For instance, the pathotypes ‘Rickettsiella melolonthae’, the causative agent of the ‘Lorsch disease’ of white grubs of European cockchafer species (Coleoptera:

Scarabaeidae) (Wille & Martignoni, 1952; Krieg, 1955), and ‘Rickettsiella tipulae’, a pathogen of the crane fly, Tipula paludosa (Diptera: Tipulidae) (Müller-Kögler, 1958; Huger & Krieg, 1967), have been considered ‘subjective synonyms’ of the species R. popilliae. Rickettsiella bacteria had originally been assigned to the taxonomic order Rickettsiales (Weiss et al., 1984) that currently belongs to the class Alphaproteobacteria, Thiazovivin solubility dmso in contrast to an alternative classification in the order Chlamydiales (Yousfi et al., 1979; Federici, 1980). However, based on 16S rRNA sequencing results from a strain of R. grylli (Roux et al., 1997), the genus Rickettsiella has been reassigned to the taxonomic family Coxiellaceae in the order Legionellales of the Gammaproteobacteria (Garrity et al., 2005). On a genomic basis, this reorganization has been largely confirmed for R. grylli (Leclerque, 2008a) and receives GSK2118436 in vitro additional support from the determination of 16S rRNA-encoding sequences from further Rickettsiella pathotypes (Kurtti et al., 2002; Czarnetzki & Tebbe, 2004; Cordaux et al., 2007; Kleespies et al., 2011; Leclerque et al., 2011), including

both ‘R. melolonthae’ (Leclerque Phospholipase D1 & Kleespies, 2008a) and ‘R. tipulae’ (Leclerque & Kleespies, 2008c). However, further arthropod-associated bacteria originally described as Rickettsiella pathotypes (Drobne et al., 1999; Radek, 2000) were reorganized in the candidate genus ‘Candidatus Rhabdochlamydia’ of the order Chlamydiales (Kostanjsek et al., 2004; Corsaro et al., 2007). The significance of these findings for the monophyly of the genus Rickettsiella has been critically discussed (Cordaux et al.,

2007; Leclerque, 2008b). Comparison of orthologous gene sequences has been widely used to infer phylogenetic relationships among bacteria, and for good reason, 16S ribosomal RNA-encoding sequences (rrs genes) have become the standard molecular chronometer in phylogenetics (Woese, 1987). However, it complies the dictates of caution not to base taxonomic and phylogenetic inference on a single genetic marker. Both the comparison of large subunit (23S) ribosomal RNA gene (rrl) sequences (Ludwig & Schleifer, 1994) and the combined use of several genetically unlinked housekeeping genes, termed multilocus sequence typing (MLST) (Maiden et al., 1998), have become the most widely accepted complementary approaches (Ludwig & Klenk, 2005). However, initial attempts to identify a universally applicable set of MLST markers largely failed to produce satisfactory results, and a wide variety of marker sets is currently employed with different groups of organisms under study.