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Quantifying oxygen management and temperature and light dependencies of nitrogen fixation by Crocosphaera watsonii

Lookup NU author(s): Professor Sam Wilson

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).

Abstract

© 2019 Inomura et al. Crocosphaera is a major dinitrogen (N2)-fixing microorganism, providing bioavailable nitrogen (N) to marine ecosystems. The N2-fixing enzyme nitrogenase is deactivated by oxygen (O2), which is abundant in marine environments. Using a cellular scale model of Crocosphaera sp. and laboratory data, we quantify the role of three O2 management strategies by Crocosphaera sp.: size adjustment, reduced O2 diffusivity, and respiratory protection. Our model predicts that Crocosphaera cells increase their size under high O2. Using transmission electron microscopy, we show that starch granules and thylakoid membranes are located near the cytoplasmic membranes, forming a barrier for O2. The model indicates a critical role for respiration in protecting the rate of N2 fixation. Moreover, the rise in respiration rates and the decline in ambient O2 with temperature strengthen this mechanism in warmer water, providing a physiological rationale for the observed niche of Crocosphaera at temperatures exceeding 20°C. Our new measurements of the sensitivity to light intensity show that the rate of N2 fixation reaches saturation at a lower light intensity (∼100 μmol m-2 s-1) than photosynthesis and that both are similarly inhibited by light intensities of 500 μmol m-2 s-1. This suggests an explanation for the maximum population of Crocosphaera occurring slightly below the ocean surface.

Publication metadata

Author(s): Inomura K, Deutsch C, Wilson ST, Masuda T, Lawrenz E, Lenka B, Sobotka R, Gauglitz MA, Saito JF, Prasil O, Follows MJ

Publication type: Article

Publication status: Published

Journal: mSphere

Year: 2019

Volume: 4

Issue: 6

Print publication date: 18/12/2019

Online publication date: 11/12/2019

Acceptance date: 06/11/2019

Date deposited: 16/12/2021

ISSN (electronic): 2379-5042

Publisher: American Society for Microbiology

URL: https://doi.org/10.1128/mSphere.00531-19

DOI: 10.1128/mSphere.00531-19

PubMed id: 31826967

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