Main Content
< Top page

The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Naegleria

Naegleria Alexeieff (ref. ID; 1618), Alexeieff, 1912 emend. Calkins, 1913 (ref. ID; 3687), Alexeief, 1912 emend. Calkins, 1913 (ref. ID; 7593) or Alexieff, 1912 emend. Calkins, 1913 (ref. ID; 7499)

Kingdom Protoctista: Phylum Zoomastigina: Class Amoebomastigota: Order Schizopyrenida Singh, 1952: Family Vahlkampfiidae Jollos, 1917, Zulueta, 1917 (ref. ID; 7499)

[ref. ID; 1618]
Minute flagellate stage with two flagella; amoeboid stage resembles Vahlkampfia, with lobopodia; cytoplasm differentiated; vesicular nucleus with a large endosome; contractile vacuole conspicuous; food vacuoles contain bacteria; cysts uninucleate; free-living in stagnant water and often coprozoic. (ref. ID; 1618)

[ref. ID; 3680]
The genus Naegleria consists of free-living, small, naked amoebae, all of which can transform from amoebae to flagellates. (ref. ID; 3680)

[ref. ID; 3762]
Because of the absence of distinctive morphologic features among different genera and species of soil amebae, cyst structure is often helpful in identifying these organisms. The shape of the cyst, the appearance of the wall, and the presence or absence of pores are reasonably reliable indicators of taxonomic affinity. (ref. ID; 3762)

[ref. ID; 4180]
Free-living amoebas of the genus Naegleria so far comprise five known species; N. gruberi, N. fowleri, N. jadini, N. lovaniensis, and N. australiensis. One of them (N. fowleri) can induce acute, fatal meningoencephalitis in man. More recently, N. australiensis has also been found to be pathogenic. All these species are difficult to identify with certainty. Morphologically indistinguishable, they are distinguished mainly on the basis of biological and antigenic criteria. With the discovery of more and more new species and the study of more strains with overlapping characteristics, none of these criteria can be considered in itself unequivocally species-specific. In antigenic studies, major cross-reactions have been reported between N. lovanienesis and N. fowleri. Biological and physiological criteria are also nonspecific and none of them can in itself characterize a Naegleria species. The biochemical characterization of Naegleria strains has therefore proved to be of greater value. It can be achieved either by the study of total proteins using isoelectric focusing, or by isoenzymatic study using electrophoresis, or isoelectic focusing. (ref. ID; 4180)

