# Microsporidian diversity and planktonic hosts: from lakes to ocean

Marina Chauvet, Cécile Lepère

► To cite this version:

Marina Chauvet, Cécile Lepère. Microsporidian diversity and planktonic hosts: from lakes to ocean. Gordon Research Conference on Marine Microbes, May 2022, Les Diablerets, Switzerland. hal-04794819

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https://hal.science/hal-04794819v1

Submitted on 21 Nov 2024

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Distributed under a Creative Commons Attribution 4.0 International License
# Microsporidian diversity and
planktonic hosts: from lakes to ocean

Marina Chauvet (✉) marina.chauvet@uca.fr),

Cécile Lepère

Laboratoire Microorganismes : Génome et Environnement (LMGE) – UMR CNRS 6023 Université Clermont Auvergne, FRANCE

## Introduction

Microsporidia are a large group of obligate intracellular eukaryotic parasites related to Fungi, primarily known as parasites of vertebrates and invertebrates as well as few protists [1]. Recent studies suggest that their diversity has been greatly underestimated, especially in aquatic ecosystems, and little is known about their hosts other than metazoans, and thus about their impact on the communities at the base of the food web [2-4].

We sampled 15 different sites across marine and freshwater environments, size-fractioned the samples and used microsporidian specific primers associated with metabarcoding to unravel the microsporidian diversity (and the associated spatial variation). Co-occurrence networks as well as TSA-FISH were eventually used to link potential hosts (planktonic eukaryotes < 150 µm) and Microsporidia diversity.

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Microsporidian diversity in freshwater (left) and marine (right) ecosystems (1853 OTUs total). From inner to outer circles: clades, groups, genera. Hatched pattern = OTUs unaffiliated beyond the group/clade.

In both ecosystems, an important part of the diversity wasn't affiliated to a genus nor even to a group. Surprisingly, *Crispospora* (parasite of chironomids eggs in freshwater) was highly abundant in both ecosystems.

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<figure><img src="image_5.png" /><figcaption>Principal Coordinates Analysis (PCoA, Bray-Curtis distances).</figcaption></figure>

<caption>Freshwater and marine microsporidian communities were quite different.</caption>

Positive correlations between microsporidian OTUs (bottom) and eukaryotic OTUs (top) in freshwater (left) and marine (right) ecosystems. One line represents one positive correlation between two OTUs (un. = unclassified).

Co-occurrence were identified with 18 eukaryotic phyla, almost 75% being with alveolates (apicomplexans, ciliates and dinoflagellates). Associations were identified with eukaryotic phyla already described as hosts (e.g. apicomplexans, ciliates, arthropods, molluscs) and with potential new hosts (mostly dinoflagellates and fungal phyla).

Microsporidian infections in dinoflagellates (genus *Ceratium*) identified in freshwater and marine samples. *Microsporidia* were targeted by TSA-FISH with a microsporidian specific probe [4].

<figure><img src="image_6.png" /></figure>

## Conclusions

This study allowed us to highlight for the first time a huge microsporidian diversity in marine samples, with an important part (46%) of the OTUs not affiliated to a genus suggesting an important reservoir of new microsporidian species and thus potential new hosts. This diversity was also widely divergent from the diversity identified in freshwater. Interestingly, most of the identified genera are described as parasites of organisms much larger than the studied size fraction (<150 µm). It therefore appears that these Microsporidia infect smaller and, so far, unknown hosts such as dinoflagellates both in marine and freshwater ecosystems. Altogether, these results indicate that the microsporidian diversity and host spectrum could be therefore more important than previously described, and their role in the functioning of aquatic ecosystems and especially marine ecosystems is undoubtedly largely unknown.