Binocular stereo-microscopy for deforming intact amoeba

A powerful and convenient method for measuring three-dimensional (3D) deformation of moving amoeboid cells will assist the progress of environmental and cytological studies as protists amoebae play a role in the fundamental environmental ecosystem. Here we develop an inexpensive and useful method for measuring 3D deformation of single protists amoeba through binocular microscopy and a newly proposed algorithm of stereo-scopy. From the movies taken from the left and right optical tubes of the binocular microscope, we detect the 3D positions of many intrinsic intracellular vesicles and reconstruct cellular surfaces of amoeboid cells in 3D space. Some observations of sampled behaviors are shown in a single-celled organism of Amoeba proteus. The resultant surface time series is then analyzed to obtain surface velocity, curvature and volume increasing rates of pseudo-pods for characterizing the movements of amoeboid cells. The limitations and errors of this method are also discussed.

A computational study of amoeboid motility in 3D: the role of extracellular matrix geometry, cell deformability, and cell-matrix adhesion

Amoeboid cells often migrate using pseudopods, which are membrane protrusions that grow, bifurcate, and retract dynamically, resulting in a net cell displacement. Many cells within the human body, such as immune cells, epithelial cells, and even metastatic cancer cells, can migrate using the amoeboid phenotype. Amoeboid motility is a complex and multiscale process, where cell deformation, biochemistry, and cytosolic and extracellular fluid motions are coupled. Furthermore, the extracellular matrix (ECM) provides a confined, complex, and heterogeneous environment for the cells to navigate through. Amoeboid cells can migrate without significantly remodeling the ECM using weak or no adhesion, instead utilizing their deformability and the microstructure of the ECM to gain enough traction. While a large volume of work exists on cell motility on 2D substrates, amoeboid motility is 3D in nature. Despite recent progress in modeling cellular motility in 3D, there is a lack of systematic evaluations of the role of ECM microstructure, cell deformability, and adhesion on 3D motility. To fill this knowledge gap, here we present a multiscale, multiphysics modeling study of amoeboid motility through 3D-idealized ECM. The model is a coupled fluid‒structure and coarse-grain biochemistry interaction model that accounts for large deformation of cells, pseudopod dynamics, cytoplasmic and extracellular fluid motion, stochastic dynamics of cell-ECM adhesion, and microstructural (pore-scale) geometric details of the ECM. The key finding of the study is that cell deformation and matrix porosity strongly influence amoeboid motility, while weak adhesion and microscale structural details of the ECM have secondary but subtle effects.

Effect of Cytoskeleton Elasticity on Amoeboid Swimming

Recently, it has been reported that the cells of the immune system, as well as Dictyostelium amoebae, can swim in a bulk fluid by changing their shape repeatedly. We refer to this motion as amoeboid swimming. Here, we explore how the propulsion and the deformation of the cell emerge as an interplay between the active forces that the cell employs to activate the shape changes and the passive, viscoelastic response of the cell membrane, the cytoskeleton, and the surrounding environment. We introduce a model in which the cell is represented by an elastic capsule enclosing a viscous liquid. The motion of the cell is activated by time-dependent forces distributed along its surface. The model is solved numerically using the boundary integral formulation. The cell can swim in a fluid medium using cyclic deformations or strokes. We measure the swimming velocity of the cell as a function of the force amplitude, the stroke frequency, and the viscoelastic properties of the cell and the medium. We show that an increase in the shear modulus leads both to a regular slowdown of the swimming, which is more pronounced for more deflated swimmers, and to a tendency toward cell buckling. For a given stroke frequency, the swimming velocity shows a quadratic dependence on force amplitude for small forces, as expected, but saturates for large forces. We propose a scaling relationship for the dependence of swimming velocity on the relevant parameters that qualitatively reproduces the numerical results and allows us to define regimes in which the cell motility is dominated by elastic response or by the effective cortex viscosity. This leads to an estimate of the effective cortex viscosity of 103 Pa ⋅ s for which the two effects are comparable, which is close to that provided by several experiments.

Cubic membrane formation supports cell survival of amoeba Chaos under starvation-induced stress

Cubic membranes (CM) are highly organized membrane structures found in biological systems. They are mathematically well defined and reveal a three-dimensional nano-periodic structure with cubic symmetry. These membrane arrangements are frequently induced in cells under stress, disease conditions, or upon viral infection. In this study, we investigated CM formation in the mitochondria of amoeba Chaos carolinense and observed a striking correlation between the organism's ability to generate CM and the cell survival under starvation. Since starvation also induces autophagy, rapamycin was used to pharmacologically induce autophagy, and interestingly, CM formation was observed in parallel. Conversely, inhibition of autophagy reverted the cubic mitochondrial inner membrane morphology to tubular structure. In starved Chaos cells, mitochondria and autophagosomes did not co-localize and ATP production was sustained. CM transition in the mitochondria during starvation or upon induction of autophagy might prevent their sequestration by autophagosomes, thus slowing their rate of degradation. Such sustained mitochondrial activity may allow amoeba Chaos cells to survive for a longer period upon starvation.

Comparative morphology and phagocytic capacity of primary human adult microglia with time-lapse imaging

Microglia provide immune surveillance within the brain and spinal cord. Various microglial morphologies include ramified, amoeboid, and pseudopodic. The link between form and function is not clear, especially for human adult microglia which are limited in availability for study. Here, we examined primary human microglia isolated from normal-appearing white matter. Pseudopodic and amoeboid microglia were effective phagocytes, taking up E. coli bioparticles using ruffled cell membrane sheets and retrograde transport. Pseudopodic and amoeboid microglia were more effective phagocytes as compared to ramified microglia or monocyte-derived dendritic cells. Thus, amoeboid and pseudopodic microglia may both be effective as brain scavengers.

Impact of light intensity and quality on chromatophore and nuclear gene expression in Paulinella chromatophora, an amoeba with nascent photosynthetic organelles

Plastid evolution has been attributed to a single primary endosymbiotic event that occurred about 1.6 billion years ago (BYA) in which a cyanobacterium was engulfed and retained by a eukaryotic cell, although early steps in plastid integration are poorly understood. The photosynthetic amoeba Paulinella chromatophora represents a unique model for the study of plastid evolution because it contains cyanobacterium-derived photosynthetic organelles termed 'chromatophores' that originated relatively recently (0.09-0.14 BYA). The chromatophore genome is about a third the size of the genome of closely related cyanobacteria, but 10-fold larger than most plastid genomes. Several genes have been transferred from the chromatophore genome to the host nuclear genome through endosymbiotic gene transfer (EGT). Some EGT-derived proteins could be imported into chromatophores for function. Two photosynthesis-related genes (psaI and csos4A) are encoded by both the nuclear and chromatophore genomes, suggesting that EGT in Paulinella chromatophora is ongoing. Many EGT-derived genes encode proteins that function in photosynthesis and photoprotection, including an expanded family of high-light-inducible (ncHLI) proteins. Cyanobacterial hli genes are high-light induced and required for cell viability under excess light. We examined the impact of light on Paulinella chromatophora and found that this organism is light sensitive and lacks light-induced transcriptional regulation of chromatophore genes and most EGT-derived nuclear genes. However, several ncHLI genes have reestablished light-dependent regulation, which appears analogous to what is observed in cyanobacteria. We postulate that expansion of the ncHLI gene family and its regulation may reflect the light/oxidative stress experienced by Paulinella chromatophora as a consequence of the as yet incomplete integration of host and chromatophore metabolisms.

