Biochemical mechanism of phosphorus limitation impairing nitrogen fixation in diazotrophic bacterium <i>Klebsiella variicola</i> W12

Abstract

Abstract Introduction Biological nitrogen (N) fixation (BNF) plays a key role in nitrogen supply in agricultural and natural ecosystems. Harnessing BNF can substantially reduce dependence on chemical fertilizer in agroecosystems and hence can contribute to sustainable agriculture. However, a number of field studies have demonstrated that BNF can be largely suppressed in phosphorus (P)‐deficient environments, while the underlying mechanism is not well understood. Materials &amp; Methods In this study, comparative proteomics and lipidomics analyses were conducted on a diazotrophic bacterium Klebsiella variicola W12 under P‐deficient and P‐replete conditions to gain insight into how P availability affects N fixation. Results Under P deficiency, N fixation activity of K. variicola W12 was severely repressed. In response to P limitation, the bacterium synthesized P‐free ornithine lipids to replace glycerophospholipids in its membrane to reduce cellular demand for P. Comparative proteomics showed that P limitation resulted in upregulation of the PhoBR two‐component system, a range of organic and inorganic P uptake and transport systems, while nitrogenase and N‐fixation‐related transcriptional regulators NifL and NifA were downregulated. Conclusion These results revealed lipid renovation as an adaptation strategy for N 2 ‐fixing microbes to survive under P stress and provided biochemical evidence on how P availability regulates BNF. A conceptual model of N–P coupling at the microbial metabolism level is therefore proposed. Our study provides a simple yet plausible explanation of how P deficiency suppresses BNF observed in the field and highlights the importance of regulating P availability to maximize the potential of BNF in agroecosystems for agriculture sustainable production.

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