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Ecology Letters is a leading ecological journal
Science Editors' Choice March 4, 2011
Biochemistry
Nicholas S. Wigginton
In the mid-20th century, Alfred Redfield posited that the bulk ratio of nitrogen to phosphorus atoms (N:P) in marine microorganisms should maintain a relatively constant value of ∼16. Work since then has shown that the ratio indeed remains relatively constant across many environments and time scales, including deep oceans and coastal waters, but questions remain about whether innate biochemical or environmental factors are responsible. Loladze and Elser compiled literature values of nutrient ratios in prokaryotic and eukaryotic microorganisms, which, combined with a theoretical model, suggest that the N:P ratio is determined by a balance of maximum macromolecule biosynthesis rates—specifically for nitrogen-rich proteins and phosphorus-rich ribosomal RNA. Although the analysis considered cases in which growth rates were optimal, an N:P ratio of ∼16 isn't necessarily always desirable for efficient growth; communities in environments where the paucity of nitrogen or phosphorus limits growth may have optimal N:P ratios that are shifted away from 16. Because one of these two nutrients is often the main limiting growth factor in aquatic and terrestrial systems, observable deviations in N:P ratios would therefore provide insight into the biogeochemical processes that shape microbial community structure.
Loladze, I. and Elser J.J. (2011) The origins of the Redfield nitrogen-to-phosphorus ratio are in a homeostatic protein:rRNA ratio, Ecology Letters, 14, 244-250
Loladze, I. and Elser J.J. (2011) The origins of the Redfield nitrogen-to-phosphorus ratio are in a homeostatic protein:rRNA ratio, Ecology Letters, 14, 244-250
Abstract.
One of the most intriguing patterns in the biosphere is the similarity of the atomic nitrogen-to-phosphorus ratio (N:P) = 16 found in waters throughout the deep ocean and in the plankton in the upper ocean. Although A.C. Redfield proposed in 1934 that the intracellular properties of plankton were central to this pattern, no theoretical significance for N:P = 16 in cells had been found. Here, we use theoretical modelling and a compilation of literature data for prokaryotic and eukaryotic microbes to show that the balance between two fundamental processes, protein and rRNA synthesis, results in a stable biochemical attractor that homoeostatically produces a given protein:rRNA ratio. Furthermore, when biochemical constants and reasonable kinetic parameters for protein synthesis and ribosome production under nutrient-replete conditions are applied in the model, it predicts a stable protein:rRNA ratio of 3 ± 0.7, which corresponds to N:P = 16 ± 3. The model also predicts that N-limitation, by constraining protein synthesis rates, will result in N:P ratios below the Redfield value while P-limitation, by constraining RNA production rates, will produce ratios above the Redfield value. Hence, one of most biogeochemically significant patterns on Earth is inherently rooted in the fundamental structure of life.
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