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Vasse, M.

Publications and source records attributed to Vasse, M..

7 recordsLinked to original sources
bioRxiv2026

Sialidase variability in Gardnerella: genetics, taxonomy, function, and clinical presentation

Bacterial vaginosis (BV) is the most common vaginal condition among women of reproductive age. Despite over six decades of research, the pathogenesis and etiology of BV remain largely unknown. Members of the Gardnerella genus are common components of the healthy vaginal microbiota, although their uncontrolled proliferation plays a key role in BV pathogenesis. Recent taxonomic revisions have highlighted extensive genetic and functional diversity among Gardnerella spp., but the relationship between genetics, taxonomy, and virulence remains elusive. Sialidases are key virulence factors in BV, degrading the protective epithelial mucus layer, facilitating colonization and releasing carbon and nitrogen sources. However, robust clinical evidence linking sialidases to increased BV risk remains limited. Here, we analyzed clinical Gardnerella isolates from BV-positive (75%) and BV-negative (25%) samples (n = 66) collected at the University Hospital of Montpellier, France. We inferred phylogenetic relationships, characterised the nanH sialidase gene repertoire, quantified in vitro sialidase activity, and evaluated antibiotic resistance profiles. Most isolates belonged to Gardnerella clades 1, 2, and 4 (63.6%, 19.7%, and 16.7%, respectively). The three nanH genes were unevenly distributed across clades: nanH1 was most common ([~]80%), highly prevalent in clades 1-3; nanH2 was rare (6%); and nanH3 ([~]38%) was predominantly found in clade 2 - typically co-occurring with nanH1. Sialidase activity varied both between and within clades, and was only weakly associated with the nanH gene repertoire. Neither taxonomy nor sialidase-associated traits were reliable predictors of BV status, and we found no clear link between taxonomy and antibiotic resistance. Together, these results reveal substantial discordance in the genotype-phenotype relationship in Gardnerella, suggesting epigenetic, physiological and/or ecological modulation. Our findings highlight the need for a better understanding of bacterial physiology, plasticity, and ecology to explain microbial traits of clinical importance.

microbiology↗
bioRxiv2024

"This training is bound for glory": selection by experimental evolution of a bacteriophage with expanded host-range and increased virulence

Viral host range expansion is predicted to evolve at the cost of reduced mean fitness. We investigated the adaptive walks of a virulent phage (Tequintavirus) in a spatially variable environment composed of four susceptible bacterial isolates and four resistant ones (Salmonella enterica serotype Tennessee, sequence types ST5018 and ST319 respectively). Starting from a single ancestral phage, we evolved multiple independent populations through serial passages on non-coevolving bacteria, following the Appelmans protocol. The phage populations evolved an expanded host range and increased virulence. Whole-genome sequencing revealed recurrent parallel mutations across populations (i.e. convergent evolution), particularly in genes encoding exo- and endo-nucleases, dUTPase, and caudal proteins. Notably, two parallel mutations in the gene coding for the Long Tail Fibre became fixed early in the evolutionary trajectories. Reverse-genetics experiments introducing these mutations into the ancestral genome expanded the host range but yielded only marginal increases in virulence, highlighting the effect of compensatory mutations. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=115 SRC="FIGDIR/small/584857v3_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@cec6b5org.highwire.dtl.DTLVardef@1579ba4org.highwire.dtl.DTLVardef@ab5ad5org.highwire.dtl.DTLVardef@1d88160_HPS_FORMAT_FIGEXP M_FIG C_FIG Highlights* A phage (Tequintavirus) was evolved on susceptible and resistant Salmonella enterica strains * Experimentally evolved phage populations displayed expanded host range and increased virulence * Convergent evolution revealed adaptive mutations modifying receptor recognition in caudal proteins * Reverse-genetic showed implication of two Long Tail Fibre mutations in host range expansion In BriefGeneralism is traditionally predicted to evolve at the cost of lower mean fitness. Contrary to this textbook view, we demonstrate that generalist phages with expanded host range and increased virulence can readily evolve in vitro and be purposely optimized for phage therapy applications.

evolutionary biology↗
bioRxiv2021

Behavioral interactions between bacterivorous nematodes and predatory bacteria in a synthetic community

