Phreatamoeba

Phreatamoeba (ref. ID; 4225 original paper)

Phreatamoeba balamuthi Chavez, Balamuth & Gong, 1986 (ref. ID; 4225 original paper)
See; Mastigamoeba balamuthi (ref. ID; 7078)

Phreatamoeba balamuthi Chavez, Balamuth & Gong, 1986 (ref. ID; 4225 original paper)

See

Mastigamoeba balamuthi (ref. ID; 7078)

Diagnosis

A free-living, polymorphic amoeba exhibiting amoeboid, flagellate, and cyst stages in its life cycle; amoebae may be flattened or subcylindrical in form, producing single broad hyaline pseudopodia bearing conical subpseudopodia; anterior end may be broader than the posterior. Length varies from 11 to 160 um. Uninucleate and multinucleate forms present in clonal populations. The nucleus contains a single central nucleolus; the nuclear membrane persists at least through metaphase. Reproduction, by binary fission four uninucleate amoebae or by plasmotomy for multinucleated ones, occurs only in the amoeboid stage. Transitory uniflagellated stage induced by addition of rice powder to the growth medium. Flagellate uninucleate, variable in shape, but typically ovoid to pyriform, length from 6 to 60 um. Flagellum directed anteriorly, closely associated with the nucleus. Cyst spherical or oval, 9-18 um in diameter; cyst wall lack pores. (ref. ID; 4225)

Descriptions

Life cycle: Under the culture conditions employed in this study, the life cycle included three forms: an amoeba, a flagellate, and a cyst. (ref. ID; 4225)

Amoeboid stage. In this study, the amoeba was observed to be the dominant stage in the life cycle. The flagellate stage could only be obtained by the addition of rice powder to the growth media. Inactive and motile amoebae alike are extremely polymorphic, their form frequently asymmetrical or irregular. They range in size from 11 to 160 mm and vary in shape from elongated to laterally expanded, the change being slow. Hyaline zones develop freely and are not restricted to pseudopodial regions, i.e. they develop laterally as well as at the advancing end. Locomotion is relatively slow and occurs by the extensions of a single broad pseudopodium bearing conical or mammilliform subpseudopodial extensions of the hyaloplasm. The subpseudopodia, continually produced and resorbed, do not appear toe be directly involved in locomotion; they develop also as hyaloplasmic extensions in stationary amoebae. The anterior ends of motile amoebae are often broader than the posterior. Uroidal filaments may be formed during locomotion. Insertion occurs by the pseudopodial englufment of particulate matter at the advancing end; egestion occurs posteriorly. Food vacuoles and at least one contractile vacuole are found in the posterior region of the body. The nucleus is of the vesicular type and contains a single, central nucleolus that breaks down prior to metaphase. Nuclei measure 2.5-4.5 mm and nucleoli 1.5-3 mm in diameter. Most amoebae are multinucleate, but uninucleate ones occurs. Of 113 amoebae surveyed, the number of nuclei/amoebae ranged from 1 to 46, with an average of ca. 15. Binucleate forms are rarely encountered. The mitotic index of an axenically grown population was determined to be 5.5% (n=1025) of the posterior on studied; only two specimens were uninucleate, such a low frequency of dividing uninucleate amoebae suggests that uninuclearity is a transient rather than a stable condition in axenic culture. Mitosis within multinucleate individuals is synchronous although asynchronous division does occur rarely. Asynchronous nuclear divisions have been reported in the Myxogastria and for cells in tissue culture. Stained preparations show metaphase chromosomes in a single band along the equatorial region. Cytokinesis in multinucleate amoebae occurs by a process of plasmotomy and is independent of nuclear division. Amoebae were also examined using electron microscope. The smooth surface seen with the light microscope appears rugose by scanning microscopy. (ref. ID; 4225)
Flagellate stage. This form, though highly variable, is most often ovoidal to pyriform, its length ranging from 6 to 50 um. Despite its variable shape, the flagellate- unlike the amoeba- is polarized. A single, vesicular nucleus containing a central nucleolus is located anteriorly, associated with the single flagellum; a single contractile vacuole occurs posteriorly. The flagellum, directed anteriorly and measuring ca. 40 um in length, arises from one of a pair of kinetosomes. The anterior end at times forms a pronounced cone which appears in protargol preparations to be formed of delicate granular material. Swimming is characterized by a side-to-side movement of the anterior end in the direction of the flagellum. This movement is generally constant, but on occasion, forward progress is interrupted by a seemingly ineffectual flailing of the flagellum. Occasionally, The flagellum may be extended directly ahead of the cell, immobile surface for an actively probing tip. The flagellate may also crawl across a substratum by means of temporary pseudopodia, but the flagellum persists and swimming can be resumed momentarily. The length of time spent in this transitory stage was not determined. The flagellate stage does not undergo binary fission but is derived from the amoeba as a result of transformation. Uninucleate amoebae, often produced by reversion, may undergo mitosis and give rise to daughter cells which they become flagellates, or they may, if multinucleate, undergo plasmotomy to form "buds" that change to typical flagellates. Flagella may develop either during plasmotomy (i.e. while the "buds" share a common cytoplasm) or following it. Although other factors possibly affecting the amoeba-to-flagellate transformation remain to be investigated, a nutritional factor may be involved since flagellate could not be obtained unless rice powder was added to the medium. Such addition to bacterized cultures induced transformation, but the addition of purified rice starch did not; moreover, the lowering of tonicity, a well known method for inducing transformation in Naegleria gruberi (Schardinger, 1899) (Fulton 1972), was ineffectual. Flagellates were observed ca. 25 hr after addition of rice powder, their number increasing with time, but some amoebae always failed to undergo transformation. No attempt was made to quantify the response of P. balamuthi to rice powder. (ref. ID; 4225)

