Encysted Stages Research Articles

On the Encystment of Leptomonas sp. (Kinetoplastida: Trypanosomatidae), a Parasite of the Silkworm, Bombyx mori Linnaeus

SYNOPSIS. Promastigotes of Leptomonas sp., a flagellate parasite of the silkworm, Bombyx mori, multiplied by binary fission with the following sequence of events: duplication of the flagellum; division of the kinetoplast and the nucleus; spatial separation of the kinetoplast: and cytokinesis resulting in the formation of 2 daughter promastigotes. In the early stages of encystment, promastigotes aggregated in a rosette and assumed a stumpy form. The nucleus and kinetoplast of the stumpy promastigotes were double, suggesting a possibility of fusion of the organism in the rosette. When most of the promastigotes in the cluster became stumpy, each individual was isolated from the cluster and acquired a thick coat with an acidophilic substance, thus forming a cyst.

Echinostome Cercarial Penetration and Metacercarial Encystment as Mortality Factors for a Second Intermediate Host, Biomphalaria glabrata

Cercarial penetration and metacercarial encystment of Echinostoma liei in Biomphalaria glabrata caused high mortality of juvenile snails (3-8 mm in diameter) after 4 to 6 days of continuous exposure to about 150 cercariae per snail per day. Larger snails (10-13 mm) withstood cercarial penetration longer, significant mortality appearing 16 days after exposure. Life-table analysis showed that the snail mortality rate per age interval increased with increasing exposure to echinostome penetration. Single exposures of 3- and 6-mm snails to 500 cercariae caused 97% mortality for the former and 84% for the latter within 2 days. Snails surviving the first 2 days did not suffer further mortality when infected with as many as 488 metacercariae. Thus, mortality seems to result from penetration and early stages of encystment, rather than the presence of large numbers of metacercariae in the pericardial region. Growth of 3-mm snails exposed to 10 or 100 cercariae and of 6-mm snails to 500 cercariae was significantly less than the growth of unexposed controls after 20 days. Cercariae rapidly located the snails, 90% penetrating within 1 hr when individual, 6-mm snails were exposed to 100 cercariae in 5 ml of water. The high rate of cercarial penetration needed to cause snail mortality suggests that echinostome penetration and encystment will not cause much mortality of snail intermediate hosts in nature unless the density of echinostome cercariae is high.

Effect of Cycloheximide on the Encystment and Ultrastructure of the Ciliate, Histriculus

SYNOPSIS The effect of cycloheximide on the experimentally induced synchronous encystment of a hypotrich ciliate, Histriculus, was examined and the cytoplasmic ultrastructures of the control and the inhibitor‐treated organisms were compared. Encystment was divided into the following 5 stages based on observations of living cells: stage 1, cells with brown cytoplasm; stage 2, cells with smooth, transparent cytoplasm: stage 3, spindle‐shaped cells; stage 4, spherical cells without cyst walls; and stage 5, young cysts with cyst walls. When cycloheximide treatment was preceded by stage 2, encystment and transformation into the next stages were totally blocked, whereas even in the presence of the inhibitor, stage 4 and stage 5 cells encysted normally, and stage 3 cells transformed into stage 4 although they did not form cyst walls. On the basis of ultrastructural studies it is suggested that the formation and excretion of ectocyst precursors are severely inhibited by cycloheximide and that polysome formation, active in stages 1 and 2, might be almost finished by stage 3. The role of lysosomal enzymes in the early stages of encystment are discussed.

Microfossils, Macrofossils, and Stromatolites from Middle Proterozoic Belt Supergroup, Montana: ABSTRACT