KARYOTYPING OF AMOEBA PROTEUS

In this paper, the protocol which we have developed to get satisfactory spreads of Amoeba proteus mitotic chromosomes is presented, and the process of karyotyping this amoeba species is described. This protocol allows obtaining of extended chromosomic with repeatable chromomeres pattern in individual chromosomes. We have shown that metaphase in «B»-strain amoebae (one of the type strains of A. proteus in the Amoebae Strains Collection at the Institute of Cytology) contains 27 chromosome pairs with homologous chromomeric pattern. It is ascertained that chromomeric pattern is chromosome-specific feature. The bank of images of DAPI- and YoYo1-banded individual metaphase chromosomes of «B»-strain of A. proteus is presented.

Wrinkling of a spherical lipid interface induced by actomyosin cortex

Actomyosin actively generates contractile forces that provide the plasma membrane with the deformation stresses essential to carry out biological processes. Although the contractile property of purified actomyosin has been extensively studied, to understand the physical contribution of the actomyosin contractile force on a deformable membrane is still a challenging problem and of great interest in the field of biophysics. Here, we reconstitute a model system with a cell-sized deformable interface that exhibits anomalous curvature-dependent wrinkling caused by the actomyosin cortex underneath the spherical closed interface. Through a shape analysis of the wrinkling deformation, we find that the dominant contributor to the wrinkled shape changes from bending elasticity to stretching elasticity of the reconstituted cortex upon increasing the droplet curvature radius of the order of the cell size, i.e., tens of micrometers. The observed curvature dependence is explained by the theoretical description of the cortex elasticity and contractility. Our present results provide a fundamental insight into the deformation of a curved membrane induced by the actomyosin cortex.

Species-specific cell mobility of bacteria-feeding myxamoebae in plasmodial slime molds

On decaying wood or litter in forests, plasmodial slime molds (myxomycetes) represent a large fraction of eukaryotic protists that feed on bacteria. In his seminal book Experimental Physiology of Plants (1865), Julius Sachs referred to the multinucleate plasmodium of myxomycetes, which were considered at that time as primitive plants (or fungi). Today it is well established that myxomycetes are members of the Amoebozoa (Protista). In this study we compare the mobility of myxamoebae of 3 European species, Lycogala epidendrum (order Liceales), Tubulifera arachnoidea, and Trichia decipiens (order Trichiales). Using agar plates, on which 3 separate bacterial species were cultivated as prey organisms (Methylobacterium mesophilicum, Escherichia coli, Agrobacterium tumefaciens), we document large differences in cell motility between the myxomycetes investigated. In addition, we show that the 3 species of myxamoebae can be distinguished based on their average cell size. These data shed light on the mode of co-occurrence via differential substrate utilization in these members of the Amoebozoa.

RNase P RNA from the recently evolved plastid of Paulinella and from algae

The RNase P RNA catalytic subunit (RPR) encoded in some plastids has been found to be functionally defective. The amoeba Paulinella chromatophora contains an organelle (chromatophore) that is derived from the recent endosymbiotic acquisition of a cyanobacterium, and therefore represents a model of the early steps in the acquisition of plastids. In contrast with plastid RPRs the chromatophore RPR retains functionality similar to the cyanobacterial enzyme. The chromatophore RPR sequence deviates from consensus at some positions but those changes allow optimal activity compared with mutated chromatophore RPR with the consensus sequence. We have analyzed additional RPR sequences identifiable in plastids and have found that it is present in all red algae and in several prasinophyte green algae. We have assayed in vitro a subset of the plastid RPRs not previously analyzed and confirm that these organelle RPRs lack RNase P activity in vitro.

Presence of Legionella and free-living Amoebae in composts and bioaerosols from composting facilities

Several species of Legionella cause Legionnaires' disease (LD). Infection may occur through inhalation of Legionella or amoebal vesicles. The reservoirs of Legionella are water, soil, potting soil and compost. Some species of free-living amoebae (FLA) that are naturally present in water and soil were described as hosts for Legionella. This study aimed to understand whether or not the composting facilities could be sources of community-acquired Legionella infections after development of bioaerosols containing Legionella or FLA. We looked for the presence of Legionella (by co-culture) and FLA (by culture) in composts and bioaerosols collected at four composting facilities located in southern Switzerland. We investigated the association between the presence of Legionella and compost and air parameters and presence of FLA. Legionella spp. (including L. pneumophila) were detected in 69.3% (61/88) of the composts and FLA (mainly Acanthamoeba, Vermamoeba, Naegleria and Stenamoeba) in 92.0% (81/88). L. pneumophila and L. bozemanii were most frequently isolated. FLA as potential host for Legionella spp. were isolated from 40.9% (36/88) of the composts in all facilities. In Legionella-positive samples the temperature of compost was significantly lower (P = 0.012) than in Legionella-negative samples. Of 47 bioaerosol samples, 19.1% (9/47) were positive for FLA and 10.6% (5/47) for L. pneumophila. Composts (62.8%) were positive for Legionella and FLA contemporaneously, but both microorganisms were never detected simultaneously in bioaerosols. Compost can release bioaerosol containing FLA or Legionella and could represent a source of infection of community-acquired Legionella infections for workers and nearby residents.

Amphitremida (poche, 1913) is a new major, ubiquitous labyrinthulomycete clade

Micro-eukaryotic diversity is poorly documented at all taxonomic levels and the phylogenetic affiliation of many taxa – including many well-known and common organisms - remains unknown. Among these incertae sedis taxa are Archerella flavum (Loeblich and Tappan, 1961) and Amphitrema wrightianum (Archer, 1869) (Amphitremidae), two filose testate amoebae commonly found in Sphagnum peatlands. To clarify their phylogenetic position, we amplified and sequenced the SSU rRNA gene obtained from four independent DNA extractions of A. flavum and three independent DNA extractions of A. wrightianum. Our molecular data demonstrate that genera Archerella and Amphitrema form a fully supported deep-branching clade within the Labyrinthulomycetes (Stramenopiles), together with Diplophrys sp. (ATCC50360) and several environmental clones obtained from a wide range of environments. This newly described clade we named Amphitremida is diverse genetically, ecologically and physiologically. Our phylogenetic analysis suggests that osmotrophic species evolved most likely from phagotrophic ancestors and that the bothrosome, an organelle that produces cytoplasmic networks used for attachment to the substratum and to absorb nutrients from the environments, appeared lately in labyrithulomycete evolution.