Comments

The taxonomic system proposed by Page, unlike other systems, on the synthesis of many kinds of data, provides the most reasonable criteria for the placement of new amoebae. Phreatamoeba balamuthi, however, exhibits features that, if used separately, would place it in different taxa but when used collectively, distinguish it from all known naked amoebae. The pseudopodia of P. balamuthi for example, are essentially mayorellid, a characteristic of the Paramoebidae, a family described as "Amoebida with more or less flattened locomotive form and a broad anterior hyaline zone, from which in most genera several to many conical to fine pseudopodia are produced..." (Page 1972). On the basis of this feature alone P. balamuthi should be classified in the Conopodina; however, it is typically multinucleate and has a flagellate stage, a feature not characteristic for this group. The vegetative stage of P. balamuthi is predominantly multinucleate feature typically found in the Pelobiontida. Unlike the Pelobiontida, however, its locomotion form is more or less flattened -rather than cylindrical- and its protoplasmic streaming lacks bidirectional fountain flow. Moreover, a flagellate stage is not found within this order. The life cycle of P. balamuthi differs from that of extant plasmodial forms, yet it is similar to that found in some members of the Eumycetozoea, its only deficiency being the inability to form fruiting bodies. The temporary flagellate stage present in the life cycle of P. balamuthi is a feature shared by members of the Schizopyrenida, but members of this order have a different locomotive form and behavior, moving by hemispherical hyaloplasmic eruptions, sometimes alternating to either side, and they do no produce sub-pseudopodia. In the Schizopyrenida, both the nucleus and the nuclear membrane persist during division, whereas the nucleolus of P. balamuthi breaks down during division, and the nuclear membrane persists at least through metaphase. Also, members of this order are typically uninucleate. In P. balamuthi the flagellate stage lacks the rostrum collar, and cytostome that distinguish other amoebo-flagellates. Instead, it resembles Naegleria gruberi and Adelphamoeba galeacystis Napolitano, Wall & Gans, 1970 in its inability to reproduce as a flagellate and differs from the Mastigamoebidae, zooflagellates whose members possess a permanent flagellum. Perhaps the most distinctive feature of the flagellate in P. balamuthi is the presence of a cone-like microtubular complex in association with the nucleus. A similar structure has been described in a free-living flagellate and in the flagellate stage of some members of the Eumycetozoea. Our results show that this polymorphic amoebo-flagellate is so distinctive that a new genus and species must be created for it. The familial and suprafamilial relationship are still unsettled, but the presence of a cone-like structure suggests a possible affinity to the Eumycetozoea. Phreatamoeba balamuthi appears to occupy an intermediate position between the 'true' amoebae and the Eumycetozoea. (ref. ID; 4225)

Etymology

Phreatamoeba balamuthi, from phreat- (Gr.) = well (isolated from well-water) and balamuthi in honor of the late Professor William Balamuth. (ref. ID; 4225)

Habitat

Fresh-water. (ref. ID; 4225)