Food Vacuole Membrane Research Articles

Effects of chloroquine on the feeding mechanism of the intraerythrocytic human malarial parasite Plasmodium falciparum.

Ultrastructural investigations of P. falciparum cultivated in vitro in human erythrocytes revealed new features of the feeding mechanism of the parasite. Mature trophozoites and schizonts take up a portion of the host cytosol by endocytosis which is restricted to cytostomes and which involves the invagination of both parasitophorous and parasite membranes. The resulting endocytic vesicles, surrounded by two concentric membranes, migrate towards the central food vacuole membrane. The external membrane of the endocytic vesicles apposes that of the food vacuole, leading to the internalization of vesicles bounded by a single membrane into the vacuole space where they are rapidly degraded. We conclude from this sequence of events that endocytic vesicles fuse with the food vacuole. Treatment of infected cells with therapeutic concentrations of chloroquine inhibited the last step of the feeding process, i.e. vacuolar degradation. This was manifested by the accumulation within the vacuolar space of intact vesicles bounded by single membranes. The implications of these findings for the antimalarial activity of chloroquine are discussed.

The effect of concanavalin A on egestion of food vacuoles in Tetrahymena

The ability of concanavalin A (conA) to disrupt food vacuole elimination at the cytoproct of Tetrahymena pyriformis, strain GL-C, was investigated using fluorescence microscopy and thin section electron microscopy. ConA was found to induce “tails” in Tetrahymena. These tails were specifically stained by fluorescent conA. Thin section observations of conA-treated cells revealed that these tails were the result of abnormal egestion of food vacuole contents at the cytoproct. Tail formation appears to result from an inhibition of endocytosis of food vacuole membrane during egestion. Instead, the food vacuole membrane appears to be cast out of the cell, along with the contents of the vacuole. The mechanism of this inhibition may be related to an apparent absence of microtubules or microfilamentous mat in the cytoproct region of conA-treated cells. Although conA is ingested into food vacuoles in large amounts, conA appears to affect endocytosis only from outside the cell; ingested conA does not appear to be effective. ConA may exert its influence by binding to the cytoproct region. The ability of conA to induce tail formation is inhibited by sugars specific to it. Numerous membranous vesicles are found in association with the oral cilia and cytoproct region of conA-treated cells. These vesicles may be the conA-binding material reported to be secreted by Tetrahymena.

Ultrastructural characteristics of algal digestion by Climacostomum virens (Ciliata) (Ehrenberg) stein

Phagocytosis and digestion in Climacostomum virens were investigated using the flagellate Chlorogonium elongatum as food. The flagellates are pushed through the buccal tube to be enclosed in food vacuoles in the cytopharyngeal region at the base of the buccal tube. Cytopharyngeal vesicles contribute membrane to the forming food vacuoles. Within 3–5 min after ingestion, small vesicles, presumably primary lysosomes, surround the food vacuole and fuse with it. Electron-lucent folds develop in the food vacuole membrane 3–6 h after feeding. Electron dense evaginations from the vacuole are detected 9–24 h after ingestion. Folds and evaginations appear to be involved in the resorption and transport of digested material through the cytoplasm. Defecation of undigested residues at the cytoproct occurs 12–24 h after ingestion. The membrane of the defecation vacuole fragments to form numerous vesicles as the undigested residues are discharged.

Pseudopod formation and membrane production during prey capture by a heliozoon (feeding by Actinophrys, II)

AbstractTwo phases of prey capture by the heliozoon Actinophrys sol are documented by electron microscopy. The phases are those of prey adhesion to the predator and enclosure of the prey by the predator. Adherence is brought about by numerous small pieces of adhesive membrane produced by the predator at the site of prey contact. Some of the heliozoan extrusomes expel their contents at this time, but the significance of this event is unclear. Enclosure of the prey is effected by a funnelshaped pseudopodium. This is drawn over the prey by the action of the leading margin. The ultrastructural appearance of the cytoplasm of the leading margin differs from the rest of the cell, being homogeneous and finely filamentous. Both force and traction for the progression of the pseudopod are generated primarily at the tip. During the development of the funnel‐pseudopod, extrusomes expand and fuse with each other and with the plasma membrane. Their investing membrane is thereby made available as food vacuole membrane.

