Exogenous Factors Affecting Respiration in Tetrahymena pyriformis*

Abstract

SYNOPSIS. Respiration of Tetrahymena pyriformis W, grown in Proteose peptone‐glucose medium, was determined by Warburg's direct and indirect methods. The Qo2 varied inversely with cell concentration under exogenous conditions (cells in conditioned medium, i.e., one which had supported growth) as determined by both methods, and under endogenous conditions (washed cells suspended in salts solution) when determined by the indirect method. Endogenous respiration, measured by the direct method, was low but independent of cell concentration.Respiration, determined by the direct method, was little affected by lowered O2 availability, but varied directly with nutrient availability. The inhibitor, malonate, which also stimulates respiration at greater dilutions, inhibited respiration at 10−2M when present with low cell concentrations, but stimulated at high cell concentrations.The reduced respiration at higher cell concentrations is thought less due to lack of O2 than to CO2 accumulation and competition for nutrients. Consideration of these variables is essential in comparing data from the literature.