Pyrocystis lunula Schütt is a unicellular photoautotrophic dinoflagellate, commonly found in marine environments, displaying circadian‐controlled bioluminescence. Because of this species' characteristics, effects of pollutants on bioluminescence in P. lunula may make for an easy and simple bioassay that would be valuable for toxicity testing and the protection of coastal resources. This study therefore investigated the short‐term effects of metals and organic pollutants on the recovery of the bioluminescent potential in P. lunula. Recovery of bioluminescence was strongly inhibited in a dose‐dependent manner by all reference contaminants tested, the system being most sensitive to copper and cadmium (4‐h IC50s 0.96 and 1.18 μM, respectively), followed by phenanthrene, lead, SDS, and nickel (4‐h IC50s 1.64, 12.8, 15.6, and 73.1 μM, respectively), whereas relatively high concentrations of phenol were needed to elicit a response (4‐h IC50 1.64 mM). Except for exposure to lead and nickel, the inhibitory effects of cadmium, copper, and all organic pollutants were reversible, with P. lunula recovering 80%–100% of its bioluminescence potential after a period of 72 h in uncontaminated medium. Our results show that the restoration of bioluminescence in P. lunula is sensitive to the reference contaminants tested and obtains highly reproducible results.

Marine dinoflagellates are the main contributors to a phenomenon commonly known as “phosphorescence of the sea”. Several investigators using different dinoflagellate species have shown that dinoflagellate bioluminescence is regulated by a circadian rhythm. Diverse bioluminescent systems exist in different organisms; however, all systems utilize an enzyme luciferase and the substrates luciferins, which show inter‐species cross‐reactivity. In marine dinoflagellates, luciferase and luciferin are localized in specific organelles, termed scintillons, which are usually located in close proximity to the vacuole during their active state. Bioluminescence is stimulated by mechanical stress or by acidification of the medium. Nicolas and co‐workers (1987, J. Cell Biol. 105: 723‐735) suggested that bioluminescence is triggered by an acidification of the scintillon caused by events that depolarize the tonoplast (proton trigger model). However, little is known about the signal transduction cascade that relays the mechanical stimulus perceived at the plasma membrane to the tonoplast. This study investigates the response of the bioluminescent system of Pyrocystis lunula to various parameters such as age of culture, light quality and quantity, disturbance (handling), sensitivity to chemicals, etc. to determine, if the bioluminescent response of P. lunula suitable for measuring environmental toxicants. The assay system used measures bioluminescence in response to mechanical stimuli or acidification allowing us to determine, if the response varies amongst the two different types of stimulation under different experimental conditions. The use of cell‐permeant inhibitors for certain signaling pathways in this assay may help to biochemically characterize events involved in signal transduction from the plasma membrane to the scintillon.