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

• Main Authors: Gauglitz, Julia M. (Author), Follows, Michael J (Author)
• Other Authors: Massachusetts Institute of Technology. Department of Biology (Contributor), Woods Hole Oceanographic Institution (Contributor), Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences (Contributor)
• Format: Article
• Language: English
• Published: American Society for Microbiology, 2020-05-19T15:44:26Z.
• Subjects: Article
• Online Access: Get fulltext

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.
Gordon and Betty Moore Foundation (Grant GBMF 3778)
National Science Foundation (U.S.) (Grant OCE-1558702)
National Science Foundation (U.S.) (Grant OCE-PRF 1421196)
Simons Foundation. Postdoctoral Fellowship in Marine Microbial Ecology (Award 544338)
Simons Foundation. Simons Collaboration on Ocean Processes and Ecology (Award 544338)
Simons Foundation. Simons Collaboration on Ocean Processes and Ecology (Award 329108)
Simons Foundation. Simons Collaboration on Computational Biogeochemical Modeling of Marine Ecosystems (Award 549931)