Starvation and Encystment of a Soil Amoeba Hartmannella castellanii*

SYNOPSIS. The behavior of the amoeba H. castellanii was investigated in various carbon and nitrogen deficient media with a view to developing a satisfactory replacement medium for the study of encystment and excystment. Media which had been devised for other soil amoebae did not cause H. castellanii to encyst. In these media there was an efflux of material from the cells which was independent of osmolarity but which was minimized by the addition of magnesium. Maximal encystment occurred in a medium containing magnesium chloride alone. The cysts produced in the magnesium chloride replacement medium are viable and readily excyst when resuspended in the growth medium. The cysts contain cellulose, which is not present in the vegetative amoebae, and differ from the amoebae in their greater resistance to induced lysis and mechanical injury.     

Carbohydrate Utilization by the Soil Amoeba Hartmannella castellanii

SYNOPSIS. Carbohydrate utilization by 9 strains of Hartmannella castellanii has been studied by growing the amoebae in a chemically defined medium which did not support growth without an added energy source. Strains differed in the utilization of sucrose, raffinose, melibiose and mannitol. The strains which did not use sucrose for growth were shown to metabolize this sugar: ¹⁴CO₂ was produced and ¹⁴C incorporated into TCA isoluble compounds when the amoebae were grown in the presence of radioactive sucrose.     

Growth and Bacteriolytic Activity of a Soil Amoeba, Hartmannella glebae

A soil amoeba, Hartmannella glebae, could grow on a variety of gram-positive and gram-negative bacteria, although the rate of growth was faster in the presence of gram-negative bacteria. The amoeba, however, could not use yeasts, molds, or a green alga as a nutritional source. The extract prepared from amoebae grown in the presence of Aerobacter aerogenes and Alcaligenes faecalis could lyse intact cells and cell walls of many gram-positive bacteria at different rates. The spectrum of lytic activity was similar to that of egg-white lysozyme, with the exception that several species and strains of Bacillus, Micrococcus, and Staphylococcus were resistant to lysozyme and susceptible to the extract. The gram-negative bacteria tested were resistant.     

Associations of the soil amoeba Hartmannella rhysodes with the bacterial causative agents of plague and pseudotuberculosis in an experiment]

Some aspects of relationships between soil ameba and the causative agents of plague and pseudotuberculosis, capable of forming natural associations, are considered. Ameba can phagocytose bacteria causing plague and pseudotuberculosis. Cases of the preservation of individual bacterial cells at the stationary phase and in precysts of amebae have been registered.     

Quantitative Detection of the Free-Living Amoeba Hartmannella vermiformis in Surface Water by Using Real-Time PCR

A real-time PCR-based method targeting the 18S rRNA gene was developed for the quantitative detection of Hartmannella vermiformis, a free-living amoeba which is a potential host for Legionella pneumophila in warm water systems and cooling towers. The detection specificity was validated using genomic DNA of the closely related amoeba Hartmannella abertawensis as a negative control and sequence analysis of amplified products from environmental samples. Real-time PCR detection of serially diluted DNA extracted from H. vermiformis was linear for microscopic cell counts between 1.14 × 10⁻¹ and 1.14 × 10⁴ cells per PCR. The genome of H. vermiformis harbors multiple copies of the 18S rRNA gene, and an average number (with standard error) of 1,330 ± 127 copies per cell was derived from real-time PCR calibration curves for cell suspensions and plasmid DNA. No significant differences were observed between the 18S rRNA gene copy numbers for trophozoites and cysts of strain ATCC 50237 or between the copy numbers for this strain and strain KWR-1. The developed method was applied to water samples (200 ml) collected from a variety of lakes and rivers serving as sources for drinking water production in The Netherlands. Detectable populations were found in 21 of the 28 samples, with concentrations ranging from 5 to 75 cells/liter. A high degree of similarity (≥98%) was observed between sequences of clones originating from the different surface waters and between these clones and the reference strains. Hence, H. vermiformis, which is highly similar to strains serving as hosts for L. pneumophila, is a common component of the microbial community in fresh surface water.     

The Physiology of Encystment of Hartmannella castellanii*

SYNOPSIS. Some aspects of the physiology of encystment of the soil amoeba Hartmannella castellanii in a replacement encystment medium consisting of 5 × 10^-2 M MgCl₂ have been investigated. It is suggested that measurement of the cellulose produced during encystment in the synthesis of the cyst wall is a more reliable measure of the process than other methods tried. The degree of encystment was dependent on the physiologic state of the amoebae and the composition of the growth medium, but the initial pH of the encystment medium (C. 4.0-8.5) had little effect on the process. The requirement for Mg during encystment was probably not due to its deficiency during growth. Encystment was inhibited to varying extents by inhibitors of protein synthesis, tetracycline and chloramphenicol and also by arsenate, arsenite and iodoacetate; sodium fluoride, malonate and 2, 4-dinitrophenol were without marked effect. Addition of glucose and α-ketoglutarate to the replacement medium led to improvement in the encystment response. The presence of glutamate and histidine during encystment led to cell death. Other carbon and nitrogen sources had no effect. During encystment there was an increase in the metabolic activity of the amoebae, as measured by their oxygen consumption. This was accompanied by a decrease of about 40% in cellular dry weight and protein content. Of the other chemical components, there were marked initial increases in the levels of total carbohydrates and pentose which were followed by their depletion during cellulose synthesis. Encystment was completed after about 64 hr when the synthesis of cellulose was complete and the oxygen uptake of the amoebae fell to an immeasurable level.     

