Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, United States of America.
National Herbarium of New South Wales, The Royal Botanic Gardens and Domain Trust, Sydney, NSW, Australia.
PLoS One. 2018 Nov 29;13(11):e0208282. doi: 10.1371/journal.pone.0208282. eCollection 2018.
Nitrogen fixation provides bioavailable nitrogen, supporting global ecosystems and influencing global cycles of other elements. It provides an additional source of nitrogen to organisms at a cost of lower growth efficiency, largely due to respiratory control of intra-cellular oxygen. Nitrogen-fixing bacteria can, however, utilize both dinitrogen gas and fixed nitrogen, decreasing energetic costs. Here we present an idealized metabolic model of the heterotrophic nitrogen fixer Azotobacter vinelandii which, constrained by laboratory data, provides quantitative predictions for conditions under which the organism uses either ammonium or nitrogen fixation, or both, as a function of the relative supply rates of carbohydrate, fixed nitrogen as well as the ambient oxygen concentration. The model reveals that the organism respires carbohydrate in excess of energetic requirements even when nitrogen fixation is inhibited and respiratory protection is not essential. The use of multiple nitrogen source expands the potential niche and range for nitrogen fixation. The model provides a quantitative framework which can be employed in ecosystem and biogeochemistry models.
固氮为全球生态系统提供了生物可利用的氮，并影响了其他元素的全球循环。它为生物体提供了额外的氮源，但代价是生长效率降低，这主要是由于细胞内氧气的呼吸控制。然而，固氮细菌可以利用二氮气体和固定氮，从而降低能量成本。在这里，我们提出了异养固氮菌 Azotobacter vinelandii 的理想化代谢模型，该模型受实验室数据的限制，可以对生物体在使用铵或固氮或两者作为碳水化合物、固定氮以及环境氧浓度相对供应率的函数的条件下进行定量预测。该模型表明，即使在氮固定受到抑制且不需要呼吸保护时，生物体也会过度呼吸碳水化合物以满足能量需求。使用多种氮源扩大了固氮的潜在生态位和范围。该模型提供了一个定量框架，可以用于生态系统和生物地球化学模型。
