Serovar-specific genomic features of Hardjo: implications for host adaptation.

INTRODUCTION

Leptospirosis, caused by spp. is one of the most widespread zoonoses worldwide. It affects both domestic and wild animals, with ruminants serving as a primary reservoir for serovar Hardjo. This serovar causes long-term colonisation of the kidney and genital tract. Hardjo strains are taxonomically assigned to two species: and . However, the molecular basis of Hardjo adaptation remains poorly understood. Comparative genomic analysis of strains classified as the Hardjo serovar and other non-Hardjo serovars of the same species may help identify genetic determinants associated with host adaptation and species-specific cellular immune responses. Unfortunately, these pathogens are highly fastidious, and only a limited number of whole genomes have been sequenced to date.

MATERIALS AND METHODS

Four serovar Hardjo European isolates were sequenced. Using these new sequences alongside publicly available genomes of strains classified as Hardjo and non-Hardjo serovars, we performed comparative genomic analyses.

RESULTS

Hardjo strains formed a distinct phylogenetic clade and harboured unique variants, including an intact gene and a modified start codon. We identified 88 Hardjo-specific orthologues, some located in putative genomic islands outside locus. Several encoded proteins related to mobile elements, toxin-antitoxin systems or signal transduction. Enhanced biofilm formation in Hardjo strains supports a host-adapted phenotype.

CONCLUSION

This study expands the genomic dataset for serovar Hardjo and provides novel insights into its genetic distinctiveness, suggesting potential factors that may facilitate colonisation and persistence in ruminant hosts.