Carbon Transfer from the Host Diatom Enables Fast Growth and High Rate of N-2 Fixation by Symbiotic Heterocystous Cyanobacteria

0524463 - MBÚ 2021 RIV CH eng J - Journal Article
Inomura, K. - Follett, C.L. - Masuda, Takako - Eichner, Meri - Prášil, Ondřej - Deutsch, C.
Carbon Transfer from the Host Diatom Enables Fast Growth and High Rate of N-2 Fixation by Symbiotic Heterocystous Cyanobacteria.
Plants. Roč. 9, č. 2 (2020), č. článku 192. E-ISSN 2223-7747
R&D Projects: GA ČR GA16-15467S; GA MŠMT(CZ) LO1416
Institutional support: RVO:61388971
Keywords : DDA * nitrogen fixation * diatom
OECD category: Microbiology
Impact factor: 3.935, year: 2020
Method of publishing: Open access
https://www.mdpi.com/2223-7747/9/2/192

Diatom-diazotroph associations (DDAs) are symbioses where trichome-forming cyanobacteria support the host diatom with fixed nitrogen through dinitrogen (N-2) fixation. It is inferred that the growth of the trichomes is also supported by the host, but the support mechanism has not been fully quantified. Here, we develop a coarse-grained, cellular model of the symbiosis between Hemiaulus and Richelia (one of the major DDAs), which shows that carbon (C) transfer from the diatom enables a faster growth and N-2 fixation rate by the trichomes. The model predicts that the rate of N-2 fixation is 5.5 times that of the hypothetical case without nitrogen (N) transfer to the host diatom. The model estimates that 25% of fixed C from the host diatom is transferred to the symbiotic trichomes to support the high rate of N-2 fixation. In turn, 82% of N fixed by the trichomes ends up in the host. Modeled C fixation from the vegetative cells in the trichomes supports only one-third of their total C needs. Even if we ignore the C cost for N-2 fixation and for N transfer to the host, the total C cost of the trichomes is higher than the C supply by their own photosynthesis. Having more trichomes in a single host diatom decreases the demand for N-2 fixation per trichome and thus decreases their cost of C. However, even with five trichomes, which is about the highest observed for Hemiaulus and Richelia symbiosis, the model still predicts a significant C transfer from the diatom host. These results help quantitatively explain the observed high rates of growth and N-2 fixation in symbiotic trichomes relative to other aquatic diazotrophs.
Permanent Link: http://hdl.handle.net/11104/0308823