Age-related changes in neutral lipid content of Paramecium primaurelia as revealed by nile red

Cellular neutral lipid content of Paramecium primaurelia was measured during culture and clonal life using nile red (9-diethylamino-5H-benzo[alpha] phenoxazine-5-one), a dye utilized for lipid analysis in both mammalian cells and in ciliated protozoa. Lipid droplets in P. primaurelia are concentrated in the anterior pole of the cell; their number is maximum in early log phase cells and decreases in late log phase cells. The quantitative determination of neutral lipids was obtained measuring the fluorescence from the excitation and emission spectra of 480 nm and 540 nm, respectively. Neutral lipid content decreases linearly during the log phase of growth while the decline is minimum during the stationary phase. In the late log phase, the amount is 30% of that of the early log-phase cells. Though the cell size declines too, cell area and lipid content decreases are not correlated in the middle log phase, because the maximum lipid reduction is obtained when the cell size is relatively constant. The cellular lipid content also changes during the clonal life. Neutral lipids decrease discontinuously (r = -0.75, P < 0.05) as the fission age increases. No relationship was found between lipid content and food vacuole formation during both culture and clonal life.