Biology subjects

Hamet, J.

Publications and source records attributed to Hamet, J..

3 recordsLinked to original sources

bioRxiv2026

The attachment rate of Vibrio anguillarum strains to microplastics strongly varies with abiotic and biotic factors

Microplastics (MPs), resulting from plastic objects and waste degradation, are increasingly abundant, particularly in marine environments. They exhibit a hydrophobic surface on which biofilms form easily. Metagenomic analyses of these biofilms have revealed that they often contain bacterial species potentially pathogenic to humans or animals. For this reason, MPs are suspected to present a risk for public health by acting as a vector for pathogenic bacteria species. To better understand this hazard, we studied different factors potentially affecting the bacterial attachment rate to MPs. Focusing on the fish pathogen Vibrio anguillarum, a collection of 16 strains was assembled and GFP-labelled. Their attachment rates were measured using fluorescence microscopy on three types of MPs (milled polypropylene and polyethylene terephthalate particles and commercially available polystyrene beads). A strong effect of the particle type was found, likely linked to both the chemical composition of the particles and the surface characteristics, with higher attachment rates on rough particles. Our results also revealed a strong intra-specific variation in attachment rate, highlighting the need of testing several strains of the same species to assess attachment rate and related hazards. Finally, it was observed that when a biofilm already formed on the MPs (by field-incubation of the MPs along the Mediterranean French coast), differences in attachment rates between particle types were erased. It was concluded that the attachment rate of V. anguillarum depends on a combination of biotic and abiotic factors, which makes risk assessment of MPs as vectors of pathogenic bacteria species a very complex task.

microbiology↗

bioRxiv2025

Environmental complexity constrains evolutionary adaptation across taxa

Complex environments combining multiple stressors are the new norm worldwide. Adaptive evolution will be critical to population persistence under these combined challenges, but how environmental complexity affects the pace of evolution remains poorly understood. Using a meta-experimental evolution approach, we exposed 14 species, from bacteria to unicellular eukaryotes and plants, to single stressors and their pairwise combinations for multiple generations, while keeping the overall stress level comparable. Populations evolving under combined stressors tended to have lower fitness increase in the selective environments, higher fitness reductions in the control environment, and shallower relation between initial maladaptation and fitness gain, than under single stressors. However, these responses varied with species and stressor type. Accounting for such constraints on evolutionary dynamics should prove crucial for the management of biodiversity. Significance StatementA pressing challenges for modern science and society in the face of ongoing global change is understanding what limits the capacity of living organisms to adapt to complex environments combining multiple stressors. To answer to this question, we conducted a large-scale meta-experimental evolution design across a diversity of organisms, exposing them for multiple generations to either single or combined-stress treatments. Combined stressors led to less adaptive fitness gain than single stressors, and imposed additional costs through reduced fitness in non-stressful conditions. This unique combination of meta-experimental approach with a careful distinction between environmental complexity and overall stress allowed us to gain robust quantitative evidence on how environmental complexity can impact the pace of evolution.

evolutionary biology↗

bioRxiv2024

Hurdles to Horizontal Gene Transfer: Synonymous variation determines antibiotic resistance phenotype across species

Evidence that synonymous mutations and synonymous gene variants have fitness effects have accumulated recently. Since horizontal gene transfer represents a change in the genome of expression of the transferred gene, we hypothesized that the codon usage preferences of a horizontally transferred gene could determine the conferred fitness advantage or disadvantage, condition the immediate success of the transfer and in the longer term orient transfers. To test this hypothesis, we characterized resistance levels of synonymous variants of a gentamicin resistance gene, inserted into a broad-host range plasmid and transformed into three different bacterial species Escherichia coli, Acinetobacter baylyi and Pseudomonas aeruginosa. We revealed a strong species effect, explained in part by differences in plasmid copy number between host species. Importantly, the relative levels of resistance conferred by each synonymous variant were not conserved across species, indicating that these phenotypic effects are due to differing compatibility between the transferred variants and the receiver bacterial genomes. This species-variant interaction confirms that the codon composition of a gene can be a determinant of post-horizontal gene transfer success. However, the similarity in codon usage between the synonymous variants and the host genome only explained the phenotypic differences between variants in one species, P. aeruginosa. Further investigations of the effects of local codon usage, translation bottlenecks and internal Shine-Dalgarno sequences did not reveal common universal mechanisms across our three bacterial species and point to multiple paths leading from the synonymous sequence to phenotype and a species-specific sensitivity to these different paths.

evolutionary biology↗