The production of dihydrogen (H₂) is an enigmatic yet obligate component of biological dinitrogen (N₂) fixation. This study investigates the effect on H₂ production by N₂ fixing cyanobacteria when they are exposed to either air or a gas mixture consisting of argon, oxygen, and carbon dioxide (Ar:O₂:CO₂). In the absence of N₂, nitrogenase diverts the flow of electrons to the production of H₂, which becomes a measure of Total Nitrogenase Activity (TNA). This method of argon-induced hydrogen production (AIHP) is much less commonly used to infer rates of N₂ fixation than the acetylene reduction (AR) assay. We provide here a full evaluation of the AIHP method and demonstrate its ability to achieve high-resolution measurements of TNA in a gas exchange flow-through system. Complete diel profiles of H₂ production were obtained for N₂ fixing cyanobacteria despite the absence of N₂ that broadly reproduced the temporal patterns observed by the AR assay. Comparison of H₂ production under air versus Ar:O₂:CO₂ revealed the efficiency of electron usage during N₂ fixation and place these findings in the broader context of cell metabolism. Ultimately, AIHP is demonstrated to be a viable alternative to the AR assay with several additional merits that provide an insight into cell physiology and promise for successful field application.

中文翻译：

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评估氩气诱导制氢作为测量蓝藻固氮的方法

二氢 (H ₂ ) 的产生是生物二氮 (N ₂ ) 固定的一个神秘但必须的组成部分。本研究调查了当N ₂固定蓝藻暴露于空气或由氩气、氧气和二氧化碳 (Ar:O ₂ :CO ₂ )组成的气体混合物时，它们对 H ₂产生的影响。在不存在 N ₂的情况下，固氮酶将电子流转移到 H ₂的产生，H ₂成为总氮酶活性 (TNA) 的量度。这种氩气诱导制氢 (AIHP) 方法很少用于推断 N _{2 的}速率固定比乙炔还原 (AR) 测定法。我们在此提供对 AIHP 方法的全面评估，并展示其在气体交换流通系统中实现 TNA 高分辨率测量的能力。尽管不存在 N ₂，但仍获得了 N ₂固定蓝藻的 H ₂生产的完整日照分布图，N ₂广泛再现了 AR 测定观察到的时间模式。空气下H ₂产量与 Ar:O ₂ :CO _{2 的比较}揭示了 N ₂期间电子使用的效率固定并将这些发现置于更广泛的细胞代谢背景下。最终，AIHP 被证明是 AR 测定的可行替代方案，具有几个额外的优点，可提供对细胞生理学的深入了解并有望成功进行现场应用。