Biology subjects

Gallet, A.

Publications and source records attributed to Gallet, A..

9 recordsLinked to original sources

bioRxiv2026

The influence of nutrient enrichment and fish addition on microbial communities in water and fish guts during mesocosm experiments conducted in a tropical freshwater lagoon (Lagoon Aghien, Cote dIvoire)

Freshwater ecosystems in the intertropical zone have received considerably less scientific attention than those in temperate regions, with the notable exception of a few large and iconic lakes, such as Lake Victoria. Consequently, the diversity, functioning, and pollution sensitivity of microbial communities in these systems remain poorly understood. To investigate the short-term responses of microbial communities to nutrient enrichment and fish addition, we conducted in situ mesocosm experiments at two stations in a freshwater lagoon near Abidjan (Cote dIvoire). Phosphorus enrichment, either alone or in combination with nitrogen, led to a consistent increase in bacterial abundance across mesocosms, suggesting a potential phosphorus limitation of bacterial growth by these nutrients and consequently a potential competition for this resource between bacteria and microphytoplankton. In contrast, picophytoplankton abundances showed no clear or consistent response to nutrient enrichment, suggesting that other ecological processes may play a more important role in regulating these communities. High-throughput Illumina sequencing revealed contrasting patterns in the relative abundance of cyanobacterial and chloroplast-associated reads, depending on both nutrient enrichment and fish addition. These results, consistent with those obtained by cell counting in a previous study, suggest a potential top-down control of cyanobacteria by fish in Lagoon Aghien. In addition, nutrient (phosphorus and nitrogen combined) enrichment and fish addition significantly affected the amplicon sequence variant (ASV) composition of bacterial communities. Overall, these findings provide new insights into the drivers shaping microbial community structure in tropical freshwater ecosystems and are discussed in the context of previously published data on phytoplankton dynamics from the same experimental system.

ecology↗

bioRxiv2025

Chronic dietary ingestion of Bacillus thuringiensis spores promotes intestinal inflammation and aging in non-target adult Drosophila

Bacillus thuringiensis (Bt), a spore-forming Gram-positive bacterium, is the leading microbial insecticide used in both organic and conventional agriculture to fight lepidopteran larvae. Bt insecticides, which consist of a mix of Bt spores and crystals of entomopathogenic toxins (Cry toxins), kill target pest larvae rapidly after ingestion by destroying their intestinal epithelium. The potential adverse effects of chronic consumption of Bt spores by non-target organisms have not been thoroughly investigated. In this study, using adult Drosophila melanogaster, a non-target dipteran organism of Bt insecticides, we show that chronic ingestion of agricultural doses of spores in the diet reduces lifespan. Our results demonstrate that Bt spore ingestion affects gut morphology, promotes dysplasia, alters septate junctions and enhances epithelial permeability. In addition, we observed increased levels of inflammatory signaling pathways and reactive oxygen species. Taken together, our results indicate that chronic consumption of Bt spores promotes inflammation and oxidative stress, leading to premature aging of the gut and early lethality in Drosophila. Extended to non-target insects, which account for 85% of animal biodiversity, our study suggests that highly persistent Bt spores may have unintended long-term effects on the environment.

physiology↗

bioRxiv2025

A tumor-suppressive role of the PRC1 Polycomb epigenetic complex in the maintenance of adult Drosophila intestinal stem cell identity

