Biology subjects

Rigaut-Jalabert, F.

Publications and source records attributed to Rigaut-Jalabert, F..

3 recordsLinked to original sources

bioRxiv2022

Insight into diatoms diversity at two European coastal sites (LTER-MC in the Mediterranean Sea and SOMLIT-Astan in the Western English Channel) using a DNA metabarcoding approach

Diatoms are among the most successful marine eukaryotic phytoplankton groups. Their diversity has been investigated in the worlds oceans through expeditions and observations carried out from the equator to the poles. Traditionally, diatom species have been distinguished based on morphological characters of their frustules, but high-throughput sequencing offers new, high-resolution data that can be used to re-examine spatial and/or temporal patterns of diversity. Here we investigated diatoms genetic diversity using metabarcoding (18S V4 rRNA gene) obtained along the years 2011 to 2013 at two coastal time series stations (SOMLIT-Astan and LTER-MareChiara) installed respectively off Roscoff in the Western English Channel and in the Gulf of Naples in the Mediterranean Sea. Diatom species pools detected were different, which fitted with previous observations and with our expectations, since these stations are installed in two contrasted pelagic habitats (permanently-mixed versus stratified in summer). However, this analysis also shows a pool of common ASVs among which some are persistent and dominant in both sites. The observed synchronous variations in relative read abundances of shared ASVs assigned to Chaetoceros socialis, C. tenuissimus, Cyclotella, Mediolabrus comicus and Leptocylindrus aporus at the two geographically distant sites could indicate that internal controls of growth rate and sexual reproduction, rather that external environmental parameters are at work.

ecology↗

bioRxiv2022

Comparative thermophysiology of marine Synechococcus CRD1 strains isolated from different thermal niches in iron-depleted areas

Marine Synechococcus cyanobacteria are ubiquitous in the ocean, a feature likely related to their extensive genetic diversity. Amongst the major lineages, clades I and IV preferentially thrive in temperate and cold, nutrient-rich waters, whilst clades II and III prefer warm, nitrogen or phosphorus-depleted waters. The existence of such cold (I/IV) and warm (II/III) thermotypes is corroborated by physiological characterization of representative strains. A fifth clade, CRD1, was recently shown to dominate the Synechococcus community in iron-depleted areas of the world ocean and to encompass three distinct ecologically significant taxonomic units (ESTUs CRD1A-C) occupying different thermal niches, suggesting that distinct thermotypes could also occur within this clade. Here, using comparative thermophysiology of strains representative of these three CRD1 ESTUs we show that the CRD1A strain MITS9220 is a warm thermotype, the CRD1B strain BIOS-U3-1 a cold temperate thermotype, and the CRD1C strain BIOS-E4-1 a warm temperate stenotherm. Curiously, the CRD1B thermotype lacks traits and/or genomic features typical of cold thermotypes. In contrast, we found specific physiological traits of the CRD1 strains compared to their clade I, II, III and IV counterparts, including a lower growth rate and photosystem II maximal quantum yield at most temperatures and a higher turnover rate of the D1 protein. Together, our data suggests that the CRD1 clade prioritizes adaptation to low-iron conditions over temperature adaptation, even though the occurrence of several CRD1 thermotypes likely explains why the CRD1 clade as a whole occupies most iron-limited waters.

microbiology↗

bioRxiv2021

Seasonal temporal dynamics of marine protists communities in tidally mixed coastal waters

Major seasonal community reorganizations and associated biomass variations are landmarks of plankton ecology. However, the processes determining marine species and community turnover rates have not been fully elucidated so far. Here, we analyse patterns of planktonic protist community succession in temperate latitudes, based on quantitative taxonomic data from both microscopy counts and ribosomal DNA metabarcoding from plankton samples collected biweekly over 8 years (2009-2016) at the SOMLIT-Astan station (Roscoff, Western English Channel). Considering the temporal structure of community dynamics (creating temporal correlation), we elucidated the recurrent seasonal pattern of the dominant species and OTUs (rDNA-derived taxa) that drive annual plankton successions. The use of morphological and molecular analyses in combination allowed us to assess absolute species abundance while improving taxonomic resolution, and revealed a greater diversity. Overall, our results underpinned a protist community characterised by a seasonal structure, which is supported by the dominant OTUs. We detected that some were partly benthic as a result of the intense tidal mixing typical of the French coasts in the English Channel. While the occurrence of these microorganisms is driven by the physical and biogeochemical conditions of the environment, internal community processes, such as the complex network of biotic interactions, also play a key role in shaping protist communities.

ecology↗