Biology subjects

Trefault, N.

Publications and source records attributed to Trefault, N..

3 recordsLinked to original sources

bioRxiv2025

Patagonian fjords/channels vs. open ocean: phytoplankton molecular diversity in Southern Chilean coast

Environmental filtering hypothesis studies have revealed immense diversity of microorganisms across oceans; however, these studies are scarce along the Southeast Pacific coast. In this work, we describe the molecular diversity of phytoplankton communities from two biogeographic areas with contrasting oceanographic characteristics, namely fjords and channels versus the open Pacific Ocean (36{degrees}S to 53{degrees}S). Both areas have seen an increase in the frequency and intensity of Harmful Algal Bloom events (HABs). Using a molecular approach based on metabarcoding of the SSU ribosomal gene, we retrieve micro-phytoplankton diversity, community composition, and biogeographical patterns. The ASVs assigned to Dinophyceae and Bacillariophyta classes show differences in richness and dominance between both studied areas. The diversity pattern described in this work shows a higher harmful potential in fjord/channel areas versus the open ocean, which provides grounds for future studies about the factors triggering temporal variations in phytoplankton communities within these two contrasting environments.

ecology↗

bioRxiv2022

Arctic phytoplankton spring bloom diversity across the marginal ice zone in Baffin Bay

Phytoplankton under-ice blooms have been recently recognized as an important Arctic phenomenon for global primary production and biogeochemical cycling. Drastic sea-ice decline in both extension and thickness enables the development of early blooms, sometimes hundreds of kilometers beneath the pack ice. Baffin Bay is a semi-enclosed sea where Arctic and North Atlantic water masses interact. It is totally covered by sea-ice by March and ice-free by August/September. In the present work, we investigated the phytoplankton community structure across the marginal ice zone between the ice-free, Atlantic-influenced, east and the ice-covered, Arctic-influenced, west Baffin Bay using 18S rRNA high-throughput amplicon sequencing, flow cytometry cell counting and numerous environmental and biological data collected and compiled in the scope of the Green Edge project. Sampling was performed during June-July 2016 in a total of 16 stations with around 6 depths each. Stations were clustered into "Under Ice" (UI), "Marginal Ice Zone" (MIZ) and "Open Water" (OW) on the basis of its sea ice cover upon sampling. Phytoplankton community structure was analyzed by 18S rRNA metabarcoding with the microdiversity approach. The UI sector was characterized by a shallow nitracline, high pico-phytoplankton abundance and a shared dominance between Micromonas and Phaeocystis in the 0.2-3 {micro}m size fraction, as well as an increased contribution of Cryptophyceae and non-diatom Ochrophyta in the 3-20 {micro}m size fraction. Several amplicon sequence variants (ASVs) were flagged as indicator for the UI+MIZ sector group, including known ice-associated taxa such as the diatoms Melosira arctica and Pseudo-nitzschia seriata, but also specific ASVs assigned to the green alga Micromonas polaris and the cryptophyte Falcomonas daucoides, the silicoflagellate Dictyocha speculum, one member of the uncultivated MOCH-2 group, and a Pterosperma sp. (green algae) rarely seen in other metabarcoding datasets, including from the Arctic. The OW sector harbored a community adapted to a nutrient-depleted/high light environment, with a significant contribution of the haptophytePhaeocystis pouchetii and big centric diatoms, including several Thalassiosira species.

microbiology↗

bioRxiv2019

Global phylogeography and ancient evolution of the widespread human gut virus crAssphage

Microbiomes are vast communities of microbes and viruses that populate all natural ecosystems. Viruses have been considered the most variable component of microbiomes, as supported by virome surveys and examples of high genomic mosaicism. However, recent evidence suggests that the human gut virome is remarkably stable compared to other environments. Here we investigate the origin, evolution, and epidemiology of crAssphage, a widespread human gut virus. Through a global collaboratory, we obtained DNA sequences of crAssphage from over one-third of the worlds countries, and showed that its phylogeography is locally clustered within countries, cities, and individuals. We also found colinear crAssphage-like genomes in both Old-World and New-World primates, challenging genomic mosaicism and suggesting that the association of crAssphage with primates may be millions of years old. We conclude that crAssphage is a benign globetrotter virus that may have co-evolved with the human lineage and an integral part of the normal human gut virome.

microbiology↗