Fine Structure of the Mastigont System in Tritrichomonas foetus (Riedmüller)*

SYNOPSIS. Tritrichomonas foetus shares many fine-structural features with the previously described genera of the subfamily Trichomonadinae. These include the arrangement and structure of the kinetosomes, of most rootlet filaments, including the sigmoid filaments of kinetosome #2, as well as those of the parabasal apparatus and of the pelta-axostyle complex. On the other hand, this species, and presumably all other Tritrichomonas augusta-type flagellates, differ from Trichomonadinae in certain important details. Among the features which T. foetus does not share with Trichomonadinae are the fine structure of the costa and of the undulating membrane, as well as several organelles not found in the latter subfamily. The costal base of Trichomonadinae is replaced in T. foetus and other Tritrichomonadinae by a comb-like structure, extending between the costa and the infrakinetosomal body. The suprakinetosomal body, connected to kinetosome #2 in the region of attachment of the sigmoid filaments, and the infrakinetosomal body, which appears to contribute to the proximal marginal lamella, are organelles evidently restricted to Tritrichomonadinae. The undulating membrane consists of 2 parts. The proximal part is a fold-like differentiation of the dorsal body surface, the dorsal part of which contains the proximal marginal lamella. The distal part of the undulating membrane, with no obvious physical connection to the fold, encloses the distal marginal lamella in its ventral, and the microtubules of the recurrent flagellum in its dorsal area. The organelle of T. foetus which by its size, certain structural characteristics, and relationship with the undulating membrane and some organelles, including the paracostal granules, is analogous to the costa of Trichomonadinae and of Trichomitopsis termopsidis (subfamily Tritrichomonadinae), conforms in the structure of its periodic cross-striations to that of the parabasal filaments of the latter organisms; its origin corresponds closely to that of parabasal filament 2 of Trichomonadinae.     

Fine Structure of Trichomitus batrachorum (Perty)*

SYNOPSIS. Trichomitus batrachorum (Perty) shares with Trichomonadinae most of its fine-structural characteristics, especially those pertaining to the undulating membrane that consists of a high body fold, enclosing the loop-shaped, periodic marginal lamella, and of the recurrent flagellum applied to the fold. This flagellate has also certain structures, i.e. the costal base, comb-like organelle, and well developed marginal lamella, in common with Monocercomonas. It shares with Hypotrichomonas the costal base; large pelta; very fine fibers perpendicular to, and connecting the axostylar microtubules; structural details of the most proximal segment of the marginal lamella; and general relationships between dorsal body fold (poorly developed in Hypotrichomonas) and the recurrent flagellum. All these electronmicroscopic findings support the crucial position of Trichomitus in the evolutionary sequence Monocercomonas→Hypotrichomonas→Trichomitus→ Trichomonadinae suggested previously by lightmicroscopic observations. Further, Trichomitus shares with all Tritrichomonadinae the comb-like structure, not found either in Hypotrichomonas or Trichomonadinae; and it has in common with Tritrichomonas also the costa with Type A periodicity, being the only member of Trichomonadinae with this type of supporting organelle. It appears, therefore, that Trichomitus-type organisms represent an important link in the evolution of all Trichomonadidae from Monocercomonadidae.     

