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Rickettsiella is a genus of the family Coxiellaceae. It should not be confused with Rickettsia. It is currently considered of the Gammaproteobacteria. However, its placement under Coxiellaceae instead of Legionellaceae has been challenged.

Molecular Signatures and Taxonomy

Members of the genera Rickettsiella and Diplorickettsia 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 (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 Diplorickettsia.

Additionally, three CSIs were identified as uniquely shared between Diplorickettsia, Rickettsiella and Coxiella, another genus belonging to the family Coxiellaceae. The absence of Aquicella species (the remaining genus within the family Coxiellaceae) from the shared CSIs suggests that the genera Coxiella, Diplorickettsia and Rickettsiella share a common ancestor exclusive of Aquicella.

References

1. "Rickettsiella Philip, 1956". GBIF. Retrieved March 13, 2014.
2. Rickettsiella at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
3. Leclerque A (June 2008). "Whole genome-based assessment of the taxonomic position of the arthropod pathogenic bacterium Rickettsiella grylli". FEMS Microbiol. Lett. 283 (1): 117–27. doi:10.1111/j.1574-6968.2008.01158.x. PMID 18422627.
4. ^ Saini, Navneet; Gupta, Radhey S. (July 2021). "A robust phylogenetic framework for members of the order Legionellales and its main genera (Legionella, Aquicella, Coxiella and Rickettsiella) based on phylogenomic analyses and identification of molecular markers demarcating different clades". Antonie van Leeuwenhoek. 114 (7): 957–982. doi:10.1007/s10482-021-01569-9. ISSN 1572-9699. PMID 33881638.

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