Energetics of the smallest: Do bacteria breathe at the same rate as whales?

Abstract

Power laws describing the dependence of metabolic rate on body mass have been established for many taxa, but not for prokaryotes, despite the ecological dominance of the smallest living beings. Our analysis of 80 prokaryote species with cell volumes ranging more than 1,000,000-fold revealed no significant relationship between mass-specific metabolic rate q and cell mass. By absolute values, mean endogenous mass-specific metabolic rates of non-growing bacteria are similar to basal rates of eukaryote unicells, terrestrial arthropods and mammals. Maximum mass-specific metabolic rates displayed by growing bacteria are close to the record tissue-specific metabolic rates of insects, amphibia, birds and mammals. Minimum mass-specific metabolic rates of prokaryotes coincide with those of larger organisms in various energy-saving regimes: sit-and-wait strategists in arthropods, poikilotherms surviving anoxia, hibernating mammals. These observations suggest a size-independent value around which the mass-specific metabolic rates vary bounded by universal upper and lower limits in all body size intervals.

Figure 1

Limits and scopes of mass-specific metabolic rate in the living organisms. Solid and open circles: endogenous and growth mass-specific metabolic rates of prokaryotes. Boxes, diamonds and triangles (MIN): metabolic rates of eukaryotes in various energy-saving regimes. Dotted circles (MAX): record mass-specific metabolic rates per unit working tissue mass during peak activities in various organisms. Asterisks: basal metabolic rates of whales and elephants. Solid lines: fitted equations for endogenous/standard/basal metabolic rate in, U, unicellular eukaryotes at 20 °C (Vladimirova & Zotin 1985), A, terrestrial arthropods at 25 °C (Lighton et al. 2001) and, M, mammals (Peters 1983), respectively. P, prokaryotes. Crossed circles: standard metabolic rate corresponding to body size class with maximum species numbers in terrestrial arthropods and mammals; mean endogenous respiration of the studied prokaryotes and unicellular eukaryotes (Vladimirova & Zotin 1985). Dashed lines: the uniform minimum, maximum and hypothesized optimum values of mass-specific metabolic rate of the living matter. Numeric values and literature sources for all points shown in the figure are given in the Electronic Appendix.