Abstract
BACKGROUND: The zoonotic pathogen Francisella tularensis is the etiological agent of tularemia. Tularemia in humans is mainly caused by F. tularensis subspecies tularensis and holarctica, but beneath some opportunistic Francisella species, like F. novicida and F. philomiragia, further genera of the family Francisellaceae have been described, such as Allofrancisella, Parafrancisella and Pseudofrancisella. Less is known about these genera. In the presented study we describe a German Allofrancisella isolate which was originally described as Francisella sp. strain W12-1067. RESULTS: Phylogenetic analysis and chemotaxonomy revealed that Francisella sp. strain W12-1067 is a separate species of the genus Allofrancisella and therefore was named A. heilbronnii. A. heilbronnii shows several genotypic and phenotypic differences to other Allofrancisella species, in growth, LPS and fatty acid composition. The genome size is 1,706,635 bp. A plasmid (6,872 bp) was found within the genome of A. heilbronnii, which is designated as pFW12. It encodes six open reading frames including a replication initiation protein and an iglD (tssk). We showed that pFW12 is transferable and stable in other Francisallaceae species, such as F. tularensis ssp. holarctica, F. novicida and A. inopinata. CONCLUSION: Francisella sp. strain W12-1067 belongs to the genus Allofrancisella and now is designated as A. heilbronnii. In this work we present the annotated, complete genome and plasmid sequence. The genus Allofrancisella seems to be the only member of Francisellaceae which is negative for the genes of the major virulence island named Francisella pathogenicity island (FPI). A putative cryptic plasmid, pFW12, was found in A. heilbronnii, which is transferable and stable into other Francisallaceae species. Therefore, pFW12 could be used as a Francisellaceae-specific vector. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12866-025-04600-5.