Respiration rates in heterotrophic, free-living protozoa

Abstract

Published estimates of protozoan respiratory rates are reviewed with the object of clarifying their value in ecological studies. The data show a surprisingly large variance when similarly sized cells or individual species are compared. This is attributed to the range of physiological states in the cells concerned. The concept of basal metabolism has little meaning in protozoa. During balanced growth, energy metabolism is nearly linearly proportional to the growth rate constant; at the initiation of starvation, metabolic rate rapidly declines. Motility requires an insignificant fraction of the energy budget of protozoans. For growing cells, metabolic rate is approximately proportional to weight(0.75) and the data fall nearly exactly on a curve extrapolated from that describing the respiration rates of poikilotherm metazoans as a function of body weight. It is conceivable that protozoan species exist with lower maximum potential growth and metabolic rates than those predicted from cell volume and the equations derived from the available data. However, the lack of information concerning the state of the cells studied prevents verification of this idea. Laboratory measurements of protozoan respiratory rates have no predictive value for protozoa in nature other than delimiting a potential range. For small protozoans, this range may, on an individual basis, represent a factor of 50.

Metabolic rate links density to demography in Tetrahymena pyriformis

“…The relationship was linear, which is consistent with Fenchel and Finlay's (1983) observation that production is linearly related to metabolic rate in protists. As expected, as metabolism fuels production (Brown and Sibly, 2006), individuals had the highest metabolic rates and highest division rates at low densities.…”

“…As body mass has a strong effect on B pc across species (Fenchel and Finlay, 1983), we checked to see whether the decrease in metabolic rate was due to declining cell size. Volume decreased nonsignificantly (P40.25) throughout the course of the experiment (Figure 4a).…”

“…That the data are well predicted by our resource-distribution model strongly implicates this interpretation. In addition, a series of studies with protists showed that starvation can reduce B pc up to about an order of magnitude, indicating that access to food resources has a direct and rapid effect on the energy use of these organisms (Fenchel and Finlay, 1983). Unlike earlier studies that measured starvation-state respiration rates by transferring individuals into a non-nutrient media, we measured metabolic rates of an active population growing in response to a fixed rate of food provisioning.…”

Water column anoxia: vertical zonation of planktonic protozoa

“…In the case of ciliates the length and diameter of individual species were measured and it was assumed that they have an ellipsoidal shape. These results are here presented as g organic carbon, assuming 0.09 g C ml-' for bacteria (Ferguson & Rublee 1976) and 0.07 g C ml-' for protozoa (Fenchel & Finlay 1983).…”

Mean mass-specific metabolic rates are strikingly similar across life's major domains: Evidence for life's metabolic optimum

“…However, these studies have mostly focused on the scaling of metabolic rate, rather than on the absolute magnitudes of metabolic rates; key groups such as prokaryotes, invertebrates, algae, or vascular plants were typically poorly represented; and, finally, unlike the larger animals, the smallest species were included into analyses without controlling for their physiological state. Because metabolic rates of growing unicells are much higher (at least 10-20 times) than endogenous rates, their comparison with the standard metabolic rates of larger species is a source of significant systematic errors in interpreting the dependence of metabolic rate on body size (19)(20)(21).…”