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Award Detail

Doing Business As Name:American Museum Natural History
  • Eunsoo Kim
  • (212) 769-5510
Award Date:02/06/2015
Estimated Total Award Amount: $ 80,606
Funds Obligated to Date: $ 80,606
  • FY 2015=$80,606
Start Date:06/01/2015
End Date:05/31/2019
Transaction Type:Grant
Awarding Agency Code:4900
Funding Agency Code:4900
CFDA Number:47.050
Primary Program Source:040100 NSF RESEARCH & RELATED ACTIVIT
Award Title or Description:Collaborative Research: Role of small-sized protists in the microbial loop with emphasis on interactions between mixotrophic protists and picocyanobacteria
Federal Award ID Number:1458095
DUNS ID:061202768
Parent DUNS ID:061202768
Program Officer:
  • Michael Sieracki
  • (703) 292-7585

Awardee Location

Street:Central Park West at 79th St
City:New York
Awardee Cong. District:08

Primary Place of Performance

Organization Name:American Museum Natural History
Street:Central Park West at 79th Street
City:New York

Abstract at Time of Award

Protists are mostly single-celled, eukaryotic microorganisms, including algae and protozoans. They are ubiquitous, diverse, and major contributors in oceanic food webs. Determining their taxonomic identity and the extent to which they contribute to carbon and nutrient cycles (whereby carbon and minerals are continuously changed chemically in the environment and reincorporated in living organisms) are among the major goals of this study. Moreover, the investigators will study how they respond to environmental change, one of the most important and challenging current problems in oceanography. Answering these questions is fundamental to understanding how living organisms in the ocean environment interact with one another and contribute to the health and productivity of the ocean. The main goal of the project is to investigate biotic interactions of small-sized protists with very tiny cyanobacteria also known as picocyanobacteria, which represent the most abundant photosynthetic organisms in the ocean. These studies will be done both in ocean environments and in laboratory experimental settings. Considering the limited knowledge on this topic, the work planned in this project promises important and exciting discoveries. Two early career female scientists will lead this project. In addition, one postdoctoral scholar, one graduate student, and at least three undergraduate summer interns will participate in the proposed research activities. The principal investigators will create a strong public outreach program that will engage middle school students in hands-on activities related to ocean sciences, and will produce a video in collaboration with the Education Department at the American Museum of Natural History. The video will summarize the major findings of the proposed research. It can be used in schools and in informal learning settings, including access by the public on the Internet through the Museum's Science Bulletins web page. Single-celled eukaryotic microorganisms or protists, though largely outnumbered by picocyanobacteria (Prochlorococcus and Synechococcus), contribute significantly to ocean carbon biomass and primary productivity, partially by virtue of their larger cell size. In addition, small planktonic protists can regulate picocyanobacteria abundance through grazing. The main goal of this project is to investigate biotic interactions of planktonic pico- and nano-sized eukaryotes with picocyanobacteria, both in the field and in laboratory settings. A set of field- and culture-based experiments will be conducted, using state-of-the-art methodologies, including fluorescence-activated cell sorting, isotope and fluorescent stain labeling, and next-generation molecular sequencing to address the research objectives. Operationally, this project is structured around two objectives: Objective 1 is to assess the contribution of small protists to carbon and nutrient cycling through measurement of primary production, bacterivory, mixotrophy and phosphorus uptake in major microbial groups, and evaluate the role of nutrient availability in controlling mixotrophy. Objective 2 will focus on assessing the distribution and diversity of small-sized protists that feed on picocyanobacteria and further evaluate the role of nutrient availability among the protists that are mixotrophic. To reach these objectives field-based experiments will be conducted in contrasted environments: the North Pacific subtropical gyre (phosphorus replete, dominated by Prochlorococcus at Sta. ALOHA) and the North West Mediterranean sea (phosphorus deplete, dominated by Synechococcus at Sta. DYFAMED). Complementary experiments using model protists and picocyanobacteria will be conducted using controlled cultures in the lab. The work will provide critical new information on the phylogenetic diversity and function of marine microbial eukaryotes, with emphasis on their ecological role as predators (phagotrophy, mixotrophy) on, and competitors with, the picoyanobacteria Prochlorococcus and Synechococcus.

Publications Produced as a Result of this Research

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? Duhamel, S., E. Kim, B. Sprung, and O. R. Anderson "Small pigmented eukaryotes play a major role in carbon cycling in the P-depleted western subtropical North Atlantic, which may be supported by mixotrophy" Limnol. Oceanogr, v., 2019, p..

