Optimization of biomass composition explains microbial growth-stoichiometry relationships

Area of Science:

• Microbial Ecology
• Biogeochemistry
• Theoretical Ecology

Background:

• Microbial physiology and biomass stoichiometry link microbial dynamics to ecosystem processes.
• The growth-rate hypothesis (GRH) predicts positive correlations between growth rate, RNA content, and biomass phosphorus (P) content.
• The conditions under which GRH applies to microorganisms are not fully understood.

Purpose of the Study:

• To develop a model explaining microbial biomass stoichiometry responses to variable resource stoichiometry.
• To test if growth maximization trade-offs explain GRH validity under different nutrient limitations.
• To investigate implications for microbial nutrient mineralization and cycling.

Main Methods:

• Developed a theoretical model of microbial growth and biomass stoichiometry.
• Tested model predictions against experimental data on bacterial macromolecular composition and biomass stoichiometry.
• Compared model outcomes to a strictly homeostatic biomass model.

Main Results:

• Mechanistically demonstrated why GRH is valid under P limitation but not N limitation.
• Showed lower variability in growth rate-biomass stoichiometry relationships under P limitation compared to N or C limitation.
• Supported theoretical results with experimental data from two bacterial species.

Conclusions:

• The proposed optimization mechanism explains GRH validity and variability under different nutrient limitations.
• This mechanism increases microbial nitrogen (N) and P mineralization during organic matter decomposition.
• Findings have significant implications for understanding nutrient cycling in ecosystems.