Department of Biology, Washington University, St. Louis, MO, USA.
Department of Chemical Engineering, University of Toronto, Toronto, ON, Canada.
Nat Commun. 2024 May 2;15(1):3712. doi: 10.1038/s41467-024-48039-0.
The discovery of nitrogen fixation in unicellular cyanobacteria provided the first clues for the existence of a circadian clock in prokaryotes. However, recalcitrance to genetic manipulation barred their use as model systems for deciphering the clock function. Here, we explore the circadian clock in the now genetically amenable Cyanothece 51142, a unicellular, nitrogen-fixing cyanobacterium. Unlike non-diazotrophic clock models, Cyanothece 51142 exhibits conspicuous self-sustained rhythms in various discernable phenotypes, offering a platform to directly study the effects of the clock on the physiology of an organism. Deletion of kaiA, an essential clock component in the cyanobacterial system, impacted the regulation of oxygen cycling and hindered nitrogenase activity. Our findings imply a role for the KaiA component of the clock in regulating the intracellular oxygen dynamics in unicellular diazotrophic cyanobacteria and suggest that its addition to the KaiBC clock was likely an adaptive strategy that ensured optimal nitrogen fixation as microbes evolved from an anaerobic to an aerobic atmosphere under nitrogen constraints.
在单细胞蓝藻中发现固氮作用为原核生物中存在生物钟提供了第一个线索。然而，由于其遗传操作的顽固性，它们无法作为解析时钟功能的模型系统。在这里，我们探索了现在具有遗传可操作性的单细胞固氮蓝藻 Cyanothece 51142 的生物钟。与非固氮生物钟模型不同，Cyanothece 51142 在各种可识别的表型中表现出明显的自我维持节律，为直接研究时钟对生物体生理学的影响提供了一个平台。在蓝藻系统中，kaiA 是一个必需的生物钟组件，kaiA 的缺失会影响氧循环的调节，并阻碍固氮酶的活性。我们的发现表明，生物钟的 KaiA 组件在调节单细胞固氮蓝藻的细胞内氧动力学方面发挥作用，并表明其与 KaiBC 时钟的添加可能是一种适应性策略，确保了微生物在氮限制下从厌氧环境向需氧环境进化过程中最佳的固氮作用。
