Reclassification of Wolbachia persica as Francisella persica comb. nov and emended description of the family Francisellaceae

The taxonomic status of the bacterium Wolbachia persica is described, and based on the evidence presented, transfer of this species to the genus Francisella as Francisella persica comb. nov. is proposed. This reclassification is supported by data generated from genomic comparisons of W. persica ATCC VR-331(T) (=FSC845(T)=DSM 101678(T)) to other near neighbours, including Francisella tularensis subsp. novicida. The full-length 16S rRNA gene sequence of strain ATCC VR-331(T) had 98.5 % nucleotide identity to the cognate gene in F. tularensis, with the highest similarity to subspecies novicida. Phylogenetic trees of full-length 16S rRNA gene, gyrA and recA sequences from species of the genera Wolbachia (class Alphaproteobacteria) and Francisella (class Gammaproteobacteria) indicated that W. persica ATCC VR-331(T) was most closely related to members of the genus Francisella and not Wolbachia. Local collinear blocks within the chromosome of strain ATCC VR-331(T) had considerable similarity with F. tularensis subsp. novicida, but not with any Wolbachia strain. The genomes of strain ATCC VR-331(T) and F. tularensis subsp. novicida Utah 112(T) (=ATCC 15482(T)) contained an average nucleotide identity mean of 88.72 % and median of 89.18 %. Importantly, the genome of strain ATCC VR-331(T) contained one Francisella Pathogenicity Island, similar to F. tularensis subsp. novicida, as well as the Francisella-specific gene fopA1 and F. tularensis-specific genes fopA2 and lpnA (also referred to as tul4). In contrast to the obligate intracellular genus Wolbachia, strain ATCC VR-331(T) and facultative intracellular Francisella can replicate in specialized cell-free media. Collectively, these results demonstrate that Wolbachia persica should be reclassified in the genus Francisella as Francisella persica comb. nov. The type strain of Francisella persica comb. nov. is ATCC VR-331(T) (=FSC845(T)=DSM 101678(T)). An emended description of the family Francisellaceae is also provided.