Biology subjects

Clairet, J.

Publications and source records attributed to Clairet, J..

4 recordsLinked to original sources

bioRxiv2026

Seasonal patterns in Synechococcus pigment diversity at two temperate sites with contrasting oceanic regimes

Competition for light has driven extensive pigment diversification among phytoplankton species, yet how this diversity shapes their spatiotemporal distribution in the field has been little studied so far. The cyanobacterium Synechococcus is an ideal model for addressing this issue, since this group has colonized most light spectral niches in marine environments. Here, we used an approach based on marker read recruitment from metagenomes to analyze the seasonal succession of Synechococcus pigment types (PTs) at two time-series stations off French coasts exhibiting contrasting oceanic regimes. Marked seasonality was observed at both sites. The shallow, permanently mixed English Channel site SOMLIT-Astan was characterized by an alternation between green-light specialists (PT 3a) peaking in spring, and chromatic acclimaters type A (PT 3dA) accounting for most of the Synechococcus community in winter. In contrast, the pigment diversity was much higher at the deep Mediterranean station BOUSSOLE. In the upper layer, the two main PTs were the blue light specialists (PT 3c), which dominated the community in summer and fall, and PT 3dA cells, which were more abundant in spring. The third most abundant PT was chromatic acclimaters type B (PT 3dB), which accounted for up to 15% of the surface community in late fall. Strikingly, PT 3dA was dominant at depth during most of the year. Multivariate analyses between PT abundances, clade abundances and environmental factors, notably water color indexes, suggested new associations between PTs to specific clades and ecological niches. This study provides novel insights for refining distribution models of Synechococcus PTs and phytoplankton groups in general.

microbiology↗

bioRxiv2025

Competition for light color between marine Synechococcus strains with fixed and variable pigmentation

Competition between phytoplankton species for light has triggered an extensive diversification of photosynthetic pigments. In Synechococcus cyanobacteria, three major pigment types occur in the ocean: blue light (BL) specialists that have a high ratio of the BL-absorbing chromophore phycourobilin (PUB) to the green light (GL)-absorbing chromophore phycoerythrobilin (PEB), GL specialists that have a low PUB:PEB ratio, and cells that modify their PUB:PEB ratio to match the ambient color, a process called Type IV chromatic acclimation (CA4). The abundance of CA4-capable cells in marine ecosystems suggests that CA4 confers a fitness advantage in certain light conditions compared to cells with fixed pigmentation. This hypothesis was tested by performing mono- and co-cultures of a BL specialist, a GL specialist and a CA4-capable strain in chemostats under different light conditions. Monocultures enabled us to parameterize a resource competition model that was used to predict competition between the three pigment types in co-cultures. In line with the model predictions, the BL specialist won in low blue light and the GL specialist won in low and high green light. Interestingly, we found that while the CA4-capable strain was at a disadvantage at low light, it was able to outcompete specialists in high blue light. IMPORTANCESynechococcus cyanobacteria are ubiquitous and abundant in the lit layer of most marine ecosystems. This ubiquity relies in part on the wide pigment diversity of their light-harvesting complexes, with three main pigment types thriving in open ocean waters: green light specialists, blue light specialists and chromatic acclimaters, the latter being capable of matching their pigment content to the ambient spectral field. Here, we simulated the competition for light color that occurs between these pigment types in the field by co-culturing them in various light color and intensity conditions, and compared the resulting data to that of a competition model. This study provides new insights on how this key group of phytoplankton colonized the various spectral niches of the marine environment.

microbiology↗

bioRxiv2023

3D RNA profile of habenulae in the catshark Scyliorhinus canicula: a reference in jawed vertebrates

We report the generation of a spatially resolved RNA profile of the habenulae in a chondrichthyan, the catshark Scyliorhinus canicula. The digital profiles obtained for candidate markers of the broad territories previously characterized in this species reflect their broad characteristics, including left- or right asymmetric distributions. We use spatial autocorrelation and autocorrelation as measures to analyze these data and identify novel territory markers. These analyses lead to a refined molecular characterization of catshark habenulae and lead to extended lists of markers for the major territories previously identified. They confirm the marked asymmetry of the catshark habenulae, both in its lateral and medial components. In addition, they highlight a bilateral lateral to medial organization in radial bands, which may reflect a temporal regulation of neurogenesis. These data lead to a novel reference to explore the lmode of evolution of habenulae and of their asymmetries across gnathostomes.

developmental biology↗

bioRxiv2023

Differential acclimation kinetics of the two forms of Type IV chromatic acclimaters occurring in marine Synechococcus cyanobacteria

Synechococcus is one of two most abundant phytoplanktonic organisms of the Ocean and also displays the widest variety of pigmentation of all marine oxyphotrophs, which makes it ideally suited to colonize the variety of spectral niches occurring in the upper-lit layer of oceans. Seven Synechococcus pigment types (PTs) have been described based on the composition and chromophorylation of their light-harvesting complexes, called phycobilisomes (PBS). The most sophisticated and abundant Synechococcus PT (3d) gathers cells capable of Type IV chromatic acclimation (CA4), i.e. to reversibly modify the ratio of the blue light-absorbing phycourobilin (PUB) to the green light-absorbing phycoerythrobilin (PEB) in PBS in order to match the ambient light color. Although two genetically distinct types of CA4-capable strains, so-called PTs 3dA and 3dB, have been evidenced and found to be equally abundant in the Ocean, reasons for their prevalence in natural Synechococcus populations remain obscure. Here, acclimation experiments in different blue to green ratios of representatives of these two PTs showed that in mixed blue-green light conditions, PT 3dB strains displayed significantly higher PUB:PEB ratios than their PT 3dA counterparts. Thus, PTs 3dA and 3dB seem to differ in the ratio of blue to green light required to trigger the CA4 process. Furthermore, shift experiments between 100% BL and 100% GL conditions, and conversely, also revealed discrepancies in the acclimation pace between the two types of chromatic acclimaters, which may explain their co-occurrence in some blue green light niches.

microbiology↗