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In two previous papers (Le Guyader & Hyver, 1990, J. theor. Biol.143, 233-250; 1991, J. theor. Biol.150, 261-276) we proposed a one- and subsequently a two-dimensional model to account for the existence and shape of invariant zones in the cortex of Paramecium. The hypothesis was made that a Ca2+ wave stopped at the boundary of the invariant zones, thus determining their shapes. The distribution of Ca2+ conductances was assumed to be known and was approximately the same as that determined experimentally. In this paper we have attempted to model the distribution of these conductances so as to reduce the arbitrariness of the model. The proposed model therefore now has three main levels. The first level simulates the distribution of Ca2+ conductances; the second represents the Ca2+/calmodulin interaction; and the third level simulates the phosphorylated and dephosphorylated forms of a kinase. The only factor generating asymmetry is the difference in the values of some constants on opposite sides of the ventral suture. It has thus been demonstrated theoretically that the basic asymmetries of the Paramecium cell can be thought of as the consequences of a morphological asymmetry. The validity of the model was tested by simulation of the temporal development of homopolar doublets of Paramecium, which agreed well with experimental results.

This study investigated the interaction of inorganic aqueous Eu(III), Pb(II), and U(VI) with Paramecium sp., a representative single-celled protozoan that lives in freshwater. Living and prekilled Paramecium cells were tested. The prekilled cells were killed with a fixative. After 24 h exposure of the cells to inorganic aqueous solutions containing Eu(III) or U(VI), analyses by microparticle-induced X-ray emission with a focused beam (1 μm) did not detect Eu and U in the living cells, whereas Eu and U were detected in the prekilled cells. Size exclusion chromatography coupled with on-line ultraviolet-visible detection and elemental detection by inductively coupled plasma mass spectrometry of the aqueous phases collected after the living cell experiments revealed that a fraction of the Eu, Pb, and U in the aqueous phase bound to a large (ca. 250 kDa) Paramecium biomolecule and formed a metal-organic complex. The characteristics of the biomolecule were consistent with those of the soluble glycoproteins covering the surfaces of Paramecium cells. These results show that Paramecium cells transform inorganic aqueous Eu, Pb, and U to organic complexes. This paper discusses the relation between this novel complexation and the sorption of these heavy elements on Paramecium cells.

Paramecium species are extremely valuable organisms to enable experiments for the reestablishment of endosymbiosis. This is investigated in two different systems, the first with Paramecium caudatum and the endonuclear symbiotic bacterium Holospora species. Although most endosymbiotic bacteria cannot grow outside the host cell as a result of their reduced genome size, Holospora species can maintain their infectivity for a limited time. We found that an 89-kDa periplasmic protein has an important function for Holospora's invasion into the target nucleus, and that Holospora alters the host gene expression; the host thereby acquires resistance against various stresses. The second system is the symbiosis between P. bursaria and symbiotic Chlorella. Alga-free P. bursaria and the algae retain the ability to grow without a partner. Consequently, endosymbiosis between the aposymbiotic host cells and the symbiotic algae can be reestablished easily by mixing them. We now found four checkpoints for the reestablishment of the endosymbiosis between P. bursaria and the algae. The findings in the two systems provide excellent opportunities for us to elucidate not only infection processes but also to assess the associations leading to eukaryotic cell evolution. This paper summarizes recent progresses on reestablishment of the primary and the secondary endosymbiosis in Paramecium.

Paramecium calkinsi (Ciliophora, Protozoa) is a euryhaline species which was first identified in freshwater habitats, but subsequently several strains were also collected from brackish water. It is characterized by clockwise spiral swimming movement and the general morphology of the “bursaria type.” The present paper is the first molecular characterization of P. calkinsi strains recently collected in distant regions in Russia using ITS1-5.8S- ITS2-5′LSU rDNA (1100 bp) and COI (620 bp) mtDNA sequenced gene fragments. For comparison, our molecular analysis includes P. bursaria, exhibiting a similar “bursaria morphotype” as well as species representing the “aurelia type,” i.e., P. caudatum, P. multimicronucleatum, P. jenningsi, and P. schewiakoffi, and some species of the P. aurelia species complex (P. primaurelia, P. tetraurelia, P. sexaurelia, and P. tredecaurelia). We also use data from GenBank concerning other species in the genus Paramecium and Tetrahymena (which used as an outgroup). The division of the genus Paramecium into four subgenera (proposed by Fokin et al. 2004) is clearly presented by the trees. There is a clear separation between P. calkinsi strains collected from different regions (races). Consequently, given the molecular distances between them, it seems that these races may represent different syngens within the species.

