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- Foster, Rachel A., et al.
(author)
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Richelia
- 2022
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In: Bergey's Manual of Systematics of Archaea and Bacteria. - : John Wiley & Sons. - 9781118960608 ; , s. 1-17
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Book chapter (peer-reviewed)abstract
- Ri.che'li.a. N.L. fem. n. Richelia, named for the Danish admiral Andreas du Plessis de Richelieu (1852–1932).Cyanobacteria / Cyanobacteria / Cyanobacteriales / Nostocaceae / RicheliaFilamentous heterocyst-forming, Gram-stain-negative, aerobic, phototrophic, N2-fixing, and occurring either as free-living or most often associated with several marine diatom genera (Rhizosolenia, Hemiaulus, and Chaetoceros). Filaments (trichomes) contain variable numbers of sheathless vegetative cells and one terminal heterocyst. Filaments lack akinetes and have limited motility via gliding. Gas vesicles are absent. Cyanophycin granules can be present in vegetative cells and heterocysts. Glycogen appears as large deposits, and thylakoids are dispersed randomly. Reproduce by normal cell division and asynchronous with one host diatom Rhizosolenia. DNA G + C content (mol%) from draft genomes varies 33–39%; genome size varies 3.42–6.04 Mb. Reduces atmospheric N2 with nitrogenase. Known habitats are warm (24–27.5°C), marine, and oligotrophic seas with intermediate (32 PSU) to fully marine (36 PSU) salinities. Biogeochemically relevant as N2 fixers and drivers of carbon export. Have been reported in all major ocean basins (Atlantic, Pacific, and Indian) and smaller seas (Mediterranean Sea and Red Sea).DNA G + C content (mol%): 33–39 (genome sequence).Type species: Richelia intracellularis Schmidt in Ostenfeld and Schmidt 1901.
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| 2. |
- Flores, Enrique, et al.
(author)
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Adaptation to an Intracellular Lifestyle by a Nitrogen-Fixing, Heterocyst-Forming Cyanobacterial Endosymbiont of a Diatom
- 2022
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In: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 13
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Journal article (peer-reviewed)abstract
- The symbiosis between the diatom Hemiaulus hauckii and the heterocyst-forming cyanobacterium Richelia intracellularis makes an important contribution to new production in the world’s oceans, but its study is limited by short-term survival in the laboratory. In this symbiosis, R. intracellularis fixes atmospheric dinitrogen in the heterocyst and provides H. hauckii with fixed nitrogen. Here, we conducted an electron microscopy study of H. hauckii and found that the filaments of the R. intracellularis symbiont, typically composed of one terminal heterocyst and three or four vegetative cells, are located in the diatom’s cytoplasm not enclosed by a host membrane. A second prokaryotic cell was also detected in the cytoplasm of H. hauckii, but observations were infrequent. The heterocysts of R. intracellularis differ from those of free-living heterocyst-forming cyanobacteria in that the specific components of the heterocyst envelope seem to be located in the periplasmic space instead of outside the outer membrane. This specialized arrangement of the heterocyst envelope and a possible association of the cyanobacterium with oxygen-respiring mitochondria may be important for protection of the nitrogen-fixing enzyme, nitrogenase, from photosynthetically produced oxygen. The cell envelope of the vegetative cells of R. intracellularis contained numerous membrane vesicles that resemble the outer-inner membrane vesicles of Gram-negative bacteria. These vesicles can export cytoplasmic material from the bacterial cell and, therefore, may represent a vehicle for transfer of fixed nitrogen from R. intracellularis to the diatom’s cytoplasm. The specific morphological features of R. intracellularis described here, together with its known streamlined genome, likely represent specific adaptations of this cyanobacterium to an intracellular lifestyle.
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