Nanochlorum eucaryotum: a Very Reduced Coccoid Species of Marine Chlorophyceae

Nanochlorum eucaryotum was isolated from a sea water aquarium housing different sponge species, cucumarias, small crustaceans and annelids. This bright green marine alga differs from all other known coccoid species. Its most prominent features are its very small cell size (1.5 pm) and its reduced cellular organization. Its cell contains one nucleus, one chloroplast, one mitochondrium and small vacuoles. Sometimes a Golgi apparatus can be seen. No other subcellular features have been observed. The cell wall is thin and smooth and does not contain any material of high electron density; only dividing cells show a rougher surface. The cells split into two daughter cells. No sexual reproduction has been observed in this organism. We have analyzed the ultrastructural cell organization, the amount of total DNA and RNA per cell, the pigment composition, the growth requirements and the sensitivity towards different inhibitors (chloramphenicol, cycloheximid, penicillin, lysozym and cellulase). The results afford the introduction of a new species; a new family or suborder of coccoid green algae is discussed.