THE REQUIREMENT FOR SILICON IN SYNURA PETERSENII (CHRYSOPHYCEAE)1,2

A silicon requirement for growth is demonstrated for an alga other than a diatom. Concentrations of less than 1 μM silicate greatly decreased the growth rate of Synura petersenii Korshikov and caused morphological changes. Half of maximum growth rate (μ_max= 1.12 divisions/day) appeared at a concentration of only 0.23 μM silicate. Germanium dioxide inhibited, growth considerably; the degree of inhibition varying from none to almost 100% depending upon both Si and Ge concentrations. The amount of silicon deposited in the external scales of S. petersenii is comparable per unit area to that of diatoms. S. petersenii is able to deplete the medium of silicate to very low levels. The feasibility of batch culture techniques for this kind of work is discussed briefly.