Biology subjects

Lassalle, F.

Publications and source records attributed to Lassalle, F..

8 recordsLinked to original sources

bioRxiv2025

Benchmarking of Human ReadRemoval Strategies for Viral andMicrobial Metagenomics

Human reads are a key contaminant in microbial metagenomics and enrichment-based studies, requiring removal for computational efficiency, biological analysis, and privacy protection. Various in silico methods exist, but their effectiveness depends on the parameters and reference genomes used. Here, we assess different methods, including the impact of the updated T2T-CHM13 human genome versus GRCh38. Using a synthetic dataset of viral and human reads, we evaluated performance metrics for multiple approaches. We found that the usage of high-sensitivity configuration of Bowtie2 with the T2T-CHM13 reference assembly significantly improves human read removal with minimal loss of specificity, albeit at higher computational cost compared to other methods investigated. Applying this approach to a publicly available microbiome dataset, we effectively removed sex-determining SNPs with little impact on microbial assembly. Our results suggest that our high-sensitivity Bowtie2 approach with the T2T-CHM13 is the best method tested to minimise identifiability risks from residual human reads.

genomics↗

bioRxiv2022

Genomic epidemiology of the cholera outbreak in Yemen reveals the spread of a multi-drug resistance plasmid between diverse lineages of Vibrio cholerae

The humanitarian crisis in Yemen led in 2016 to the biggest cholera outbreak documented in modern history, with more than 2.5 million suspected cases to date. In late 2018, epidemiological surveillance showed that V. cholerae isolated from cholera patients had turned multi-drug resistant (MDR). We generated genomes from 260 isolates sampled in Yemen between 2018 and 2019 to identify a possible shift in circulating genotypes. 84% of V. cholerae isolates were serogroup O1 belonging to the seventh pandemic El Tor (7PET) lineage, sublineage T13 - same as in 2016 and 2017 - while the remaining 16% of strains were non-toxigenic and belonged to divergent V. cholerae lineages, likely reflecting sporadic gut colonisation by endemic strains. Phylogenomic analysis reveals a succession of T13 clones, with 2019 dominated by a clone that carried an IncC-type plasmid harbouring an MDR pseudo-compound transposon (PCT). Identical copies of these mobile elements were found independently in several unrelated lineages, suggesting exchange and recombination between endemic and epidemic strains. Treatment of severe cholera patients with macrolides in Yemen from 2016 to early 2019 coincides with the emergence of the plasmid-carrying T13 clone. The unprecedented success of this genotype where an SXT-family integrative and conjugative element (SXT/ICE) and an IncC plasmid coinhabit show the stability of this MDR plasmid in the 7PET background, which may durably reduce options for epidemic cholera case management. We advocate a heightened genomic epidemiology surveillance of cholera to help control the spread of this highly-transmissible, MDR clone.

microbiology↗

bioRxiv2021

Taxonomy of Rhizobiaceae revisited: proposal of a new framework for genus delimitation

The alphaproteobacterial family Rhizobiaceae is highly diverse, with 168 species with validly published names classified into 17 genera with validly published names. Most named genera in this family are delineated based on genomic relatedness and phylogenetic relationships, but some historically named genera show inconsistent distribution and phylogenetic breadth. Most problematic is Rhizobium, which is notorious for being highly paraphyletic, as most newly described species in the family being assigned to this genus without consideration for their proximity to existing genera, or the need to create novel genera. In addition, many Rhizobiaceae genera lack synapomorphic traits that would give them biological and ecological significance. We propose a common framework for genus delimitation within the family Rhizobiaceae. We propose that genera in this family should be defined as monophyletic groups in a core-genome gene phylogeny, that are separated from related species using a pairwise core-proteome average amino acid identity (cpAAI) threshold of approximately 86%. We further propose that the presence of additional genomic or phenotypic evidence can justify the division of species into separate genera even if they all share greater than 86% cpAAI. Applying this framework, we propose to reclassify Rhizobium rhizosphaerae and Rhizobium oryzae into the new genus Xaviernesmea gen. nov. Data is also provided to support the recently proposed genus "Peteryoungia", and the reclassifications of Rhizobium yantingense as Endobacterium yantingense comb. nov., Rhizobium petrolearium as Neorhizobium petrolearium comb. nov., Rhizobium arenae as Pararhizobium arenae comb. nov., Rhizobium tarimense as Pseudorhizobium tarimense comb. nov., and Rhizobium azooxidefex as Mycoplana azooxidifex comb. nov. Lastly, we present arguments that the unification of the genera Ensifer and Sinorhizobium in Opinion 84 of the Judicial Commission is no longer justified by current genomic and phenotypic data. We thus argue that the genus Sinorhizobium is not illegitimate and now encompasses 17 species.

