Defense Date


Document Type


Degree Name

Doctor of Philosophy


Microbiology & Immunology

First Advisor

S. Gaylen Bradley


Organisms of the genus Naegleria differentiate from feeding, dividing amebae into temporary swimming flagellates when deprived of nutrients. Factors critical for enflagellation of the pathogenic species, N. fowleri, were delineated and optimal conditions established for evoking reproducible conversion of N.fowleri populations. N. fowleri enflagellation differed from that of N. gruberi in its dependence upon growth phase, population density during enflagellation and in the timing and extent of the conversion. N. fowleri amebae from stationary phase cultures grown at 37°C, washed free of medium and suspended in nutrient~free ameba saline, acquired flagella and converted to mature flagellates in a synchronous manner beginning 90 minutes after subculture to ameba saline. No prolonged intermediate round phase occurred during N. fowleri enflagellation such as has been seen with N. gruberi. Enflagellation of N. fowleri was prevented by actinomycin D and cycloheximide added at the time of subculture to non-nutrient medium. Delayed additions of the same inhibitors caused hastened reversion of flagellates, suggesting a requirement for continued synthesis. Ultrastructural changes during N. fowleri enflagellation generally paralleled those observed in E. gruberi except that flagellum outgrowth in the former occurred on cells while still ameboid. An extensive complement of cell polypeptides continued to be synthesized at a reduced level during enflagellation; no limited number of species was made in exceptional abundance. A moderate number of qualitative and quantitative changes were detected in the amounts of individual polypeptides resolved by two-dimensional electrophoresis when amebae enflagellated, some of which also occurred in a non-enflagellating g, fowleri strain and may therefore be related to starvation. Quantitative, computer-assisted densitometric analyses of polypeptide autoradiograms revealed that larger and more acidic proteins were relatively more abundant in amebae than in flagellates and that a correlation existed between molecular size and charge of N. fowleri polypeptides.

Several observations in both E. fowleri and N. gruberi enflagellation implicate regulatory mechanisms in addition to, or coordinated with, de novo protein synthesis. Enflagellation of Naegleria species provides a useful paradigm in which to study the contributions of various regulatory processes upon the expression of a differentiated state in an eukaryotic cell.


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