High amino acid osmotrophic incorporation by marine eukaryotic phytoplankton revealed by click chemistry

Abstract

Abstract The osmotrophic uptake of dissolved organic compounds in the ocean is considered to be dominated by heterotrophic prokaryotes, whereas the role of planktonic eukaryotes is still unclear. We explored the capacity of natural eukaryotic plankton communities to incorporate the synthetic amino acid L-homopropargylglycine (HPG, analogue of methionine) using biorthogonal noncanonical amino acid tagging (BONCAT), and we compared it with prokaryotic HPG use throughout a 9-day survey in the NW Mediterranean. BONCAT allows to fluorescently identify translationally active cells, but it has never been applied to natural eukaryotic communities. We found a large diversity of photosynthetic and heterotrophic eukaryotes incorporating HPG into proteins, with dinoflagellates and diatoms showing the highest percentages of BONCAT-labelled cells (49 ± 25% and 52 ± 15%, respectively). Among them, pennate diatoms exhibited higher HPG incorporation in the afternoon than in the morning, whereas small (≤5 μm) photosynthetic eukaryotes and heterotrophic nanoeukaryotes showed the opposite pattern. Centric diatoms (e.g. Chaetoceros, Thalassiosira, and Lauderia spp.) dominated the eukaryotic HPG incorporation due to their high abundances and large sizes, accounting for up to 86% of the eukaryotic BONCAT signal and strongly correlating with bulk 3H-leucine uptake rates. When including prokaryotes, eukaryotes were estimated to account for 19–31% of the bulk BONCAT signal. Our results evidence a large complexity in the osmotrophic uptake of HPG, which varies over time within and across eukaryotic groups and highlights the potential of BONCAT to quantify osmotrophy and protein synthesis in complex eukaryotic communities.

Irene Forn
Irene Forn
Technician
Marta Sebastián
Marta Sebastián
Staff scientist
Clara Cardelús
Clara Cardelús
Technician
Ramon Massana
Ramon Massana
Staff scientist

I am microbial ecologists with a deep interest in protist ecology and evolution

Josep M. Gasol
Josep M. Gasol
Staff scientist
Clara Ruiz-González
Clara Ruiz-González
Staff scientist