''Rickettsiella'' is a genus of the family

Coxiellaceae The Coxiellaceae are a family in the order Legionellales. ''Coxiella burnetii'' is the best-described species in this group. The bacterium ''Rickettsiella melolonthae'' was initially assigned to the ''Coxiellaceae'', but is considered part of t ...

. It should not be confused with ''

Rickettsia ''Rickettsia'' is a genus of nonmotile, gram-negative, nonspore-forming, highly pleomorphic bacteria that may occur in the forms of cocci (0.1 μm in diameter), bacilli (1–4 μm long), or threads (up to about 10 μm long). The genus was n ...

''. It is currently considered of the

Gammaproteobacteria ''Gammaproteobacteria'' is a class of bacteria in the phylum ''Pseudomonadota'' (synonym ''Proteobacteria''). It contains about 250 genera, which makes it the most genus-rich taxon of the Prokaryotes. Several medically, ecologically, and scienti ...

. However, its placement under Coxiellaceae instead of Legionellaceae has been challenged.

Molecular Signatures and Taxonomy

Members of the genera ''Rickettsiella'' and ''

Diplorickettsia ''Diplorickettsia massiliensis'' species is an obligate intracellular, gram negative bacterium isolated from Ixodes ricinus ticks collected in Slovak republic forest geographically from southeastern part of Rovinka in 2006.Mediannikov, O., et al. ...

'' are observed to form a reliable clade in phylogenetic trees constructed from various datasets of concatenated protein sequences and 16S rRNA sequences, suggesting that they might belong to a single genus. Genomic analyses identified 12

conserved signature indels Conserved signature inserts and deletions (CSIs) in protein sequences provide an important category of molecular markers for understanding phylogenetic relationships. CSIs, brought about by rare genetic changes, provide useful phylogenetic markers ...

(CSIs) that are specific for this clade in the proteins inositol monophosphatase, lysyl-tRNA synthetase, elongation factor P-(R)-beta-lysine ligase, tol-Pal system beta propeller repeat protein TolB, FKBP-type peptidyl-prolyl cis-trans isomerase, response regulator transcription factor, 30S ribosomal protein S2, glycine cleavage system aminomethyltransferase GcvT, M3 family metallopeptidase, lysm peptidoglycan-binding domain-containing protein and oligopeptide transporter. The presence of these CSIs reliably distinguishes this clade from other Legionellales species in molecular terms, further supporting the combination of the genera ''Rickettsiella'' and ''

.'' Additionally, three CSIs were identified as uniquely shared between ''

,'' ''Rickettsiella'' and '' Coxiella,'' another genus belonging to the family ''

.'' The absence of '' Aquicella'' species (the remaining genus within the family ''

)'' from the shared CSIs suggests that the genera ''Coxiella,

'' and ''Rickettsiella'' share a common ancestor exclusive of '' Aquicella.''

References

Legionellales Bacteria genera {{Legionellales-stub