Nutrient uptake in Tetrahymena pyriformis

Abstract

Several morphological structures have been implicated in nutrient uptake in the ciliate protozoon, Tetrahymena pyriformis: food vacuoles, various types of vesicles and the plasma membrane. It is the object of this report to discuss the roles of these organelles in food uptake. Measurements of multiplication rates under conditions where food vacuole formation could be controlled experimentally suggested that the food vacuoles (about 5 rtm in diameter) were essential for rapid cell multiplication in various standard growth media. If, however, concentrations of certain specific nutrients (different for different strains of T. pyriformis) were high, then the cells could multiply rapidly even when food vacuoles were absent. Furthermore, multiplication rates of cells supplied with particulate or dissolved egg albumin as the amino acid source, suggested that the food vacuoles took up particulate egg albumin well, but dissolved egg albumin poorly. The role in food uptake of vesicles with a diameter of less than 1 vm remains largely unknown. Our present knowledge of them is not yet sufficiently detailed to permit estimations of the rates with which they are formed or of their total number per cell. The plasma membrane has carrier-mediated uptake sites for a number of nutrients such as amino acids and nucleosides. It is likely that this type of uptake mechanism plays a quantitatively important role in T. pyriformis whenever such compounds are present in the extracellular fluid.

Magnetic purification of mating Tetrahymena

“…To demonstrate a similar difference in particle uptake between mating and non-mating cells, firm pairs (five hours after the first pairs have formed) were isolated into small drops of growth medium containing India ink, and observed both for pair separation and ink uptake into food vacuoles. In addition, non-mating cells from the same mating mixtures were isolated into the ink-nutrient broth; ink filled food vacuoles were easily seen in these control cells within 15 minutes, in agreement with previous studies (12). On the other hand, when isolated into ink-growth medium and observed repeatedly soon thereafter, 0 out of 378 pairs formed food vacuoles, and non showed vacuole formation until, on the average, five hours after pair separation.…”

Directed motility of phagosomes inTetrahymena thermophila requires actin and Myo1p, a novel unconventional myosin

“…Membrane invagination within the oral cavity is the major pathway for endocytosis/phagocytosis in Tetrahymena [Kitajima and Thompson, 1977;Rasmussen, 1976;Nilsson, 1977]. Internalized vacuoles, known as food vacuoles or phagosomes, contain particulates or only fluids when cells are cultured in a non-particulate axenic medium.…”

“…Relatively few studies have attempted to define biochemical and morphological markers for stages of vacuole maturation in Tetrahymena. Earlier studies recognized membrane fusions as integral to the maturation process [Kitajima and Thompson, 1977;Rasmussen, 1976]. More recently, overlay-GTP assays on proteins from isolated Tetrahymena phagosomes revealed the presence of ras superfamily GTPases whose electrophoretic pattern changed with phagosomes isolated at different stages of maturity [Meyer et al, 1998].…”

MYO1, a Novel, Unconventional Myosin Gene Affects Endocytosis and Macronuclear Elongation inTetrahymena thermophila

“…In Tetrahymena , an endocytic cycle involves membrane transport, fusion, and recycling in the food vacuole‐forming region of the oral structure. A food vacuole originates from several precursor vesicles that fuse with the plasma membrane in the oral region and eventually separate from it (Rasmussen 1976). The detached vesicle fuses with lysosome membranes to form a mature food vacuole (Kitajima and Thompson 1977; Rasmussen 1976).…”

“…A food vacuole originates from several precursor vesicles that fuse with the plasma membrane in the oral region and eventually separate from it (Rasmussen 1976). The detached vesicle fuses with lysosome membranes to form a mature food vacuole (Kitajima and Thompson 1977; Rasmussen 1976). Although actin has been localized to the food vacuole‐forming region of the Tetrahymena oral apparatus (Méténier 1984), the precise involvement of actin in this process remains obscure.…”