Variation of electrophoretic karyotypes among Naegleria spp.

All species and subspecies of the genus Naegleria were subjected to karyotype analysis by contour-clamped homogeneous electric field and transverse alternating-field electrophoresis. The former technique proved to be superior in detecting differences in karyotype. The chromosome pattern of each species and subspecies was found to be distinct. Between 15 and 23 bands were resolved, with chromosome sizes ranging from a few hundred kilobases to about 1.5 Mb. Hybridisation with cloned rDNA identified one band in all species, corresponding to the rDNA plasmid that does not migrate according to its molecular weight because it is circular. In Willaertia magna a similar size distribution was found, in contrast to Giardia and Entamoeba, which have only very large chromosomes. Within the pathogenic N. fowleri some strains showed slight differences in chromosome pattern. The karyotype differed more between strains within the subspecies N. and andersoni than between the two species N. fowleri and N. lovaniensis. The results suggest that karyotype analysis cannot be used to identify a Naegleria species but is useful for stock identification, gene localisation, genetic exchange studies and epidemiological investigation of the pathogenic N. fowleri.