Export pumps in Epulopiscium fishelsoni, the symbiotic giant gut bacterium in Acanthurus nigrofuscus.

Activity of the potential antixenobiotic efflux pumps of Epulopiscium fishelsoni (epulos), the symbiotic giant gut bacterium of the algivorous surgeonfish Acanthurus nigrofuscus, was studied in vivo using various specific substrates and microfluorometry. Kinetic and inhibitor analyses revealed the following vital efflux activities: (1) verapamil-sensitive efflux of amphiphilic cationic compounds rhodamine B, Hoechst 33342, and ethidium bromide; (2) verapamil-sensitive efflux of hydrophobic neutral fluorescein diacetate; (3) verapamil-insensitive efflux of hydrophilic anionic fluorescein; and (4) verapamil-insensitive efflux of glutathione-S-bimane. Cytosolic enzymes, nonspecific esterase and glutathione S-transferase, were shown to participate in xenobiotic metabolism. The results suggest that the activity of the potential efflux pump in epulos are similar to those described in other bacteria but are kinetically characterized by an unusually high transport rate, probably mediated by hyperplasia of the plasma membrane. Further studies of the export pumps in epulos may unmask their evolutionary adaptation to a xenobiotic-rich host gut content.