Award: OCE-1540158

Rising carbon dioxide concentrations in the atmosphere influence ocean chemistry causing a similar increase in ocean carbon dioxide concentration. This process is called ocean acidification. Photosynthetic microbes called phytoplankton in the sunlit surface ocean take up this carbon dioxide, and convert it to biomass just like land plants. This process consumes carbon dioxide and produces oxygen, fueling the marine food web. Phytoplankton, just like land plants, are very different from each other forming different functional groups. This project sought to understand how different functional groups of phytoplankton would respond to elevated carbon dioxide in the water at levels expected by year 2100 – both in the short term, and over the long-term, to give phytoplankton a chance to adapt to these new conditions. The primary goals of this project were to: 1) examine how increased carbon dioxide affects the major functional groups of marine phytoplankton; 2) grow phytoplankton for many generations in elevated carbon dioxide to see how they will adapt; and 3) compare how adapted phytoplankton respond to elevated carbon dioxide relative to their ancestors. We learned that different functional groups of phytoplankton respond differently to increased carbon dioxide, in some cases changing growth rates, chemical make-up of their cells, and their basic metabolic processes. These responses were non-linear, meaning that the changes did not always decrease or increase consistently with increasing carbon dioxide. This provides important baseline information for ongoing efforts to predict how the future ocean will work. We also found that phytoplankton evolved quickly when grown in the carbon dioxide environment we predict will exist 80 years from now. We kept cultures growing in the lab by taking away old culture media, and adding fresh, over and over again for about four years. Because the phytoplankton cells had to keep growing throughout this time, they went through about 500 generations, or cell divisions, and that made it possible for rare mutants that had different characteristics to outcompete the organisms we started the cultures with. In the end, the "evolved cultures" almost always grew faster than the "ancestor cultures", but the amount their growth rate increased was different for different phytoplankton functional groups. Groups whose ancestors grew slower at year 2100 carbon dioxide evolved faster in that environment than those who initially grew faster, and vice versa. If future experiments can reproduce that finding, it will provide valuable insight into how evolution works for microbes in a changing environment. We are also able to preserve these evolved cultures in "suspended animation" by freezing them in liquid nitrogen. They can be "brought back to life" later to let us study their adaptations more closely. We have sequenced their DNA genomes, revealing many changes that took place over the course of the 500 generations of evolution, some of which are responsible for the changes in growth rate we observed. Future work will examine these mutations in more detail to understand from a biochemical perspective how phytoplankton adapt to rising carbon dioxide. While we were working on this project, we also developed an educational curriculum that brings authentic microbial research into the classroom for undergraduate students. By fusing classical and molecular microbiology with an innovative "agar art" exercise, students get to design and execute their own experiments, sometimes making discoveries that prompt further research. This course has been implemented at a wide variety of colleges, exposing a diverse group of students to what it’s like to work in a professional microbiology lab. Last Modified: 03/05/2020 Submitted by: James J Morris