Bourhy, P. | bioRxiv Science

bioRxiv2026

Leptospira infection in European hedgehogs (Erinaceus europaeus): occurrence, diversity and associated risk factors in Greater Paris, France.

Background Leptospirosis is a zoonotic infectious disease whose prevalence is increasing in mainland France. While rodents are common reservoirs of pathogenic Leptospira, the pathogen diversity detected in French human clinical cases exceeds that currently identified in local rodents, suggesting that some unidentified host species may carry strains of public health importance. The aim of this study was to investigate Leptospira infection in a population of rescued injured hedgehogs (Erinaceus europaeus) in Ile-de-France, as well as to characterize the circulating genotypes and serogroups. Methodology/principal findings In 2023-2024, kidneys from 270 dead hedgehogs collected by the Veterinary University Hospital for Wild Fauna at the National Veterinary School of Alfort, France, were tested for leptospiral DNA by real-time PCR. Twenty-two percent of individuals were qPCR-positive. Positive samples were genotyped to identify circulating species and species-groups (SGs) with L. interrogans SG5 being the most common. In addition, the Microscopic Agglutination Test was performed on 245 blood samples, with Australis identified as the predominant serogroup. The effect of individual and environmental variables on Leptospira infection status of hedgehogs was assessed, with age and season identified as significant predictors of infection. Conclusions/significance Our findings suggest that hedgehogs can harbour pathogenic Leptospira in Ile-de-France. Further investigation is warranted to establish the epidemiological links between hedgehogs and other host species, including humans. A finer-scale analysis of the ecological features at the sampling sites could also help better understand the risk factors of Leptospira infection in hedgehogs at a smaller spatial scale.

molecular biology↗

bioRxiv2025

Replication coordination marks the domestication of large extrachromosomal replicons in bacteria

Bacterial genomes often include extrachromosomal replicons (ERs), ranging from small plasmids to nearly chromosome-sized elements, that foster genome plasticity and adaptation. Despite their prevalence, the mechanisms underlying ER domestication and their long-term adaptation within bacterial hosts remain largely unexplored. By analyzing over 40,000 complete bacterial genomes, we identified two main ER categories: small ERs with diverse GC content and large ERs ([≥]10% the size of the main chromosome) that closely match the GC content of the chromosome. Across multiple phyla, marker frequency analyses showed that large ERs maintain a 1:1 copy number with the chromosome. Another key finding of this study is that large ERs terminate replication in synchrony with the chromosome. Hi-C contact maps revealed consistent ori-ori interactions between chromosomes and ERs. In large ERs, inter-replichore and ter-ter interactions, along with the recruitment of key chromosomal segregation motifs, suggest the co-option of chromosome-associated replication and segregation machineries. Together, our findings indicate that as ERs become larger, they become increasingly reliant on chromosome-driven processes for stable inheritance, potentially explaining why they do not exceed the size of the chromosome.

microbiology↗