Protacanthamoeba

1. Protacanthamoeba caledonica Page, 1981 (ref. ID; 3991 original paper)
2. Protacanthamoeba invadens (Singh & Hanumaiah, 1979) n. comb. (ref. ID; 3991)

Protacanthamoeba caledonica Page, 1981 (ref. ID; 3991 original paper)

Diagnosis

Descriptions

• Light microscopy: In the locomotive form these amoebae are indistinguishable from Acanthamoeba, though they occasionally have, either on a glass substratum or agar a drawn-out posterior region, unusual in Acanthamoeba. Acanthopodia, up to 8 um long, are produced from the dorsal surface or front edge of the hyaline lobopodium and carried back along the sides as the amoeba advances, sometimes contributing to a group of uroidal filaments. The lengths of 100 amoebae, including few with a drawn-out posterior end, were 13.9-60.0 um, mostly less than 40 um, with a mean of 26.7 um, and their length/width ratios 1.0-3.6 (mean 1.6). The locomotive rates of 10 amoebae at 22 degrees C were 4.6-13.9 um, or 0.2-0.4 times their lengths, per min. The nucleus has a single central nucleolus. Diameters of 25 nuclei in live amoebae were 7.0-9.2 um (mean 8.3 um), with their nucleoli 3.8-6.2 um (mean 5.3 um). In stained preparations, diameters (n=25) were: nuclei 4.7-8.4 um (mean 6.3 um), nucleoli, 2.6-4.7 um (mean 3.5 um). In each set, a few nuclei were somewhat elongate. Occasional binucleate cells were seen in stained preparations made from one-day-old cultures. The cytoplasm often contained many spherical, yellowish bodies about 1 um in diameter or less, which took up Sudan black stain. The floating form, produced when amoebae were suspended in liquid, was more or less rounded, with acanthopodia whose length often nearly equaled the diameter of the central mass. The diameters of the central cell masses of 70 floating forms, measured in three groups at different times, were 12-26 um, with means of 18.1 um, 19.2 um, and 20.4 um for the three groups. No detailed study of mitosis was made, but the nucleolus disappeared during mitosis, and a rather conspicuous spindle remnant like than figured by Singh (1952) for Hartmannella glebae was often seen in telophase, persisting even when cytokinesis was far advanced. The cysts sometimes occurs singly, usually in groups, even in plaques of hundred closely appressed and adherent to each other. They were usually circular to oval in outline, rarely slightly reniform because of pressure on one side. The wall was usually smooth, even when two layers were distinguishable, but there was often a slight separation in the wall at some points, with slight wrinkling of the separated outer part. Rarely the separation extended around all or most of the periphery. No ostioles, as seen in many Acanthamoeba, were found, no opercula, present in all Acanthamoeba though difficult to perceive in the intact cysts of a few species, were observed. Nor was there a regular peripheral layer of coarse cytoplasmic granules as commonly seen in Acanthamoeba. The cysts were uninucleate; in a few, as sometimes in Acanthamoeba, the nucleolar material appeared to be separated into two bodies. Measurements of 100 cysts on each of three separate occasions gave diameters (the greatest for each cyst) of 11-21 um, with means on the three occasions of 16.0 um, 16.7 um, and 16.8 um. Twenty-five cysts were measured to establish the ratio of the thickness (vertical diameter) to the greatest horizontal diameter, giving: greatest diameter, 13.1-20 um (mean 16.4 um); thickness, 8-11 um (mean 10 um); ratio of thickness:greatest diameter, 0.5-0.7 (mean 0.6). These cysts were therefore thickly lenticular. In 25 living cysts, the nuclear diameters were 4.7-6.5 um (mean 5.8 um), the nucleoli 1.9-3.7 um (mean 2.8 um). Reduction in size of nuclei and relative size of nucleoli during encystment has been observed in many amoebae. (ref. ID; 3991)
• Electron microscopy: A longitudinal section of a locomotive form shows a little anterior hyaloplasm and the small posterior hyaloplasmic region, which, with the uroidal filaments when these are present, makes up the uroid. A section of a lobopodium with some of the acanthopodia produced from it contained tracts of oriented filaments extending from deep in the lobopodium into the acanthopodia, with masses of less oriented material between the filament tracts. This presence of non-oriented material between the filamentous tracts accords with the suggested "tent-pole" function of acanthopodia, although it does not prove that hypothesis. The filaments appeared to extend the length of acanthopodia, resembling observations on acanthopodia of Acanthamoeba castellanii and elongated sub-pseudopodia of other genera. Some remnants of this internal structure could be discerned in some of the uroidal filaments derived from acanthopodia. The nuclear envelope was ca. 30-40 nm thick, with many nucleopores, but the outer surface was not covered with ribosomes. Although the nucleoli of some cells appeared fairly dense, usually with lighter lacunae, they were often less dense and markedly heterogeneous. Mitochondria were mostly oval to sausage-shaped in section, with a maximum length somewhat over 2 um. Anastomosing of tubular cristae was observed less frequently than in some