Diel changes in sedimentation characteristics of Ditylum brightwelli: Changes in cellular lipid and effects of respiratory inhibitors and ion‐transport modifiers1

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Abstract
Temperature‐controlled seawater columns were used to investigate settling rates of Ditylum brightwelli grown on light‐dark schedules. Ficoll density gradient centrifugation was used to examine the effects of KCN, DNP, and the ion‐transport modifiers valinomycin, nigericin, and gramicidin on sedimentation characteristics in the gradients. Sedimentation rates were minimal at the end of the dark period (L8: D16; L12: D12) and maximal during the latter half of the light period. The presence of maximum lipid per cell during the period of maximum settling rate argues against a fat‐mediated buoyancy mechanism. Cells exposed to respiratory inhibitors, valinomycin, or nigericin sedimented more rapidly than did control cells; gramicidin appeared to decrease sedimentation rate. The effectiveness of these agents suggests that settling rate in this diatom is controlled through ion regulation.