Recently, the latest research of the microbial functional genomics team led by Professor Min Lin (Biotechnology Research Institute, Chinese Academy of Agricultural Sciences) indicated that the genome of root-associated bacterium Pseudomonas stutzeri A1501 contained a horizontal acquisition of a nitrogen-fixing (nif) island controlled by two regulatory networks of different evolutionary origins, and the non-coding RNA played an important role in optimizing nitrogen fixation. The related result was online published in the latest issue of the PNAS.

To our knowledge, the nitrogen-fixing bacteria from the rhizosphere possess a meticulous and rigorous regulatory system to adapt to the complex and changeable environment in the long-time evolutionary process. However, in the associative nitrogen-fixing bacteria, the mechanism of signal response is unclear and none of the non-coding RNAs have been described so far as being involved in the regulation of nitrogen fixation.

The molecular biology study showed that during evolution of P. stutzeri, NfiS was apparently recruited by nifK mRNA as a novel activator in response to specific environmental cues and optimized nitrogenase activity by affecting the mRNA stability and translation efficiency of nifK. This study provides a new regulatory pathway between stress resistance and nitrogen fixation mediated by an ncRNA for optimal nitrogen fixation. NfiS is the first described case of a bacterial small RNA involved in the regulation of nitrogenase activity via a direct base paring interaction and expected to be a candidate component for intelligent control of biological nitrogen fixation.

The further study revealed two major evolutionary events occurred in the process of the evolution of nitrogen fixing Pseudomonas: (1) Pseudomonas stutzeri A1501 fixes nitrogen following the horizontal acquisition of a nitrogen-fixing (nif) island; (2) Pseudomonas stutzeri A1501 optimizes the nitrogenase activities by a meticulous regulation of the recruited NfiS. The two major evolutionary events give the Pseudomonas stutzeri A1501 stronger adaptability to the environment. The discovery and regulatory mechanism of NfiS will lay the important theoretical foundation for breaking the restriction of carbon and nitrogen limiting factor of associative nitrogen fixation in field application, enhancing associative nitrogen fixing efficiency and the achievement of crop section of fertilizer production efficiency of non-leguminous crops.

This work was supported by the National Basic Research Program of China and National Science Foundation of China. Dr. Yuhua Zhan and Yongliang Yan are the co-first authors of the paper, and Professor Min Lin is the corresponding author.