Interacting Bioenergetic and Stoichiometric Controls on Microbial Growth

Microorganisms rely on the exchange of mass and energy with their surroundings to sustain growth. While carbon and nitrogen are central to microbial metabolism, their interplay with energy availability remains poorly understood. Prior research has shown that growth rates depend on the balance of carbon and nitrogen uptake. However, the combined effects of these factors under various environmental conditions remain unclear. This gap motivated the need for a unified theoretical framework. Existing models often treat carbon, nitrogen, and energy separately, which limits their predictive power. The lack of integration hinders accurate predictions of microbial responses to environmental changes. This study addresses the need for a holistic approach to microbial growth. Understanding these interactions is essential for modeling microbial activity in natural and engineered systems.

The aim of this study is to develop a theoretical framework that integrates carbon, nitrogen, and energy fluxes to predict microbial growth rates. Researchers sought to explore how these factors interact under different environmental conditions. The study focuses on scenarios where carbon, nitrogen, or energy is limited. By quantifying growth under these conditions, the authors aim to improve microbial growth modeling. The framework considers the stoichiometry of carbon and nitrogen uptake. It also accounts for the degree of reduction of organic matter and electron acceptor availability. The goal is to clarify how these factors jointly influence growth. This approach provides a more comprehensive view of microbial physiology.

The researchers developed a theoretical model that incorporates carbon, nitrogen, and energy fluxes. They used this model to simulate microbial growth under various limiting conditions. The framework accounts for the C:N ratio and the degree of reduction of organic matter. It also considers the availability of electron acceptors and nitrogen sources. The model was tested under oxic and anoxic conditions. The researchers compared growth rates when inorganic nitrogen sources were ammonium or nitrate. They evaluated how different electron acceptors affect growth efficiency. The model was validated against existing data on microbial metabolism.

The growth rate peaks at intermediate organic matter reduction under oxic and carbon-limited conditions. This peak is not observed under nitrogen-limited conditions. Ammonium as a nitrogen source yields higher growth rates than nitrate under oxic conditions. This is due to the energetic cost of nitrate reduction. Under anoxic conditions, denitrifiers and DNRA microbes show distinct growth responses. DNRA is favored under extreme nitrate limitation and reduced organic matter. Denitrifiers are favored when nitrate is abundant and organic matter is oxidized. Growth rates decrease when low-energy electron acceptors like sulfate are used.

The authors propose that bioenergetics provides a useful framework for predicting microbial growth rates. This approach integrates carbon, nitrogen, and energy fluxes to explain growth under various conditions. The model explains how the degree of organic matter reduction affects growth. It also clarifies the role of nitrogen sources and electron acceptors in growth dynamics. The findings suggest that ammonium is more efficient than nitrate under oxic conditions. The model supports the idea that DNRA and denitrification are favored under different resource conditions. The results highlight the importance of considering both stoichiometry and energy availability. This framework offers a more accurate way to model microbial growth in complex environments.