccolithophore with a long fossil record, extending back to the late Cretaceous ca. 100 Ma. A recent study revealed close phylogenetic relationships between B. bigelowii, Chrysochromulina parkeae Prymnesiophyceae, and a prymnesiophyte that forms a symbiotic association with the nitrogen-fixing cyanobacterium UCYN-A. In order to further examine these relationships, we conducted transmission electron microscopic and molecular phylogenetic studies of B. bigelowii. TEM studies showed that, in addition to organelles, such as the nucleus, chloroplasts and mitochondria, B. bigelowii contains one or two spheroid bodies with internal lamellae. In the 18S rDNA tree of the Prymnesiophyceae, C. parkeae fell within the B. bigelowii clade, and was close to B. bigelowii Genotype III 99.89% similarity. Plastid 16S rDNA sequences obtained from B. bigelowii were close to the unidentified sequences from the oligotrophic SE Pacific Ocean e.g. HM133411 99.86% similarity. Bacterial16S rDNA sequences obtained from B. bigelowii were identical to the UCYN-A sequence AY621693 from Arabian Sea, and fell in the UCYN-A clade. From these results, we suggest that; 1 C. parkeae is the alternate life cycle stage of B. bigelowii sensu stricto or that of a sibling species of B. bigelowii, and 2 the spheroid body of B. bigelowii originated from endosymbiosis of the nitrogen-fixing cyanobacterium UCYN-A.



Author: Kyoko Hagino , Ryo Onuma, Masanobu Kawachi, Takeo Horiguchi

Source: http://plos.srce.hr/



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