Cytological and Ecological Observations on the Flagellate Transformation of Naegleria gruberi

Abstract

Phase-contrast microscopic examination of N. gruberi (Schardinger) during flagellate transformation and reversion revealed the following cytological features: Flagella were formed by filamentous extension from endoplasmic protrusion. One, 2 or 3 pairs of flagella were formed from a single protrusion. Occasionally a 2nd protrusion gave rise to the 3rd pair of flagella. A chromatin body of cytoplasmic origin was always present at the base of the protrusion or of the flagella, and is believed to be the parabasal body. Occasionally one chromatin body was seen at the base of each pair of flagella. Alternating bands of light and dark areas were seen in the flagella soon after they were formed and persisted throughout the flagellate stage. Reversion from flagellate to amoeba stage was accomplished by absorption of the flagella, the shedding of one or more flagella and the absorption of the rest, or by casting-off a small part of the body to which the flagella were attached. The following effects of environmental factors on flagellate transformation were observed. As many as 35% of the tropho-zoites underwent flagellate transformation in water when they were in metacystic stage or were harvested from plate cultures up to 12 hours incubation at 25[degree]-27[degree]; as the cultural age advanced, the % amoebae undergoing transformation became progressively lower. Prolonged cultivation in a liquid medium at 25[degree]-27[degree], or on an agar medium at 37[degree], resulted in temporary loss of ability to form flagellates. The freezing of tro-phozoites up to 40 min. and of cysts up to 1 week at -25[degree] to -30[degree] stimulated flagellate transformation. An increase in water temperature from 25-27[degree] to 37[degree] or decrease to 8-10[degree] suppressed the transformation, but after the flagellates were formed, the former temperature change shortened while the latter lengthened duration of the flagellate stage. Freezing of the amoebae in the flagellate stage at -25[degree] to -30[degree] exerted no adverse effect on their return to amoeboid form when the freezing time did not exceed 30 min. Cultures developed from single organisms isolated in the flagellate stage yielded amoebae showing flagellate transformation characteristics similar to those yielded by ordinary cultures.