Culture-independent characterization marine protists suggests complex, potentially antagonistic interactions with diverse bacteria

Marine protists are diverse and play a significant role in global carbon fixation and cycling. However, their interactions with other microbes, particularly in the microenvironment surrounding the protist remain poorly characterized primarily due to disruptions that occur during cultivation. We utilized size-fractioned in-situ pump data from the Bermuda Atlantic Timeseries Study site (BATS), fluorescence-activated cell sorting and whole genome sequencing to identify and functionally characterize microbes associated with diverse marine protists. Their microbiome was dominated by members of the Planctomycetota, Verrucomicrobiota, and Bacteroidota. These taxa encoded a diverse repertoire of non-essential metabolic functions, centred around carbohydrate-active enzymes (CAZymes) and complementary modules. Most of the bacterial lineages encoded secretion systems, pili or flagella, enabling varying degrees of motility and attachment to surfaces. This suggests extracellular lifestyles and periods of attachment to the eukaryote. Notably, all bacteria encoded families of CAZymes that were specific to the breakdown of modified glycoproteins on the protists cell surface. This indicates that these lineages might not only utilize bioavailable carbohydrates secreted by phytoplankton during photosynthesis but could also break down live protist cell wall components. The diversity and evolutionary position of the novel symbiont-host relationships of marine protists revealed in this study enable us to better understand of the diverse interactions and flow of resources through marine protists.

Presentation Preference: Oral

Primary Presenter: Fabian Wittmers, Oregon State University (wittmerf@oregonstate.edu)

Authors:

Fabian Wittmers, Josephine Bay Paul Center for Comparative Molecular Biology and Evolution, Marine Biological Laboratory  (fwittmers@mbl.edu)

Camille Poirier, Ocean EcoSystems Biology Unit, GEOMAR Helmholtz Centre for Ocean Research  (camille.l.poirier@gmail.com)

Jacqueline Comstock, Department of Ecology, Evolution, and Marine Biology/Marine Science Institute, University of California  (jcomstock@ucsb.edu)

Lillian Henderson, Department of Ocean Sciences, Rosenstiel School of Marine, Atmospheric, and Earth Science, University of Miami  (lillian.henderson@earth.miami.edu)

Hilary Close, Department of Ocean Sciences, Rosenstiel School of Marine, Atmospheric, and Earth Science, University of Miami  (hclose@miami.edu)

Craig Carlson, Department of Ecology, Evolution, and Marine Biology/Marine Science Institute, University of California  (craig_carlson@ucsb.edu)

Alexandra Worden, osephine Bay Paul Center for Comparative Molecular Biology and Evolution, Marine Biological Laboratory  (azworden@mbl.edu)