Role of small-sized protists in the microbial loop. This work was funded by US-NSF grant #1458070

 

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 the proposed work is to investigate biotic interactions of planktonic pico- and nano-sized eukaryotes with picocyanobacteria, both in the field and in laboratory settings. Our approach is to use 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 to address our research objectives. Operationally, this project is structured around two objectives: Objective 1 is to assess the contribution of small-sized 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 focuses 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. 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.

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August 2021: Postdoctoral scientist Sophie Charvet published her work in Scientific Reports: Charvet S., Kim E., Subramanian A., Montoya J., and S. Duhamel. 2021. Small pigmented eukaryote assemblages of the western tropical North Atlantic around the Amazon River plume during spring discharge. Scientific Reports 11(1), 16200. doi.org/10.1038/s41598-021-95676-2. Open access

 

March 2021: Graduate student Nick Bock and Postdoctoral scientist Sophie Charvet published their work in the ISME Journal: Bock, Nicholas A., Sophie Charvet, John Burns, Yangtsho Gyaltshen, Andrey Rozenberg, Solange Duhamel, and Eunsoo Kim. “Experimental Identification and in Silico Prediction of Bacterivory in Green Algae.” The ISME Journal, March 2, 2021. doi: 10.1038/s41396-021-00899-w.

Beyond the paper: https://naturemicrobiologycommunity.nature.com/posts/feeding-in-green-algae-illuminated-by-live-labeled-bacteria

See the press release here: https://www.eurekalert.org/pub_releases/2021-03/amon-lso030121.php?site_version=e4

and here: https://blogs.ei.columbia.edu/2021/03/03/yes-flesh-eating-algae-real-like-prey-alive/

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May 2019: our team published results from our field work experiments at BATS related to Objectives 1 and 2: Duhamel S., E. Kim, B. Sprung, and O. R. Anderson. 2019. Small pigmented eukaryotes play a major role in carbon cycling in the P‐depleted western subtropical North Atlantic, which may be supported by mixotrophy. Limnology and Oceanography, 64, 2424–2440, doi:10.1002/lno.11193

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June 2018: Nick published his first paper related to this project: Bock N.A., Van Wambeke F., Dion M., and S. Duhamel. 2018. Microbial community structure in the western tropical South Pacific. Biogeosciences, 15, 3909-3925, doi:10.5194/bg-15-3909-2018. Open access

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January 2018: Sophie Charvet joined the lab to work on this project. Sophie is a postdoctoral scientist and is collaborating with Nick and expand the physiological experiments with modern molecular tools such as genomics and transcriptomics. Welcome and good luck Sophie!

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September 2016: First paper published from this project:  Kim E., Sprung B., Duhamel S., Filardi C., M.K. Shin. 2016. Oligotrophic lagoons of the South Pacific Ocean are home to a surprising number of novel eukaryotic microorganisms. Environmental Microbiology, 18(12), 4549–4563. doi: 10.1111/1462-2920.13523. Access 

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July 2016: Nick Bock joined the lab and is pursuing this research for his Ph.D.: Welcome and good luck Nick!

        Nick is using the model organism Cymbomonas to study the feeding behavior of mixotrophic small-sized marine protists. For more information about Cymbomonas, check this great video by our collaborator Dr. Eunsoo Kim: https://www.youtube.com/watch?v=lafL_mmv3EA  and the following publication: Maruyama S, Kim E (2013). A Modern Descendant of Early Green Algal Phagotrophs. Curr Biol 23: 1081-1084.