Short communicationEvaluation of drugs and stationary growth on the cell cycle of Giardia intestinalis

We examined the effect of aphidicolin, colchicine, demecolcine, fluorouracil, hydroxyurea, and nocodazole, as well as nutrient deprivation on the Giardia intestinalis cell cycle. Aphidicolin was the only drug that was able to block the cell cycle at a specific stage (G1/S), and permit cells to resume growth at a high rate upon its removal. Nutrient deprivation resulted in a portion of G2/M cells completing mitosis and cytokinesis in synchrony during the recovery period, but this synchrony was shortly lost and a sample containing a predominance of G1 cells could not be obtained. Flow cytometry analysis of normal and untreated Giardia cultures showed the occasional appearance of a small percentage of cells with a DNA content of 16C, which is twice the DNA content of G2 cells. However, this 16C peak is larger and more frequently observed in drug-treated Giardia. These 16C are likely produced from endoreplication of 8C/G2 cells, and we propose that they represent a pre-encystation stage that is induced by drug treatments and other stressors.

94Highlights► Small amount of 16C cells from endoreplication in Giardia trophozoite cultures. ► The 16C cells may be a stress response that is induced by drug treatment. ► Aphidicolin blocks the cell cycle at G1/S and can synchronize DNA synthesis. ► Giardia treated with nocodazole continue DNA replication without cell division. ► Complete cell cycle synchrony cannot be achieved by nutrient deprivation.