E Kim, B Sprung, S Duhamel, C Filardi, MK Shin "Oligotrophic Lagoons of the South Pacific Ocean Are Home to a Surprising Number of Novel Eukaryotic Microorganisms" Environmental Microbiology, v., 2016, p..

Project Outcomes Report


This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.

Determining the taxonomic identity of marine single-cell eukaryotic microorganisms, the extent to which they contribute to carbon and nutrient cycling, and how they respond to environmental change remain among the major challenges in oceanography. Answering these questions is fundamental to understanding marine ecosystem functioning and to predicting how the marine environment will respond to global changes. Although the abundance, distribution, and ecological roles of eukaryotic microorganisms (i.e. those, unlike bacteria, having a separate compartment for storing genetic materials) have been the focus of many studies, there is still much to be learned, particularly for the smaller-sized members of eukaryotes, that are increasingly being recognized as important to oceanic biogeochemical cycling. This project filled major gaps in our understanding of the diversity and function of <20 µm microbial eukaryotes, with emphasis on their ecological role as predators (e.g. eating bacteria) and competitors with the picocyanobacteria Prochlorococcus and Synechococcus, the most abundant phototrophic cells in the ocean. We used a set of field- and culture-based experiments in combination with state-of-the-art methodologies, including fluorescence-activated cell sorting, isotope and fluorescent stain labeling, and next-generation molecular sequencing. We determined that despite their low abundance relative to picocyanobacteria, small microbial eukaryotes have a disproportionate contribution to carbon cycling. For example, in the western subtropical North Atlantic, although small photosynthetic eukaryotes (< 5 μm) were only ~ 5% of the microbial phytoplankton cell abundance in surface layers of the ocean, they represented at least two thirds of the microbial phytoplankton carbon biomass and fixed more CO2 than picocyanobacteria, accounting for roughly half of the volumetric CO2 fixation by the microbial phytoplankton, or a third of the total primary production. We also learned that phosphate assimilation rates of very small eukaryotes (< 5 μm) were generally higher than of picocyanobacteria but, when normalized to biovolumes, picocyanobacteria assimilated roughly four times more phosphate than small eukaryotes, indicating different strategies to cope with phosphate limitation. This outcome has consequences for ocean biology and biogeochemistry, since our results underline an imbalance in the CO2 to phosphate uptake rate ratios, which may be explained by bacterial predation providing microbial eukaryotes with their largest source of phosphate. Our work also significantly advanced our understanding of the ecological role of small microbial eukaryotes as predators of bacteria and the factors regulating their mode of nutrition. For example, in the phosphate-depleted western subtropical North Atlantic we found that bacterivory by photosynthetic microbial eukaryotes, less than 5 μm in size, was reduced when phosphate was added during experimental incubations, indicating that their feeding rate is regulated by phosphate availability. In laboratory culture experiments, we further confirmed the role of phosphate availability in regulating bacterial consumption by the small-sized marine green alga known as Cymbomonas tetramitiformis. Our team also screened small-sized green algae available in culture collections for their potential to eat bacteria using color-tagged live bacteria, a protocol developed for the project. From this effort, several marine green algae that previously assumed to be simply photosynthetic, were identified to be capable of eating bacteria as food source. We also conducted series of culture and feeding experiments to identify environmental factors that influence their bacterial feeding behavior. Overall, it appears that their eat bacteria more when the soluble nutrients become scarce. Further, we have gathered molecular sequence data from these algae in order to better understand their feeding behavior at the molecular level. Finally, our work significantly advanced our knowledge of small microbial eukaryotes’ diversity in oligotrophic seawater. For example, we sequenced samples from eight tropical lagoon sites of the South Pacific and revealed a surprising number of novel eukaryotic microorganisms. Overall, this project furthered knowledge regarding the influence of understudied, but key, marine microbes in the functioning of marine food webs and biogeochemical cycling.  


This project supported the work of two early career scientists, two graduate students, a post-doctoral researcher as well as helped train several undergraduate and high school students, including women and minorities in the fields of science, technology, engineering, and mathematics (STEM). Results from the project have been published in peer-reviewed journals (five manuscripts as of August 2019, plus several in preparation), and disseminated through presentations at scientific meetings and databases. This research also stimulated new international collaborations. Our findings have also been shared at many public outreach events, including sciences fairs, science festivals and open houses in Museums and Universities.


Last Modified: 08/30/2019
Modified by: Eunsoo Kim

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