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Title: Evaluation of argon‐induced hydrogen production as a method to measure nitrogen fixation by cyanobacteria

The production of dihydrogen (H2) is an enigmatic yet obligate component of biological dinitrogen (N2) fixation. This study investigates the effect on H2production by N2fixing 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 N2fixation 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 H2production were obtained for N2fixing cyanobacteria despite the absence of N2that broadly reproduced the temporal patterns observed by the AR assay. Comparison of H2production under air versus Ar:O2:CO2revealed the efficiency of electron usage during N2fixation 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.

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Journal Name:
Journal of Phycology
Page Range / eLocation ID:
p. 863-873
Medium: X
Sponsoring Org:
National Science Foundation
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