Zeng Yan, Cui Lingwei, Wang Mengmei, Huang Lu, Jiang Mingyue, Liu Ying, Gao Yongqiang, Zheng Yanning
State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.
College of Life Sciences, University of the Chinese Academy of Sciences, Beijing, China.
Appl Environ Microbiol. 2025 May 21;91(5):e0046525. doi: 10.1128/aem.00465-25. Epub 2025 Apr 10.
In addition to catalyzing the biological nitrogen fixation, iron-only (Fe-only) nitrogenase is also able to reduce carbon dioxide (CO) to formate (HCOO) and methane (CH). AnfA is responsible for the transcriptional activation of the gene cluster for Fe-only nitrogenase, whose expression is repressed by fixed nitrogen. However, it remains unclear how AnfA is regulated to control the expression of Fe-only nitrogenase. Here, we found that in , P proteins play a critical role in regulating the expression of Fe-only nitrogenase genes via AnfA. We hypothesize that the deuridylylated P protein GlnK1, which was upregulated in the presence of ammonium (NH), could inhibit AnfA activity by forming a potential AnfA-GlnK1 complex. This likely serves as a fail-safe mechanism to prevent from expressing Fe-only nitrogenase when AnfA is accidentally expressed under nitrogen-excess conditions. The uridylylated P protein GlnK2, which was upregulated in response to nitrogen starvation, stimulated the expression of an active AnfA hexamer that further activated the expression of Fe-only nitrogenase under nitrogen-fixing and Mo-free conditions. This study provides new insights into the regulation of Fe-only nitrogenase in .IMPORTANCEThe expression and maturation of nitrogenase are tightly regulated by ambient nitrogen levels, which limits the persistence and efficiency of biological nitrogen fixation. This study offers new insights into the regulatory mechanism of AnfA by P proteins in . Understanding the regulation of AnfA, the transcriptional activator of the Fe-only nitrogenase gene cluster, could provide strategies to better control the expression of iron-only nitrogenase. Nitrogen-fixing bacteria that constitutively express iron-only nitrogenase have the potential to be developed into promising biofertilizers, as their nitrogen-fixing activity is enhanced and independent of molybdenum availability in the soil.
除了催化生物固氮作用外，仅含铁（Fe-only）的固氮酶还能够将二氧化碳（CO）还原为甲酸（HCOO）和甲烷（CH）。AnfA负责仅含铁固氮酶基因簇的转录激活，其表达受到固定态氮的抑制。然而，目前尚不清楚AnfA是如何被调控以控制仅含铁固氮酶的表达的。在这里，我们发现，在[具体物种]中，P蛋白在通过AnfA调控仅含铁固氮酶基因的表达中起关键作用。我们推测，在铵（NH）存在下上调的去尿苷酸化P蛋白GlnK1可能通过形成潜在的AnfA-GlnK1复合物来抑制AnfA活性。这可能是一种故障安全机制，以防止[具体物种]在氮过量条件下意外表达AnfA时表达仅含铁固氮酶。响应氮饥饿而上调的尿苷酸化P蛋白GlnK2刺激了活性AnfA六聚体的表达，该六聚体在固氮和无钼条件下进一步激活了仅含铁固氮酶的表达。这项研究为[具体物种]中仅含铁固氮酶的调控提供了新的见解。
重要性
固氮酶的表达和成熟受到环境氮水平的严格调控，这限制了生物固氮的持续性和效率。这项研究为[具体物种]中P蛋白对AnfA的调控机制提供了新的见解。了解仅含铁固氮酶基因簇的转录激活因子AnfA的调控机制，可为更好地控制仅含铁固氮酶的表达提供策略。组成型表达仅含铁固氮酶的固氮细菌有潜力被开发成为有前景的生物肥料，因为它们的固氮活性增强且不依赖于土壤中钼的可用性。
