Endosymbiotic interaction of Braarudosphaera bigelowii and its endosymbint

A coccolithophore haptophyte Braarudosphaera bigelowii possesses a cyanobacterial endosymbiont. The endosymbiont performs nitrogen fixation in the host cell, and receives fixed carbon from the host. The endosymbiont is also known as UCYN-A or Candidatus Atelocyanobacterium thalassa, which is unculturable. UCYN-A consists of at least six sub-lineages, UCYN-A1 to UCYN-A2. Of these, the genome of UCYN-A1 and UCYN-A2 were sequenced. The genomes lack some essential genes for such as TCA cycle and Calvin cycle. A flagellate haptophyte Chrysochromulina parkeae is considered as a synonym and an alternate life cycle stage of B. bigelowii. The aim of this study is to understand endosymbiotic relationship of B. bigelowii and its endosymbiont.