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Hydrogen cycling by the unicellular marine diazotroph crocosphaera watsonii strain WH8501∇

Lookup NU author(s): Professor Sam Wilson

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Abstract

The hydrogen (H2) cycle associated with the dinitrogen (N 2) fixation process was studied in laboratory cultures of the marine cyanobacterium Crocosphaera watsonii. The rates of H2 production and acetylene (C2H2) reduction were continuously measured over the diel cycle with simultaneous measurements of fast repetition rate fluorometry and dissolved oxygen. The maximum rate of H2 production was coincident with the maximum rates of C2H2 reduction. Theoretical stoichiometry for N2 fixation predicts an equimolar ratio of H2 produced to N2 fixed. However, the maximum rate of net H2 production observed was 0.09 nmol H2 μg chlorophyll a (chl a)-1 h-1 compared to the N2 fixation rate of 5.5 nmol N2 μg chl a-1 h-1, with an H2 production/N2 fixation ratio of 0.02. The 50-fold discrepancy between expected andobserved rates of H2 production was hypothesized to be a result of H2 reassimilation by uptake hydrogenase. This was confirmed by the addition of carbon monoxide (CO), a potent inhibitor of hydrogenase, which increased net H2 production rates ∼40-fold to amaximumrate of 3.5 nmol H2 μg chl a -1 h-1. We conclude that the reassimilation of H 2 by C. watsonii is highly efficient (>98%) and hypothesize that the tight coupling between H2 production and consumption is a consequence of fixing N2 at nighttime using a finite pool of respiratory carbon and electrons acquired from daytime solar energy capture. The H2 cycle provides unique insight into N2 fixation and associated metabolic processes in C. watsonii. © 2010 American Society for Microbiology.

Publication metadata

Author(s): Wilson ST, Tozzi S, Foster RA, Ilikchyan I, Kolber ZS, Zehr JP, Karl DM

Publication type: Article

Publication status: Published

Journal: Applied and Environmental Microbiology

Year: 2010

Volume: 76

Issue: 20

Pages: 6797-6803

Print publication date: 13/08/2010

Online publication date: 13/08/2010

ISSN (print): 0099-2240

ISSN (electronic): 1098-5336

Publisher: American Society for Microbiology

URL: https://doi.org/10.1128/AEM.01202-10

DOI: 10.1128/AEM.01202-10

PubMed id: 20709832

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