Chromatin modulators, like Polycomb group proteins, are key epigenetic regulators of gene expression and are frequently mutated in cancers. In adult stem cells, epigenetic regulation maintains their identity and controls their differentiation during homeostasis or aging, but its direct role in tumorigenesis remains unclear. Here we developed a novel tumor model in Drosophila by exploring the function of Polycomb Repressive Complex 1 (PRC1) in adult intestinal stem cells (ISCs). Disrupting core PRC1 components in ISCs induces the formation of small cell clusters devoid of intestinal markers, a novel phenotype linked to premature mortality under stress. These clusters exhibit neoplastic characteristics such as overproliferation and continuous growth in serial transplantations, leading to their designation as tumor-initiating intestinal cells (TIICs). While JAK/STAT signaling contributes to TIIC growth, the NF-{kappa}B-related Toll/Imd immune pathways restrict their expansion independently of cell death. Altogether, our results highlight PRC1 as an epigenetic tumor suppressor in adult stem cells. AUTHOR SUMMARYOur research explores how stem cells in the adult intestine stay healthy and avoid becoming cancerous. We focused on a group of proteins called Polycomb Repressive Complex 1 (PRC1), which help regulate which genes are turned off in a cell. While these proteins are known to play important roles during development and cancer prevention, their function in the adult intestine has been less clear. Using the fruit fly Drosophila, we discovered that when PRC1 function is lost in intestinal stem cells, abnormal clusters of cells begin to form. These clusters grow uncontrollably, lose their normal identity, and can keep growing when transplanted--traits that are typical of cancer. Interestingly, we also found that parts of the immune system, specifically NF-{kappa}B-related pathways, can act inside these tumor cells to limit their growth--revealing a protective role that hasnt been seen before in the adult gut. This work provides new insights into how epigenetic regulation and immune signaling work together to keep stem cells from turning cancerous. It opens up new possibilities for understanding how cancers begin and how the body may naturally resist them, even at the level of the tissue.

cancer biology↗

bioRxiv2024

Spatial and temporal coordination of Duox/TrpA1/Dh31 and IMD pathways is required for the efficient elimination of pathogenic bacteria in the intestine of Drosophila larvae

Multiple gut antimicrobial mechanisms are coordinated in space and time to efficiently fight foodborne pathogens. In Drosophila melanogaster, production of reactive oxygen species (ROS) and antimicrobial peptides (AMPs) together with intestinal cell renewal play a key role in eliminating gut microbes. A complementary mechanism would be to isolate and treat pathogenic bacteria while allowing colonization by commensals. Using real-time imaging to follow the fate of ingested bacteria, we demonstrate that while commensal Lactiplantibacillus plantarum freely circulate within the intestinal lumen, pathogenic strains such as Erwinia carotovora or Bacillus thuringiensis, are blocked in the anterior midgut where they are rapidly eliminated by antimicrobial peptides. This sequestration of pathogenic bacteria in the anterior midgut requires the Duox enzyme in enterocytes, and both TrpA1 and Dh31 in enteroendocrine cells. Supplementing larval food with hCGRP, the human homolog of Dh31, is sufficient to block the bacteria, suggesting the existence of a conserved mechanism. While the IMD pathway is essential for eliminating the trapped bacteria, it is dispensable for the blockage. Genetic manipulations impairing bacterial compartmentalization result in abnormal colonization of posterior midgut regions by pathogenic bacteria. Despite a functional IMD pathway, this ectopic colonization leads to bacterial proliferation and larval death, demonstrating the critical role of bacteria anterior sequestration in larval defense. Our study reveals a temporal orchestration during which pathogenic bacteria, but not innocuous, are confined in the anterior part of the midgut in which they are eliminated in an IMD pathway dependent manner. AUTHOR SUMMARYTypically, when considering the immune response of animals to infection, we focus on classical immunity, encompassing both innate and adaptive aspects such as antimicrobials and circulating immune cells. However, a broader perspective on immunity includes additional strategies that enhance host protection, such as behavioral avoidance and internal mechanisms that restrict pathogen propagation. In our study using Drosophila larvae as a model, we uncovered spatially and temporally interconnected events that are crucial for effectively combating intestinal infections. Our findings reveal a two-step defense mechanism: first, the larvae rapidly discriminate between bacterial strains, effectively confining hazardous ones in the anterior section of the intestine. These blocked bacteria trigger the synthesis and release of antimicrobial peptides by the host, which ultimately eradicate the entrapped pathogens. Our experiments show that larvae capable of both limiting bacteria spreading and producing antimicrobial peptides withstand infections. In contrast, the absence of either one of these sequential defenses results in high mortality among the larvae, emphasizing the importance of each step and the necessity of their precise coordination in the immune response.

