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  1. Article ; Online: Author Correction

    Takako Masuda / Keisuke Inomura / Naoto Takahata / Takuhei Shiozaki / Yuji Sano / Curtis Deutsch / Ondřej Prášil / Ken Furuya

    Communications Biology, Vol 6, Iss 1, Pp 1-

    Heterogeneous nitrogen fixation rates confer energetic advantage and expanded ecological niche of unicellular diazotroph populations

    2023  Volume 1

    Keywords Biology (General) ; QH301-705.5
    Language English
    Publishing date 2023-06-01T00:00:00Z
    Publisher Nature Portfolio
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  2. Article ; Online: Active nitrogen fixation by Crocosphaera expands their niche despite the presence of ammonium – A case study

    Keisuke Inomura / Takako Masuda / Julia M. Gauglitz

    Scientific Reports, Vol 9, Iss 1, Pp 1-

    2019  Volume 11

    Abstract: Abstract Unicellular nitrogen fixer Crocosphaera contributes substantially to nitrogen fixation in oligotrophic subtropical gyres. They fix nitrogen even when significant amounts of ammonium are available. This has been puzzling since fixing nitrogen is ... ...

    Abstract Abstract Unicellular nitrogen fixer Crocosphaera contributes substantially to nitrogen fixation in oligotrophic subtropical gyres. They fix nitrogen even when significant amounts of ammonium are available. This has been puzzling since fixing nitrogen is energetically inefficient compared with using available ammonium. Here we show that by fixing nitrogen, Crocosphaera can increase their population and expand their niche despite the presence of ammonium. We have developed a simple but mechanistic model of Crocosphaera based on their growth in steady state culture. The model shows that the growth of Crocosphaera can become nitrogen limited despite their capability to fix nitrogen. When they fix nitrogen, the population increases by up to 78% relative to the case without nitrogen fixation. When we simulate a simple ecological situation where Crocosphaera exists with non-nitrogen-fixing phytoplankton, the relative abundance of Crocosphaera increases with nitrogen fixation, while the population of non-nitrogen-fixing phytoplankton decreases since a larger fraction of fixed nitrogen is consumed by Crocosphaera. Our study quantitatively supports the benefit of nitrogen fixation despite the high electron/energy costs, even when an energetically efficient alternative is available. It demonstrates a competitive aspect of Crocosphaera, permitting them to be regionally significant nitrogen fixers.
    Keywords Medicine ; R ; Science ; Q
    Language English
    Publishing date 2019-10-01T00:00:00Z
    Publisher Nature Portfolio
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  3. Article ; Online: A quantitative model of nitrogen fixation in the presence of ammonium.

    Keisuke Inomura / Jason Bragg / Lasse Riemann / Michael J Follows

    PLoS ONE, Vol 13, Iss 11, p e

    2018  Volume 0208282

    Abstract: Nitrogen fixation provides bioavailable nitrogen, supporting global ecosystems and influencing global cycles of other elements. It provides an additional source of nitrogen to organisms at a cost of lower growth efficiency, largely due to respiratory ... ...

    Abstract Nitrogen fixation provides bioavailable nitrogen, supporting global ecosystems and influencing global cycles of other elements. It provides an additional source of nitrogen to organisms at a cost of lower growth efficiency, largely due to respiratory control of intra-cellular oxygen. Nitrogen-fixing bacteria can, however, utilize both dinitrogen gas and fixed nitrogen, decreasing energetic costs. Here we present an idealized metabolic model of the heterotrophic nitrogen fixer Azotobacter vinelandii which, constrained by laboratory data, provides quantitative predictions for conditions under which the organism uses either ammonium or nitrogen fixation, or both, as a function of the relative supply rates of carbohydrate, fixed nitrogen as well as the ambient oxygen concentration. The model reveals that the organism respires carbohydrate in excess of energetic requirements even when nitrogen fixation is inhibited and respiratory protection is not essential. The use of multiple nitrogen source expands the potential niche and range for nitrogen fixation. The model provides a quantitative framework which can be employed in ecosystem and biogeochemistry models.
    Keywords Medicine ; R ; Science ; Q
    Subject code 551
    Language English
    Publishing date 2018-01-01T00:00:00Z
    Publisher Public Library of Science (PLoS)
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  4. Article ; Online: Impact of Increased Nutrients and Lowered pH on Photosynthesis and Growth of Three Marine Phytoplankton Communities From the Coastal South West Atlantic (Patagonia, Argentina)

    Takako Masuda / Ondřej Prášil / Virginia E. Villafañe / Macarena S. Valiñas / Keisuke Inomura / E. Walter Helbling

    Frontiers in Marine Science, Vol

    2021  Volume 8

    Abstract: Effect of global change variables on the structure and photosynthesis of phytoplankton communities was evaluated in three different sites of the Patagonian coast of Argentina: enclosed bay (Puerto Madryn, PM), estuarine (Playa Unión, PU), and open waters ...

    Abstract Effect of global change variables on the structure and photosynthesis of phytoplankton communities was evaluated in three different sites of the Patagonian coast of Argentina: enclosed bay (Puerto Madryn, PM), estuarine (Playa Unión, PU), and open waters (Isla Escondida, IE). We exposed samples to two contrasting scenarios: Present (nutrients at in situ levels) vs. Future (with lowered pH and higher nutrients inputs), and determined growth and photosynthetic responses after 2 days of acclimation. Under the Future condition phytoplankton growth was higher in the estuarine site compared to those in PM and IE. This effect was the most pronounced on large diatoms. While the increase of photosynthetic activity was not always observed in the Future scenario, the lower photosynthetic electron requirement for carbon fixation (Φe,C = ETR/PmB) in this scenario compared to the Present, suggests a more effective energy utilization. Long-term experiments were also conducted to assess the responses along a 4 days acclimation period in PU. Diatoms benefited from the Future conditions and had significantly higher growth rates than in the Present. In addition, Φe,C was lower after the acclimation period in the Future scenario, compared to the Present. Our results suggest that the availability, frequency and amount of nutrients play a key role when evaluating the effects of global change on natural phytoplankton communities. The observed changes in diatom growth under the Future scenario in PU and IE and photosynthesis may have implications in the local trophodynamics by bottom up control.
    Keywords global change ; plankton community structure ; carbon incorporation ; oxygen production ; PSII photochemistry ; Science ; Q ; General. Including nature conservation ; geographical distribution ; QH1-199.5
    Subject code 333
    Language English
    Publishing date 2021-02-01T00:00:00Z
    Publisher Frontiers Media S.A.
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  5. Article ; Online: Quantifying nitrogen fixation by heterotrophic bacteria in sinking marine particles

    Subhendu Chakraborty / Ken H. Andersen / André W. Visser / Keisuke Inomura / Michael J. Follows / Lasse Riemann

    Nature Communications, Vol 12, Iss 1, Pp 1-

    2021  Volume 14

    Abstract: N2 fixation by heterotrophic bacteria has recently been found to take place on sinking marine particles, but an understanding of its regulation and importance is lacking. Here the authors develop a trait-based model for this N2 fixation, finding that ... ...

    Abstract N2 fixation by heterotrophic bacteria has recently been found to take place on sinking marine particles, but an understanding of its regulation and importance is lacking. Here the authors develop a trait-based model for this N2 fixation, finding that this once overlooked process could have global importance.
    Keywords Science ; Q
    Language English
    Publishing date 2021-07-01T00:00:00Z
    Publisher Nature Portfolio
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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