Genome sequence of Candidatus Arsenophonus lipopteni, the exclusive symbiont of a blood sucking fly Lipoptena cervi (Diptera: Hippoboscidae)

<jats:title>Abstract</jats:title><jats:p><jats:italic>Candidatus</jats:italic> Arsenophonus lipopteni (<jats:italic>Enterobacteriaceae</jats:italic>, <jats:italic>Gammaproteobacteria</jats:italic>) is an obligate intracellular symbiont of the blood feeding deer ked, <jats:italic>Lipoptena cervi</jats:italic> (Diptera: Hippoboscidae). The bacteria reside in specialized cells derived from host gut epithelia (bacteriocytes) forming a compact symbiotic organ (bacteriome). Compared to the closely related complex symbiotic system in the sheep ked, involving four bacterial species, <jats:italic>Lipoptena cervi</jats:italic> appears to maintain its symbiosis exclusively with <jats:italic>Ca. Arsenophonus lipopteni</jats:italic>. The genome of 836,724 bp and 24.8 % GC content codes for 667 predicted functional genes and bears the common characteristics of sequence economization coupled with obligate host-dependent lifestyle, e.g. reduced number of RNA genes along with the rRNA operon split, and strongly reduced metabolic capacity. Particularly, biosynthetic capacity for B vitamins possibly supplementing the host diet is highly compromised in <jats:italic>Ca. Arsenophonus lipopteni</jats:italic>. The gene sets are complete only for riboflavin (B2), pyridoxine (B6) and biotin (B7) implying the content of some B vitamins, e.g. thiamin, in the deer blood might be sufficient for the insect metabolic needs. The phylogenetic position within the spectrum of known <jats:italic>Arsenophonus</jats:italic> genomes and fundamental genomic features of <jats:italic>Ca. Arsenophonus lipopteni</jats:italic> indicate the obligate character of this symbiosis and its independent origin within Hippoboscidae.</jats:p>