microbiology↗

bioRxiv2020

Revisiting the taxonomy of Allorhizobium vitis (i.e. Agrobacterium vitis) using genomics - emended description of All. vitis sensu stricto and description of Allorhizobium ampelinum sp. nov.

BackgroundAllorhizobium vitis (formerly named Agrobacterium vitis or Agrobacterium biovar 3) is the primary causative agent of crown gall disease of grapevine worldwide. We obtained and analyzed whole-genome sequences of diverse All. vitis strains to get insights into their diversification and taxonomy. ResultsPairwise genome comparisons and phylogenomic analysis of various All. vitis strains clearly indicated that All. vitis is not a single species, but represents a species complex composed of several genomic species. Thus, we emended the description of All. vitis, which now refers to a restricted group of strains within the All. vitis species complex (i.e. All. vitis sensu stricto) and proposed a description of a novel species, All. ampelinum sp. nov. The type strain of All. vitis sensu stricto remains the current type strain of All. vitis, K309T. The type strain of All. ampelinum sp. nov. is S4T. We also identified sets of gene clusters specific to the All. vitis species complex, All. vitis sensu stricto and All. ampelinum, respectively, for which we predicted the biological function and infer the role in ecological diversification of these clades, including some we could experimentally validate. All. vitis species complex-specific genes confer tolerance to different stresses, including exposure to aromatic compounds. Similarly, All. vitis sensu stricto-specific genes confer the ability to degrade 4-hydroxyphenylacetate and a putative compound related to gentisic acid. All. ampelinum-specific genes have putative functions related to polyamine metabolism and nickel assimilation. Congruently with the genome-based classification, All. vitis sensu stricto and All. ampelinum were clearly delineated by MALDI-TOF MS analysis. Moreover, our genome-based analysis indicated that Allorhizobium is clearly separated from other genera of the family Rhizobiaceae. ConclusionsComparative genomics and phylogenomic analysis provided novel insights into the diversification and taxonomy of Allorhizobium vitis species complex, supporting our redefinition of All. vitis sensu stricto and description of All. ampelinum. Our pan-genome analyses suggest that these species have differentiated ecologies, each relying on specialized nutrient consumption or toxic compound degradation to adapt to their respective niche.

genomics↗

bioRxiv2019

Whole genome sequencing of Herpes Simplex Virus 1 directly from human cerebrospinal fluid reveals selective constraints in neurotropic viruses.

Herpes Simplex Virus type 1 (HSV-1) chronically infects over 70% of the global population. Clinical manifestations are largely restricted to recurrent epidermal vesicles. However, HSV-1 also leads to encephalitis, the infection of the brain parenchyma, with high associated rates of mortality and morbidity. In this study, we performed target enrichment followed by direct sequencing of HSV-1 genomes, using target enrichment methods on the cerebrospinal fluid (CSF) of clinical encephalitis patients and from skin swabs of epidermal vesicles on non-encephalopathic patients. Phylogenetic analysis revealed high inter-host diversity and little population structure. By contrast, samples from different lesions in the same patient clustered with similar patterns of allelic variants. Comparison of consensus genome sequences shows HSV-1 has been freely recombining, except for distinct islands of linkage disequilibrium (LD). This suggests functional constraints prevent recombination between certain genes, notably those encoding pairs of interacting proteins. Distinct LD patterns characterised subsets of viruses recovered from CSF and skin lesions, which may reflect different evolutionary constraints in different body compartments. Functions of genes under differential constraint related to immunity or tropism and provide new hypotheses on tissue-specific mechanisms of viral infection and latency.

evolutionary biology↗

bioRxiv2019

Diversity and evolution of surface polysaccharide synthesis loci in Enterobacteriales

