AUTHOR=Li Jin , Pan Hu , Yang Hui , Wang Chong , Liu Huhu , Zhou Hui , Li Peiwang , Li Changzhu , Lu Xiangyang , Tian Yun 

TITLE=Rhamnolipid Enhances the Nitrogen Fixation Activity of Azotobacter chroococcum by Influencing Lysine Succinylation

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.697963

DOI=10.3389/fmicb.2021.697963

ISSN=1664-302X

ABSTRACT=<p>The enhancement of nitrogen fixation activity of diazotrophs is essential for safe crop production. Lysine succinylation (K<sup>Suc</sup>) is widely present in eukaryotes and prokaryotes and regulates various biological process. However, knowledge of the extent of K<sup>Suc</sup> in nitrogen fixation of <italic>Azotobacter chroococcum</italic> is scarce. In this study, we found that 250 mg/l of rhamnolipid (RL) significantly increased the nitrogen fixation activity of <italic>A. chroococcum</italic> by 39%, as compared with the control. Real-time quantitative reverse transcription PCR (qRT-PCR) confirmed that RL could remarkably increase the transcript levels of <italic>nifA</italic> and <italic>nifHDK</italic> genes. In addition, a global K<sup>Suc</sup> of <italic>A. chroococcum</italic> was profiled using a 4D label-free quantitative proteomic approach. In total, 5,008 K<sup>Suc</sup> sites were identified on 1,376 succinylated proteins. Bioinformatics analysis showed that the addition of RL influence on the K<sup>Suc</sup> level, and the succinylated proteins were involved in various metabolic processes, particularly enriched in oxidative phosphorylation, tricarboxylic acid cycle (TCA) cycle, and nitrogen metabolism. Meanwhile, multiple succinylation sites on MoFe protein (NifDK) may influence nitrogenase activity. These results would provide an experimental basis for the regulation of biological nitrogen fixation with K<sup>Suc</sup> and shed new light on the mechanistic study of nitrogen fixation.</p>