Low-Ammonium Environment Increases the Nutrient Exchange between Diatom-Diazotroph Association Cells and Facilitates Photosynthesis and N2 Fixation-a Mechanistic Modeling Analysis

Meng Gao; Gabrielle Armin; Keisuke Inomura

doi:10.3390/cells11182911

Low-Ammonium Environment Increases the Nutrient Exchange between Diatom-Diazotroph Association Cells and Facilitates Photosynthesis and N₂ Fixation-a Mechanistic Modeling Analysis

Cells. 2022 Sep 17;11(18):2911. doi: 10.3390/cells11182911.

Authors

Meng Gao¹, Gabrielle Armin¹, Keisuke Inomura¹

Affiliation

¹ Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882, USA.

Abstract

Diatom-diazotroph associations (DDAs) are one of the most important symbiotic dinitrogen (N₂) fixing groups in the oligotrophic ocean. Despite their capability to fix N₂, ammonium (NH₄⁺) remains a key nitrogen (N) source for DDAs, and the effect of NH₄⁺ on their metabolism remains elusive. Here, we developed a coarse-grained, cellular model of the DDA with NH₄⁺ uptake and quantified how the level of extracellular NH₄⁺ influences metabolism and nutrient exchange within the symbiosis. The model shows that, under a fixed growth rate, an increased NH₄⁺ concentration may lower the required level of N₂ fixation and photosynthesis, and decrease carbon (C) and N exchange. A low-NH₄⁺ environment leads to more C and N in nutrient exchange and more fixed N₂ to support a higher growth rate. With higher growth rates, nutrient exchange and metabolism increased. Our study shows a strong effect of NH₄⁺ on metabolic processes within DDAs, and thus highlights the importance of in situ measurement of NH₄⁺ concentrations.

Keywords: DDA; ammonium; carbon; cell flux model; diatom; diazotroph; nitrogen; nitrogen fixation; nutrient exchange; photosynthesis.

Publication types

Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

Ammonium Compounds*
Carbon
Diatoms* / metabolism
Nitrogen / metabolism
Nitrogen Fixation
Nutrients
Photosynthesis

Substances

Ammonium Compounds
Carbon
Nitrogen

Grants and funding

This research was funded by the U.S. National Science Foundation (subaward SUB0000525 from Princeton to KI) and the Rhode Island Science and Technology Advisory Council (AWD10732).