Thermodynamics Underpinning the Microbial Community-Level Nitrogen Energy Metabolism.

Nitrogen compounds often serve as crucial electron donors and acceptors in microbial energy metabolism, playing a key role in biogeochemical cycles. The energetic favorability of nitrogen oxidation-reduction (redox) reactions, driven by the thermodynamic properties of these compounds, may have shaped the evolution of microbial energy metabolism, though the extent of their influence remains unclear. This study quantitatively evaluated the similarity between energetically superior nitrogen reactions, identified from 988 theoretically plausible reactions, and the nitrogen community-level network, reconstructed as a combination of enzymatic reactions representing intracellular to interspecies-level reaction interactions. Our analysis revealed significant link overlap rates between these networks. Notably, composite enzymatic reactions aligned more closely with energetically superior reactions than individual enzymatic reactions. These findings suggest that selective pressure from the energetic favorability of redox reactions can operate primarily at the species or community level, underscoring the critical role of thermodynamics in shaping microbial metabolic networks and ecosystem functioning.