Dual capacity for nutrient uptake in tetrahymena importance of the oral uptake system for Fe and Cu uptake

Abstract

We have reported that a mutant of Tetrahymenapyriformis with heat-sensitive development of the oral apparatus can be grown indefinitely without food vacuoles if the medium is supplemented with folinic acid and a mixture of trace metal salts. We report here that the trace metal mixture can be replaced completely and specifically by salts of iron and copper. Fe(ll) and Fe(lll) are interchangeable. Addition of citrate has proven useful to reduce precipitate formation and improve the reproducibility of growth of the mutant cell. Thus it appears to serve as an Fe buffer. From the increased concentrations of Fe and Cu required to permit good growth of the mutant strain at 37~ we conclude that the oral uptake system plays a much more important role in the case of these two metals than the surface uptake system. The oral uptake system may facilitate Fe uptake in at least two ways: a) by a mechanical concentration of precipitates affected by the ciliary membranelles surrounding the oral cavity and, b) by lowering of the pH of the food vacuole and thereby releasing Fe from precipitates and from complexes which cannot be transported across the membrane as such. The second factor may also be important in Cu uptake. A specific effect of Mg and Fe uptake or retention in the mutant strain growing without food vacuoles has been detected. The significance of this effect remains unclear. Practical implications of the findings are discussed.

Nutrient uptake in Tetrahymena pyriformis

“…Few investigators have compared the contribution of the food vacuoles to total nutrient uptake of T. pyriformis (LWOFF (55), SEAMAN (98,99), PRUETT, CONNER & PRUETT (77), NILSSON (63), RASMUSSEN (79,80), RASMUSSEN • OR1AS (84,85) and ORIAS & RASMUSSEN (71,72)). There are, therefore, no reasonably detailed descriptions of nutrient uptake for this cell.…”

Utilization of iron complexes in an animal cell

“…The synthetic nutrient medium consists of amino acids, glucose, vitamins, salts, citrate, nucleosides, and trace metals (Holz et al, 1962;Rasmussen and Modeweg-Hansen, 1973;Orias and Pollock, 1975;Rasmussen and Orias, 1976). DIII was maintained in synthetic medium containing 3 pM ferric chloride, but no citrate (Suhr-Jessen and Rasmussen, 19821, and starved for iron when also ferric chloride was excluded.…”

“…This combined with the use of mutants with temperature-sensitive capacity for food vacuole formation allows an assessment of the role of the different cellular uptake mechanisms (Rasmussen and Orias, 1976;Orias and Rasmussen, 1977;Suhr-Jessen and Rasmussen, 1982;Rasmussen et al, 1984). Here we examine the Fe(II1) requirement and toxicity in the presence and absence of iron chelators.…”

“…Uptake of ferritin and tris-acetylacetonato-Fe(lll) is independent of food vacuole formation and seems to occur by micropinocytosis and by plasma membrane translocation, respectively.The synthetic nutrient medium for the ciliate Tetrahyrnena offers excellent opportunities for studies on the interrelations between components of the medium and their effects on the cells. This combined with the use of mutants with temperature-sensitive capacity for food vacuole formation allows an assessment of the role of the different cellular uptake mechanisms (Rasmussen and Orias, 1976;Orias and Rasmussen, 1977;Suhr-Jessen and Rasmussen, 1982;Rasmussen et al, 1984). Here we examine the Fe(II1) requirement and toxicity in the presence and absence of iron chelators.…”

“…Population densities were determined in aseptically removed samples 18 and 42 hours after inoculation by the use of a calibrated electronic cell counter. Cell densities were converted to number of doublings, and the data presented are average values of at least six and most often more than ten independent experiments spaced weeks apart.The synthetic nutrient medium consists of amino acids, glucose, vitamins, salts, citrate, nucleosides, and trace metals (Holz et al, 1962;Rasmussen and Modeweg-Hansen, 1973;Orias and Pollock, 1975;Rasmussen and Orias, 1976). DIII was maintained in synthetic medium containing 3 pM ferric chloride, but no citrate (Suhr-Jessen and Rasmussen, 19821, and starved for iron when also ferric chloride was excluded.…”