amoebae, and intracristal granules were present. The matrix of mitochondria fixed for an hour at 20 degrees was consistently dense than that in cell fixed by other methods. The Golgi region was prominent and extensive (up to 4.2 um across, usually somewhat less) and often contained two or more stacks of flattened sacs, transverse and longitudinal sections of membranous tubules, and vesicles up to 0.3 um in diameter. Whenever both Golgi apparatus and nucleus were present in the same section, they were close together. Often two Golgi areas were seen in a cell, suggesting that that is the normal number. Centriole-like bodies identical in structure to those found in several species of Acanthamoeba were seen in material treated with glutaraldehyde at 20 degrees C, always in association with the Golgi apparatus. The centriole-like body consisted of amorphous-looking electron-dense outer layers each ca. 30 nm thick, and, sandwiched between them, two rows of circular structures described by Willaert, Stevens & Tyndall (1978) as "resembling beads on a string", this inner region being ca. 60 nm thick. The way in which the centriole-like body seemed to fade away at either end suggested that it is a circular plaque, and both the appearance and the size of the two rows of circular structures sandwiched between the amorphous layers suggested that these might be sections of microtubules like those radiating out from the centriole-like body. In at least one cell, two such bodies, each in a separated Golgi region, were observed; unfortunately, the nucleus was not present in these sections. Microtubules were sometimes seen passing through Golgi regions in which no centriole-like bodies were seen, and there were a few configurations suggesting such bodies even in cells fixed by methods other than the optimal one. The rough endoplasmic reticulum, in the form of flattened lengths, was not abundant in trophic cells; the smooth endoplasmic reticulum appeared to take type same form, though a few open vesicles were also present. The contractile vacuole, several stages of which were seen, appeared to belong to Patterson's morphological type D, though with the vesicles of the spongiome so numerous in early diastole that it somewhat resembled his type C. Food vacuoles with the ingested organisms still intact usually appeared to contain on one bacterium each. Several morphological changes characterized encysting cells even in early stages with the contractile vacuole still functioning. Such cells were well rounded up, generally somewhat oval in section, with the entire surface having a rippled appearance, probably from the exocytotic activity of many small vesicles bringing wall material to the surface. The first wall layer laid down was made up of fibrous material, with the fibers running parallel to the cell surface as a whole but not following the numerous exocytotic depression, though some material in those depressions appeared to be of the same texture. The cytoplasm was denser than that of trophic amoebae, and rough endoplasmic reticulum was often abundant. The most conspicuous inclusions were ovoid or spherical membrane-bound bodies, their greatest diameter up to 3 um but usually somewhat smaller. The dense contents of these bodies sometimes appeared to be amorphous, but were often seen to be in large part crystalline arrangements of spherules each measuring about 25 nm. There can be little doubt that these are the "ribonucleo-protein-containing vesicles" identified by Schuster & Svihla (1968) in their study of Naegleria gruberi as "autophagosomal-like vacuoles" and by Bowers & Korn (1969) and Willaert, Stevens & Tyndall (1978) as autolysosomes in Acanthamoeba. The contents of these vesicles were complex and included polysaccharides, as shown by Thiery preparations. Large numbers of lipid bodies were present in encysting cells. The mature cyst wall was ca. 0.3 um thick, excluding material in the surface depressions, where not split. It could be divided into three principal regions, from the outside: (1) fibrous, with fibers parallel to the surface, shown not only by its position but also by its textural resemblance to be identical with the material first secreted; (2) dense, apparently amorphous but with a suggestion that it may be composed of tightly-packed bodies; (3) finely granular, less dense but thicker than either of the preceding. Splitting frequently occurred within the fibrous outer layer and between the outer and middle layer, giving rise in light-microscopical observations to the deceptive appearance of a true exocyst and endocyst. The innermost of the three principal regions was usually subdivided by one or two trilaminar boundaries, the inner one of which might not continue around the entire periphery. Furthermore, the material closest to the cell membrane and in the depressions of the cell surface appeared slightly darker than the rest of the inner region, which may thus be divided into three or four strata, all consisting of morphologically similar material. This inner region was less densely stained by the Thiery treatment than are the two outer ones. (ref. ID; 3991)

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Type materials