Discrepancies between cell volume and organic content in semi-continuous cultures of a marine microalga

Changes in average cell volume, measured by now cytometry, and cell organic content were studied in light/dark synchronized semi-continuous cultures of the marine microalga Phaeodactylum tricornutum. Cell volume and organic content both increased with nutrient concentration at all the renewal rates tested. Cell volume against renewal rate, at each nutrient concentration, followed a U-shaped curve with smallest cells at intermediate renewal rates. In contrast, cell organic content decreased continuously with increasing renewal rate. The variation in eel volume and organic content, related to culture conditions, should be taken into account if biochemical composition and productivity of microalgal cultures are assessed on the basis of cell counts.