[ref. ID; 7499]
The taxonomy of the genus Naegleria is variously based on trophozoite and cyst morphology (Lee et al. 1985), on physiology, on nuclear division type (Sogin et al. 1986), and more recently on molecular similarity (Baverstock et al. 1989, Clark et al. 1989). (ref. ID; 7499)
[Cysts]: Spherical cysts, each with a single nucleus and occasional cytoplasmic inclusions, 8-20 um in diameter, with a well-defined wall pierced by several pores, each less than 1 um in diameter and plugged with material lighter in color than the surrouding wall. 2-7 pores per cysts. Some amoebae appear to be in the process of excysting; protoplasm is seen emerging from a pore in the partly empty cyst wall. The globular shape and continuous contact of the cytoplasm with the cyst wall separates these cysts from Acanthamoeba and Adelphamoeba. The outer wall is smooth and round, in contrast to most cysts of Vahlkampfia (= Schizopyrenus) (Singh and Das 1970) and Tetramitus (Lee et al. 1985; Singh and Das 1970) that are more often wrinkled and irregular. The pores also separate the cysts from Vahlkampfia and Tetramitus, which generally excyst by wall dissolution (Robbins 1976; Sogin et al. 1986); such pores are characteristic of Naegleria (Lee et al. 1985; Schuster 1979; Singh and Das 1970). The high number of pores separates most of these cysts from cysts of N. fowleri, which generally have one to two pores which are inconspicuous under light microscopy (Schuster 1979). In short, most of these cysts are very close to those of "smooth" strains of living N. gruberi. Some of the fossil cysts, however, are somewhat larger than most Naegleria cysts and morphologically resemble Willaertia (Robinson et al. 1989) (= Protonaegleria; (Dyer 1990)). (ref. ID; 7499)
Type material; UCMP (University of California Museum of Palentology) D-797, slide KS-2. (ref. ID; 7499)
  1. Naegleria americana (ref. ID; 4647 original paper)
  2. Naegleria andersoni (ref. ID; 4647)
  3. Naegleria antarctica (ref. ID; 4647 original paper)
  4. Naegleria australiensis De Jonckheere, 1981 (ref. ID; 7593 original paper) reported author and year? (ref. ID; 4120, 4180, 4647)
  5. Naegleria australiensis australiensis (ref. ID; 64)
  6. Naegleria australiensis italica Jonckheere, Pernin, Scaglia & Michel, 1984 (ref. ID; 4120 original paper) reported author and year? (ref. ID; 64)
  7. Naegleria bistadialis (Puschkarew, 1913) (ref. ID; 3687) reported year? (ref. ID; 1618)
  8. Naegleria byersi (ref. ID; 4647 original paper)
  9. Naegleria dobsoni (ref. ID; 4647 original paper)
  10. Naegleria endoi (ref. ID; 4647 original paper)
  11. Naegleria fowleri (Carter, 1970) (ref. ID; 7593) reported author and year? (ref. ID; 64, 3680, 3930, 4085, 4120, 4134, 4180, 4230, 4647, 6766)
  12. Naegleria gallica (ref. ID; 4647 original paper)
  13. Naegleria gruberi (Schardinger, 1899) (ref. ID; 3687, 7511, 7593) reported year? (ref. ID; 1543, 1618) reported author and year? (ref. ID; 64, 152, 3680, 3762, 3930, 4120, 4180)
    Syn; Amoeba gruberi Schardinger, 1899 (ref. ID; 3687)
  14. Naegleria italica (ref. ID; 4647)
  15. Naegleria jadini (Willaert & Le Ray, 1973) (ref. ID; 7593) reported author and year?(ref. ID; 64, 3680, 4060)
  16. Naegleria jamiesoni (ref. ID; 4647)
  17. Naegleria johanseni (ref. ID; 4647 original paper)
  18. Naegleria kroszi Lepsi, 1960 (ref. ID; 3687 original paper)
  19. Naegleria laresi (ref. ID; 4647 original paper)
  20. Naegleria lovaniensis (Stevens, De Jonckheere & Willaert, 1980) (ref. ID; 7593) reported author and year? (ref. ID; 64, 3680, 4120, 4180, 4647), lovaniensis lovaniensis (ref. ID; 4343)
  21. Naegleria lovaniensis tarasca Rivera, Cerva et al. 1990 (ref. ID; 4343 original paper)
  22. Naegleria martinezi (ref. ID; 4647 original paper)
  23. Naegleria mexicana (ref. ID; 4647 original paper)
  24. Naegleria notanda Lepsi, 1960 (ref. ID; 3687 original paper)
  25. Naegleria pagei (ref. ID; 4647)
  26. Naegleria pringsheimi (ref. ID; 4647)
  27. Naegleria schusteri (ref. ID; 4647 original paper)
  28. Naegleria soli (Martin & Lewis, 1914) (ref. ID; 3687)
    Syn; Amoeba soli Martin & Lewis, 1914 (ref. ID; 3687)
  29. Naegleria sturti (ref. ID; 4647)
  30. Naegleria tihangensis (ref. ID; 4647)
  31. Naegleria wherryi Lepsi, 1960 (ref. ID; 3687 original paper)

Naegleria australiensis De Jonckheere, 1981 (ref. ID; 7593 original paper) reported author and year? (ref. ID; 4120, 4180, 4647)

Descriptions

Free-living amoeba, pathogenic for mice. The general aspect of the amoebic form of PP 397 is the same as for all Naegleria. The organism is moving rapidly by formation of eruptive, hyaline pseudopodia. Amoebae readily transform into flagellates upon incubation at 37 degrees C in distilled water. The round cyst with pores is also typical for Naegleria. Three to 8 distinct pores (mean 4.6) with a thickend rim are observed in empty cysts. Sometimes the outer wall is separated from the inner a wall. (ref. ID; 7593)