Amoeboid cells use protrusions for walking, gliding and swimming

Amoeboid cells crawl using pseudopods, which are convex extensions of the cell surface. In many laboratory experiments, cells move on a smooth substrate, but in the wild cells may experience obstacles of other cells or dead material, or may even move in liquid. To understand how cells cope with heterogeneous environments we have investigated the pseudopod life cycle of wild type and mutant cells moving on a substrate and when suspended in liquid. We show that the same pseudopod cycle can provide three types of movement that we address as walking, gliding and swimming. In walking, the extending pseudopod will adhere firmly to the substrate, which allows cells to generate forces to bypass obstacles. Mutant cells with compromised adhesion can move much faster than wild type cells on a smooth substrate (gliding), but cannot move effectively against obstacles that provide resistance. In a liquid, when swimming, the extending pseudopods convert to side-bumps that move rapidly to the rear of the cells. Calculations suggest that these bumps provide sufficient drag force to mediate the observed forward swimming of the cell.

Phospholipids trigger Cryptococcus neoformans capsular enlargement during interactions with amoebae and macrophages

A remarkable aspect of the interaction of Cryptococcus neoformans with mammalian hosts is a consistent increase in capsule volume. Given that many aspects of the interaction of C. neoformans with macrophages are also observed with amoebae, we hypothesized that the capsule enlargement phenomenon also had a protozoan parallel. Incubation of C. neoformans with Acanthamoeba castellanii resulted in C. neoformans capsular enlargement. The phenomenon required contact between fungal and protozoan cells but did not require amoeba viability. Analysis of amoebae extracts showed that the likely stimuli for capsule enlargement were protozoan polar lipids. Extracts from macrophages and mammalian serum also triggered cryptococcal capsular enlargement. C. neoformans capsule enlargement required expression of fungal phospholipase B, but not phospholipase C. Purified phospholipids, in particular, phosphatidylcholine, and derived molecules triggered capsular enlargement with the subsequent formation of giant cells. These results implicate phospholipids as a trigger for both C. neoformans capsule enlargement in vivo and exopolysaccharide production. The observation that the incubation of C. neoformans with phospholipids led to the formation of giant cells provides the means to generate these enigmatic cells in vitro. Protozoan- or mammalian-derived polar lipids could represent a danger signal for C. neoformans that triggers capsular enlargement as a non-specific defense mechanism against potential predatory cells. Hence, phospholipids are the first host-derived molecules identified to trigger capsular enlargement. The parallels apparent in the capsular response of C. neoformans to both amoebae and macrophages provide additional support for the notion that certain aspects of cryptococcal virulence emerged as a consequence of environmental interactions with other microorganisms such as protists.

A key event in C. neoformans pathogenesis is capsule enlargement in mammalian hosts. Historically, this phenomenon was attributed to high CO₂ and iron deprivation but the magnitude of capsular enlargement observed in vivo cannot be consistently replicated in vitro. This paper reports that C. neoformans responds to polar lipid extracts with massive capsule enlargement, with some cells having dimensions comparable to the giant cells observed in vivo. Phospholipids are identified in this paper as the inducers of capsule enlargement. Our work is important because this is the first host-derived molecule that has been identified as a stimulus of massive capsule enlargement thus providing a potential mechanism for the capsular enlargement observed in vivo. Furthermore, the fact that the signal is common to both macrophages and amoebae suggests that the capsule enlargement response to phospholipids is a mechanism for fungal sensing of phagocytic cell predators. This provides another example of a correspondence between a possible environmental signal and a mechanism of virulence.

Temporal analysis of protozoan lysis in a microfluidic device

A microfluidic device was fabricated and characterized for studying cell lysis of Arcella vulgaris, a nonpathogenic amoeba, over time. The device contains a series of chambers which capture cells allowing them to be subsequently exposed to a constant flow of biocidal agent. With this microfluidic system, individual cells are observed as they undergo lysis. This allows high-throughput measurements of individual lysis events, which are not possible with conventional techniques. Differences in lysis and decay times for Arcella were seen at different flow rates and concentrations of benzalkonium chloride, a biocidal detergent. The efficacy of benzalkonium chloride, chlorhexidine digluconate, phenol, sodium dodecyl sulfate, and Triton X-100 were compared, revealing information on their mechanisms of action. The presented device allows cell capture, controlled exposure to chemical biocides, and observation of lysis with single-cell resolution. Observations at the single cell level give insight into the mechanistic details of the lysis of individual Arcella cells vs. the population; decay times for individual Arcella cells were much shorter when compared to a population of 15 cells.

Phylogeny, evolution, and taxonomy of vannellid amoebae

We sequenced 18S rRNA genes from 21 vannellid amoebae (Amoebozoa; Vannellidae), including nearly all available type cultures, and performed a comprehensive phylogenetic analysis for 57 Vannellidae sequences. The results show that species of Vannella and Platyamoeba are completely mixed and do not form distinct clades. Several very closely related species pairs exist, each with a Vannella and a Platyamoeba species differing in only a few nucleotides. Therefore, presence (Vannella) or absence (Platyamoeba) of glycostyles in the cell surface coat is an invalid generic distinction; the genera must be merged. As Vannella has priority, we formally transferred Platyamoeba species into Vannella, except for the non-vannellid P. stenopodia, here renamed Stenamoeba stenopodia gen. n. comb. n. and transferred to the family Thecamoebidae. Our trees show that Vannella glycostyles were probably easily and repeatedly evolutionarily lost. We have established a new genus Ripella, with distinct morphology and sequence signatures for Vannella platypodia and morphologically similar species that form a clearly separate clade, very distant from other Vannellidae. Vannellids form four well-separated single-genus clades: Vannella sensu stricto, Ripella, Clydonella, and Lingulamoeba. Species of the revised genus Vannella comprise four closely related, well-supported subclades: one marine and three freshwater. Here, we provide an illustrated checklist for all 40 known Vannellidae species.

A multigene analysis of Corallomyxa tenera sp. nov. suggests its membership in a clade that includes Gromia, Haplosporidia and Foraminifera

We combine a morphological description with a multigene analysis to assess the phylogenetic placement of a poorly known amoeboid taxon Corallomyxa within the eukaryotic tree of life. A detailed morphological analysis including transmission electron microscopy and light microscopy of Corallomyxa sp. ATCC 50975 demonstrates that this isolate is a new species, herein designated, Corallomyxa tenera sp. nov. This species possesses features of the genus, such as a multinucleate, reticulate plasmodium with localized bidirectional streaming and occasional formation of surface buds, but is differentially characterized from other species by its delicate appearance, short duration of the anastomosing reticulate network and production of round smooth-walled cysts. The new species also lacks some features found in some Corallomyxa species, including cytoplasmic condensation and an electron dense "chromocenter". A Bayesian analysis of four concatenated genes (SSU-rDNA, actin, alpha- and beta-tubulin) from a wide diversity of eukaryotes places the new species together with taxa placed in the putative supergroup 'Rhizaria'. All molecular loci refute the traditional placement of Corallomyxa within the supergroup 'Amoebozoa', which includes other Mycetozoidea and Lobosea. Maximum likelihood and Bayesian analyses of the two well-sampled genes, SSU-rDNA and actin, with increased taxon sampling of 'Rhizaria' show a close affinity of Corallomyxa with Foraminifera, Gromia and, for SSU-rDNA, Haplosporidia. We further identify a novel stem, herein designated E23-13-1, in the predicted SSU-rDNA secondary structure that supports this relationship. A hypothesis is presented for the evolution of morphological and molecular synapomorphies in a clade containing Gromia, Corallomyxa, Foraminifera and Haplosporidia.