Essentially unmetamorphosed strata exposed in the eastern part of the Beltian basin contain a wide variety of middle Proterozoic fossils and stromatolites. Organically preserved microfossils are abundant in shales of the Chamberlain Shale and Newland Limestone (ca. 1,400 m.y.) in the Little Belt Mountains. This assemblage includes tubular filaments which appear to represent mainly the preserved sheaths of Lyngbya-like oscillatoriacean cyanophytes and sphaeromorphs which might in turn represent the preserved outer sheaths of colonial coccoid cyanophytes or possibly the encystment stages of eukaryotic algae. The sphaeromorphs include forms (e.g., Kildinella sp.) which are potentially useful for intercontinental biostratigraphic correlation. Tabular microstructure defined by hematite particles and probably representing outlines of sheaths of oscillatoriacean cyanophytes in calcareous stromatolites of the Snowslip Formation (ca. 1,100 m.y.) in Glacier National Park represent one of the few occurrences of Proterozoic microfossils preserved within wholly calcareous rocks. Microfossils also occur in association with syngenetic sulfides in shales of the Appekunny Argillite (ca. 1,300 m.y.) in Glacier National Park. Macroscopic carbonaceous compressions occur in shales of the Newland Limestone (ca. 1,400 m.y.) in the Little Belt Mountains and probably represent macroscopic, and possibly eukaryotic, algae. Stromatolites are particularly abundant, diverse, and well exposed in strata ranging from 1,400 to 1,100 m.y. old in Glacier National Park. In addition to having paleoenvironmental significance, inclined conical stromatolites provide paleocurrent information useful in basin analysis, and branched columnar forms are potentially useful time-stratigraphic indicators. End_of_Article - Last_Page 468------------

1400-Million-Year-Old Shale-Facies Microbiota from the Lower Belt Supergroup, Montana

Carbonaceous shales of the Middle Proterozoic Newland Limestone, Belt Supergroup, Little Belt Mountains, Montana, contain abundant and well-preserved filamentous and spheroidal microfossils. The filamentous forms, ranging from less than 1 to 12 micrometers in width, are interpreted as representing the preserved sheaths of at least four species of nostocalean cyanophytes. The spheroidal forms, ranging from 15 to 108 micrometers in size, are evidently planktonic forms and are tentatively interpreted as representing the encystment stage of eukaryotic algae. The Newland microbiota is adaptable to petrographic thin-section work, and useful for evaluating the potential of such microfossils for intercontinental biostratigraphic correlation. It is the oldest shale-facies microbiota presently known from North America.

Evaluation of membrane-bound black bodies in trophozoites and cysts of Naegleria spp

Various Naegleria strains were examined to determine the possible origin and significance of membrane-bound black bodies that were found in all exponentially growing cell populations. The bodies, 40–80 nm in diameter, were distributed randomly in the cytoplasm of Naegleria with ultrastructural features typical of trophozoites. No evidence was obtained that the contents of the black bodies were synthesized in the rough endoplasmic reticulum (ER) and packaged by membranous components, which could be a primitive “Golgi complex” in these amoebae. Examination of cells in various stages of encystment indicated that at least some of the cyst wall material was synthesized and packaged by the rough ER. After condensation into amorphous granules in the cisternae, the cyst wall material appeared in vesicles of the rough ER; these were frequently seen in close proximity to the cell membrane in the vicinity of developing cyst wall. Amorphous granules (∼100 nm in diameter), which had variable densities and did not appear to be membrane bound, were seen in the cytoplasm of encysting cells. The substance of these granules also seemed to be incorporated into the cyst wall. The membrane-bound black bodies appeared to be destroyed in lysosomal elements during encystment. The membrane-bound black bodies were concluded to be characteristic of trophozoites and unrelated to encytment of Naegleria.

Differentiation of Physarum flavicomum: Metabolic patterns and the role of amino acids in the control of encystment

Haploid myxamoebae-swarm cells of Physarum flavicomum , grown in semidefined medium, differentiated in a nonnutrient salts solution to produce dormant microcysts. Over 90% of the original cell population converted to microcysts after 72 h of incubation. The intracellular content of protein, neutral hexose and RNA decreased significantly during encystment, but the DNA content was relatively stable. A change in metabolic patterns occurred during differentiation since encysting cells, but not growing cells, actively catabolized protein amino acids. Whether encystment progressed or not was determined by the extracellular availability of certain amino acids. The condition of amino acid imbalance and not glucose availability initiated the differentiation of the vegetative cells to microcysts. Only the branched chain aliphatic amino acids, leucine, isoleucine, and valine (in that order), were significant determinants of the encystment process. The compounds which inhibited encystment also inhibited intracellular proteolysis. Radioactive amino acids were actively taken up from the salts solution by encysting cells and incorporated into protein. Proteins formed in the early stages of encystment were degraded to a certain extent as encystment proceeded. However, [ 14 C]leucine-labeled proteins produced by encysting cells were degraded and catabolized less than those labeled with [ 14 C]isoleucine and [ 14 C]valine.

