SILICON METABOLISM IN DIATOMS. VI. SILICIC ACID UPTAKE BY A COLORLESS MARINE DIATOM, NITZSCHIA ALBA LEWIN AND LEWIN(1) (2)

Abstract

Cells of the colorless, heterotrophic diatom Nitzschia alba, after removal from the culture medium, were able to absorb silicic acid from a salt solution lacking carbon, nitrogen, and phosphorus. Silicic acid uptake continued for approximately 12 hr. At low cell densities (ca. 2.5×10(5) cells/ml), the cell number doubled under these conditions. At high cell densities (ca. 2 ×10(6) cells/ml) no cell division resulted. When such cells were washed with a salt solution, their ability to absorb silicic acid was somewhat impaired. The degree of impairment became progressively more pronounced after subsequent washing treatments. A heat-stable factor washed from the cells and present in the first "wash water" was able to restore completely the ability of washed cells to absorb silicic acid. The factor was not identified. Aspartic acid (5 ± 10(-4) M) or glutamine (5 ±10(-4) M) when added to the saline solution similarly promoted complete recovery. A t such concentrations, these substances had only a slight effect on unwashed cells. A solution of 5 ±10(-4) M Na glutamate (or aspartic acid plus glutamine) had an men more pronounced effect, and in addition promoted cell division or growth" of unwashed cells. Several other amino acids and other compounds tested were apparently without effect.