The intracellular cyanobacteria of Paulinella chromatophora: endosymbionts or organelles?

Endosymbiotic relationships are common across the tree of life and have had profound impacts on cellular evolution and diversity. Recent molecular investigations of the amoeba Paulinella chromatophora have raised a timely and important question: should obligatory intracellular cyanobacteria in Paulinella be considered new organelles, or do plastids and mitochondria hold a unique stature in the history of endosymbiotic events? We argue that drawing a sharp distinction between these two organelles and all other endosymbionts is not supported by accumulating data, neither is it a productive framework for investigating organelle evolution.

New aspects of membrane dynamics of Amoeba proteus contractile vacuole revealed by vital staining with FM 4-64

The contractile vacuole (CV) cycle of Amoeba proteus has been studied by phase contrast and electron microscopy. However, the understanding of membrane dynamics in this cycle is still poor. In this study, we used live imaging by fluorescence microscopy to obtain new insights. We succeeded in staining the CV with a styryl dye, FM 4-64 (N-(3-triethylammoniumpropyl)-4-(6-(4-(diethylamino)phenyl)hexatrienyl)pyridinium dibromide), and obtained the following results. (1) The CV membrane was directly stained with the dye in the external medium when the CV pore opened upon contraction. This indicates that transfer of plasma membrane to the CV does not occur. (2) The membrane dynamics during the CV cycle were elucidated. In particular, the fluorescent CV membrane was maintained as an aggregate just after contraction and the vacuole re-formed from the aggregate. Staining was maintained during continued contraction cycles. We conclude that the CV membrane is maintained during the CV cycle.

Actin dynamics in Amoeba proteus motility

We studied the distribution of the endogenous Arp2/3 complex in Amoeba proteus and visualised the ratio of filamentous (F-actin) to total actin in living cells. The presented results show that in the highly motile Amoeba proteus, Arp2/3 complex-dependent actin polymerisation is involved in the formation of the branching network of the contractile layer, adhesive structures, and perinuclear cytoskeleton. The aggregation of the Arp2/3 complex in the cortical network, with the exception of the uroid and advancing fronts, and the spatial orientation of microfilaments at the leading edge suggest that actin polymerisation in this area is not sufficient to provide the driving force for membrane displacement. The examined proteins were enriched in the pinocytotic pseudopodia and the perinuclear cytoskeleton in pinocytotic amoebae. In migrating amoebae, the course of changes in F-actin concentration corresponded with the distribution of tension in the cell cortex. The maximum level of F-actin in migrating amoebae was observed in the middle-posterior region and in the front of retracting pseudopodia. Arp2/3 complex-dependent actin polymerisation did not seem to influence F-actin concentration. The strongly condensed state of the microfilament system could be attributed to strong isometric contraction of the cortical layer accompanied by its retraction from distal cell regions. Isotonic contraction was limited to the uroid.

The impact of cleaner processing on nutrient availability in the bleached kraft industry

The pulp and paper industry has invested heavily over recent years in cleaner processing, to reduce losses and minimise its impact on the environment. Over the past fifteen years, a New Zealand integrated bleached kraft mill has undergone a comprehensive programme of upgrades to increase production, reduce water consumption and streamline its biological treatment process. Whilst the overall discharge of contaminants from the site decreased, the treatment system performance did not show a concurrent improvement as may have been expected. Reduced BOD removal, low dissolved oxygen levels, and poor solids settlability were symptomatic of phosphorus limitation in the aerated lagoon treatment system. The wastewater entering the system was found to be phosphorus limited at a BOD:P ratio of 100:0.2. Mono-ammonium-phosphate was supplemented, at approximately 30 kg P/d, to raise the phosphorus levels to a BOD:P ratio of 100:0.3. Treatment efficiencies improved very quickly after phosphorus dosage, with a 50% reduction in BOD and TSS discharge, a significant increase in dissolved oxygen levels, and improved BOD removal (85% to 93%). This case study demonstrates that whilst more closed operation can result in reduced discharge of organic loads, there may be negative impacts on the availability of nutrients for balanced biological growth.

Two new Tetramitus species (Heterolobosea, Vahlkampfiidae) from cold aquatic environments

Characterisation of the protists of cold environments provides important background for assessing the effects of climate change on microbial communities. Tetramitus angularis n. sp., from aquatic environments in Iceland and Switzerland, is the first vahlkampfiid recognised to have a characteristic Tetramitus flagellate stage combined with pre-formed excystment pores, which are not typical of this genus. T. angularis amoebae have a typical vahlkampfiid locomotive form and contain prominent lipid inclusions. Flagellates have a collar and cytostome, and can be mono- to multi-nucleate with corresponding change in cell shape from cylindrical to ellipsoidal and variable number of flagella. Cysts are round to semi-angular and have 2-5 pores closed by protruding, translucent plugs. A second organism, T. parangularis n. sp. from Alaska, has similar cysts but a flagellate stage has not been recognised; ITS sequence divergence is consistent with species criteria in the Vahlkampfiidae. Phylogenetic analysis of sequence data for the 5.8S rDNA region clusters the new spp. with T. rostratus, T. entericus and T. waccamawensis.

A Method for Estimating Cell Volume of Amoebae Based on Measurements of Cell Length of Motile Forms: Physiological and Ecological Applications

A novel method of estimating the cell volume of non-testate, free-living amoebae is presented. Measurements of the length (L) of motile forms of some amoebae, obtained by applying some basic rules, can be used to calculate diameter (D) using a relatively simple formula, derived from regression analysis (N=39): D=0.6L. Important physiological and ecological variables, including carbon content and respiratory rate, can then be easily calculated using this estimated cell volume.

Doppler flow imaging of cytoplasmic streaming using spectral domain phase microscopy

Spectral domain phase microscopy (SDPM) is a function extension of spectral domain optical coherence tomography. SDPM achieves exquisite levels of phase stability by employing common-path interferometry. We discuss the theory and limitations of Doppler flow imaging using SDPM, demonstrate monitoring the thermal contraction of a glass sample with nanometer per second velocity sensitivity, and apply this technique to measurement of cytoplasmic streaming in an Amoeba proteus pseudopod. We observe reversal of cytoplasmic flow induced by extracellular CaCl2, and report results that suggest parabolic flow of cytoplasm in the A. proteus pseudopod.

