Irreversibly increased nitrogen fixation in Trichodesmium experimentally adapted to elevated carbon dioxide

• Published in: Nature communications Vol. 6; no. 1; p. 8155
• Main Authors: Hutchins, David A., Walworth, Nathan G., Webb, Eric A., Saito, Mak A., Moran, Dawn, McIlvin, Matthew R., Gale, Jasmine, Fu, Fei-Xue
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-09-2015; Nature Publishing Group; Nature Pub. Group
• Subjects: 631/158/857; 704/106/829/826; 82; 82/80; Acidification; Adaptation, Physiological - drug effects; Adaptation, Physiological - physiology; Anthropogenic factors; Biological Evolution; Carbon dioxide; Carbon Dioxide - pharmacology; Cell lines; DNA methyltransferase; Fitness; Growth rate; Humanities and Social Sciences; Microorganisms; multidisciplinary; Nitrogen; Nitrogen fixation; Nitrogen Fixation - drug effects; Nitrogen Fixation - physiology; Oceans and Seas; Oscillatoria - drug effects; Oscillatoria - growth & development; Oscillatoria - physiology; Phosphorus; Phosphorus - metabolism; Reproductive fitness; Science; Science (multidisciplinary); Trichodesmium
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms9155

Nitrogen fixation rates of the globally distributed, biogeochemically important marine cyanobacterium
Trichodesmium
increase under high carbon dioxide (CO
2
) levels in short-term studies due to physiological plasticity. However, its long-term adaptive responses to ongoing anthropogenic CO
2
increases are unknown. Here we show that experimental evolution under extended selection at projected future elevated CO
2
levels results in irreversible, large increases in nitrogen fixation and growth rates, even after being moved back to lower present day CO
2
levels for hundreds of generations. This represents an unprecedented microbial evolutionary response, as reproductive fitness increases acquired in the selection environment are maintained after returning to the ancestral environment. Constitutive rate increases are accompanied by irreversible shifts in diel nitrogen fixation patterns, and increased activity of a potentially regulatory DNA methyltransferase enzyme. High CO
2
-selected cell lines also exhibit increased phosphorus-limited growth rates, suggesting a potential advantage for this keystone organism in a more nutrient-limited, acidified future ocean.
The long-term response of marine cyanobacteria to increased anthropogenic CO
2
are not known. Here, Hutchins
et al
. show that
Trichodesmium
exposed to long-term selection at elevated CO
2
display irreversible increases in nitrogen fixation and growth rates, even after returning to present day conditions.