Studies of Marine Planktonic Diatoms:ii. Use of Cyclotella Nana Hustedt for Assays of Vitamin B12 in Sea Water

Cyclotella nana Hustedt, a small centric diatom requiring vitamin B12, was tested as a potential assay organism for that vitamin. Dose–response curves, measured by optical density and cell count, showed a linear relation between growth and B12 concentration between 0 and at least 2 μμg/ml of the vitamin. Since the diatom is hardy, grows rapidly under a variety of conditions, and may be preserved for later examination, it represents a useful assay organism for certain applications such as oceanographic exploration.