Abstract
BackgroundLeptospirosis is an emerging infectious disease worldwide that can cause high morbidity and mortality rates in humans and animals. The causative spirochetes have reservoirs in mammalian hosts, but there has been limited analysis of the genomes of isolates recovered from animals. The aims of this study were to characterize genomic features of two Leptospira interrogans strains recently isolated from asymptomatic dogs in Thailand (strains CUDO5 and CDUO8), and to perform comparative genome analyses with other strains. Molecular adaptive evolution in L. interrogans as signaled by positive selection also was analyzed.ResultsWhole genome sequence analysis revealed that strains CUDO5 and CUDO8 had genome sizes of approximately 4.9 Mbp with 35.1% GC contents. Using monoclonal antibodies, strains CUDO5 and CUDO8 were identified as serovars Paidjan and Dadas, respectively. These strains harbored genes known to be associated with acute and chronic infections. Using Single Nucleotide Polymorphisms phylogeny (SNPs) with 97 L. interrogans strains, CUDO5 and CUDO8 had closest genetic relatedness with each other. Nevertheless, the serovar determinant region (rfb locus) showed variations in the genes encoding sugar biosynthesis. Amongst 13 representative L. interrogans strains examined for molecular adaptive evolution through positive selection under the site-model of Phylogenetic Analysis of Maximum Likelihood, genes responsible for iron acquisition (tlyA and hbpA), motility (fliN2, flgK, and flhB) and thermal adaptation (lpxD1) were under increased selective pressure.ConclusionsL. interrogans serovar Paidjan strain CUDO5 and serovar Dadas strain CUDO8 had close genetic relatedness as analyzed by SNPs phylogeny. They contained genes with established roles in acute and chronic leptospirosis. The rfb locus in both serovars showed gene variation associated with sugar biosynthesis. Positive selection analysis indicated that genes encoding factors involved in motility, temperature adaptation, and iron acquisition were under strong positive selection in L. interrogans. These may be associated with adaptation in the early stages of infection.
Highlights
Leptospirosis is an emerging infectious disease worldwide that can cause high morbidity and mortality rates in humans and animals
For L. interrogans strain CUDO5, the A5-Miseq de novo genome assembler generated 163 scaffolds with 124.47 times genome coverage and an N50 of 111,967 bp: the genome size was estimated at 4.94 Mbp with a 35.1% GC content
The present study reports the first genomic characterization of L. interrogans strains isolated from dogs in Thailand, and presents a comparative genome analysis of these with the published genomes of another 12 Leptospira species
Summary
Leptospirosis is an emerging infectious disease worldwide that can cause high morbidity and mortality rates in humans and animals. The aims of this study were to characterize genomic features of two Leptospira interrogans strains recently isolated from asymptomatic dogs in Thailand (strains CUDO5 and CDUO8), and to perform comparative genome analyses with other strains. Gram-negative spirochetes of the genus Leptospira cause the disease Leptospirosis, which is one of the most important zoonotic infectious conditions worldwide, including in Thailand [1, 2]. More than 300 serovars have been described based on antigenic diversity in the lipopolysaccharide (LPS) structure on the cell surface. These different serovars can be identified using the cross-agglutination absorption test (CAAT) [3]
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