immunology↗

bioRxiv2023

Multi-omics analyses from a single sample: Prior metabolite extraction does not alter the 16S rRNA-based characterization of prokaryotic community in a diversity of sample types

Massive sequencing of the 16S rRNA gene has become a standard first step to describe and compare microbial communities from various samples. Parallel analysis of high numbers of samples makes it relevant to the statistical testing of the influence of natural or experimental factors and variables. However, these descriptions fail to document changes in community or ecosystem functioning. Non-targeted metabolomics are a suitable tool to bridge this gap, yet extractions protocols are different. In this study, prokaryotic community compositions are documented by 16S rRNA sequencing after direct DNA extraction, or after metabolites extraction followed by DNA extraction. Results obtained using the V3-V4 region on non-axenic cultures of cyanobacteria, lake water column, biofilm, gut of wild and lab-reared fish, indicate that prior extraction of metabolites does not influence the obtained image of prokaryotic communities. This validates sequential extraction of metabolites followed by DNA as a way to combine 16S rRNA sequencing with metabolome characterization from a single sample. This approach has the potential to complement community structure characterization with a proxy of their functioning, without the uncertainties associated with the use of separate samples.

microbiology↗

bioRxiv2022

Gut microbiota and holobiont metabolome composition of the Medaka fish (Oryzias latipes) are affected by a short exposure to the cyanobacterium Microcystis aeruginosa

Blooms of toxic cyanobacteria are a common stress encountered by aquatic fauna. Evidence indicates that long-lasting blooms affect fauna-associated microbiota. Because of their multiple roles, host-associated microbes are nowadays considered relevant to ecotoxicology, yet the respective timing of microbiota versus functional changes in holobionts response needs to be clarified. The response of gut microbiota and holobionts metabolome to exposure to a dense culture of Microcystis aeruginosa was investigated as a microcosm-simulated bloom in the model fish species Oryzias latipes (medaka). Both gut microbiota and gut metabolome displayed significant composition changes after only 2 days of exposure. A dominant symbiont, member of the Firmicutes, plummeted whereas various genera of Proteobacteria and Actinobacteriota increased in relative abundance. Changes in microbiota composition occurred earlier and faster compared to metabolome composition, suggesting that the microbiota drives the holobionts response. Liver and muscle metabolome were much less affected than guts, supporting that gut and associated microbiota are in the front row upon exposure. This study highlights that even short cyanobacterial blooms, that are increasingly frequent, trigger changes in microbiota composition and holobiont metabolome. It emphasizes the relevance of multi-omics approaches to explore organisms response to an ecotoxicological stress. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=118 SRC="FIGDIR/small/499308v1_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@112a904org.highwire.dtl.DTLVardef@16589forg.highwire.dtl.DTLVardef@1146629org.highwire.dtl.DTLVardef@3f25e4_HPS_FORMAT_FIGEXP M_FIG C_FIG Highlights- A 2-day exposure to a simulated M. aeruginosa bloom is enough to sharply decrease the Firmicute/Proteobacteria ratio in the gut of Oryzias latipes fish. - The exposure induced changes in metabolome composition after 2 days in the gut and 4 days in the liver. - The gut bacterial microbiota response occurred faster than metabolomes; we hypothesize that changes in gut microbiota may drive the gut metabolome compositional changes.

microbiology↗

bioRxiv2021

Disruption of fish gut microbiota composition and holobiont metabolome by cyanobacterial blooms

