Control of Flagellum Number in Naegleria

Abstract

This paper describes the production of supernumerary flagella by flagellates of Naegleria gruberi exposed to sublethal temperature shocks during the amoeba-to-flagellate transformation. When transformed at any constant temperature below 34°C, cells of N. gruberi strain NB-1 may develop from 1 to 4 flagella, but biflagellate cells predominate and the average number of flagella per cell in these populations is approximately 2.2. Populations exposed to a 38°C temperature shock during transformation develop about twice as many flagella as controls (average number of flagella per cell is approximately 4.5). The individual response of cells is extremely heterogeneous: some develop no more than the normal 2 flagella, whereas others develop as many as 18. At least half the cells produce 5 or more flagella, as opposed to fewer than 1% with 5 or more flagella in control populations. Multiflagellate cells and populations are normal in appearance, apart from the excess flagella and resulting disorientation of the normal swimming pattern. The supernumerary flagella, their basal bodies and the rhizoplast (which is also occasionally doubled) are indistinguishable from those of normal cells. Maximal production of flagella occurs over the narrow temperature range from 37.5 to 38.5°C and is related to the duration of exposure to a given temperature: optimal flagellum induction is ob tamed following a 45-50 min exposure to a 38.2°C temperature shock. After approximately 1 h the flagellates revert to amoebae, losing both normal and supernumerary flagella. Populations of these amoebae followed through 2 more cycles of retransformation and reversion developed the normal number of flagella (2.2). Clones isolated from multiflagellate populations were identical to normal populations, developing approximately 2.1 flagella per flagellate at normal temperatures and 4.5 flagella per flagellate when temperature shocked again.