Harvest of planktonic marine algae by centrifugation into gradients of silica in the CF-6 continuous-flow zonal rotor.

Abstract

1. Cells of four different phytoplankton species were harvested from cultures using gradients of colloidal silica (Ludox) in the CF-6, a continuous-flow zonal rotor.2. The efficiency of harvesting ("fractional clean-out") was > 0.99 for three of the algae and > 0.78 for the smallest species (Synechococcus bacillaris).3. Growth rates of the algae subcultured after harvesting in Ludox were similar to those unharvested controls, but Synechococcus showed a lag period of about four days after harvesting.4. The rates of photosynthesis and respiration of cells harvested in Ludox gradients were, in most cases, about ⅓ to ⅕ of the pre-harvest rates. Dunaliella tertiolecta showed no loss of photosynthetic or respiratory activity.5. This method has application to the collection of algae from dilute cultures and from natural waters when cells are needed in good physiological condition.