Type material

PP 397 was isolated in 1973 from flood drainage water in South Australia. (ref. ID; 7593)

Measurements

When grown of E. coli at 37 degrees C the trophozite measures 20.7 um (range 14.5 to 29.5) by 9.3 um (range 4 to 19) while the cyst has a mean diameter of 11.6 um (range 8.5 to 19). (ref. ID; 7593)

Naegleria bistadialis (Puschkarew, 1913) (ref. ID; 3687) reported year? (ref. ID; 1618)

Descriptions

Cyst with a smooth wall. (ref. ID; 1618)

Naegleria fowleri (Carter, 1970) (ref. ID; 7593) reported author and year? (ref. ID; 64, 3680, 3930, 4085, 4120, 4134, 4180, 4230, 4647, 6766)

Descriptions

Genetic variation. (ref. ID; 6766)

Comments

The amoeboflagellate Naegleria fowleri is a highly virulent, free-living, human pathogen. The first isolates of N. fowleri were all from human patients with Naegleria meningoencephalitis, from several countries and continents. (ref. ID; 4085)

Naegleria gruberi (Schardinger, 1899) (ref. ID; 3687, 7511, 7593) reported year? (ref. ID; 1543, 1618) reported author and year? (ref. ID; 64, 152, 3680, 3762, 3930, 4120, 4180)

Synonym

Amoeba gruberi Schardinger, 1899 (ref. ID; 3687)

Descriptions

Cyst uninucleate; cyst wall with several apertures; stagnant water and often coprozoic. Chang cultivated this amoeba in a buffered sucrose agar with its original bacterial associate, Proteus mirablis. Flagella were formed by filamentous protrusion of endoplasm, 1-3 pairs of flagella being produced from a single protrusion. A body, held to be "parabasal body" was always present at the base of the protrusion or flagella which showed alternating light and dark bands. The transformation from flagellate to amoeboid stage took place 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. (ref. ID; 1618)

Cyst: The cyst wall, which appeared uniformly thick at the light microscope level, was found to consist of a moderately thick inner component and a loosely fitting outer component; the latter frequently became eroded in old cysts and was not readily observed. These 2 parts of the wall joined at the region on the cyst pore. The thick inner component formed a collar, ~ 600 nm deep, around the pore. The collar was filled with an electron-lucent mucoid plug. Which was covered by a continuation of the outer wall component. The nucleus with its dense, central endosome was readily seen. Starting at the nuclear envelope and extending into the cytoplasm of the encysted ameba was series of channels; these appeared to penetrate into all areas of the cytoplasm. Another feature of the young cyst was the present of dense cytoplasmic vacuoles. These were either food vacuoles present when the ameba encysted or autophagic vacuoles containing ribonucleoprotein derived from digestion of cellular organelles, particularly mitochondria. As the cysts aged, mitochondria and vesicles of the endoplasmic reticulum became difficult to see, owing to an increase in density of cytoplasm. Dense granules ~100 nm in diameter, were observed in the cytoplasm, particularly at the periphery. These are probably similar to the Golgi vesicles described from encysting Acanthamoeba castellanii (Bowers & Korn 1969). Since Naegleria has no Golgi apparatus, these granules are referred to here as secretory granules. In Acanthamoeba, the contents of the vesicles apparently are incorporated into the forming cyst wall (Bowers & Korn 1969); the same is probably true of the secretory granules of Naegleria and so-called black bodies observed in encysting Schizopyrenus russelli (Maitra, Sagar & Agarwala 1974). The source of these vesicles in Naegleria is unknown. With age, the cytoplasmic contents of the encysted amebae pulled in and away from the wall, thus contributing to a still greater density. (ref. ID; 3762)