A new ballistosporous species of Protostelium

During surveys of the protostelids of the Hawaiian Islands and the South Island of New Zealand, an undescribed species of Protostelium was discovered fruiting on collections of substrates found in several sites on the southern and western parts of the island of Hawaii and from one site near Port Elizabeth, New Zealand. The new species, P. okumukumu, has a sporocarp with a bipartite stalk that supports a single, spherical spore. The basal portion of the stalk is straight and rigid. The upper part of the stalk is a nearly spherical apophysis. The junction between the stalk base and the apophysis is flexible such that the spore and apophysis swing back and forth as a unit. Spores are forcibly discharged from the stalk, and only the straight base of the stalk is left behind. Amoebae typical of the taxon Protostelium germinate from the spores, and when an amoeba differentiates into a prespore cell, it becomes lozenge shaped (nearly ellipsoid) in top view, as is typical for species of Protostelium. This represents the seventh species of protostelids described to have forcible spore discharge, and the possibility of forcible discharge needs to be examined in several other species.

[Gimenez staining: a rapid method for initial identification of legionella pneumophila in Amoeba trophozoite]

OBJECTIVE

To establish a rapid staining method for facilitating initial identification of Legionella pneumophila in amoebal trophozoite.

METHODS

Acanthamoeba polyphaga and Legionella pneumophila were co-cultured under laboratory condition. At consecutive time points during the culture, smears of the cultured products were made on glass slides for staining purposes. Different types of stainings including Gram's staining, Gimenez staining, Giemsa staining and immunofluorescence were used to determine the best method for the identification of amoebal pathogens.

RESULTS

Gimenez staining technique is simpler and yields better results as compared with the other three stainings. Gimenez stain gives the best color and contrast for amoeba and amoebal Legionella Amoeba trophozoites and/or cysts showed a distinct purplish blue with amoebal Legionella in red. Amoebal Legionella can be distinguished clearly at an earlier time of co cul ture, providing a proper sensitivity. It takes only 10 minutes to finish the operation. The other techniques require the use of expensive reagents, are relatively time-consuming, and involve complex staining procedures.

CONCLUSION

Gimenez staining is of value for the initial identification of amoebal pathogens, and it is suitable for laboratory diagnosis.

Functional characterization of contractile vacuole isolated from Amoeba proteus

Contractile vacuoles (CVs) released from cells of Amoeba proteus were used to analyze its function in vitro. When CV was transferred to a hypertonic medium, its volume decreased within 10 sec. When it was subsequently returned to its original medium, it quickly started swelling. However, it ruptured before recovering its initial volume. These results suggested that the CV membrane is semi-permeable and that the fluid is collected by the osmotic gradient in vivo. The water permeability of membrane of isolated CV was calculated from the rate of osmotic volume change to be 0.94 microm/sec . OsM. This high value suggested that CV membrane is equipped with water channel. CV contracted (or burst) quickly upon addition of 1 mM ATP. Contraction was induced by ATP, but not by other nucleotides, GTP, ITP, ADP, or the analogues of ATP, AMP-PNP and ATPgammaS. It was suggested that the contraction of isolated CV was caused by increase in the tension of its membrane by ATP.

Kinetics of cell spreading

Cell spreading is a fundamental event where the contact area with a solid substrate increases because of actin polymerization. We propose in this Letter a physical model to study the growth of the contact area with time. This analysis is compared with experimental data using the ameoba Dictyostelium discoideum. Our model couples the stress, which builds up at the margin of the contact area when the cell spreads, to the biochemical processes of actin polymerization. This leads to a scaling analysis of experimental data with a characteristic time whose order of magnitude compares well with our experimental results.

[Light and electron microscopic investigation of Pelomyxa prima (Gruber, 1884) (Peloflagellatea, Pelobiontida)]

Cell organization of a multinuclear pelobiont Pelomyxa prima has been studied at the light and electron microscopic levels. Motile individuals demonstrate a characteristic drop-like or pyriform shape and reach 550 microkm in length. The cell cover is represented by a well-developed, morphologically differentiated glycocalyx 80-100 nm thick. The cytoplasm contains many structural vacuoles. The nuclei are of vertical type, numbering up to several nuclei in large individuals. Numerous cytoplasmic microtubules are associated with the external membrane of the nuclear envelope. Separate non-motile flagella are distributed throughout the cell surface, being more numerous in the posterior body end and uroidal zone of the protist. Basal bodies of the flagella are extremely long, being deeply immersed into the cytoplasm. These bodies are surrounded by a muff of electron-dense material, with numerous microtubules radiating from it. A compact bundle of microtubules starts from the base of a basal body axially into the cytoplasm. Besides, a band-like lateral microtubular rootlet is present. The number of microtubules in the axoneme of undulipodia is unstable. Neither mitochondria, nor Golgi complex were found. Two species of bacterial endocytobionts are present in the cytoplasm in considerable numbers.

Viability of amoebae, fungal conidia, and yeasts: rapid assessment by flow cytometry

Conventional methods for the evaluation of antimicrobials and disinfecting solutions with microorganisms involve culture-based techniques, which are time-consuming and underestimate the number of viable organisms. Rapid detection and viability measurements of microorganisms in homogenous and heterogenous microbial populations have been greatly enhanced by recent advances in the use of fluorescent stains in flow cytometry (FCM). FCM has been applied to enumerate, differentiate, and identify microorganisms, determine protein and DNA content of cells, analyze the physiological state of individual cells, and analyze the interaction of drugs, antibiotics, and antimicrobials with microbial cells. Four physiological states of cells can be distinguished by FCM: (1) reproductively viable, (2) metabolically active, (3) intact, and (4) permeabilized.FCM permits a rapid and quantitative measurement of the optical characteristics of cells as they pass through, in a single file, a focused beam of light. As cells are carried within a fast-flowing fluid stream and through the focus of exciting light, three parameters are measured: forward angle light scatter, side angle light scatter, and fluorescence emitted by dyes that have specific interaction with intracellular components of individual cells. FCM data that are presented in histogram and dot plots can be generated to give information on a variety of properties of interest among cells in the population as a whole.FCM offers major advantages in multiparameter data acquisition and multivariate data analysis, high-speed analysis, and cell-sorting capabilities. Disadvantages may be associated with the cost, which is usually over 100,000 (US Dollars) for a typical laser-based flow cytometer with just analyzing capabilities. Another disadvantage is that skilled personnel are usually required to operate these complex instruments so as to get optimum performance. A schematic overview of flow cytometry is presented in Fig. 1.