Bacterial capsules and lipopolysaccharides are diverse surface polysaccharides (SPs) that serve as the frontline for interactions with the outside world. While SPs can evolve rapidly, their diversity and evolutionary dynamics across different taxonomic scales has not been investigated in detail. Here, we focused on the bacterial order Enterobacteriales (including the medically-relevant Enterobacteriaceae), to carry out comparative genomics of two SP locus synthesis regions, cps and kps, using 27,334 genomes from 45 genera. We identified high-quality cps loci in 22 genera and kps in 11 genera, around 4% of which were detected in multiple species. We found SP loci to be highly dynamic genetic entities: their evolution was driven by high rates of horizontal gene transfer (HGT), both of whole loci and component genes, and relaxed purifying selection, yielding large repertoires of SP diversity. In spite of that, we found the presence of (near-)identical locus structures in distant taxonomic backgrounds that could not be explained by recent exchange, pointing to long-term selective preservation of locus structures in some populations. Our results reveal differences in evolutionary dynamics driving SP diversity within different bacterial species, with lineages of Escherichia coli, Enterobacter hormachei and Klebsiella aerogenes most likely to share SP loci via recent exchange; and lineages of Salmonella enterica, Citrobacter sakazakii and Serratia marcescens most likely to share SP loci via other mechanisms such as long-term preservation. Overall, the evolution of SP loci in Enterobacteriales is driven by a range of evolutionary forces and their dynamics and relative importance varies between different species.

evolutionary biology↗

bioRxiv2019

Phylogenomic analysis reveals the basis of adaptation of Pseudorhizobium species to extreme environments

The family Rhizobiaceae includes many genera of soil bacteria, often isolated for their association with plants. Herein, we investigate the genomic diversity of a group of Rhizobium species and unclassified strains isolated from atypical environments, including seawater, rock matrix or polluted soil. Based on whole-genome similarity and core genome phylogeny, we show that this group corresponds to the genus Pseudorhizobium. We thus reclassify Rhizobium halotolerans, R. marinum, R. flavum and R. endolithicum as P. halotolerans comb. nov., P. marinum comb. nov., P. flavum comb. nov. and R. endolithicum comb. nov., respectively, and show that P. pelagicum is a synonym of P. marinum. We also delineate a new chemolithoautotroph species, P. banfieldiae sp. nov., whose type strain is NT-26T (= DSM 106348T = CFBP 8663T). This genome-based classification was supported by a chemotaxonomic comparison, with gradual taxonomic resolution provided by fatty acid, protein and metabolic profiles. In addition, we used a phylogenetic approach to infer scenarios of duplication, horizontal transfer and loss for all genes in the Pseudorhizobium pangenome. We thus identify the key functions associated with the diversification of each species and higher clades, shedding light on the mechanisms of adaptation to their respective ecological niches. Respiratory proteins acquired at the origin of Pseudorhizobium are combined with clade-specific genes to encode different strategies for detoxification and nutrition in harsh, nutrient-poor environments. Finally, we predict diagnostic phenotypes for the distinction of P. banfieldiae from other Pseudorhizobium species, including autotrophy and sensitivity to the azo dye Congo Red, which we experimentally validated.

microbiology↗

bioRxiv2019

Automated reconstruction of all gene histories in large bacterial pangenome datasets and search for co-evolved gene modules with Pantagruel

The availability of bacterial pangenome data grows exponentially, requiring efficient new methods of analysis. Currently popular approaches for the fast comparison of genomes have the drawback of not being based on explicit evolutionary models of diversification. Making sense of bacterial genome evolution, and notably in the accessory genome, requires however to take into account the complex processes by which the genomes evolve. Here we present the Pantagruel bioinformatic software pipeline, which enables the construction of a complete bacterial pangenome database geared towards the inference of gene evolution scenarios using gene tree/species tree reconciliation. Pantagruel is a modular pipeline that combines state-of-the-art external software with unique new methods. It can be executed with no supervision to perform a standard pangenome analysis, or be configured by advanced users to integrate methods of choice. A relational database underlies its data structure, allowing efficient retrieval of the large-scale data generated by integrative analyses of pangenome evolutionary history. From the reconstructed gene evolution scenarios, two main outputs are derived: firstly the gene tree-aware assignation of orthology, allowing the fine analysis of gene gain and loss history over the species phylogeny, and secondly a network of gene-to-gene association based on correlated events in scenarios of gene evolution, leading to the definition of co-evolved gene modules. Pantagruel is available as an open source software package at https://github.com/flass/pantagruel.

bioinformatics↗