Primary Lysosomes of the Ciliate Pseudomicrothorax dubius: Cytochemical Identification and Role in Phagocytosis*

SYNOPSIS. Filamentous cyanobacteria are ingested through the cytopharynx of the ciliate Pseudomicrothorax dubius. The cytopharynx is a complex of microtubules and microfilaments located in a highly vesiculated cytoplasm, the phagoplasm. Two types of membrane‐bounded phagoplasmic vesicles can be distinguished by their differences in size, fine structure, and acid phosphatase (AcPase) content. One type has a homogeneous, electron‐dense interior which is AcPase‐positive. These vesicles are present in fed cells and in unfed cells devoid of food vacuoles, and thus appear to be primary lysosomes. During phagocytosis, exocytosis within the cytopharynx of the primary lysosomes results in the elaboration of a food vacuole. The vacuole grows by incorporation of lysosomal membrane; lysosomal hydrolases are liberated into the vacuole. Within less than 1 second of AcPase's entry into the food vacuole, it is detectable within the cyanobacterial cytoplasm, and within 5 seconds, destruction of the cyanobacterial filament is observed. It is hypothesized that the rapidity of hydrolase penetration of the cyanobacterial cell wall is the result of the action of molecules analogous to the “killing agents” of neutrophil leukocytes, which rapidly render bacterial envelopes permeable. AcPase, and presumably other hydrolases, are present in the cyanobacterial filament when filament destruction occurs; they thus appear implicated in this process. Hydrolases may activate an autodestruction mechanism in the cyanobacterium. Firm adherence of the food vacuole membrane to the cyanobacterial filament is demonstrated, and its role in phagocytosis is discussed.

Membrane recycling at the cytoproct of Tetrahymena.

Exocytosis and membrane recycling at the cytoproct (cell anus) of Tetrahymena pyriformis were studied using thin-section electron microscopy. Single cells were fixed at specific times relative to the elimination of the vacuole's contents--before elimination, at elimination, 3--5 s and 10--15 s following elimination. The closed cytoproct is distinguished from other pellicular regions by a single membrane at the cell surface which is circumscribed by an electron-opaque flange that links or welds the plasma membrane to the underlying alveolar margins. Microtubules originating in the flange pass inward where they lie over, and possibly guide, the approaching food vacuoles to the cytoproct. Food facuoles near the cytoproct are also accompanied by coats of microfilaments. These microfilaments appear to be active in the channelling and endocytosis of food vacuole membrane. Upon cytoproct opening the plasma membrane and food vacuole membrane fuse. Elimination seems to be essentially passive and is accomplished by re-engulfment of the old food vacuole membrane which is constantly associated with microfilaments. Reengulfment of all the food vacuole membrane requires 10--15 s and results in a closed cytoproct. The membrane remnants embedded in microfilaments form a cluster under the closed cytoproct. At the periphery of this cluster remnants take the shape of 70--130-nm spherical vesicles or 0.2-micrometer-long flattened vesicles.

Further investigations on the prelethal effects of the killing action of kappa containing killer stocks of Paramecium aurelia

AbstractKappa symbionts of two stocks of Paramecium aurelia were isolated and their killing activity tested on sensitive paramecia. The symbionts from stock 51, which is a hump killer, induce sensitive animals to cease the formation of food vacuoles due to changes at the bottom of the buccal cavity in the food vacuole forming area (the naked ribbed wall). Instead of normal food vacuoles only narrow elongated outpocketings are formed. Food vacuoles which have been formed during treatment contain kappa symbionts. After disintegration due to digestion of the symbiont cells the R bodies unwind and penetrate the food vacuole membranes. Food vacuoles disintegrate so that their contents (food bacteria) are found surrounded by the cytoplasm. Later there are present uncoiled R bodies in the cytoplasm and cytoplasmic blebs on the surface of the pellicle. At the same time affected paramecia become less motile, most probably due to the occlusion of cilia by the folds formed by the blebs round them and eventually by penetration of the cytoplasm into the cilia themselves. After prolonged treatment there are great accumulations of lipid droplets in the cytoplasm of sensitive animals.Kappa symbionts from the vacuolizing stock 562 cause rather similar prelethal symptoms. In addition, these kappa symbionts induce the macronuclei in sensitive paramecia to become spherical instead of elongated, their contents somewhat optically denser and the macronuclear envelope less discernible. Secondly, mitochondria undergo very noticeable necrotic changes in the case of treatment with stock 562 kappa symbionts and also to a lesser extent in stock 51. Furthermore, kappa toxin of stock 562 causes deciliation of affected sensitive paramecia and in later stages lipid droplets accumulate in the cytoplasm.It is suggested that the primary target of kappa toxins of both stocks are the biological membranes in various subcellular structures of sensitive paramecia.

Food vacuole membrane growth with microtubule-associated membrane transport in Paramecium.