Fine Structure of the Mastigont System in Tritrichomonas muris (Grassi)*

SYNOPSIS. Tritrichomonas muris shares many fine-structural details with the previously described members of the family Trichomonadidae, and especially with the organisms belonging to the subfamily Tritrichomonadinae. Among the features which T. muris has in common with all Trichomonadidae and in all probability with other Trichomonadida are the arrangement and structure of: the kinetosomes; many rootlet filaments, including the sigmoid filaments of kinetosome #2; the parabasal apparatus; and the pelta-axostyle complex. The structures which T. muris-type flagellates share with other Tritrichomonadinae, and especially with Tritrichomonas augusta-type species (including T. foetus), but not with Trichomonadinae that have been studied to date, are: the Type A costa; a comb-like structure, which appears to have replaced the costal base of Trichomonadinae and of Hypotrichomonas; the suprakinetosomal body, rudimentary in T. muris; and the infrakinetosomal body. The undulating membrane, like that of T. augusta-type organisms, consists of a proximal and a distal part. The proximal part, which contains the proximal marginal lamella, is less developed in T. muris than in T. augusta-type flagellates, being represented by a relatively low ridge for the entire length of the organism. The distal part of the membrane in T. muris, on the other hand, is more highly developed; it is a heavy cord, with a distal marginal lamella which consists of a large triangular organelle having a highly ordered structure and 2 less well defined cords distal to this organelle. The tubules of the recurrent flagellum occupy the area distal to the cords. The sigmoid filaments of kinetosome #2, unlike those of other Trichomonadidae examined to date, extend posteriorly to the peltar-axostylar junction; they seem to terminate within the cytoplasm near, but not connected to the axostyle. In addition to the Type A costa, there is a small rootlet filament, which appears to be homologous to the rudimentary costa noted in Hypotrichomonas. Some of the paraxostylar and paracostal granules consist of an outer, relatively dense layer and an inner “core” of moderate density; between the 2 there is a lucent ring. The discussion deals in some detail with the possible nature of the paraxostylar and paracostal granules in trichomonads. The taxonomic status of Tritrichomonas cricetus (Wantland) [Tritrichomonas criceti (Wantland) emend. Levine] and Trichomonas criceti Ray & Sen Gupta is discussed in an appendix; it is concluded that both of these names are synonyms of T. muris (Grassi).     

The Mastigont System of Trichomonas gallinae (Rivolta) as Revealed by Electron Microscopy

SYNOPSIS. The fine structure of Trichomonas gallinae has been examined by electron microscopy and correlated with previous light microscope observations. A composite diagram of the flagellate, derived from both types of examination, is presented. Details of relationships of various mastigont organelles are documented by electron micrographs. The extent of the pelta and its connection to the capitulum of the axostyle have been determined. Four types of kinetosome rootlets have been described. One consists of superficial “filaments” radiating from each of the 9 triplet microtubules of kinetosomes #1, #2 and #3. A 2nd type of rootlet structure is represented by single comma-shaped filaments emerging clockwise from kinetosomes #1 and #3. The filament from kinetosome #1 has a periodic structure similar to that of the marginal lamella with which it is believed to connect. A 3rd type of rootlet emerges from kinetosome #2 as a sheet of about 9 filaments which traverse a sigmoid course and terminate on the inner surface of the microtubules of the pelta near the peltar-axostylar junction. The 4th set of structures consists of the costa and parabasal filaments. These structures have major periodicities of similar dimension but have readily differentiable repeating units. The costa appears to originate at the kinetosome of the recurrent flagellum, but its origin is also contiguous with that of parabasal filament 2 which has some continuity with kinetosomes #2 and #3. Parabasal filament 1, on the other hand, arises solely from or near kinetosome #2. Occasional observations of a costa and a parabasal filament in juxtaposition over a great part of their length has led to the suggestion that the parabasal filament may play a role in the development of the costa. Periodic and filamentous structures have been observed in paraxostylar and paracostal granules and in nearby cytoplasm. Their possible role in providing substance for the developing axostyle and the costa is discussed. The results are discussed in the light of available information pertaining to structure of various trichomonad species as revealed by light and electron microscopy.     

Structure of Pentatrichomonas hominis (Davaine) as Revealed by Electron Microscopy*

