MITOTIC SYNCHRONY IN NAEGLERIA AMEBAE

Amebae of Naegleria gruberi can be cultured in suspension in buffer containing a dense suspension of Aerobacter aerogenes. At 30 °C the amebae grow exponentially with a doubling time of 2 h. Flagellates are rare in these cultures, but the amebae from liquid cultures transform into flagellates when washed relatively free of Aerobacter. If a growing culture of amebae is shifted to 38-39 °C, division ceases and the amebae increase in volume. After 100 min at the high temperature, when the volume of the amebae has nearly doubled, if the amebae are returned to 30 °C a single burst of mitosis occurs. Usually 80 to 90% of the amebae divide within one quarter of the normal doubling time, and 60 to 70% of the amebae may be found in mitosis simultaneously. After the single division, the amebae usually return to exponential growth, though occasionally a second synchronous division has been obtained. Amebae sampled at any time during a synchronized division are able to transform into flagellates. Some amebae, sampled just prior to division, complete nuclear but not cytoplasmic division, and become binucleate. © 1969.