# Functional diversity of microbial eukaryotes in a meromictic lake: coupling between metatranscriptomic and a trait-based approach

Arthur Monjot¹, Gisèle Bronner¹, Damien Courtine¹, Corinne Cruaud², Corinne Da Silva³, Jean-Marc Aury³, Frederick Gavory³, Anne Moné¹, Agnes Vellet¹, Ivan Wawrzyniak¹, Jonathan Colombet¹, Hermine Billard¹, Didier Debros¹, Cécile Lepère¹

¹ CNRS, Laboratoire Microorganismes : Génome et Environnement, Université Clermont Auvergne, Clermont-Ferrand, F-63000, France
² Genoscope, Institut de Biologie François Jacob, Commissariat à l'Energie Atomique (CEA), Université Paris-Saclay, Evry, France
³ Génomique Métabolique, Genoscope, Institut François Jacob, CEA, CNRS, Univ Evry, Université Paris-Saclay, 91057 Evry, France

## Introduction

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**Background:** While invisible to the naked eye, microorganisms are crucial components of the Earth's ecosystem, underpinning all biogeochemical cycles and supporting the existence of higher trophic life forms. Among microorganisms, our knowledge about microbial eukaryotes is poor compared to Bacteria. Moreover, in comparison to marine environments, freshwater ecosystems have received less attention although they contain a great microbial diversity.

**Objectives:** In our study functional diversity of understudied freshwater microbial eukaryotes was investigated with an original approach which couples a trait-based methodology and a metatranscriptomic analysis. Expressed functions and ecological strategies of microbial eukaryotes were studied for the first time in relation to oxygen presence/absence and size fractions in a model meromictic lake (Pavin, France).

## Materials & Methods

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## Functional diversity

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## Metabolic potential

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## Conclusion

This study targeting microbial eukaryotes is the first combining trait-based approach and metatranscriptomic in a freshwater meromictic lake. The analysis of differentially expressed genes with taxonomic affiliation and functional group allows the identification of differentially expressed orthologous genes (KOs) as well as metabolic and cellular processes that could complement trait-based definition of functional groups. This approach allows to highlight microbial eukaryote ecological strategies according to different forcing variables. Parasites (i.e. fungi) and mixotrophs strongly differed according to the living zone, parasites in relation to their phytoplankton hosts occurring in surface and mixotrophs in relation to genera trophic abilities (obligate/facultative mixotrophs). Numerous microbial eukaryotes are also able to thrive in absence of oxygen such as saprotrophs expressing transcripts related to sulfur and nitrate metabolism as well as organic matter degradation in the monimolimnion. Photosynthetic microbial eukaryotes are also present in this zone raising the hypothesis of unknown anaerobic metabolisms.

*Swimmer & heavy-covered photo-autotrophs

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