Ultrastructure of the Giant Amoeba Pelomyxa palustris*

SYNOPSIS. The ultrastructure of the herbivorous amoeba Pelomyxapalustris was studied. Nuclear division is not understood in this amoeba, and evidence for the method of nuclear division was sought. This species typically has many spheroidal nuclei which are similar within a given cell. However, some amoebae from our collections differed from this common type in both the number and structure of their nuclei. This suggested stages associated with nuclear division. One current hypothesis of nuclear division in this organism is that of nuclear budding. Our evidence is more in accord with this method than with mitosis. The cytoplasm contained no mitochondria, Golgi bodies, contractile vacuoles or crystals. Most amoebae had 2 types of bacteria (bacteroids or endosymbionts) in their cytoplasm; a separate vesicle enclosed each of these. Characteristically, only 1 type of bacterium (B_n) surrounded the nucleus. Another type (B) was found elsewhere in the cytoplasm. Also in the cytoplasm were the following: food vacuoles enclosing various algae, relatively clear vacuoles and vesicles, glycogen, various electron-opaque particles, and occasional microtubules. The plasmalemma was smooth, lacking the external fringe which characterizes other large fresh-water amoebae.     

Contractility of Glycerinated Amoeba proteus and Chaos-chaos*

Immediate contact with large volumes of cold 50% (v/v) buffered glycerol preserved typical ameboid shape of Chaos chaos and Amoeba proteus with no visible distortions. These technics allowed determination of the contraction sites in these glycerinated models upon application of ATP-Ca-Mg-solutions. The ectoplasmic tube was the main site of contraction. Preliminary EM investigations revealed thick and thin filaments, associated with the ectoplasmic tube near the plasmalemma, which appeared to be the basis for the contractility of the ectoplasmic tube. There was no predominant contraction of the pseudopodial tips or the endoplasm in these models. The changes of volume were as much as 50%, and in some cases were not accompanied by any change in the length of the ameba; however, lengthwise contractions of the ectoplasmic tube in some amebae occurred to as much as 25%. The data substantiate a basic requirement of the ectoplasmic tube contraction theory of ameboid locomotion.     

Serologic Changes Associated with the Encystment of Axenically Grown Hartmannella culbertsoni*

SYNOPSIS. Serologic reactions elicited by sonically ruptured trophic and cystic forms of Hartmannella culbertsoni were studied. The antigens of trophic amoebae reacted with their homologous rabbit antiserum showing multiple precipitin lines which could not be seen when the reacting antigens were treated with trypsin prior to application on the Ouchterlony plates. Antigens of trophic amoeba did not react with antiserum against cysts. Cyst antigens reacted with their homologous antiserum only after trypsin treatment. Antigens prepared from trophozoites excysting from cysts reacted positively with the antiserum against antigens of trophic amoebae. Antigens of trophic as well as cystic forms fixed guinea pig complement in presence of their homologous antisera. With the trophic form, this property was abolished after trypsin treatment. Non-specific complement fixation mediated by cyst antigens was abolished by treatment with cellulase. Antiserum against trophic amoebae immobilized trophozoites and, in the presence of guinea pig complement, led to their lysis.     

The Feeding of Amoeba proteus on Paramecium aurelia*

SYNOPSIS. Density of prey (Paramecium aurelia) and predator (Amoeba proteus) were varied while volume of inorganic medium was kept constant. Variations in density of prey had little effect on the rates of feeding and reproduction of the amoebae; but with increasing predator density the amoebae captured the paramecia less rapidly and ingested fewer before dividing, altho division size did not change appreciably. Therefore, amoebae of a low density population with a constant food supply carry more nutritional reserves from generation to generation than do those in a denser population.     

