Genetic and electron-microscopic characterization of Rickettsiella tipulae, an intracellular bacterial pathogen of the crane fly, Tipula paludosa

Rickettsiella tipulae is an intracellular bacterial pathogen of larvae of the crane fly, Tipula paludosa (Diptera: Tipulidae) and has previously been claimed to represent an independent species within the genus Rickettsiella. Recently, this taxon has been reorganized and transferred as a whole from the α-proteobacterial order Rickettsiales to the γ-proteobacterial order Legionellales. Here we present the electron-microscopic identification of this rickettsial pathogen together with the first DNA sequence information for R. tipulae. The results of our 16S rDNA-based phylogenetic analysis demonstrate that the transfer to the order Legionellales is justified for R. tipulae. However, there is no phylogenetic basis to consider R. tipulae an independent species, but instead conclusive evidence substantiating its species level co-assignment with Rickettsiella melolonthae. Furthermore, implications of our results for a possible reorganization of the internal structure of the genus Rickettsiella are discussed.