Respiration rates in heterotrophic, free-living protozoa

Area of Science:

• Microbiology
• Ecological Physiology
• Cellular Respiration

Background:

• Published estimates of protozoan respiratory rates exhibit significant variance.
• This variability is primarily attributed to diverse physiological states within protozoan cells.
• The concept of basal metabolism is not directly applicable to protozoa.

Purpose of the Study:

• To review published estimates of protozoan respiratory rates.
• To clarify the ecological significance of these respiratory rates.
• To identify factors influencing metabolic rates in protozoa.

Main Methods:

• Review and analysis of existing literature on protozoan respiration.
• Comparison of respiratory rates across different protozoan species and sizes.
• Examination of the relationship between metabolic rate, growth rate, and body weight.

Main Results:

• Metabolic rate is linearly proportional to growth rate during balanced growth.
• Metabolic rate declines sharply at the onset of starvation.
• For growing cells, metabolic rate scales with weight^0.75, aligning with poikilotherm data.
• Motility accounts for a negligible portion of the protozoan energy budget.

Conclusions:

• Laboratory-derived protozoan respiratory rates provide a potential range but limited predictive power for natural populations.
• Physiological state is a critical determinant of metabolic rate, overshadowing cell size or species in some cases.
• Further research is needed on the physiological status of cells to refine metabolic rate predictions.