Use of nile red as a rapid measure of lipid content in ciliates

We report the use of nile red as a rapid and inexpensive method to estimate cellular lipids in three species of Paramecium and in Tetrahymena by the direct application of the dye to living or fixed cells without extraction and purification. Qualitative estimates of the relative changes in the lipid content of cells of varying culture ages were obtained using fluorescence microscopy, while semiquantitative determinations were obtained by measuring the total fluorescence from the emission spectrum (excitation, 535 nm) of fixed cells treated with excess nile red. The relative amounts of neutral (excitation, 488 nm; emission, 540 nm) and polar (excitation, 535 nm; emission, 680 nm) lipids were approximated using fluorescence intensity at these selected spectral conditions to avoid any spill over from each other. The patterns of change with culture age in total lipids in Tetrahymena and in total, neutral and polar lipids in Paramecium obtained using nile red agreed well with published gravimetric data for these ciliates.