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 / Richelia
Filamentous 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.