Sulfonic acid metabolism in the diatom Navicula pelliculosa

Sulfate uptake and the cellular levels of three sulfonic acids, cysteinolic acid, sulfopropanediol, and the plant sulfolipid, were followed using 35S-sulfate labeled cells of the diatom Navicula pelliculosa in silicate starvation synchrony, sulfur deficiency, and chase experiments. Sulfate uptake was nearly completely inhibited during silicate starvation but was resumed 3 hr after silicate addition (synchrony induction). Cysteinolic acid and sulfopropanediol levels decreased rapidly after silicate addition, although an earlier decrease in cysteinolic acid was noted, possibly in response to sulfate uptake inhibition. No decrease in the sulfur-containing lipids was noted. A metabolically active role for cysteinolic acid as a reservoir of reduced sulfur was indicated, relative to sulfopropanediol and the plant sulfolipid, on the basis of rapid utilization and turnover during sulfur deficiency and chase experiments. It was suggested that sulfopropanediol was formed by a reductive deamination of cysteinolic acid.