Immunodetection and intracellular localization of caldesmon-like proteins in Amoeba proteus

Caldesmon immunoanalogues were detected in Amoeba proteus cell homogenates by the Western blot technique. Three immunoreactive bands were recognized by polyclonal antibodies against the whole molecule of chicken gizzard caldesmon as well as by a monoclonal antibody against its C-terminal domain: one major and two minor bands corresponding to proteins with apparent molecular masses of 150, 69, and 60 kDa. The presence of caldesmon-like protein(s) in amoebae was revealed as well in single cells after their fixation, staining with the same antibodies, and recording their total fluorescence in a confocal laser scanning microscope. Proteins recognized by the antibodies bind to filamentous actin. This was established by a cosedimentation assay in cell homogenates and by colocalization of the caldesmon-related immunofluorescence with the fluorescence of filamentous actin stained with rhodamine-labelled phalloidin, demonstrated in optical sections of single cells in a confocal microscope. Caldesmon is colocalized with filamentous actin in the withdrawn cell regions where the cortical actomyosin network contracts and actin is depolymerized, in the frontal zone where actin is polymerized again and the cortical cytoskeleton is reconstructed, inside the nucleus and in the perinuclear cytoskeleton, and probably at the cell-to-substratum adhesion sites. The regulatory role of caldesmon in these functionally different regions of locomoting amoebae is discussed.

Effect of Rho family GTP-binding proteins on Amoeba proteus

While there is a number of studies on the effects of Rho GTPases on the actin-based cytoskeleton in higher eukaryotes, studies in protozoans are rather limited. The problem seems to be intriguing since the structure of protozoan cytoskeletons is distinct from most vertebrate cells. By blocking endogenous Rho family proteins of highly motile Amoeba proteus with C3 transferase and antibodies against human RhoA and Rac1, we tried to assess the in vivo role of these proteins in amoebae. In migrating amoebae, both proteins are concentrated in the cortical layer and seem to colocalize with filamentous actin. Endogenous Rac1, but not RhoA, is accumulated in the perinuclear cytoskeleton. Blocking Rac- or Rho-like proteins caused distinct and irreversible changes in the locomotive shape of the examined amoebae and significant inhibition of their migration. Amoebae microinjected with anti-Rac1 antibodies were contracted, shortened, and developed only few wide pseudopodia. More pronounced changes were observed in cells treated with anti-RhoA antibodies. They exhibited an atypical locomotion not leading to their effective displacement. After treatment with 50 microg of C3 transferase per ml, cells rapidly contracted and almost completely rounded up, became refractile with the granules beaten into a dense mass, detached from the surface and died. Ten times lower concentration of the enzyme caused similar changes as the inhibition of endogenous RhoA-like protein. These results indicate that Rho family-based regulation plays a key role in amoebic migration.

Compensation mechanism in tumor cell migration: mesenchymal-amoeboid transition after blocking of pericellular proteolysis

Invasive tumor dissemination in vitro and in vivo involves the proteolytic degradation of ECM barriers. This process, however, is only incompletely attenuated by protease inhibitor-based treatment, suggesting the existence of migratory compensation strategies. In three-dimensional collagen matrices, spindle-shaped proteolytically potent HT-1080 fibrosarcoma and MDA-MB-231 carcinoma cells exhibited a constitutive mesenchymal-type movement including the coclustering of beta 1 integrins and MT1-matrix metalloproteinase (MMP) at fiber bindings sites and the generation of tube-like proteolytic degradation tracks. Near-total inhibition of MMPs, serine proteases, cathepsins, and other proteases, however, induced a conversion toward spherical morphology at near undiminished migration rates. Sustained protease-independent migration resulted from a flexible amoeba-like shape change, i.e., propulsive squeezing through preexisting matrix gaps and formation of constriction rings in the absence of matrix degradation, concomitant loss of clustered beta 1 integrins and MT1-MMP from fiber binding sites, and a diffuse cortical distribution of the actin cytoskeleton. Acquisition of protease-independent amoeboid dissemination was confirmed for HT-1080 cells injected into the mouse dermis monitored by intravital multiphoton microscopy. In conclusion, the transition from proteolytic mesenchymal toward nonproteolytic amoeboid movement highlights a supramolecular plasticity mechanism in cell migration and further represents a putative escape mechanism in tumor cell dissemination after abrogation of pericellular proteolysis.

Diverse chemotactic responses of Dictyostelium discoideum amoebae in the developing (temporal) and stationary (spatial) concentration gradients of folic acid, cAMP, Ca(2+) and Mg(2+)

The responses of Dictyostelium discoideum amoebae to developing (temporal) and stationary (spatial) gradients of folic acid, cAMP, Ca(2+), and Mg(2+) were studied using the methods of computer-aided image analysis. The results presented demonstrate that the new type of experimental chambers used for the observation of single cells moving within the investigated gradients of chemoattractants permit time lapse recording of single amoebae and determination of the trajectories of moving cells. It was found that, besides folic acid and cAMP (natural chemoattractants for Dictyostelium discoideum amoebae), also extracellular Ca(2+) and Mg(2+) are potent inducers of these cells' chemotaxis, and the amoebae of D. discoideum can respond to various chemoattractants differently. In the positively developing gradients of folic acid, cAMP, Ca(2+), and Mg(2+) oriented locomotion of amoebae directed towards the higher concentration of the tested chemoattractants was observed. However, in the negatively developing (temporal) and stationary linear (spatial) gradients, the univocal chemotaxis of amoebae was recorded only in the case of the Mg(2+) concentration gradient. This demonstrates that amoebae can respond to both developing and stationary gradients, depending upon the nature of the chemoattractant. We also investigated the effects of chosen inhibitors of signalling pathways upon chemotaxis of D. discoideum amoebae in the positively developing (temporal) gradients of tested chemoattractants. Verapamil was found to abolish the chemotaxis of amoebae only in the Ca(2+) gradients. Pertussis toxin suppressed the chemotactic response of cells in the gradients of folic acid and cAMP but did not prevent chemotaxis in those of Ca(2+) and Mg(2+), while quinacrine inhibited chemotaxis in the gradients of folic acid, cAMP, and Ca(2+) but only slightly affected chemotaxis in the Mg(2+) gradient. None of the tested inhibitors causes inhibition of cell random movement, when applied in isotropic solution. Also EDTA and EGTA up to 50 mM concentration did not inhibit locomotion of amoebae in control isotropic solutions.

[Specific long-term cellular changes under effects of low doses of radiation]

We examined the peculiar form of a tissue postirradiative reaction characterizing by massive, dose-independent transition of cell populations to the steady state modification with the essential raise of cell damage and cell loss probability as compared with the probability level of the same alterations in controls. We described some other signs of such type of cellular transformation. It was found that the indicated cellular condition occurred both in active and slowly proliferating tissues. The reaction occurred at relatively low doses of irradiation. Some nonmutagenic factors also may evoke such effects. Our experimental data allow us to suppose the epigenetic mechanizms taking part in the induction and preservation of such alterations. The discovered form of cellular reaction manifestating in different biological objects may be considered as some general biological tendency. The importance of the studied reaction in the pathogenesis of late consequences of low dose irradiation is discussed.