SYNOPSIS. Fine structure of Pentatrichomonas hominis is described in the light of previous light microscopic findings. The relationships among kinetosomes #1-#4 and R are like those previously reported orhomonas gallinae, and the same is true of the rootlet filaments associated with the several kinetosomes. The kinetosome (I) of the independent flagellum is situated just behind the reflection of the sigmoid filaments of kinetosome #2 onto the pelta and parallels these filaments for a considerable distance. The peltaraxostylar junction consists of 3 layers: the capitulum of the axostyle (outer, the pelta (intermediate, and the sigmoid rootlets of kineto some #2 (inner). The pelta overlaps the axostylar capitulum to a variable extent. The parabasal body consists of elongate and flattened cisternae of smooth endoplasmic reticulum surrounded by numerous small vesicles. There are 2 typically cross-striated parabasal filaments, filament 2 probably contributing most, if not all, the material to the slender, periodic organelle that underlies the parabasal body and usually does not extend far beyond the posterior end of the nucleus. The periodic costa is paralleled by paracostal granules, but there are few, if any, paraxostylar granules. The ultrastructure of the costa appears to be a network of flattened hexagons, with a single fibril projecting thru each of the hexagonal areas. The major cross-striations are made up largely of densely-stained filaments which are occasionally cut in cross section. The undulating membrane consists of a cytoplasmic fold extending from the dorsal surface of the organism and of the attached part of the recurrent flagellum, which is closely applied to the fold. The segment of the membrane dorsal to the flagellum, presumably the “accessory filament,” contains the marginal lamella, a membrane folded upon itself and with periodicity virtually indistinguishable from that of the rootlet filament of kinetosome #1.     

Structure of a Nonpathogenic Histomonad from the Cecum of Galliform Birds and Revision of the Trichomonad Family Monocercomonadidae Kirby*

SYNOPSIS. The nonpathogenic flagellate from the cecum of fowl, hitherto known as Histomonas wenrichi Lund, is an actively ameboid organism equipped with 4 flagella. Three of the flagella, subequal in length, are applied to one another for a short distance anterior to their origin in the kinetosomal complex and typically terminate in knob-like expansions; the 4th flagellum originates independently of the others and ends in a fine filament. A short, wide pelta is joined to the anterior part of the broad, spatulate axostylar capitulum applied to the left-ventral surface of the ellipsoidal, spheroidal, or ovoidal nucleus. Posterior to the nucleus the capitulum narrows into a slender axostylar trunk, which does not project beyond the body surface. The parabasal body, associated with a long, stout parabasal filament, is dorsal and to the right of the nucleus. On the basis of the flagellar number, the parasite is placed in a new genus Parahistomonas. A new subfamily, Protrichomonadinae, is created within the appropriately emended trichomonad family Monocercomonadidae for Parahistomonas wenrichi (Lund) comb. nov. as well as for Histomonas meleagridis (Smith) and Protrichomonas legeri (Alexeieff).     

Organization and composition of the striated roots supporting the Golgi apparatus,the so-called parabasal apparatus,in parabasalid flagellates

Summary— In parabasalid flagellates, trichomonads and hypermastigids, the stack of cisternae of the Golgi apparatus are supported by striated roots attached to the basal bodies of flagella forming the so-called parabasal apparatus. Monoclonal antibodies raised for several trichomonad species, Monocercomonas, Trichomonas and Tetratrichomonas, label the parabasal fibre in immunofluorescence or immunogold staining and protein bands in immunoblotting. Several antibodies cross-react between trichomonad species, and one of them labels the homologous parabasal fibre in the hypermastigids: Trichonympha, Joenia, Pseudotrichonympha and Holomastigotoides. Considering the molecular mass range of the labelled proteins (100–135 kDa) and the lack of antibody cross-reactivity with the striated root proteins (centrin, assemblin, kinetodesmal protein, ciliary root proteins of epithelial ciliated cells) of other organisms, these proteins recognized by these antibodies seem to represent a new class of protein forming striated roots. The occurrence and significance of parabasal organization in eukaryogenesis is discussed.     

A Freeze-Fracture Electron Microscope Study of Trichomonas vaginalis Donné and Tritrichomonas foetus (Riedmüller)1