Microscopists making observations on living cells are often faced with the challenge of getting those cells to hold still for extended observation times. This paper presents an overview/summary of a range of techniques for non-destructive immobilization of living cells (with an emphasis on protozoa), permitting microscopic observations and photography. A variety of chemical and physical immobilization techniques are discussed, but particular attention is paid to a comparative discussion of the mechanical devices (rotocompressors or microcompressors) used for reversible trapping of living cells.

The continuous increase in the number of new chemicals as well as the discharges of solid and liquid wastes triggered the need for simple and inexpensive bioassays for routine testing. In recent years, there has been increasing development of methods (particularly rapid tests) for testing environmental samples. This paper describes the quick toxic evaluation of an organophosphorus insecticide, acephate ( O , S -dimethyl acetylphosphoramidothioate) on Paramecium caudatum for acute and sub-acute toxicity studies with reference to morphology, behaviour, and its generation time. The lethal concentrations for 10 min and 2 h were determined by probit method, as 500 mg L −1 and 300 mg L −1 , respectively. Higher concentrations of 10 min exposure caused cell lysis with disintegration of cell membrane and precipitation of protoplasm. Combination of conventional light microscopy and computerized video tracking systems were used to study the locomotor behaviour of paramecia. The test organism was under stress and exhibited an initial increase and subsequent decrease in the swimming speed when exposed to 1/4, 1/2, 3/4, and LC 50 concentrations for 10 min (125, 250, 375, and 500 mg L −1 , respectively). Similar changes were also noticed when paramecia were exposed to LC 50 for 2 h. In a separate set of experiments, the number of generations and generation time in 24 h was evaluated with respect to the different sub-lethal concentrations (30, 60, 120, and 240 mg L −1 ). The number of generations decreased and generation time extended significantly in a concentration dependent manner. The results indicate that the Paramecium toxicity assay could be used as a complimentary system to rapidly elucidate the cytotoxic potential of insecticides. The major advantages associated with these tests are: they are inexpensive, simple, user-friendly, space saving, and seem to be attractive alternatives to conventional bioassays.

Despite the close relationship with the genus Paramecium , the species of which have a great variety of bacterial endocytobionts, a similar rich diversity of endocytobionts was not found in the genus Frontonia . This difference may probably be due to the different mode of feeding of the latter ciliates, which are chiefly algivorous. In this paper the first finding of microorganisms inside the nuclear apparatus of a Frontonia species is described. In a freshwater population of F. leucas bacteria were found in the macronuclei of almost 100% of specimens collected. Infected cells were investigated by light and electron microscopy. The endocytobionts show considerable variation of size: from 1 × 0.4 to 16 × 0.8 μm, some of the bacteria bearing a number of viral capsids. Certain of the bacteria showed cytoplasmic areas of different density. According to the results of in situ hybridization the bacteria belong to the alpha subgroup of proteobacteria. Simultaneously with the bacteria the host cells contained numerous Chlorella algae in the cytoplasm, which is not a common feature for F. leucas.

Summary In this paper we describe the expression of green fluoresent protein (GFP) as a reporter in vivo to monitor transformation in Paramecium cells. This is not trivial because of the limited number of strong promoters available for heterologous expression and the very high AT content of the genomic DNA, the consequence of which is a very aberrant codon usage. Taking into account differences in codon usage we selected and modified the original GFP open reading frame (ORF) from Aequorea victoria and placed the altered ORF into the Paramecium expression vector pPXV. Injection of the linearized plasmid into the macronucleus resulted in a cytoplasmic fluorescence signal in the clonal descendants, which was proportional to the number of copies injected. Southern hybridization indicated the establishment and replication of the plasmid during vegetative growth. Expression was also monitored by Northern and Western analysis. The results indicate that the modified GFP can be used in Paramecium as a reporter for transformation as an alternative to selection with antibiotics and that it may also be used to construct and localize fusion proteins.

In this paper we present a fluorescence microscopy investigation of the digestive process of Litonotus lamella, which we used as a prototype of the raptorial feeding behaviour. The sequence of its digestive processes, from the capture of the prey (Euplotes crassus) to the formation of digestive vacuoles was evidenced using Acridine Orange, a high quantum yield fluorescent vital probe which has a great affinity with the acid vesicle compartments. Acid vesicle localization and displacement during digestion consisted of the following phases: in starved Litonotus vesicles were localized in the neck of the ciliate; after the capture, they were displaced around the vacoule containing the prey in early digestiion, whereas in advanced digestion tens of digestive vacuoles containing Euplotes fragments were spread over the body of the predator; 1 h after capture, the digestive process was complete, and acid vesicles reorganized in the neck of the predator. The most important feature we observed was that the digestive process occurred not in the single phagosome as in filter feeder ciliates, such as Paramecium, but in many digestive vacuoles scattered all over the predator cytoplasm, which asynchronously digest prey fragments.