Response of amoeboid microglia/brain macrophages in fetal rat brain exposed to a teratogen

This study examined the time course response of amoeboid microglia/brain macrophages in the rat fetus induced by a single intraperitoneal injection of cyclophosphamide, a teratogen, into the mother rat at 13 days of gestation. Compared to the normal fetal brain, a marked increase in amoeboid microglia was observed in the telencephalon and diencephalon of experimental fetuses, especially in those killed at embryonic day 15. Conglomerations of microglia occurred in the dorsal and superior neuroepithelium of diencephalon, basal telencephalon, cortical neuroepithelium, and hippocampal formation as identified with OX-42, OX-18, and ED-1 by immunohistochemistry. Rhodamine isothiocynate (RhIc) as a tracer was injected via the tail vein into the pregnant rat to assess the phagocytic capability of these cells. Following the tracer injection, none of microglial cells in normal fetal brain was detectable. RhIc, however, was readily taken up by amoeboid microglia in fetal brain with injury insult. Double labeling has shown that the RhIc-labeled cells were immunoreactive with ED-1, OX-42, OX-18, and OX-6, confirming their microglial nature. Microglial proliferation was assessed by immunohistochemistry using bromodeoxyuridine, which showed a marked increase in mitotic activity. Confocal microscopic analysis revealed that a varying number of microglia coexpressed iNOS, macrophage colony-stimulating factor (M-CSF), and ICAM-1. RT-PCR analysis showed increased expression of M-CSF mRNA. Furthermore, colony-stimulating factor-1 receptor mRNA was localized in microglia by in situ hybridization. The present results suggest that NO along with M-CSF and ICAM-1 is involved in microglial proliferation in prenatal brain injury.

Neoparamoeba Page, 1987: light and electron microscopic observations on six strains of different origin

Although amoebic gill disease (AGD) has emerged as one of the most severe health problems in the fish industry, proof of the identity of AGD agents from various localities is still missing. Six strains of amoebae designated until recently as Paramoeba species (the agents of AGD) were studied in cultures by light and electron microscopy. Although they were isolated from gills of different hosts (Dicentrarchus labrax and Scophthalmus maximus) and from distant localities, their morphology was identical. The strains differed from Paramoeba eilhardi, the type species of the genus, in that they lacked the boat-shaped microscales on the cell surface but could be safely identified as belonging to the genus Neoparamoeba Page, 1987. Transmission electron microscopy revealed the presence of a symbiotic organism, Perkinsiella amoebae Hollande, 1980, in all strains under study. The only difference among the strains examined was found in the size of trophozoites, which could be attributed to the different origins of the strains, but until more refined diagnostic methods are available, in addition to N. pemaquidensis, the closely related species N. aestuarina also has to be taken into consideration as the agent of AGD.

Interaction of actin filaments with the plasma membrane in Amoeba proteus: studies using a cell model and isolated plasma membrane

We prepared a cell model of Amoeba proteus by mechanical bursting to study the interaction between actin filaments (AFs) and plasma membrane (PM). The cell model prepared in the absence of Ca2+ showed remarkable contraction upon addition of ATP. When the model was prepared in the presence of Ca2+, the cytoplasmic granules formed an aggregate in the central region, having moved away from PM. Although this model showed contraction upon addition of ATP in the presence of Ca2+, less contraction was noted. Staining with rhodamine-phalloidin revealed association of AFs with PM in the former model, and a lesser amount of association in the latter model. The interaction between AFs and PM was also studied using the isolated PM. AFs were associated with PM isolated in the absence of Ca2+, but were not when Ca2+ was present. These results suggest that the interaction between AFs and PM is regulated by Ca2+.

Chemotaxis of Amoeba proteus in the developing pH gradient within a pocket-like chamber studied with the computer assisted method

A new "U" shaped, pocket-like chamber was used to observe the chemotactic responses of individual cells. This method permits monitoring of both the development of the concentration gradient of a tested substance and cell locomotion. We investigated the chemotactic responses of Amoeba proteus and observed that the amoebae moved in positively and negatively developing [H+] gradients towards the solution of lower pH in a pH range 5.75-7.75. The chemotactic response of amoebae to [H+] gradients required the presence of extracellular calcium ions. It was blocked and random locomotion was restored by the replacement of calcium with magnesium in the cell medium. Time-lapse video recording and data processing were accomplished with computer-assisted methods. This made it possible to compare selected methods of data presentation and analysis for cells locomoting in isotropic and anisotropic conditions. The cell trajectories were determined and displayed in circular diagrams, lengths of cell tracks and final cell displacements were estimated and a few parameters characterizing cell locomotion were computed.

Immediate and long-term galvanotactic responses of Amoeba proteus to dc electric fields

The long-term and immediate galvanotactic responses of Amoeba proteus to the direct current electric fields (dcEFs) were studied with the methods of computer-aided image analysis. It was found that in contrast to earlier reports, amoebae continued locomotion towards cathode (the negative pole) for hours and the increase in the field strength in the range 300-600 mV/mm caused the straightening of cell trajectories accompanied by the decreased frequency of the lateral pseudopods formation and lesser change in the speed of cell movement. In the cell regions pointing to the anode, the formation of new pseudopodia was prevented and the higher cEFs strength the more extended were the regions in which formation of new pseudopods was inhibited. Replacement of calcium with magnesium in the extracellular medium reduced the galvanotactic cell responses. Research on the localisation and kinetics of the primary cell responses to the dcEF or to change in its direction revealed that the primary cell responses occurred at the anode oriented cell regions. The cell response to the field reversal appeared to be localised and to take place in less than 1 sec. First the retraction and withdrawal of the anode-directed pseudopodium was observed whereas the uroid (cell tail) moved for 10-40 sec in the original direction before it begun to react to the field reversal. The exposure of amoebae to the dcEFs sensitised them to the reversion in the field direction and induced an acceleration of cell responses. The results presented are difficult to reconcile with the attempt to explain the cell galvanotaxis as a consequence of the membrane protein lateral electrophoresis or electroosmosis. It is suggested that the lateral electrophoresis of ions and the modification of ionic conditions at the vicinity of ion channels may be involved in the induction of fast responses of cells to external dcEFs.

An exploration of the accuracy of an invasive method for measuring the volume of specimens of Amoeba proteus

A method is described for measuring the volume of individual specimens of Amoeba proteus which utilizes an easily constructed compressor to flatten the specimen to a known thickness. The microscopic image of the flattened specimen is captured on tape, digitized and analysed with the NIH Image software. The results from one specimen are given to illustrate the sources and magnitude of errors affecting these volume measurements.