Two strains of Trichomonas vaginalis, JH162A, with low pathogenicity, and Balt 44, with high pathogenicity, as well as one highly pathogenic strain, KV-1, of Tritrichomonas foetus were studied by freeze-fracture electron microscopy. The protoplasmic faces (PFs) of the cell membranes of all three strains of both species had similar numbers of intramembranous particles (IMPs); however, the particles in the external faces (EFs) of these membranes were least abundant in Trichomonas vaginalis strain Balt 44 and most numerous in those of strain JH162A of this species. In Tritrichomonas foetus strain KV-1 the number of IMPs in the EF was close to but somewhat lower than that in the mild strain of the human urogenital trichomonad. In both species, the anterior, but not the recurrent, flagella had rosette-like formations, consisting of ～9 to 12 IMPs on both the PFs and EFs. The numbers and distribution of the rosettes appeared to vary among different flagella and in different areas of individual flagella of a single organism belonging to either species. The freeze-fracture electron micrographs provided a more complete understanding of the fine structure of undulating membranes of Trichomonadinae, as represented by Trichomonas vaginalis, and of Tritrichomonadinae (the Tritrichomonas augusta-type), as exemplified by Tritrichomonas foetus, than was gained from previous transmission and scanning electron microscope studies. Typically three longitudinal rows of IMPs on the PF of the recurrent flagellum of Trichomonas vaginalis were noted in the area of attachment of this flagellum to the undulating membrane. The functional aspects of the various structures and differences between certain organelles revealed in the two trichomonad species by the freeze-fracture method are discussed.     

Structure of Hypotrichomonas acosta (Moskowitz) (Monocercomonadidae,Trichomonadida) as Revealed by Electron Microscopy*

SYNOPSIS. The fine structure of Hypotrichomonas acosta resembles in many respects that of Trichomonadidae, and especially of members of the sub-family Trichomonadinae which have been examined to date by electron microscopy. In addition, the flagellate has certain ultrastructural differences from the latter organisms, some of which are of phylogenetic significance. Among these, the structure of the undulating membrane and the apparently occasional presence of a fine filament which may be considered as homologous to the costa of Trichomonadidae are the most important. The undulating membrane is represented by a rather low and otherwise poorly developed dorsal cytoplasmic fold with an ill-defined distal marginal lamella; the recurrent flagellum is applied near the dorsum of the fold. In a very few preparations a relatively short filament, of a diameter falling below the resolution limits of light microscope, is seen in a position which corresponds to that of the costa of Trichomonadidae. The identity of the filament as a probable rudimentary costa is supported also by the character of its periodicity. The rare appearance of the rudimentary costa among hundreds of sections may be explained either by its minute dimensions or by its absence from many hypotrichomonads. Other structures recorded for the first time in trichomonads are: the fine filamentous connections of the axostylar microtubules; the branching of parabasal filament 2; and the unusually organized, perhaps helical, polysomes, which are found in addition to the ribosomal complexes associated with the endoplasmic reticulum and commonly found in trichomonads. A detailed analysis of interconnections among various mastigont structures is presented and several kinds of cytoplasmic inclusions are described. H. acosta is of interest in the study of the nuclear envelope and presence of nuclear pores, which are numerous and conspicuous in this flagellate. The fine structure of the hypotrichomonad is discussed in relation to that of other trichomonads and in some instances to that of other protozoa.     

Phylogenetic Relationships of the Glycolytic Enzyme, Glyceraldehyde-3-Phosphate Dehydrogenase, from Parabasalid Flagellates

Over 90% of the open reading frame of gap genes for glycolytic glyceraldehyde-3-phosphate dehydrogenase (GAPDH; EC 1.2.1.12) was obtained with PCR from five species of Parabasala. With gap1 from Trichomonas vaginalis obtained earlier, the data include two sequences each for three species. All sequences were colinear with T. vaginalis gap1 and shared with it as a synapomorphy a 10- to 11-residue insertion not found in any other gap and an S-loop with characteristic features of eubacterial GAPDH. All residues known to be highly conserved in this enzyme were present. The parabasalid sequences formed a robust monophyletic group in phylogenetic reconstructions with distance-based, maximum-parsimony, and maximum-likelihood methods. The two genes of the amphibian commensal, Trichomitus batrachorum, shared a common ancestor with the rest, which separate into two well-supported lineages. T. vaginalis and Tetratrichomonas gallinarum (both representatives of Trichomonadinae) formed one, while Monocercomonas sp. and Tritrichomonas foetus formed the other. These data agreed with and/or were close to published reconstructions based on other macromolecules. They did not support the ancestral position of Monocercomonas sp. proposed on the basis of morphological characteristics but confirmed an early emergence of Trichomitus batrachorum. The sequence pairs obtained from three species indicated either gene duplications subsequent to the divergence of the corresponding lineages or a strong gene conversion later in these lineages. The parabasalid clade was a robust part of the eubacterial radiation of GAPDH and showed no relationships to the clade that contained all other eukaryotic gap genes. The data clearly reveal that the members of this lineage use in their glycolytic pathway a GAPDH species with properties and an evolutionary history that are unique among all eukaryotes studied so far. Received: 28 April 1997 / Accepted: 14 October 1997     

