Biology subjects

Fauvet, C.

Publications and source records attributed to Fauvet, C..

4 recordsLinked to original sources

bioRxiv2026

Epidemic Risks associated with high-temperature replicating infectious hematopoietic necrosis virus (IHNV) field isolates: from molecular characterization to host pathogen interactions

Infectious hematopoietic necrosis virus (IHNV) is a WOAH-notifiable pathogen responsible for severe acute disease in salmonids at temperatures ranging from 4 to 14{degrees}. At higher water temperatures, the disease is generally associated with reduced mortality and lower viral replication. In the context of climate change, rising water temperatures could favor the emergence of thermotolerant strains while representing a major physiological and metabolic stress potentially altering fish's immune responses. This study aims to characterize the impact of increasing water temperatures on IHNV replication and host-pathogen interactions. Following pre-screening, the replication kinetics of the reference strain N61 and two field isolates RtNag0a and SA-22 were characterized in EPC (Epithelioma Papulosum Cyprini) and RTG-2 (Rainbow trout gonad) cell lines at 14, 20 and 22{degrees}. Virulence and host-pathogen interactions were subsequently investigated in vivo in zebrafish (Zf) larvae using complementary microinjection and bath immersion infection models at 21.5 and 23.5{degrees}. In vitro studies revealed distinct thermal replication profiles, distinguishing thermosensitive from thermotolerant isolates, although these phenotypes were influenced by the cellular environment. The zebrafish model enabled the characterization of virulence and antiviral host responses associated with thermotolerant IHNV isolates. Notably, waterborne infection proved effective, contrasting with previous reports describing this exposure route as unsuitable for IHNV studies. These findings expand the growing list of emerging European IHNV genotypes capable of replicating at elevated temperatures (>20{degrees}) and establish zebrafish larvae as a relevant model for virulence assessment of field isolates. Together, these results provide valuable insights into the potential impact of climate warming on IHNV epidemiology and support efforts to predict and anticipate future outbreaks under changing environmental conditions.

pathology↗

bioRxiv2026

Molecular characterization of thermo-adapted Novirhabdovirus variants and virulence in vivo in rainbow trout and zebrafish at different temperatures.

Controlling viral diseases in fish is a challenge for the sustainable development of aquaculture and improving the health of fish farms. Infectious hematopoietic necrosis virus (IHNV) is a major pathogen in aquaculture. It infects cold-water fish, but loses its infectivity at temperatures above 20{degrees}C. Since fish are poikilothermic animals, their body temperature fluctuates according to that of their environment. Faced with current climate change, it is crucial to understand how these pathogens will adapt to rising temperatures. Through a strategy simulating the impact of global warming, this virus has been progressively thermo-adapted to 25{degrees}C. The selected variant, IHNV25, replicates at 25{degrees}C while maintaining efficient replication at low temperatures, like its parental strain. Genome sequencing and a reverse genetics approach revealed that only 9 amino acid substitutions, distributed across 4 of the 6 viral genes, were essential for thermo-adaptation. Although IHNV25 was highly attenuated in its natural host, the rainbow trout, at any temperatures, it proved highly virulent when injected in zebrafish larvae at 20{degrees}C and 25{degrees}C, inducing severe symptoms identical to those observed in trout (hemorrhages, oedema, and exophthalmia). At both temperatures, mortality was preceded by a massive viral replication and a delayed and inefficient interferon and inflammatory response. Unlike the parental strain, IHNV25 was also capable of infecting larvae by bath immersion at 25{degrees}C, entering via the caudal fin, thus demonstrating its ability to cross the species barrier. The identification of viral markers of thermo-adaptation will therefore be of great interest for the epidemiological surveillance of field isolates.

microbiology↗

bioRxiv2025

Nucleoside Binding by a Surface Lipoprotein Governs Conjugative ICE Acquisition in Ruminant Mycoplasmas

Integrative and conjugative elements (ICEs) are major mediators of horizontal gene transfer (HGT) in bacteria. However, the role of recipient cells in their acquisition has received little attention. Using the ruminant pathogens Mycoplasma agalactiae and Mycoplasma bovis as minimal models, we combined genome-wide transposon mutagenesis with high-throughput mating assays to identify recipient factors required for ICE acquisition. The surface lipoprotein P48 emerged as the primary determinant of ICE uptake in both species. Structural and functional analyses revealed that P48 is the substrate-binding component of an ABC transporter with nucleoside-binding capacity. A single point mutation that abolished nucleoside binding drastically reduced ICE acquisition, demonstrating that P48-mediated nucleoside recognition is essential for conjugative transfer. However, ICE uptake did not require nucleoside transport, as inactivation of the transporter permease blocked nucleoside analog toxicity but not ICE invasion. Loss of P48 also triggered transcriptional activation of vestigial ICE genes, suggesting that surface recognition affects the intracellular state of the recipient. Remarkably, ICE transmission from recipient-derived donors was unaffected by P48 loss, underscoring its acquisition-specific role. Together, these results reveal a previously unrecognized, surface-exposed recipient factor critical for efficient ICE transfer in mycoplasmas and identify nucleotide binding as a central function in conjugation. By demonstrating that recipient-encoded functions can directly control ICE dissemination, this work challenges the donor-centric paradigm of bacterial conjugation and suggests new strategies to restrict horizontal gene flow in pathogenic and synthetic mycoplasmas. IMPORTANCEIntegrative and conjugative elements (ICEs) are mobile DNA elements that drive bacterial conjugation, a major process by which bacteria exchange genes. Although conjugation has been studied for decades, the focus has been almost exclusively on donor cells and the ICE itself, leaving the role of recipient cells largely overlooked. Using the wall-less ruminant pathogens Mycoplasma agalactiae and Mycoplasma bovis as minimal models, we discovered that a single recipient lipoprotein is required for efficient ICE uptake. Our data show that nucleoside recognition by P48, but not transport, is critical for conjugation, revealing an unexpected mechanistic link between nutrient sensing and gene acquisition. These findings shift the paradigm of conjugation from a donor-driven process to one jointly determined by donor and recipient functions. By identifying a recipient-encoded determinant of ICE transfer, this work opens new avenues to control horizontal gene flow in both pathogenic and engineered bacteria. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=151 SRC="FIGDIR/small/677790v1_ufig1.gif" ALT="Figure 1"> View larger version (26K): org.highwire.dtl.DTLVardef@f7cc15org.highwire.dtl.DTLVardef@77a34eorg.highwire.dtl.DTLVardef@82699corg.highwire.dtl.DTLVardef@1e3be93_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2025

In silico reconstruction of a salmonid alphavirus virion reveals distinctive structural and molecular features implicated in virulence in vivo

Salmonid alphavirus (SAV) poses a significant disease threat to aquaculture. Recently, new alphaviruses from several fish species have been discovered. However, little is known about their biology and diseases potential. Alphaviruses are considered to have originated from a marine environment; therefore, studying fish alphaviruses can inform on the evolutionary history of the genus. Contrary to many terrestrial alphaviruses, there are currently no experimentally-determined structures for aquatic alphaviruses, severely limiting their study. In this work, we harness the power of structural bioinformatics and AlphaFold to reconstruct an entire SAV virion, thereby revealing an exposed and distinctive -helical feature in its E2 envelope protein. Using an integrative approach, we explore the sequence diversity and evolutionary conservation of this predicted feature and investigate the functional consequences of variations on viral fitness and virulence. This study provides a novel framework paving the way to better understand aquatic alphavirus pathogenicity and host species adaptation.

microbiology↗