Biology subjects

Guerin, S.

Publications and source records attributed to Guerin, S..

5 recordsLinked to original sources

bioRxiv2026

Paradoxical energetics in the polar diatom Fragilariopsis cylindrus exposed to extreme low light

In the Arctic Ocean, diatoms initiate blooms under sea ice at extreme low-light levels, yet the limits and mechanisms behind this capability remain unknown. We investigated the steady-state physiological and molecular responses of the polar diatom Fragilariopsis cylindrus across a light gradient (0.1 to 30 {micro}mol photons m-2 s-1), representative of under-ice winter to early spring conditions, and reveals distinct strategies to cope with low light at both ends of this range. While cells optimize photon capture efficiency between 3 and 15 {micro}mol photons m-2 s-1 relative to 30 {micro}mol photons m-2 s-1, this strategy collapses below 1 {micro}mol photons m-2 s-1. In this dim-light regime, cells activate non-photochemical quenching and a sustained xanthophyll cycle, which indicates a paradoxical requirement for energy dissipation despite extreme photon scarcity. While cell division arrests at 0.18 {micro}mol photons m-2 s-1, photosynthetic electron transport seems to remain possible down to 0.1 {micro}mol photons m-2 s-1, which suggests an uncoupling between photosynthesis and biomass accumulation. Crucially, this low-light regime occurs without the consumption of reserves and represents a physiological state distinct from metabolic hypometabolism in prolonged darkness. We propose that this dim-light physiological state arises when residual light absorption exceeds the energetic requirements for cellular maintenance in the absence of division. The result is a regulated imbalance dissipated through heat and carbon excretion. This mechanism allows polar diatoms to maintain a primed photosynthetic metabolism to facilitate rapid growth recovery upon the return of light after the winter solstice.

plant biology↗

bioRxiv2025

Human milk bacteria assembled into functionally distinct synthetic communities in infant formula differently affect intestinal physiology and microbiota in neonatal mini-piglets

The contribution of Human milk (HM) microbiota to infant gut health was addressed by evaluating the impact of HM bacteria, combined in two synthetic communities (SynComs) exhibiting anti-inflammatory (AI) or high immunomodulatory (HI) properties in vitro, on gut immune and barrier functions, and microbiota. Neonatal mini-piglets were fed either a formula without supplementation (CTRL) or supplemented with AI or HI SynComs, and were compared to sow milk-fed (SM) piglets over a period of 24 days. Feces were collected on postnatal day (PND) 8, and ileal, colonic and fecal samples were collected on PND24. The multifactorial analysis indicated that the two HM-derived SynComs impacted microbiota and intestinal functions differently. Several genera, mainly belonging to Bacillota, displayed different relative abundances between the formula-fed groups at both PND8 and PND24. At PND8, the fecal sIgA level in HI piglets was slightly lower than in SM piglets but markedly higher than in CTRL and AI piglets. SynComs HI and/or AI slightly increased the expression of genes involved in pro-inflammatory (IL6, TNFaR1), antioxidant (SOD2), anti-inflammatory (SOCS3) and Treg (FOXP3) pathways in ileal and colonic tissues compared with the CTRL group. Systemic immune functions were also modulated with a cytokine secretion capacity of peripheral blood mononuclear cells that tended to be higher with HI supplementation. Interestingly, SynCom bacteria were correlated with several ileal and colonic genera, and both were correlated with physiological variables. Overall, our findings support the influence of HM bacteria, provided in formulas as SynCom at a physiological concentration, on gut microbiota and functions. ImportanceEarly-life environmental factors, such as neonatal diet, influence the gut microbiota, which plays a key role in the functional development of the gut. However, the role of the human milk (HM) microbiota, particularly with regard to the immunomodulatory properties of HM bacteria, is not well understood. This study investigates the differential effects of two synthetic communities with a similar taxonomic composition representative of the taxonomic diversity of the HM microbiota. Thse communities exhibit contrasting immunomodulatory properties that were previously characterized using an in vitro intestinal quadricellular model. Daily supplementation with these two SynComs modulated the composition of the gut microbiota and the gut physiology differently, particularly the intestinal immune signatures. In conclusion, the functional profile of bacteria within the HM microbiota may induce distinct developmental profiles of gut physiology in infants.

physiology↗

bioRxiv2023

Hypometabolism to survive the long polar night in the diatom Fragilariopsis cylindrus

Diatoms, the major eukaryotic phytoplankton in polar regions, are essential to sustain Arctic and Antarctic ecosystems. As such, it is fundamental to understand the physiological mechanisms and associated molecular basis of their resilience to the long polar night. Here, we report an integrative approach revealing that in prolonged darkness, diatom cells enter a state of quiescence associated with reduced metabolic and transcriptional activity during which no cell division occurs. We propose that minimal energy is provided by respiration and degradation of protein, carbohydrate, and lipid stores and that homeostasis is maintained by autophagy in prolonged darkness. We also report internal structural changes that manifest the morphological acclimation of cells to darkness. Our results further indicate that immediately following a return to light, diatom cells are able to use photoprotective mechanisms and rapidly resume photosynthesis. Cell division resumed rates similar to those before darkness. Our study demonstrates the remarkable robustness of polar diatoms to prolonged darkness at low temperatures. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=160 SRC="FIGDIR/small/524047v1_ufig1.gif" ALT="Figure 1"> View larger version (55K): org.highwire.dtl.DTLVardef@1da578corg.highwire.dtl.DTLVardef@1a9ac5borg.highwire.dtl.DTLVardef@729265org.highwire.dtl.DTLVardef@1e94c18_HPS_FORMAT_FIGEXP M_FIG C_FIG TeaserTo survive the long winter, polar diatoms slow down metabolism and express genes to assure survival following return to light.

ecology↗

bioRxiv2020

KLF10 integrates circadian timing and sugar signaling to coordinate hepatic metabolism

The mammalian circadian timing system and metabolism are highly interconnected, and disruption of this coupling is associated with negative health outcomes. Kruppel-like factors (KLFs) are transcription factors that govern metabolic homeostasis in various organs. Many KLFs show a circadian expression in the liver. Here, we show that the loss of the clock-controlled KLF10 in hepatocytes results in extensive reprogramming of the mouse liver circadian transcriptome, which in turn, alters the temporal coordination of pathways associated with energy metabolism. We also show that glucose and fructose induce Klf10, which helps mitigate glucose intolerance and hepatic steatosis in mice challenged with a sugar beverage. Functional genomics further reveal that KLF10 target genes are primarily involved in central carbon metabolism. Together, these findings show that in the liver, KLF10 integrates circadian timing and sugar metabolism related signaling, and serves as a transcriptional brake that protects against the deleterious effects of increased sugar consumption.

cell biology↗

bioRxiv2018

Facilitating Patient and Public Involvement in basic and preclinical health research.

Involving patients in research broadens a researchers field of influence and may generate novel ideas. Preclinical research is integral to the progression of innovative healthcare. These are not patient-facing disciplines and implementing meaningful PPI can be a challenge. A discussion forum and thematic analysis identified key challenges of implementing PPI for preclinical researchers. In response we developed a \"PPI Ready\" planning canvas. For contemporaneous evaluation of PPI, a psychometric questionnaire and an open source tool for its evaluation were developed. The questionnaire measures information, procedural and quality assessment. Combined with the open source evaluation tool, researchers are notified if PPI is unsatisfactory in any of these areas. The tool is easy to use and adapts a psychometric test into a format familiar to preclinical scientists. Designed to be used iteratively across a research project, it provides a simple reporting grade to document satisfaction trend over the research lifecycle.

scientific communication and education↗