Biology subjects

Legeay, E.

Publications and source records attributed to Legeay, E..

3 recordsLinked to original sources

bioRxiv2026

The genome of the Delisea pulchra: a resource for the study of chemical host-microbe interactions in red algae

BackgroundRed macroalgae (Rhodophyta) are ecologically and economically important marine primary producers, yet genomic resources for most species remain scarce. Delisea pulchra, a temperate red alga known for its halogenated furanone-based chemical defenses, serves as a model for studying algal-microbe interactions, antifouling mechanisms, and disease dynamics. ResultsHere we present a high-quality genome assembly of this species. The nuclear genome comprises 134 Mbp across 271 contigs with an N50 of 1.47 Mbp and encodes 13,387 predicted protein-coding genes. Comparative genomics with other red algae revealed expansions in gene families involved in DNA methylation, and oxidative stress responses, including glutathione S-transferases and superoxide dismutases. Analysis of glycosyltransferases, sulfatases, and sulfurylases implicated in galactan biosynthesis suggests D. pulchra possesses a complex and potentially novel extracellular matrix. We also identified several vanadium haloperoxidases (vHPOs), heme-dependent haloperoxidases (hHPOs), and two type III polyketide synthase (PKS) genes unique to the D. pulchra, which together represent promising candidate genes for bromofuranone production. ConclusionThe D. pulchra genome provides a foundation for molecular investigations into defense, signaling, and host-microbe interactions. It has been deposited at the European Nucleotide Archive under accession number PRJEB101077. All datasets, annotations, and interactive tools for exploring the genome are also available through the Rhodoexplorer portal at https://rhodoexplorer.sb-roscoff.fr.

genomics↗

bioRxiv2025

A duo of fungi and complex and dynamic bacterial community networks contribute to shape the Ascophyllum nodosum holobiont

The brown alga Ascophyllum nodosum and its microbiota form a dynamic functional entity named holobiont. Some microbial partners may play a role in seaweed health through bioactive compounds crucial for normal morphology, development, and physiological acclimation. However, the full spectrum of the microbial diversity and its variations according to algal life stage, season, and location have not been comprehensively studied. This study uses 208 short-read metabarcoding samples to characterize the bacterial, archaeal, and microeukaryotic communities of A. nodosum across three nearby sites, four thallus parts, and a monthly survey, aiming to explore the dynamics of ecological interactions within the holobiont. Our results revealed that A. nodosum harbors a predominantly bacterial microbiota, varying significantly across all covariables, while archaea were virtually absent. An innovative normalization using the co-amplified host reads provided an estimation of bacterial abundance, revealing a drastic decline in May, potentially linked to epidermal shedding. In contrast, fungal communities were stable, dominated by Mycophycias ascophylli and Moheitospora sp., which remained closely associated with the host year-round. We identified a core microbiome of 22 ASVs, consistently found in all samples, including Granulosicoccus, a genus consistently abundant in other brown algal microbiota. Sequence clustering revealed multiple species which vary according seasons, even in the overall stable Granulosicoccus genus. Co-occurrence network analysis revealed putative interactions between microbial groups in response to ecological niches. Overall, these findings highlight the dynamic of bacterial interactions and stable fungal associations within the A. nodosum holobiont, providing new insights into the ecology of its microbiota.

ecology↗

bioRxiv2022

The Saccharina latissima microbiome: algal tissue matters more than region, season, and physiology

Saccharina latissima is a canopy-forming species of brown algae and, as such, is considered an ecosystem engineer. Several populations of this alga are exploited worldwide, and a decrease in the abundance of S. latissima at its southern distributional range limits has been observed. Despite its economic and ecological interest, only a few data are available on the composition of microbiota associated with S. latissima and its role in algal physiology. We studied the whole bacterial community composition associated with S. latissima samples from three locations (Brittany, Helgoland, and Skagerrak) by 16S metabarcoding analyses at different scales: algal blade part, regions, season, and physiologic state. We have shown that the difference in bacterial composition is driven by factors of decreasing importance: (i) the algal tissues (apex/meristem), (ii) the geographical area, (iii) the seasons, and (iv) the algal hosts condition (healthy vs. symptoms). Overall, Alphaproteobacteria, Gammaproteobacteria, and Bacteroidota dominated the general bacterial communities. Almost all individuals hosted bacteria of the genus Granulosicoccus, accounting for 12% of the total sequences, and eight additional core genera were identified. Our results also highlight a microbial signature characteristic for algae in poor health independent of the disease symptoms. Thus, our study provides a comprehensive overview of the S. latissima microbiome, forming a basis for understanding holobiont functioning.

microbiology↗