Type 17, Chlorophyceae.  Siderocelis sp.

Type 17, represented by a single isolate, MLO-4, has been identified as Siderocelis sp. by light microscopy.  The cells of Type 17 have thinner walls and more dense chloroplasts than many of our other isolates.  These qualities, combined with a size up to about 7 µm, make this alga a better subject for microscopy than most of our coccoids.  Members of the genus Siderocelis are characterized by grains on the cell wall, which are only barely visible on some of the cells shown above.  However, these grains are easily seen on the old mother cell wall, as shown below.  The plastids of Type 17 possess a pyrenoid, which can be easily seen in several of the cells.  Type 17 produces 18S rDNA RFLP patterns that are very different from our other Chlorophyceae, Types 1 and 10.  These results suggest that Type 17 is not closely related to Types 1 and 10.