Entry and intracellular location of Mycoplasma hominis in Trichomonas vaginalis

The parasite Trichomonas vaginalis causes one of the most common non-viral sexually transmitted infections in humans. The coexistence of different sexually transmitted diseases in the same individual is very common, such as vaginal infections by T. vaginalis in association with Mycoplasma fermentans or Mycoplasma hominis. However, the consequences and behavior of mycoplasma during trichomonad infections are virtually unknown. This study was undertaken to elucidate whether mycoplasmas enter and leave trichomonad cells and if so how. M. hominis was analyzed in different trichomonad isolates and the process of internalization and the pathway within the parasite was studied. Parasites naturally and experimentally infected with mycoplasmas were used and transmission electron microscopy, cytochemistry and PCR analyses were performed. The results show that: (1) M. hominis enters T. vaginalis cells by endocytosis; (2) some mycoplasmas use a terminal polar tip as anchor to the trichomonad plasma membrane; (3) some trichomonad isolates are able to digest mycoplasmas, mainly when the trichomonads are experimentally infected; (4) some fresh virulent isolates are able to maintain mycoplasmas as cohabitants in the cell’s interior; (5) some mycoplasmas are able to escape from the vacuole to the trichomonad cytosol, and trichomonad plasma membrane budding suggested that mycoplasmas could leave the parasite cell.     

Monocercomonas molae n. sp., a Flagellate from the Sunfish Mola mola*

SYNOPSIS. Monocercomonas molae from the hindgut of the sunfish Mola mola is described. The host was taken from southern California coastal waters in October, 1964. The body of the flagellate is 8.0 × 10.7 microns. A single basal granule complex gives rise to 4 flagella, one of which is recurrent. The axostyle is relatively stout, with argentophilic granules, and possesses a periaxostylar ring. The capitulum of the axostyle continues into the sickle-shaped pelta, and the parabasal body is rod-shaped or lobed and roughly triangular in cross-section.     

DNA fluorescent stain accumulates in the Golgi but not in the kinetosomes of amitochondriate protists.

Hindgut symbiotic trichomonads (uninucleate Caduceia versatilis, and multinucleate Stephanonympha sp. and Snyderella tabogae) from the dry-wood-eating termite Cryptotermes cavifrons (Kalotermitidae) accumulate DAPI (4,6diamidino-2-phenylindole) in the membranous sacs of the Golgi complex. This form of Golgi complex, typical of protists in the class Parabasalia, is called a parabasal body. Trichomonads contain organellar systems, mastigonts, that consist of four undulipodia (e.g. eukaryotic flagella and cilia), axostylar microtubules, a parabasal body and other structures. These cells bear from one (in the case of Caduceia) to hundreds (in the case of Snyderella) of mastigonts. These features are characteristic of their protist class (Parabasalia). The nuclei of all three species stained with DNA-specific stains: DAPI, SYTOX, acridine orange, propidium iodide, ethidium bromide and Feulgen, at optimal concentrations, but kinetosomes failed to stain at all. The nuclei, parabasal bodies and symbiotic bacteria (but no microtubular structures) fluoresced in glutaraldehyde-fixed cells stained with 1.45 microM DAPI. Parabasal bodies of Snyderella and Caduceia treated to remove lipids with Triton X-100, or treated with 5% trichloroacetic acid, lacked DAPI-fluorescence. I conclude that DNA, present as expected in nuclei and bacterial symbionts, is absent from and not associated with calonymphid kinetosomes. The reason for DNA-RNA stain accumulation in the Golgi cistemae is not clear.     

