Rapid analytical technique for the assessment of cell metabolic activity in marine microalgae

A standard method for the assessment of cell viability has been developed for marine phytoplankton using an inexpensive stain, fluorescein diacetate (FDA), at .75 microM for 10 min. A flow cytometer was used as the fluorescence detector, providing an assessment of viability for each individual particle. Cell size and chlorophyll fluorescence per cell were assessed simultaneously, permitting an assignment of viability to specific subpopulations, thus increasing the power of the technique. A reasonable correspondence between FDA mean fluorescence intensity per cell and an independent metabolic indicator, photosynthetic capacity measured by 14C, was found. Both FDA mean fluorescence intensity and photosynthetic capacity vary as a function of cell volume. Recovery after extended periods of darkness indicate that cells that are FDA negative may not be dead, but merely quiescent or inactive.