Leptospira yasudae sp. nov. and Leptospira stimsonii sp. nov., two new species of the pathogenic group isolated from environmental sources

Abstract

Four spirochetes (F1^T, B21, Yale^T and AMB6-RJ) were isolated from environmental sources: F1^T and B21 from soils of an urban slum community in Salvador (Brazil), Yale^T from river water in New Haven, Connecticut (USA) and AMB6-RJ from a pond in a horse farm in Rio de Janeiro (Brazil). Isolates were helix-shaped, aerobic, highly motile and non-virulent in a hamster model of infection. Draft genomes of the strains were obtained and analysed to determine the relatedness to other species of the genus Leptospira. The analysis of 498 core genes showed that strains F1^T/B21 and Yale^T/AMB6-RJ formed two distinct phylogenetic clades within the 'Pathogens' group (group I). The average nucleotide identity (ANI) values of strains F1^T/B21 and Yale^T/AMB6-RJ to other previously described Leptospira species were below <84 % and <82 %, respectively, which confirmed that these isolates should be classified as representatives of two novel species. Therefore, we propose Leptospirayasudae sp. nov. and Leptospirastimsonii sp. nov. as new species in the genus Leptospira. The type strains are F1^T (=ATCC-TSD-163=KIT0259=CLEP00287) and Yale^T (=ATCC-TDS-162=KIT0258=CLEP00288), respectively.

Keywords: Leptospira; leptospirosis; pathogenic; soil; water; whole-genome sequencing.

Fig. 1.

Dark-field photomicrographs of representative cells of strains F1^T (a) and Yale^T (b) showing a typical leptospiral morphology. Bars, 2 µm.

Fig. 2.

Phylogenetic tree built with 16S rRNA gene full-length sequences using the maximum-likelihood method. Values at the nodes denote bootstrap support higher than 70 % based on 1000 resampling events. The bar indicates the proportion of nucleotide substitutions. Leptonema illini 3055^T was used as the outgroup.

Fig. 3.

Core gene phylogeny. The tree was built with a concatenated alignment of 498 single copy genes present in all the analysed genomes, using RAxML with GTR substitution model. Nodes with a black circle denote 100 % bootstrap support based on 100 resampling events.