Notes on the Distribution of Hyalophysa and Gymnodinioides on Crustacean Hosts in Coastal North Carolina and a Description of Hyalophysa trageri sp. n.

SYNOPSIS. Hyalophysa chattoni Bradbury, Hyalophysa Iwoffi Bradbury & Clamp, and Gymnodinioides inkystans Minkiewicz are found on species of palaemonids, astacurans, grapsid crabs, ocypodids, anomurans, and portunids in coastal North Carolina. Hyalophysa trageri sp. n. is described from species of Uca and Sesarma. Its life cycle is like that of other exuviotrophic apostomes. Hyalophysa trageri differs from other species in the genus in the pattern of its infraciliature and the shape of the macronucleus during the trophont stage.In coastal North Carolina, H. chattoni is euryhaline and infests a great number of species. Hyalophysa Iwoffi is found in many locations on the freshwater shrimp Palaemonetes paludosus (Gibbes), and in one location on the crayfish Cambarus sp. Hyalophysa trageri is the most limited in range, being found only on semiterrestrial crabs. On some host species G. inkystans is found alone, but is sympatric with Hyalophysa on others.Possible factors restricting the distribution of these apostomes are discussed. These include the structure of their encysted stages, salinity, and the behavior of their hosts.

Levels of RNA polymerase activities during growth, encystment and germination ofPhysarum polycephalum.

Two RNA polymerases, enzyme A and enzyme B, were prepared fromPhysarum plasmodia. They are not located in the cytosol. Isolated nuclei, however, contain only a fraction of the total RNA polymerase activity: 1.5-19% depending on the nuclear preparation method.The level of RNA polymerase B shows little variation at developmental stages of growth and encystment, or in cysts and during germination, whereas RNA polymerase A displays a marked transient decrease in activity during the stationary growth phase before encystment.

Adhesion of Phytophthora palmivora zoospores: detection and ultrastructural visualization of concanavalin A-receptor sites appearing during encystment.

The binding of concanavalin A (Con A) to the cell surface of zoospores and cysts of Phytophthora palmivora was studied by radiometry (125I-Con A), ultraviolet microscopy (fluorescein-Con A) and electron microscopy peroxidase-diaminobenzidine technique). Zoospores were found to secrete during the early stages of encystment a Con A-binding material susceptible to trypsin digestion. This glycoprotein is contained in the so-called peripheral vesicles and is probably responsible for the adhesion of the encysting zoospores to solid surfaces.

Histochemical observations on the distribution of various oxidative and phosphorylative enzymes in larval digeneans parasitizing Bithynia tentaculata (Mollusca: Gastropoda).

A comparative histochemical study is made on the distribution of succinate dehydrogenases, isocitrate dehydrogenases, malate dehydrogenases, glucose-6-phosphate dehydrogenases, α-glycerophosphate dehydrogenases, alcohol dehydrogenases, lactate dehydrogenases and glycogen phosphorylases in the tissues of sporocysts, rediae, cercariae and metacercariae parasitizing the gastropod mollusc Bithynia tentaculata. The results suggest that metabolic sequences resembling the conventional Embden–Meyerhoff pathway, the Pentose-Phosphate cycle and Krebs’ citric acid cycle may be operational in these larval digeneans. Heaviest enzyme activity is evident in the redial pharynx, the cercarial and metacercarial sucker and in the cercarial tail. Presumably the enzymes giving this heavy reaction form part of the energy producing mechanism for these active organs. Encysted metacercariae show a very heavy enzyme activity when compared with the sporocysts and developing cercariae of the same species. This is presumably associated with the breakdown of food storage materials, particularly glycogen, by these encysted stages.