Evidence from a morphological study of the oral apparatus of Paramecium caudatum using electron microscope techniques have shown the existence of an elaborate structural system which is apparently designed to recycle digestive-vacuole membrane. Disk-shaped vesicles are filtered out of the cytoplasm by a group of microtubular ribbons. The vesicles, after being transported to the cytostome-cytopharynx region in association with these ribbons, accumulate next to the cytopharynx before they become fused with the cytopharyngeal membrane. This fusion allows the nascent food vacuole to grow and increase its membrane surface area. The morphology of this cytostome-cytopharynx region is described in detail and illustrated with a three-dimensional drawing of a portion of this region and a clay sculpture of the oral apparatus of Paramecium. Evidence from the literature for the transformation of food vacuole membrane into disk-shaped vesicles both from condensing food vacuoles in the endoplasm and from egested food vacuoles at the cytoproct is presented. This transformation would complete a system of digestive vacuole membrane recycling.

Food vacuole membrane in nutrient uptake by Tetrahymena.

ALTHOUGH the ciliate protozoon, Tetrahymena pyriformis was first cultivated in sterile broth more than 50 years ago1, and in chemically defined media more than 20 years ago2 its uptake of nutrients in solution is poorly understood. For example, the part played by the food vacuoles is still unknown. The vacuoles seem to be essential for rapid cell multiplication in some media3–5, but calculations show that the volume of the food vacuoles formed per unit time cannot account for the observed uptake of either acetate6 or nucleosides (present report). Previously, it was proposed that the mucous layer might be able to concentrate nutrients and thus increase their uptake7. I here present an alternative hypothesis.

The Biology and Ultrastructure of Phagotrophy in Ochromonas danica (Chrysophyceae: Chrysomdnadida)

SUMMARY: Ochromonas danica can obtain energy and required nutrients by eating several different bacteria or brewer's yeast. The phagocytic process includes aggregation of bacteria into clumps which contain and are surrounded by Ochromonas. Bacteria were phagocytized too fast to be seen while yeast took at least 5 min to be engulfed. 2,4-Dinitrophenol or sodium azide, but not sodium fluoride or iodoacetic acid, inhibited the phagocytic process; aerobic energy metabolism was necessary for phagocytosis. Food organisms were engulfed and the food vacuole migrated to the posterior end of the organism behind the leucosin vacuole. The bacteria were digested mainly in the food vacuole although secondary lysosomes were formed. Digestion of bacteria resulted in the proliferation of vesicles and membranes from the food vacuole membrane and the proliferation of membrane from the bacteria being digested.

Feeding in ciliated protozoa. I. Pharyngeal disks in Euplotes: a source of membrane for food vacuole formation?

ABSTRACT The ciliate Euplotes is able to expend a very large amount of membrane in the formation of food vacuoles. Calculations based on the rate of ingestion of the food organism Tetrahymena indicate that an amount of food vacuole membrane equivalent to approximately 50-150% of the total Euplotes cell surface area can be produced within 5-10 min. An aggregation of osmio-philic, membrane-limited ‘pharyngeal disks’ is found packed in the cytoplasm just beneath the cell surface membrane in the region of the cell mouth and cytopharynx. These disks, which can be seen also in living cells, have average dimensions of 2 μm diameter by too nm thickness, and contain tightly packed layers of a thin lamellar material. Electron micrographs have revealed the apparent fusion of the limiting membrane of disks with the cell’s plasma membrane at the base of the gullet. The lamellar disk contents are thereby released to the exterior medium in the buccal cavity, where they form a loosely packed layer over the surface membrane. It is postulated that the pharyngeal disks represent a repository of preformed membrane for use in food vacuole formation. The disk contents may also play a role in food ingestion, although this is not well defined at present. The myeloid content of old food vacuoles is very similar to that of nearby disks in the cytoplasm, suggesting that the disks may form by pinching from shrinking food vacuoles during the digestive cycle. Thus a cycle of membrane flow is envisaged, with the pharyngeal disks (1) coalescing with the surface membrane during food vacuole formation, (2) reforming by pinching from these food vacuoles during digestion, and (3) migrating back to the oral region to serve as a membrane store for subsequent food vacuole formation.

The cytoproct of Paramecium caudatum: structure and function, microtubules, and fate of food vacuole membranes.

ABSTRACT The cytoproct or cell anus of Paramecium caudatum was studied, using light optics and electron microscopy, at known times before, during and following food vacuole egestion. This was accomplished by microscopically observing single cells, fixing these cells at specific times and finally serial sectioning these individually processed cells. The cytoproct, at rest, is a long narrow ridge along the posterior suture. It contains 2 uniquely positioned components which identify this structure as the cytoproct: piles of fibres along the inside surfaces of the ridge, and microtubules passing from the epiplasm at the summit of the ridge down into the cytoplasm. The plasma membrane is continuous over the top of the ridge. The cortical basal bodies adjacent to the ridge have bundles of microtubules passing into the cytoplasm from an opaque plaque at their proximal ends. These 2 sets of microtubules may function in guiding the food vacuoles to the cytoproct. A model is presented in which motive forces generated between the microtubules and the food vacuole membrane bring the food vacuole to the cytoproct and, in addition, pull the cytoproct lips apart so that the food vacuole membrane and plasma membrane come into contact and fuse together, thus opening the food vacuole to the outside. The plasma membrane increases in area between the parting lips, possibly, as the result of intercalation of membrane vesicles into the plasma membrane at the top of the ridge. Immediately after this opening is formed the food vacuole membrane changes from a smooth topography to a highly convoluted one. The membrane is engulfed through a process of endocytosis resulting in an accumulation of membranous fragments in the cytoplasm below the cytoproct. The endocytic forces probably bring about the restitution of the cytoproct ridge by pulling the lips back together as the membrane is engulfed. A filamentous meshwork underlying the food vacuole membrane may be active in this endocytic process.

