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

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 to validly publish its name. This study aims to provide the first detailed phenotypic, ultrastructural and genomic characterization of the type strain PU01-02ᵀ. Cultivation assays demonstrated that strain PU01-02ᵀ grows aerobically in XTC-2, SF9 and LD652 cell lines at 28 °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 ~1.5 µm in length and 0.3 µm 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 haematophagous 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 R. senegalensis sp. nov. as a new species, with PU01-02ᵀ (=CSUR R184ᵀ =DSM 28250ᵀ) as the type strain.