Summary Negative gravikinesis is an acceleration-activated modulation of vertical swimming velocity which can neutralize the passive sedimentation of ciliates. This paper investigates effects of swimming velocity levels on gravikinesis. Evaluation of a large number of data of free swimming cells with velocities ranging from 500 to 2000 μ m/s show that the ratio of vertically upward (and downward) swimming cells over horizontally swimming cells is represented by linear functions with slopes of 1. This is equivalent to a constant value of gravikinesis ( Δ ) in upward swimming cells ( Δ U ) and downward swimming cells ( Δ D ) irrespective of the swimming rate. Mechanoresponses due to velocity-dependent membrane deformations (rheokinesis) do not affect determinations of gravikinesis and may not exist at all. DC-field stimulation interferes with the slopes of swimming rates depressing vertical velocities as referred to horizontal velocity. The reduction of slopes (

Paramecium is a ciliate with a cortex consisting of cortical units that are duplicated during mitosis. The duplication process is propagated from the oral area to the poles of the cell by a wave which stops abruptly at the boundary between two regions, one anterior and one posterior, which for this reason are known as invariant zones. The first simple one-dimensional model ( Le Guyader & Hyver, 1990 , J. theor. Biol. 143, 233–250.) has provided a satisfactory explanation for the stoppage of the wave, which has been assumed to correspond to a Ca2+ wave. However, it has proved necessary to pass to two dimensions in order to obtain the shape of the invariant zones. A model has therefore been established for the propagation of a Ca2+ wave over the cortex of Paramecium; the asymmetry of the anterior invariant zone arises from the asymmetry in the distribution of Ca2+ channels, which has been assumed to be the same as that determined experimentally for the Ca2+-dependent mecanoreceptors. The theoretical results appear to be qualitatively in good agreement with experimental data. The paper ends with a discussion of the meaning of the wave and its implications for the structuring of the cell.

Insertion of an opaque mask in the path of the light source of a photographic enlarger creates dark-field illumination projection of images of motile cells placed at the plane usually used for film or plate negatives. Light reflected off cells is used to expose photograhic paper located at the level of the enlarger easel. This relatively simple modification of the enlarger allows prints to be made of swim tracks of cells over a known period of time. Paramecium cells exposed to a variety of lectins and other stimuli were analyzed by this method and qualitatively different swim patterns were recorded. Quantitative analyses of forwarded swimming velocities were obtained for cells exposed to lectins. Additionally, this method was applied to obtain swim tracks of another ciliate, Tetrahymena , and of the flagellate Euglena .

The endonucleobiotic bacterium Holospora elegans inhabits the micronucleus of Paramecium caudatum. In this paper the release of the infectious form (IF) of H. elegans from its host is described. During the anaphase of the micronuclear division most of the IFs remain within the connecting piece which, therefore, may become enormously distended. In the course of the cytokinesis of the host cell the connecting piece is usually positioned in one half of the dividing cell. Long time observations with the LM combined with EM studies revealed that the connecting piece bursts shortly after cytokinesis and thus releases the IFs into the cytoplasm. The IFs are initially not surrounded by host membranes, but thirty min later all of them are enclosed by one or two host membranes. The IF containing vesicles were never observed to accumulate acridine orange or neutral red and are, therefore, supposed not to become acidified. The release of the IFs by exocytosis via the cytoproct starts about 30 min after cytokinesis and is usually finished another 30 min later. The bacterial fine structure remains unchanged during the course of release.

A simple spherical model for a finite ciliated organism is developed. This is achieved by considering two distinct regions: one being the cilia sublayer, the other the exterior flow field. The main purpose of this paper is to obtain expressions for the velocity fields through the cilia sublayer and in the exterior flow field. Graphs of the velocity field are included for two organisms Opalina and Paramecium and are compared with experimental observations for the case of Paramecium. Velocities of propulsion of 0 (100 μm/sec) for Opalina and 0 (1000 μm/sec) for Paramecium are obtained. Maximum fluid velicities are found at the top of the cilia sublayer.