Assembly of lipids into membranes in Acanthamoeba palestinensis. II. The origin and fate of glycerol- 3 H--labeled phospholipids of cellular membranes.

The membranes of Acanthamoeba palestinensis were studied by examination in fixed cells, and then by following the movements of glycerol-(3)H-labeled phospholipids by cell fractionation. Two previously undescribed structures were observed: collapsed cytoplasmic vesicles of cup shape, and plaques in food vacuole and plasma membrane similar in size to the collapsed vesicles. It appeared that the plaques formed by insertion of collapsed vesicles into membranes and/or that collapsed vesicles formed by pinching off of plaques. Fractions were isolated, enriched with nuclei, rough endoplasmic reticulum (RER), plasma membrane, Golgi-like membranes, and collapsed vesicles. The changes in specific activity of glycerol-(3)H-labeled phospholipids in these membranes during incorporation, turnover, and after pulse-labeling indicated an ordered sequence of appearances of newly synthesized phospholipids, first in nuclei and RER, then successively in Golgi membranes, collapsed vesicles, and finally, plasma membrane. In previous work we had found no large nonmembranous phospholipid pool in A. palestinensis. These observations are consistent with the hypothesis that membrane phospholipids are synthesized, perhaps as integral parts of membranes, in RER and nuclei. Subsequently, some of the newly synthesized phospholipids are transported to the Golgi complex to become integrated into the membranes of collapsed vesicles, which are precursors of the plasma membrane. Collapsed vesicles from the plasma membrane by inserting into it as plaques. When portions of the plasmalemma from food vacuoles, collapsed vesicles pinch off from their membranes and are recycled back to the cell surface.

Prelethal effects of killing action by stock 7 of Paramecium aurelia.

AbstractWhen stock 16 sensitives are exposed to kappa particles of stock 7, the kappa particles enter food vacuoles in large numbers. The kappa quickly break down, R bodies unroll and penetrate the cytoplasm, food vacuole membranes show a general breakdown, and the formation of new food vacuoles is suppressed. The observations suggest that R body unrolling is important in the toxic activity and that the food vacuole membranes may be a major site of action of the toxin.

Ultrastructural localisation of NADH- and NADPH-dehydrogenases in the erythrocytic stages of the rodent malaria parasite, [formula omitted

i) NADH- and NADPH-dehydrogenase activity was localised mainly on the concentric-membraned organelles, and to a lesser extent on the limiting membrane, food vacuole membrane and nuclear membrane of erythrocytic trophozoites of P. berghei . ii) NADH-dehydrogenase activity was present in larger amounts in the parasites than NADPH-dehydrogenase. iii) The significance of these enzymes in relation to parasite metabolism is discussed in the light of present knowledge.

Electron Microscopy of Pinocytosis and Food Vacuoles in Pelomyxa*

SYNOPSIS.Food vacuoles have been studied in various stages of the digestive process in cultures of Pelomyxa carolinensis and P. illinoisensis after feeding Tetrahymena and Paramecium. The vacuole wall formed immediately after capture of the food organism may be only 100 m/i thick. The changes observed in the food organisms indicate that first the membranes of the pellicle are ruptured, then mitochondria, cytoplasmic matrix, and nucleus are attacked; cilia and trichocysts are more resistant. The food vacuole membrane is involved first in the removal of water from the vacuole, then in transfer of cytoplasmic fluid into the vacuole, and finally in removal of digestion products from ihe vacuole by pinocyt. Vesicles which have been derived from the plasnulf—a b pinocytosis have been observed. They characteristically have a non‐turgid, non‐spherical appearance when located deep m the cytoplasm and are stainable with phosphotungstic acid. Pinocytosis and the function of food vacuole membranes are discussed. It is concluded that at leait two factors contribute to the benefits derived by amoebae from pinocytosis: (1) modification of the plasmalemma membrane near the time when it becomes the pinocytic vesicle membrane, and (2) increased surface area for diffusion.