The use of FDA and flow cytometry to measure the metabolic activity of the cyanobacteria, Microcystis aeruginoa

Abstract

Fluorescein diacetate (FDA) readily permeates cell membranes and is converted, or hydrolysed, into a fluorescent form (Fluorescein) by the non-specific esterases (ROTMAN & PAPERMASTER 1966). Although FDA has been, and still is, commonly used as a probe for cell visability, it may also indicate metabolic activity as demonstrated by BENTLEY-MOWAT (1982) who showed that algae exposed to toxins were incapable of converting FDA to Fluorescein yet were not dead as evidenced by the ability of the cells to recover. Further studies, used flow cytometry, with various algae provide additional support of FDA as a measure of the "metabolic vigour" (BERGLUND & EVERSMAN 1998, DORSEY et al, 1989) where "sick" and "healthy" cells may be distinguished from one another. Despite these findings, the potential of the FDA technique to distinguish between populations exposed to subtle environmental differences has not been adequately investigated. To test the sensitivity of the FDA technique, the growth rate of Microcystis aeruginosa at three light intensities was compared with the relative rate of FDA conversion (RFC). In addition, RFC by M. aeruginosa at two phosphorus concentration was examined. Measurements were made using a flow cytometer, which provided a rapid and sensitive procedure for measuring relative fluorescence.