The Fine Structure of the Phoront of the Apostomatous Ciliate, Hyalophysa chattoni*

SYNOPSISThe phoront of the apostomatous ciliate, Hyalophysa chattoni, is an encysted stage that is carried on the exoskeleton of its crustacean host until the ecdysis of the host. At molting the phoront rapidly metamorphoses to the feeding stage, excysts, and immediately begins to feed on exuvial fluid trapped in the cast‐off exoskeleton. The fine structure of the resting phoront resembles that of the preceding migratory stage, the tomite. A prominent ventral tuft of cilia, the ogival field, has vanished, and the trichocysts that paralleled the kinetics have disappeared. The dense inclusion bodies that were concentrated around the mouth and falciform fields have dispersed and greatly decreased in number. The cytoplasm and its membranous organelles do not appear visibly condensed or altered from the preceding stage in the life cycle. The phoront is merely quiescent instead of dormant.Unlike the few ciliate cysts previously examined by electron microscopy, the phoront's cyst is not divisible into separable layers. It resembles the loricae of certain suctoria in being formed principally of a fibrous substance, the outer surface of which has a paracrystalline pattern. The peduncle attaching the cyst to the crab's gill is a continuation of the cyst wall although its structure is somewhat modified.The most conspicuous innovation in the phoront's fine structure is the massive tracts of microtubules that run longitudinally through the macronucleus. The microtubules are in intimate contact with Feulgen‐positive chromatin masses which are crowded toward the periphery of the macronucleus.

A Myxomycete with a Singular Myxamoebal Encystment Stage

A Myxomycete with a Singular Myxamoebal Encystment Stage

A Myxomycete with a Singular Myxamoebal Encystment Stage

SUMMARYAn aberrant culture of what is probably Didymium nigripes is described in which free-living myxamoebae seemingly constitute the primary trophic phase. Following vegetative growth, most of the myxamoebae collect into simple aggregations and form mounds or erect tapered columns prior to encystment. Such columns consist of similar microcysts throughout and show no demarcation into areas of supportive vs. propagative cells. Microcysts germinate and release myxamoebae which may promptly renew vegetative growth, or in aqueous media develop flagella and form swarm cells. Plasmodia appear rarely in the myxamoebal cultures, but when formed these can be cultivated by frequent transfer to fresh substrates pre- inoculated with Escherichia coli or Aerobacter aerogenes. When not retransferred, such plasmodia either produce poorly formed sporangia within 6–8 da or, failing to fruit (as often occurs), collect into darkly pigmented moribund masses and disintegrate. Sclerotia are not formed naturally and attempts to induce sclerotization have been unsuccessful. Of special significance is the consistent reappearance after an additional week (±) of the myxamoebal stage at the sites where fructification was effected or attempted. The origin of the emergent myxamoebae is not known, but their presence, renewed growth, and subsequent encystment serve to insure continuity of the slime mold even in the absence of normal sporangia and spores.

Cell cycle, morphogenesis, and ultrastructure in the pseudoheliozoan Clathrulina elegans.

The development of the sessile pseudoheliozoan Clathrulina elegans Cienkowski (Desmothoraca, Rhizopoda, Protozoa) was followed by light and electron microscopy. The cell cycle comprises a heliozoan-like stage sitting in an organic perforated capsule, an amoeboid resp. biflagellate stage ensuring dispersal, and an encysted stage. Special reference is given to the morphogenetic processes during the flagellate-to-heliozoan transformation. The differentiation of the stalk is described in detail and a hypothesis of the morphogenesis of the capsule is presented. Granules in the filopods displaying a jerky movement, are identified as a hitherto underscribed type of haptocyst-like organelles. These “kinetocysts” are shown to be a useful marker for studying the turnover of the plasma membrane at “organelle level”. Evidence is presented that in the flagellate stage a surplus of plasma membrane is stored in numerous lacunae thus facilitating the rapid transformation into the heliozoan stage with its comparatively large surface area. The morphogenetic significance of microtubules during the formation of the stalk, the latter being an asymmetric extracellular secretion product, is elucidated. The role of microtubule nucleation sites, the precisely timed assembly and disassembly of microtubules and other factors which probably control development are discussed to some extent.