Tritrichomonas mobilensis n. sp. (Zoomastigophorea: Trichomonadida) from the Bolivian Squirrel Monkey Saimiri boliviensis boliviensis1

ABSTRACT. A trichomonad flagellate, Tritrichomonas mobilensis n. sp., is described from the large intestine of the squirrel monkey, Saimiri boliviensis boliviensis. The organism has a lanceolate body 7–10.5 μm in length; a well developed undulating membrane; a stout, tubular axostyle with periaxostylar rings that terminate in a cone-shaped segment projecting from the posterior end of the cell; and a moderately wide costa. The anterior flagella are about as long as the body, and the recurrent flagellum is of the acroneme type. All its characteristics suggest that the new species belongs in the Tritrichomonas augusta type of the subfamily Tritrichomonadinae.     

New Aspects of the Morphology of Pleurotricha lanceolata (Ciliophora, Hypotrichida): Cirral and Membranellar Patterns and Fibrillar Systems

In Pleurotricha lanceolata, the ventral somatic infraciliature presents 13 frontoventral cirri, 5 transverse cirri, one row with 18–19 left marginal cirri and two rows of right marginal cirri of different length. On the dorsal side there are six longitudinal rows of dorsal bristles, four of them bipolar and the other two less than half body length. The oral infraciliature includes the adoral zone of membranelles, with 45–55 membranelles of three or four rows of kinetosomes each, and two undulating membranes (paroral and endoral membranes), each with two rows of kinetosomes. Some structures of the oral and somatic fibrillar systems have also been examined and are similar to those described in other species of hypotrichous ciliates.     

Biochemical Cytology of Trichomonad Flagellates. II. Subcellular Distribution of Oxidoreductases and Hydrolases in Monocercomonas sp.*

A primitive trichomonad, Monocercomonas sp. (strain NS-1:PRR) from Natrix sipedon, was grown axenically in Diamond's medium. Activity of NADH oxidase, malate dehydrogenase, malate dehydrogenase (decarboxylating) and of the anaerobic enzymes, pyruvate synthase and hydrogenase as well as of several hydrolases was demonstrated in homogenates. The subcellular distribution of these activities was studied by means of analytical differential and isopycnic centrifugation of homogenates prepared in 0.25 M sucrose. NADH oxidase and malate dehydrogenase are in the nonsedimentable part of the cytoplasm. Malate dehydrogenase (decarboxylating), pyruvate synthase, and hydrogenase are associated with a large particle which equilibrates at density 1.22. In its properties, this particle corresponds to the microbody-like hydrogenosomes of Tritrichomonas foetus. The 5 hydrolases studied are associated with at least 2 different particle populations: a large particle population equilibrating at densities from 1.10 to 1.16 is the exclusive location of 3 enzymes (β-galactosidase, protease and β-N-acetylglucosaminidase), 2 of which have a pH optimum close to neutrality. These particles contain part of the acid phosphatase and β-glucuronidase. Another part of these 2 enzymes is associated with a separate population of smaller granules with equilibrium densities of 1.16 to 1.18. The 2 types of hydrolase-carrying particles are also biochemically very similar to their counterparts in T. foetus.     

Observations on Askenasia volvox (Claparède & Lachmann, 1859)

Specimens of Askenasia volvox from southwestern Indiana have a variable body shape and a size range of 29 × 22 μ m to 42 × 27 μ m. The pectinelles, membranelles, and cirri each number 47–48, and respectively have a length of 8–10, 20, and 30 μ m. The pectinelles arise from ciliary rows consisting of ～10 kinetosomes, and every membranelle originates from 2 adjacent rows of ～14–17 kinetosomes. Different algae as well as Bodo and certain other protozoa are ingested. The macronucleus, micronucleus, the cytoplasm and its inclusions, trichites, the function of the contractile vacuole, and movements and behavior are described.     

