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Braarudosphaera bigelowii
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Braarudosphaera bigelowii
Braarudosphaera bigelowii is a coastal coccolithophore in the fossil record going back 100 million years to the Late Cretaceous. Due to endosymbiontic integration, it has obtained a nitrogen-fixing organelle called a nitroplast.
The family Braarudosphaeraceae consists of single-celled coastal phytoplanktonic algae whose diploid phase is covered with calcareous scales with five-fold symmetry, called pentaliths. With 12 sides, it has a regular dodecahedral structure, approximately 10 micrometers across.
Braarudosphaera bigelowii has 2 organelles originated from cyanobacterial endosymbiosis. One is its chloroplast, which originated from secondary endosymbiosis, in which another eukaryote with a chloroplast was incorporated into its ancestor. The other is its nitroplast, which comes from a second primary endosymbiosis event (like the chromatophore of Paulinella). The ancestor of the nitroplast was different from that of the chloroplast. Both of them were able to photosynthesize. However, the nitroplast lost its ability to photosynthesize during its development into an organelle.
The nitroplast originated some 100 million years ago from a cyanobacterial endosymbiont called UCYN-A2, which allows B. bigelowii to fix nitrogen and convert it into compounds useful for cell growth. This endosymbiosis event occurred much later than that of the chloroplasts of the Archaeplastida, so many genes are still preserved in the nitroplast genome.
The number of chloroplasts and nitroplasts is fixed, so their division should synchronize with cell division to ensure that its offspring have the correct number. B. bigelowii has two chloroplasts (secondary endosymbiosis) and one nitroplast, the order of replication of them is: mitochondria, nitroplast, nucleus, then chloroplasts.
This phenomenon is previously known from diatoms in the family Rhopalodiaceae, where a nitrogen fixing and non-photosynthetic cyanobacterial endosymbiont, a diazoplast, provides the photosynthetic host cell with nitrogen.
The genus name Braarudosphaera is in honour of Norwegian botanist Trygve Braarud (1903–1985). He specialized in marine biology, and was affiliated with the University of Oslo.
The nitroplast have reduced their ancestral genes for photosynthesis, so it needs products from chloroplasts to support them. Such dependence on chloroplasts of nitroplast explain why the N2 fixation should undergo in daytime.
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Braarudosphaera bigelowii
Braarudosphaera bigelowii is a coastal coccolithophore in the fossil record going back 100 million years to the Late Cretaceous. Due to endosymbiontic integration, it has obtained a nitrogen-fixing organelle called a nitroplast.
The family Braarudosphaeraceae consists of single-celled coastal phytoplanktonic algae whose diploid phase is covered with calcareous scales with five-fold symmetry, called pentaliths. With 12 sides, it has a regular dodecahedral structure, approximately 10 micrometers across.
Braarudosphaera bigelowii has 2 organelles originated from cyanobacterial endosymbiosis. One is its chloroplast, which originated from secondary endosymbiosis, in which another eukaryote with a chloroplast was incorporated into its ancestor. The other is its nitroplast, which comes from a second primary endosymbiosis event (like the chromatophore of Paulinella). The ancestor of the nitroplast was different from that of the chloroplast. Both of them were able to photosynthesize. However, the nitroplast lost its ability to photosynthesize during its development into an organelle.
The nitroplast originated some 100 million years ago from a cyanobacterial endosymbiont called UCYN-A2, which allows B. bigelowii to fix nitrogen and convert it into compounds useful for cell growth. This endosymbiosis event occurred much later than that of the chloroplasts of the Archaeplastida, so many genes are still preserved in the nitroplast genome.
The number of chloroplasts and nitroplasts is fixed, so their division should synchronize with cell division to ensure that its offspring have the correct number. B. bigelowii has two chloroplasts (secondary endosymbiosis) and one nitroplast, the order of replication of them is: mitochondria, nitroplast, nucleus, then chloroplasts.
This phenomenon is previously known from diatoms in the family Rhopalodiaceae, where a nitrogen fixing and non-photosynthetic cyanobacterial endosymbiont, a diazoplast, provides the photosynthetic host cell with nitrogen.
The genus name Braarudosphaera is in honour of Norwegian botanist Trygve Braarud (1903–1985). He specialized in marine biology, and was affiliated with the University of Oslo.
The nitroplast have reduced their ancestral genes for photosynthesis, so it needs products from chloroplasts to support them. Such dependence on chloroplasts of nitroplast explain why the N2 fixation should undergo in daytime.
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