A RECONSIDERATION OF LIVING AND FOSSIL PYROPHACUS STEIN, 1883 (DINOPHYCEAE)1,2

SUMMARYThree previously described dinoflagellates (2 “varieties” and a “form”) that comprise the marine genus Pyrophacus Stein, 1883, are allocated, to 3 separate species for the first time after demonstration of appropriate discontinuities in their respective theca and cyst morphologies. Formerly they were called P. horologium Stein var. horologium, P. horologium var. steinii Schiller and, Pyrophacus Form B1 of Steidinger and Davis; they become P. horologium Stein, P. steinii (Schiller) nov. comb., and P. vancampoae (Rossignol) nov. comb. The newly discovered cyst stage of the latter is identical with the fossil dinoflagellate Tuberculodinium vancampoae (Rossignol) Wall, whose unusual morphology is reinterpreted to include an oblate body, 4 rows of intratabular tubercules, and a uniquely located hypotractal (posterior antapical) archeopyle. The outer wall of the newly discovered benthic encysted stage of P. horologium Stein is gelatinous and agglutinating in behavior and comparable with the amorphous “Kalyptra” that constitutes the outer wall layer of several extinct Mesozoic and Danian fossil dinoflagellates.

Ultrastructural studies of protostelids: The cyst stage ofCavostelium bisporum

The ultrastructure of encystment stages in the flagellate protostelidCavostelium bisporum was studied with sectioned material fixed in sequential glutaraldehyde-OsO4.

A scanning electron microscopic study of the encystment of Acanthamoeba castellanii

The sequential changes of the surface morphology during the induced encystment of Acanthamoeba castellanii were observed with the scanning electron microscope. The vegetative cell is covered with numerous long and slender filopodia, whereas the cyst completely lacks filopodia and has a surface composed of sculptured ridges that delimit irregular shallow craters. The initial stages of the transition from trophozoite to cyst are marked by a thickening and shortening of the filopodia. The recession of filopodia continues until the surface is covered with short stubby processes. In some cases, portions of the cell surface become quite smooth. At this stage of encystment, thin welts are also evident on the surface. These structures develop into the thick, interconnecting ridges that characterize the surface of the mature cyst.

The Respiratory Metabolism of Acanthamoeba rhysodes During Encystation

SUMMARY: The endogenous respiration of vegetative amoebae, harvested during active growth, was similar in both the culture medium and in the high salt medium used to induce the encystation of starved amoebae. The respiration of starved amoebae and early stages of encystation was suppressed in high salt medium and stimulated when returned to the culture medium. A transient increase in respiration was observed early in encystation, while the respiration of later encystation stages decreased to the low level observed in mature cysts. The respiratory metabolism of mitochondria isolated from encysting amoebae was similar to that of mitochondria from vegetative amoebae while cyst mitochondria exhibited little respiration. The catalase and acid phosphatase activities of amoebae increased during starvation and encystation.

The fine structure of Acanthamoeba castellanii (Neff strain). II. Encystment.

Encysting cells of Acanthamoeba castellanii, Neff strain, have been examined with the electron microscope. The wall structure and cytoplasmic changes during encystment are described. The cyst wall is composed of two major layers: a laminar, fibrous exocyst with a variable amount of matrix material, and an endocyst of fine fibrils in a granular matrix. The two layers are normally separated by a space except where they form opercula in the center of ostioles (exits for excysting amebae). An additional amorphous layer is probably present between the wall and the protoplast in the mature cyst. Early in encystment the Golgi complex is enlarged and contains a densely staining material that appears to contribute to wall formation. Vacuoles containing cytoplasmic debris (autolysosomes) are present in encysting cells and the contents of some of the vacuoles are deposited in the developing cyst wall. Lamellate bodies develop in the mitochondria and appear in the cytoplasm. Several changes are associated with the mitochondrial intracristate granule. The nucleus releases small buds into the cytoplasm, and the nucleolus decreases to less than half its original volume. The cytoplasm increases in electron density and its volume is reduced by about 80%. The water expulsion vesicle is the only cellular compartment without dense content in the mature cyst. The volume fractions of lipid droplets, Golgi complex, mitochondria, digestive vacuoles, and autolysosomes have been determined at different stages of encystment by stereological analysis of electron micrographs. By chemical analyses, dry weight, protein, phospholipid, and glycogen are lower and neutral lipid is higher in the mature cyst than in the trophozoite.