Experiences of a Non-Governmental Organisation (NGO) dedicated to the conservation of Arctic char <Emphasis Type="Italic">Salvelinus alpinus</Emphasis> in Ireland

Podocopid ostracods have a calcified carapace encasing their uncalcified body parts like an envelope. A marginal infold (calcified inner lamella) develops along the free margin of both valves, notably in the adult stage. Radial pore canals, which often exhibit a distinct branched shape, can be seen in the free margin and they connect to the space between the outer and inner calcified cuticles called “vestibule.” These characters associated with the marginal infold have been recognized as important criteria both taxonomically and anatomically, but the calcification process of the marginal infold has never been investigated. In this study, we observed the calcification process of the anterior free margin in Leptocythere species. The free margin of the adult specimen starts its calcification just after ecdysis, but the degree of calcification remains the same as in the juvenile until approximately 35 h after ecdysis. The marginal infold of the adult specimen then begins to calcify from its distal part around 40 h postecdysis, and short simple pore canals can still be observed in the free margin. Marginal pore canals become more branched and narrower as calcification proceeds beyond 100 h postecdysis. These results indicate that the calcification of the free margin in a podocopid carapace occurs in two steps, and needs much time to complete the process even in small species of Leptocythere. In addition, these observations provide a basis for discussion on the correlation of the carapace size, environmental factors of the habitat, and the development of the vestibule in some Krithe species, “Krithe problem.”     

Lightmicroscopic Observations on Structure and Division of Histomonas meleagridis (Smith)*

SYNOPSIS. Culture forms and lumen-dwelling phases of the ameboflagellate Histomonas meleagridis, which are structurally indistinguishable from each other, have a single flagellum. Their well-developed pelta is connected to the anterior segment of the broad, spatulate axostylar capitulum, applied to the left-ventral surface of the nearly spheroid or somewhat ellipsoid or ovoid nucleus. The capitulum narrows into a very slender axostylar trunk that tapers to a fine point and does not project beyond the body surface. The parabasal apparatus consists of a V-shaped parabasal body and a large parabasal filament. A new flagellum appears early during division and soon approaches its full length. The 2 flagella persist thruout division and each becomes the locomotory organelle of a daughter histomonad. The arms of the parental parabasal body appear to separate, each going to 1 of the daughter mastigont systems; some parabasal material is lost early in division. The 2nd arm is regenerated in each daughter parabasal body. The large parabasal filament seems not to be retained in the parental mastigont system, and new filaments are seen at both poles before 2 daughter nuclei are formed. The old axostyle degenerates from the anterior toward the posterior end; at the same time lamellar primordia of the daughter pelta-axostyle complexes appear in the separating mastigont systems that are connected by an extranuclear spindle during the entire division process. The structure and taxonomic status of H. meleagridis are discussed in the light of this and previous studies.     

A freeze-fracture electron microscope study of Trichomonas vaginalis Donné and Tritrichomonas foetus (Riedmüller)

Two strains of Trichomonas vaginalis, JH162A , with low pathogenicity, and Balt 44, with high pathogenicity, as well as one highly pathogenic strain, KV-1, of Tritrichomonas foetus were studied by freeze-fracture electron microscopy. The protoplasmic faces ( PFs ) of the cell membranes of all three strains of both species had similar numbers of intramembranous particles (IMPs); however, the particles in the external faces (EFs) of these membranes were least abundant in Trichomonas vaginalis strain Balt 44 and most numerous in those of strain JH162A of this species. In Tritrichomonas foetus strain KV-1 the number of IMPs in the EF was close to but somewhat lower than that in the mild strain of the human urogenital trichomonad . In both species, the anterior, but not the recurrent, flagella had rosette-like formations, consisting of approximately 9 to 12 IMPs on both the PFs and EFs. The numbers and distribution of the rosettes appeared to vary among different flagella and in different areas of individual flagella of a single organism belonging to either species. The freeze-fracture electron micrographs provided a more complete understanding of the fine structure of undulating membranes of Trichomonadinae , as represented by Trichomonas vaginalis, and of Tritrichomonadinae (the Tritrichomonas augusta -type), as exemplified by Tritrichomonas foetus, than was gained from previous transmission and scanning electron microscope studies. Typically three longitudinal rows of IMPs on the PF of the recurrent flagellum of Trichomonas vaginalis were noted in the area of attachment of this flagellum to the undulating membrane. The functional aspects of the various structures and differences between certain organelles revealed in the two trichomonad species by the freeze-fracture method are discussed.