BackgroundCyanobacterial blooms are one of the most common stress encountered by metazoans living in freshwater lentic systems such as lakes and ponds. Blooms reportedly impair fish health, notably through oxygen depletion and production of bioactive compounds including cyanotoxins. However, in the times of the "microbiome revolution", it is surprising that so little is still known regarding the influence of blooms on fish microbiota. In this study, an experimental approach is used to demonstrate that blooms affect fish microbiome composition and functions, as well as the metabolome of holobionts. To this end, the model teleost Oryzias latipes is exposed to simulated Microcystis aeruginosa blooms of various intensities in a microcosm setting, and the response of bacterial gut communities is evaluated in terms of composition, metagenome-encoded functions and metabolome profiling. ResultsThe gut bacterial community of O. latipes exhibits marked responses to the presence of M. aeruginosa blooms in a dose-dependent manner. Notably, abundant gut-associated Firmicutes almost disappear, while potential opportunists increase. The holobionts gut metabolome displays major changes, while functions encoded in the metagenome of bacterial partners are more marginally affected. Bacterial communities tend to return to original composition after the end of the bloom suggesting post-bloom resilience, and remain sensitive in case of a second bloom, reflecting a highly reactive gut community. ConclusionIn the context of increasingly frequent and intense blooms worldwide, results point to the relevance of accounting for short- and long-term microbiome-related effects in fish ecology, with potential outcomes relevant to conservation biology as well as aquaculture.

microbiology↗

bioRxiv2020

Promising potential of high-throughput molecular phenotyping of freshwater fishes for environmental assessment

The recent democratization of high-throughput molecular phenotyping allows the rapid expansion of promising untargeted multi-dimensional approaches (e.g. epigenomics, transcriptomics, proteomics, metabolomics, ...). Indeed, these emerging omics tools, processed for ecologically relevant species, may present innovative perspectives for environmental assessments, that could provide early warning of eco(toxico)logical impairs. In a previous pilot study (Sotton et al., Chemosphere 2019), we explore by 1H NMR the bio-indicative potential of metabolomics analyses on the liver of 2 sentinel fish species (Perca fluviatilis and Lepomis gibbosus) collected in 8 water bodies of the peri-urban Paris area (France). In the present study, we further investigate on the same samples the great potential of high-throughput UHPLC-HRMS/MS analyses. We show that the LC-MS metabolome remarkably allows clear separation of individuals according to the species, but also according to their respective sampling lakes. Interestingly, similar variations of Perca and Lepomis metabolomes occur locally indicating that site-specific environmental constraints drive the metabolome variations beyond the obvious genetic differences between the two species, and seem to be influenced by the production of noxious metabolites by cyanobacterial blooms in certain lakes. Thus, the development of such reliable environmental metabolomics approaches is constituting an innovative bio-indicative tool for ecological stress assessment, such as toxigenic cyanobacterial blooms, and aim at being further follow up.

ecology↗

bioRxiv2019

Adverse effects of Bacillus thuringiensis bioinsecticide on non-target Drosophila species

Biopesticides based on Bacillus thuringiensis (Bt) spores and toxins are alternate pest management solutions widely used to control insect pests. Their increasing use could lead to accumulation in the environment, hence leading to chronic exposure of non-target organisms. Here, we tested for potential non-intentional side-effects of chronic exposure to Bt biopesticide on larvae of non-target Drosophila species present in Bt-treated areas. Doses up to those recommended for field application (106 CFU/g of fly medium) had no effect on the fly development, whereas doses 10 to 100-fold higher (107-108 CFU/g) increased developmental time and decreased adult emergence rates in a dose-dependent manner and with varying effect amplitudes for all the species and strains tested. For all them, all larvae died before pupation at the highest dose tested (109 CFU/g). Focusing on D. melanogaster, delayed development and reduced emergence resulted from stage-dependent larval mortality, and fitness-related traits of adult flies emerging from surviving Bt biopesticide exposure were moderately increased. The effects of Bt biopesticide seemed to result from the spores/cleaved toxins synergy, and possibly additives. While recommended doses had no effect on non-target Drosophila species, misuse or local accumulation of Bt bioinsecticides in the environment could have non-intentional side-effects on fly populations with potential implications for their associated communities.

ecology↗