Acanthamoeba discriminates internally between digestible and indigestible particles.

Abstract

The capacity of Acanthamoeba to distinguish nutritive yeast particles from nonnutritive plastic beads during phagocytosis was investigated. When cells were allowed to phagocytose yeast to capacity, endocytosis stopped and subsequent presentation of particles (either yeast or beads) did not result in further uptake. By contrast, when cells were allowed to phagocytose plastic beads to capacity and a second dose of particles was presented (either yeast or beads), the cells exocytosed the internal particles and took up new ones. Yeast rendered indigestible by extensive chemical cross-linking were taken up at rates similar to those of untreated yeast, but, like beads, they were exocytosed when a second dose of particles was presented. The results show that an internal distinction is made between vacuoles containing yeast and vacuoles containing plastic beads, and they are consistent with the hypothesis that the presence within the vacuoles of material capable of being digested prevents exocytosis.Phagocytic uptake of panicles depends on a specific interaction at the cell surface which results in a localized stimulus for the cell to engulf the particle. In many cells this interaction can occur with a number of indigestible substances. For example, amebas will ingest silica, carbon particles, plastic beads, and other materials of no nutritive value (1, 2). Plastic beads, in fact, are valuable tools for studying the kinetics and mechanisms of endocytosis in a wide variety of cell types because they are indiscriminately engulfed by most cells. To understand better how cells control particle turnover rates and the related membrane recycling, we have studied how Acanthamoeba handles a nutritive particle, yeast, as compared with a nonnutritive particle, plastic bead.Acanthamoeba contains a vacuolar compartment that serves as its digestive system. This compartment is maintained by the cell at virtually constant volume and surface area under standard culture conditions (3). Nevertheless, considerable membrane flow occurs through the compartment because of endocytosis (3, 4). Membrane flow, as inferred from the rate of membrane ingestion by endocytosis, is rapid during pinocytosis (~9 surface equivalents/h) and close to zero in cells that have taken up particles to the limit of their capacity (that is, are saturated). When the cell is saturated with a digestible particle such as yeast, space for particle uptake gradually becomes available as digestion progresses and undigested residues are incorporated into defecation vacuoles to be expelled from the cell. In contrast, indigestible particles like plastic beads are ingested readily by the amebas, but cannot be reduced in volume. In the experiments reported here, in addition to testing turnover rates of different types of particles, we examined whether Acanthamoeba discriminates between inert and nutritive particles and whether they do so externally or internally. MATERIALS AND METHODSCulture Methods: Acanthamoeba castellanii (Neff strain) was cultured axenically as fol...

Mechanisms associated with Acanthamoeba castellanii (T4) phagocytosis

“…Subsequent to particle uptake, Acanthamoeba have the ability to distinguish vacuoles containing digestible and indigestible particles. For example, Bowers and Olszewski (1983) have shown that the fate of vacuoles within Acanthamoeba is dependent on the nature of particles, latex beads versus food particles. Vacuoles containing food particles are retained and digested, while latex beads are exocytosed, upon presentation of new particles.…”

Acanthamoeba: biology and increasing importance in human health

“…Subsequent to particle uptake into a vacuole, Acanthamoeba exhibit the ability to distinguish vacuoles containing digestible and indigestible particles. For example, Bowers & Olszewski (1983) have shown that the fate of vacuoles within Acanthamoeba is dependent on the nature of particles, latex beads vs. food particles. Vacuoles containing food particles are retained and digested, whereas latex beads are exocytosed, upon presentation of new particles.…”

The Phagosome: Compartment with a License to Kill

“…Some studies suggest, however, that the fate of a phagosome and the particle contained therein can be regulated by the degradability of the particle (79–83) and its hydrophilicity (83,84). A ’state‐of‐digestion‐sensing system’ is also suspected to exist in Acanthamoeba (85) and Dictyostelium (86). If the chemical nature of phagosome cargo is relevant to phagosome development, then it is not surprising that, in some systems, the maturation kinetics of LBP seems slower than that of phagosomes containing degradable contents [e.g.…”