Externalization of phosphatidylserine may not be an early signal of apoptosis in neuronal cells, but only the phosphatidylserine-displaying apoptotic cells are phagocytosed by microglia

Earlier reports on nonneural cells have shown that the normally inner plasma membrane lipid, phosphatidylserine (PS), flip-flops out during the early stages of apoptosis, whereas DNA laddering and plasma membrane permeabilization occur during the late stages. In this study, the applicability of these parameters to CNS-derived neuronal cells was tested using hippocampal HN2-5, cells that undergo apoptosis under anoxia. Because such insults on unsynchronized cells, e.g., undifferentiated HN2-5 cells, result in both early and late apoptotic cells, we mechanically separated these cells into three fractions containing (a) cells that had completely detached during anoxia, (b) cells that remained weakly attached to the tissue culture dish and, once detached by trituration in serum-containing medium, did not reattach, and (c) cells that reattached in 2-3 h. Fractions a and b contained cells that showed pronounced DNA laddering, whereas cells in fraction c did not show any DNA laddering. Double staining with fluorescein isothiocyanate-annexin V (which binds to PS) and propidium iodide (which stains the DNA in cells with a permeable cell membrane) revealed that all cells in fraction a had a permeable cell membrane (propidium iodide-positive) and PS molecules in the outer leaflet of the plasma membrane (fluorescein isothiocyanate-annexin V-positive). By contrast, fractions b and c contained cells with no externalized PS molecules. Cells in fractions a-c also showed, respectively, 50-, 21-, and 5.5-fold higher caspase-3 (CPP32) activity than that in healthy control cells. All these results show that fraction a contained late apoptotic cells, which also had the highest CPP32 activity; cells in fraction b were at an intermediate stage, when DNA laddering had already occurred; and fraction c contained very early apoptotic cells, in which no DNA laddering had yet occurred. Therefore, in the neuronal HN2-5 cells, externalization of PS occurs only during the final stages of apoptosis when the cells have completely lost their adhesion properties. Further experiments showed that ameboid microglial cells isolated from neonatal mouse brain phagocytosed only the cells in fraction a. These results show that in CNS-derived HN2-5 cells, (a) PS externalization is a late apoptotic event and is concomitant with a complete loss of surface adhesion of the apoptotic cells and (b) PS externalization is crucial for microglial recognition and phagocytosis of the apoptotic HN2-5 cells. Thus, PS externalization could be causally linked to the final detachment of apoptotic neuronal cells, which in turn prepares them for rapid phagocytosis by microglia.

[The cell biology of amebas and ameba-flagellates--parasites of man and animals]

The majority of parasitic amoebae and amoeba-flagellates are facultative parasites of animals and humans and only a few of them are obligate parasites (see reviews: Sopina, 1997; Visvesvara, Stehr-Green, 1990). Among the latter Entamoeba histolytica and among the former Naegleria fowleri and several species of Acanthamoeba are most dangerous for humans. It is still unclear whether Balamuthia mandrillaris, pathogenic for monkeys and humans, may be either obligate or facultative parasite (Visvesvara et al., 1993). Endolimax nana and Iodamoeba butschlii are commensals of humans and some animals. This review is devoted to cell biology of the above genera to provide a better understanding of cell-biological aspects of interrelations between these parasites and their hosts. In the Russian text-books on medical and veterinary parasitology these parasitic protozoa have never been regarded in terms of cell biology, and the available information seems to become out of date. This review is aimed to fill these gaps. Evidence on the ultrastructure of the above parasites, in particular that of their mitotic chromosomes, mechanisms of attachment to substratum of many of these, of locomotion and endocytosis, is provided and discussed in addition to the problem of differentiation of Naegleria amoebae into flagellates.

Labeling of amoeboid microglial cells and intraventricular macrophages in fetal rats following a maternal injection of a fluorescent dye

Amoeboid microglial cells (AMC) in fetal brains were labeled by rhodamine B isothiocyanate (RhIc) when injected intravenously or intraperitoneally into mother rats at late state of pregnancy. The fluorescent cells were immunostained with antibodies OX-42 and OX-18 that recognize complement type 3 (CR3) receptors and major histocompatibility complex class I (MHC-I) surface antigen, respectively. RhIc-labeled AMC were first observed in the cavum septum pellucidum and subependymal cysts associated with the cerebral aqueduct as well as the fourth ventricle, and subsequently at other sites including the corpus callosum and other subcortical white matter. The fluorescence intensity increased with time after RhIc administration so that after 1 day the cells were brightly labeled. The majority of the labeled cells were round, with some elongated ones bearing two or three processes. Besides AMC, macrophages in the ventricular system were also labeled. All fluorescent cells were double labeled with OX-42 and OX-18 antibodies. Present results suggest that when introduced into the maternal circulation, RhIc could readily gain access into the fetal brain through the inefficient placental, blood-brain and blood-cerebrospinal-fluid (blood-CSF) barriers. The avid uptake of RhIc in circulation by brain macrophages indicates an active scavenging role of these cells in fetal brain. The labeling of cells by maternal route offers a rapid method for study of distribution of brain macrophages in fetuses.

A Ca(2+)-dependent early functional heterogeneity in amoebae of Dictyostelium discoideum, revealed by flow cytometry

When freshly starved amoebae of Dictyostelium discoideum are loaded with the Ca(2+)-specific dye indo-1/ AM and analyzed in a fluorescence-activated cell sorter, they exhibit a quasi-bimodal distribution of fluorescence. This permits a separation of the population into two classes: H, or "high Ca(2+)-indo-1 fluorescence," and L, or "low Ca(2+)-indo-1 fluorescence." Simultaneous monitoring of Ca(2+)-indo-1 and Ca(2+)-chlortetracycline fluorescence shows that by and large the same cells tend to have high (or low) levels of both cytoplasmic and sequestered Ca2+. Next we label H cells with tetramethylrhodamine isothiocyanate (TRITC) and mix them in a 1:4 ratio with L cells. In the slugs that result, TRITC fluorescence is confined mainly to the anterior prestalk region. This implies that amoebae with relatively high Ca2+ at the vegetative stage tend to develop into prestalk cells and those with low Ca2+ into prespores. Polysphondylium violaceum, a cellular slime mold that does not possess prestalk and prespore cells, also does not display a Ca(2+)-dependent heterogeneity at the vegetative stage or in slugs. Finally, confirming earlier findings with the fluorophore fura-2 (Azhar et al., Curr. Sci. 68, 337-342 (1995)), a prestalk-prespore difference in cellular Ca2+ is present in the cells of the slug in vivo. These findings are discussed in light of the possible roles of Ca2+ for cell differentiation in D. discoideum.

Reconstitution in vitro of the motile apparatus from the amoeboid sperm of Ascaris shows that filament assembly and bundling move membranes

We have developed an in vitro motility system from Ascaris sperm, unique amoeboid cells that use filament arrays composed of major sperm protein (MSP) instead of an actin-based apparatus for locomotion. Addition of ATP to sperm extracts induces formation of fibers approximately 2 microns in diameter. These fibers display the key features of the MSP cytoskeleton in vivo. Each fiber consists of a meshwork of MSP filaments and has at one end a vesicle derived from the plasma membrane at the leading edge of the cell. Fiber growth is due to filament assembly at the vesicle; thus, fiber elongation results in vesicle translocation. This in vitro system demonstrates directly that localized polymerization and bundling of filaments can move membranes and provides a powerful assay for evaluating the molecular mechanism of amoeboid cell motility.