An Analysis of Clumping in the Soil Amoeba Mayorella palestinensis*

SYNOPSIS. Mayorella palestinensis, a small soil amoeba, clumped during active growth in axenic, fluid culture media. Clumping was not associated with starvation (as in the case of cellular slime molds) or with encystation Hartmannella rhysodes was used as a control amoeba which did not clump to the same extent, but otherwise resembled M. palestinensis. Mixtures of both amoebae formed mixed clumps, without subsequent segregation of amoebae in the clumps. Clumping by M. palestinensis was temperature dependent, localized to the surface of the amoeba and required surface conformation. The requirement for a living system could be separated from the surface specificity of M. palestinensis and satisfied with living amoebae that did not clump by themselves, i.e., H. rhysodes, but did clump with dead M. palestinensis. It is proposed that amoeba-to-amoeba adhesion is similar to foreign substrate adhesion, and that M. palestinensis adheres to itself because its surface is more suitable for adhesion than other surfaces present in the culture. A competition for adhesion exists between surfaces so that clumps can be dissociated by providing a foreign surface that is more suitable for adhesion than the surface of the amoeba.     

Sensitivity of Amoeba proteus to Morphine and N-Allylnormorphine. A Pressure Study*

SYNOPSIS. Amoebae exposed to 2 × 10^?3 M morphine appeared to have normal form and activity; however, a 1–2 fold increase in concentration resulted in retraction of pseudopodia and surface blebbing, then cytolysis. Amoebae cultured in 2 × 10^?3 morphine for 5–7 days, then transferred to toxic concentrations of morphine (5 × 10^?2 M) had their survival time increased 4–5 fold over the controls. As indicated by resistance to the solational action of high pressure, morphine distinctly increased pseudopodial stability, depending upon morphine concentration and, to a lesser degree, duration of exposure. Altho N-allylnormorphine did not appreciably affect pseudopodial stability, it did antagonize the action of morphine on pseudopodial stability, N-Allylnormorphine apparently competes for the same site as morphine. It is suggested that morphine affects the sol-gel equilibrium within the cell and thus may affect the integrity of proteins associated with pseudopodial stability.     

Scanning Electron Microscope Observations of Amoeba proteus During Phagocytosis*

SYNOPSIS. Phagocytosing Amoeba proteus at different stages of forming foodcups have been observed by scanning electron microscopy. A nonphagocytosing ameba is characterized by dorsal and lateral ridges running longitudinally over the posterior half of the cell and its attachment to the substrate over small areas. When stimulated by prey organisms, the ameba loses polarity and ridges, and adheres to the substrate more firmly over a wider area of contact. Then it forms broad pseudopods to surround its prey and this results in the formation of foodcups. The surface of all amebae is covered with small projections, and membranous blebs are often seen on the surface of phagocytosing organisms.     

Acid Metallophosphatase from the Ameba Amoeba proteus

Tartrate-resistant acid phosphatase (TR-AcPh) from the ameba Amoeba proteus is represented by 3 bands (electromorphs) revealed after disk-electrophoresis in PAAG, using 2-naphthylphosphate as substrate. The presence of 50 mmol/l MgCl₂ or CaCl₂ in the incubation mixture increases activities of all electromorphs of TR-AcPh, while of ZnCl₂, of two of them. The activity of the TR-AcPh electromorphs also rose after the 30-min incubation of the gels in MgCl₂, CaCl₂ or ZnCl₂ (10 and 100 mM) before gel staining. However, 1 M ZnCl₂, unlike 1 M CaCl₂ or 1 M MgCl₂, partly inactivated two out of three TR-AcPh electromorphs. The TR-AcPh electromorphs were inhibited by 1,10-phenanthroline (1,10-Ph), EDTA, and EGTA (all at a concentration of 5 mM) faster than by H₂O₂ (10 mM). The inactivation of the TR-AcPh electromorphs by the chelating agents did not depend (EGTA) or nearly did not depend (EDTA, 1,10-Ph) on their concentration (0.05, 0.5, and 5 mM). Out of 5 tested ions (Mg²⁺, Ca²⁺, Fe²⁺, Fe³⁺, and Zn²⁺), only Zn ions reactivated the TR-AcPh electromorphs inactivated by 1,10-Ph, EDTA or EGTA. The TR-AcPh electromorphs were reactivated worse after inactivation by EGTA than by EDTA or 1,10-Ph. It is suggested that the active site of TR-AcPh contains the zinc ion essential for catalytic activity of this enzyme, i.e., TR-AcPh of A. proteus is a metallophosphatase performing the phosphomonoesterase activity in acidic medium.     

A capillary technique for cloning Amoeba from single cells.

Each amoeba is placed in a drop of approximately 40 microliter of a balanced 'medium + food' solution introduced into the central region of a 7 cm long capillary tube which has first been fused at one end. Such amoebae divide to form clones of 20-30 cells without changing capillaries, though additional food may be required after 7-10 days. Experiments on damage induced by chemicals, cell cycle sensitivities and nuclear/cytoplasmic inheritance, which may involve the cloning of some 2-3,000 or more cells can be carried out with comparative ease. Apart from research, the capillary cloning technique has proved useful in the teaching laboratory. It is adaptable, and can be used for Protozoa other than amoebae, even for requiring sterile conditions.