Comments

Cyst: A difference in the wall was noted between cysts of N. gruberi and those of N. fowleri and N. jadini. The outer layer, seen in cysts of the former species, was not observed in the latter 2; only a single component, the equivalent of the inner wall of the N. gruberi cyst, was present with an average thickness of 125 nm. No significant difference in wall thickness was noted between cysts of N. fowleri and N. jadini; in fact, there was considerable variation in the thickness in both species (range, ~60-160 nm). Definite pores were present in the walls of N. fowleri and N. jadini cysts, but they differ from those of the N. gruberi cyst by the absence of the collar region around the opening. The pore was closed by a mucoid plug but the plug was considerably thinner than that formed in N. gruberi. The plug appeared to form from mucoid material recognizable in the cyst cytoplasm. The relative thinness of the N. fowleri cyst wall and the mucoid plug may be one of the reasons cysts of this ameba are less viable than those of N. gruberi. The pores of all 3 species had a plaque made of cyst wall material, serving as an additional closure of the pore. The absence of the plaque probably reflected the fact that it had not yet formed at the time of fixation. Plaque formation appeared to be occurring at the pore of the encysting N. jadini; a thin line of electron-dense material probably the initial stage of development, is seen at the plasma membrane in the immediate vicinity of the pore. (ref. ID; 3762)

Measurements

Amoeboid stage 10-36 by 8-18 um; flagellate stage 18 by 8 um. (ref. ID; 1618)

Naegleria lovaniensis tarasca Rivera, Cerva et al. 1990 (ref. ID; 4343 original paper)

Descriptions

The body shape is typical of limax amoebae and varies constantly depending on the temperature. Between 37 degrees C and 42 degrees C, the trophozoites are usually elongated with one main hyaline anterior pseudopodium and a well developed uroid at the posterior end, At room temperature the trophozoites acquire a more rounded shape, forming usually lobous of finger-like pseudopodia with hyaline edges. In stained slides of fixed amoebae layers, the prevailing shape is oval with short pseudopodia. (ref. ID; 4343)

Remarks

The most remarkable ultrastructural, biochemical, serological, and physiological differential characteristics found between N. lovaniensis type strain, the purepecha strain, and N. l. tarasca are shown in Table. Other features such as cytoplasmic rough endoplasmic reticulum (RER). Golgi-like structures, free-ribosomes, and membrane-bound dense bodies, although present in the three strains, do not differ significantly between them or with other Naegleriae. If the ultrastructural taxonomic criteria most commonly used at present for the gymnamoebae are considered (Carosi et al. 1977; De Jonckheere 1987; Martinez 1985; Page 1888; Stevens et al. 1980; Willaert & Le Ray 1973), the most important differences between the purepecha strain and the type strain of N. lovaniensis are the nucleolar shape and composition, and the attachment of the nucleolus to the nuclear membrane. These morphological differences are sufficient to declare the purepecha strain as a morphological variant of N. lovaniensis, given that these features are not shown by any other known strain of the same species and even of the same genus. Likewise, the most important additional ultrastructural difference found between N. l. tarasca and the type strain of N. lovaniensis -that henceforth should be named Naegleria lovaniensis lovaniensis- is, the outer surface of the external layer of the nuclear membrane which is covered with ribosomes, a typical feature found previously only in N. flowleri Carter, 1970, N. jadini Willaert & Le Ray, 1973 and N. gruberi Schardinger, 1899, but not in N. lovaniensis (Carosi et al. 1977; Stevens et al. 1978). Of greater importance is the lack of a perinuclear layer of RER, shown by N. l. tarasca, provided that the presence of this character was considered species-specific when the description of N. lovaniensis as a new species was done by Stevens et al. in 1980. Another constant morphological characteristic that appears in all specimens of N. l. tarasca, no matter if the cultures are monoxenic or axenic, young or old, or if the amoebae are in trophic or in cystic stage, is the presence of a perinuclear layer of lipid globules. The authors have not observed this characteristic in the purepecha strain nor is it described for the strains of the species N. lovaniensis in the literature (Carosi et al. 1977; Page 1988; Stevens et al. 1980). The authors also consider that the unique presence of rosette-like structures in the cytoplasm of the trophozoites, of nucleating sites in the cytoplasm of cysts, and of microtubules between the endocyst and the cell membrane of N. l. tarasca -provided they are constant and not occasional characters of the specimens- can also be used to segregate this strain from N. l. lovaniensis at the subspecies level. (ref. ID; 4343)