Towards a Non-Terminal Viability Assay for Foraminiferan Protists
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Epifluorescence microscopy and spectrofluorimetry were investigated as possible non-terminal methods to distinguish live from dead foraminifera. Seven fluorogenic probes (diacetates of fluorescein [FDA], carboxyfluorescein, dichlorofluorescein, and carboxyeosin; AM-esters of biscarboxyethylcarboxyfluorescein [BCECF-AM], calcein, and calcein blue) were tested on Allogromia laticollaris. The probes that consistently produced the brightest fluorescence signals (BCECF-AM and FDA) were judged non-toxic to Allogromia, on the basis of short-term pseudopodial deployment and long-term reproduction assays. Once protocols were established, these two probes were tested on 13 additional benthic foraminiferal species. We found that BCECF-AM is the most suitable probe for direct epifluorescence microscopy of metabolically active foraminifera, especially tectinous and transparent calcareous species. Using spectrofluorimetry, FDA showed promise for opaque species because fluorescence is detected in the incubation media after its release from the cell. However, both approaches could only be used with confidence in light of appropriate controls established for each species examined.