Phylogenetic, genomic, and morphological characterization of Rickettsia senegalensis sp. nov., a novel Rickettsia species detected worldwide

Abstract

Members of the genus Rickettsia are widespread obligate intracellular bacteria with high medical and veterinary relevance. While Rickettsia senegalensis was previously isolated from cat fleas, Ctenocephalides felis, in Senegal, a comprehensive polyphasic characterization is required for its formal taxonomic validation. This study aims to provide the first detailed phenotypic, ultrastructural, and genomic characterization of the type strain PU01-02. Cultivation assays demonstrated that strain PU01-02 grows aerobically in XTC-2, SF9, and LD652 cell lines at 28 {degrees}C in a CO2-free atmosphere. Ultrastructural examination via scanning electron microscopy using a backscattered electron detector confirmed its free cytoplasmic localization and a typical rickettsial morphology characterized by rod-shaped cells approximately 1.5 {micro}m in length and 0.3 {micro}m in width. Whole-genome sequencing yielded a 1.62-Mb genome with a G+C content of 33.2%, and three plasmids were detected. Genomic analyses confirmed its status as a distinct species, placing it within the transitional Rickettsia group, specifically inside the Rickettsia felis cluster. A review of epidemiological data revealed that rickettsial genes identical to those of R. senegalensis had already been identified in several hematophagous arthropods, including fleas and ticks parasitizing various hosts such as cats, dogs, opossums, and rodents worldwide. It has also been detected in cat tissues, suggesting a potential host-pathogen association. Based on these comprehensive characterization data, we formally propose Rickettsia senegalensis sp. nov. as a new species, with PU01-02 (= CSUR R184 = DSM 28250) as the type strain. RepositoriesThe genome sequence of Rickettsia senegalensis sp. nov. strain PU01-02T has been deposited in GenBank under accession number JBVYTQ000000000, and the rrs, gltA, ompB and sca4 gene sequences under accession numbers KF666476, KF666472, KF666470, KF666474, respectively. The plasmid accession numbers are PZ272915, PZ272916, and PZ272917, for pRS01, pRS02 and pRS03, respectively.