Theory and empirical studies in metazoans predict that apex predators should shape the behavior and ecology of mesopredators and prey at lower trophic levels. Despite the ecological importance of microbial communities, few studies of predatory microbes examine such behavioral responses and the multiplicity of trophic interactions. Here, we sought to assemble a three-level microbial food chain and to test for behavioral interactions between the predatory nematode Caenorhabditis elegans and the predatory social bacterium Myxococcus xanthus when cultured together with two basal prey bacteria that both predators can eat - Escherichia coli and Flavobacterium johnsoniae. We find that >90% of C. elegans worms failed to interact with M. xanthus even when it was the only potential prey species available, whereas most worms were attracted to pure patches of E. coli and F. johnsoniae. In addition, M. xanthus altered nematode predatory behavior on basal prey, repelling C. elegans from two-species patches that would be attractive without M. xanthus, an effect similar to that of C. elegans pathogens. The nematode also influenced the behavior of the bacterial predator: M. xanthus increased its predatory swarming rate in response to C. elegans in a manner dependent both on basal-prey identity and on worm density. Our results suggest that M. xanthus is an unattractive prey for some soil nematodes and is actively avoided when more lucrative prey are available. Most broadly, we find that nematode and bacterial predators mutually influence one anothers predatory behavior, with likely consequences for coevolution within complex microbial food webs.

ecology↗
bioRxiv2021

Allopatric divergence limits cheating range and alters genetic requirements for a cooperative trait

Social defectors may meet diverse cooperators. Genotype-by-genotype interactions may constrain the ranges of cooperators upon which particular defectors can cheat, limiting cheater spread. The bacterium Myxococcus xanthus undergoes cooperative multicellular development, but some developmental defectors cheat on cooperators during this process. In this study, interactions between a cheater disrupted at the signaling gene csgA and allopatrically diversified cooperators reveal a very small cheating range. Expectedly, the cheater failed to cheat on all natural-isolate cooperators owing to non-cheater-specific antagonisms. Surprisingly, lab-evolved cooperators that diverged from their cheating-susceptible ancestor by fewer than 20 mutations and without experiencing cheating had already exited the csgA mutants cheating range. Cooperators might also diversify in the potential for a mutation to reduce expression of cooperative trait or generate a cheating phenotype. A new csgA mutation constructed in several highly diverged cooperators generated diverse sporulation phenotypes, ranging from a complete defect to no defect, indicating that genetic backgrounds can limit the set of genomes in which a mutation creates a defector. Our results suggest that natural populations feature geographic mosaics of cooperators that have diversified in their susceptibility to particular cheaters and in the phenotypes generated by any given cooperation-gene mutation. Significance statementSelection on cooperators exploited by obligate cheaters can induce evolution of resistance to cheating. Here we show that cooperators can also rapidly evolve immunity to cheating simply as a byproduct of evolutionary divergence in environments in which cooperation and cheating at the focal trait do not occur because the trait is not expressed. We also find that differences in the genomic context in which a cooperation-gene mutation arises can profoundly alter its phenotypic effect and determine whether the mutation generates a social defect at all - a pre-requisite for obligate cheating. These findings suggest that general divergence of social populations under a broad range of environmental conditions can restrict both the set of mutations that might generate social defectors in the first place and the host range of such defectors once they arise.

evolutionary biology↗
bioRxiv2020

Hidden paths to endless forms most wonderful: Parasite-blind diversification of host quality

Evolutionary diversification can occur in allopatry or sympatry, can be unselected or driven by selection, and can be phenotypically manifested immediately or remain phenotypically latent until later manifestation in a newly encountered environment. Diversification of host-parasite interactions is frequently studied in the context of intrinsically selective coevolution, but the potential for host-parasite interaction phenotypes to diversify latently during parasite-blind evolution is rarely considered. Here we use a social bacterium experimentally adapted to several environments in the absence of phage to analyse allopatric diversification of latent host quality - the degree to which a host population supports a viral epidemic. Phage-blind evolution reduced host quality overall, with some bacteria becoming completely resistant to growth suppression by phage. Selective-environment differences generated only mild divergence in host-quality. However, selective environments nonetheless played a major role in shaping evolution by determining the degree of stochastic diversification among replicate populations within treatments. Ancestral motility genotype was also found to strongly shape patterns of latent hostquality evolution and diversification. These outcomes show that adaptive landscapes can differ in how they constrain stochastic diversification of a latent phenotype and that major effects of selection on biological diversification can be missed by focusing on trait means. Collectively, our findings suggest that latent-phenotype evolution (LPE) should inform host-parasite evolution theory and that diversification should be conceived broadly to include latent phenotypes.

evolutionary biology↗
bioRxiv2020

Ecological effects of stress drive bacterial evolvability under sub-inhibitory antibiotic treatments

1Stress is thought to increase mutation rate and thus to accelerate evolution. In the context of antibiotic resistance, sub-inhibitory treatments could then lead to enhanced evolvability, thereby fueling the adaptation of pathogens. Conducting a meta-analysis of published experimental data as well as our own experiments, we found that the increase in mutation rates triggered by antibiotic treatments is often canceled out by reduced population size, resulting in no overall increase in genetic diversity. A careful analysis of the effect of ecological factors on genetic diversity revealed that the potential for regrowth during recovery phase after treatment plays a crucial role in evolvability and is the main predictor of increased genetic diversity in experimental data.

evolutionary biology↗