Gene Sequence-Based Criteria for Identification of NewRickettsiaIsolates and Description ofRickettsia heilongjiangensissp. nov

Abstract

We propose genetic guidelines for the classification of rickettsial isolates at the genus, group, and species levels by using sequences of the 16S rRNA (rrs) gene and four protein-coding genes, the gltA, ompA, and ompB genes and gene D. To be classified as a member of the genus Rickettsia, an isolate should exhibit degrees of rrs and gltA homology with any of the 20 Rickettsia species studied of >98.1 and >86.5%, respectively. A member of the typhus group should fulfill at least two of the following four criteria: pairwise nucleotide sequence homologies with rrs, gltA, ompB, and gene D of either Rickettsia typhi or Rickettsia prowazekii of >99.4, >96.6, >92.4, and >91.6%, respectively. A member of the spotted fever group should either possess the ompA gene or fulfill at least two of the following four criteria: pairwise nucleotide sequence homologies with rrs, gltA, ompB, and gene D of any member of this group of >98.8, >92.7, >85.8, and >82.2%, respectively. The existence of a distinct "ancestral" group should be questioned. To be classified as a new Rickettsia species, an isolate should not exhibit more than one of the following degrees of nucleotide similarity with the most homologous validated species: >99.8 and > 99.9% for the rrs and gltA genes, respectively, and, when amplifiable, >98.8, >99.2, and >99.3% for the ompA and ompB genes and gene D, respectively. By use of our classification scheme, "Rickettsia heilongjiangii" belongs to a new species for which we officially propose the name Rickettsia heilongjiangensis sp. nov.The order Rickettsiales initially consisted of most of the bacteria associated with eukaryotic cells (63). On the basis of their 16S rRNA gene (rrs) sequences, Rickettsiella grylli, Coxiella burnetii, Wolbachia persica, Rochalimaea spp., Grahamella spp., Bartonella spp., Eperithrozoon ovis, and Hemobartonella spp. have been removed from the order Rickettsiales (5,7,41,43,62), which comprises only the genera Rickettsia, Orientia, Ehrlichia, Anaplasma, Neorickettsia, and Wolbachia. Historically, the genus Rickettsia was divided into three groups on the basis of phenotypic criteria: the typhus group, the spotted fever group, and the scrub typhus group (63). In 1995, Tamura et al. (53) proposed reclassification of Rickettsia tsutsugamushi (33) into a new genus, Orientia, using 16S rRNA gene sequence analysis. The same year, Stothard and Fuerst (52) suggested that Rickettsia bellii (36) and Rickettsia canadensis (27) represented a phylogenetic line that predated the typhus-spotted fever group split and, thus, were included into a fourth group named the "ancestral" group. At present, the genus Rickettsia contains 21 validated species classified into three groups: (i) the ancestral group described above; (ii) the typhus group, which includes Rickettsia prowazekii (12) and Rickettsia typhi (34); and (iii) the spotted fever group, which consists of Rickettsia rickettsii (9), Rickettsia conorii (10), Rickettsia africae (20), Rickettsia sibirica (67), Rickettsia slovaca (48), Rickettsia honei (5...

Rickettsia hoogstraalii sp. nov., isolated from hard- and soft-bodied ticks

“…Recently, gene sequence-based guidelines for taxonomic classification have been proposed and used for the classification and identification of novel rickettsial species (Fournier et al, 2003). Although the authors of this proposal stated that these criteria were objective and sufficient for the description of novel species of the genus Rickettsia, gene sequence-based criteria alone are inadequate for defining prokaryotic species and are incapable of keeping pace with the levels of diversity that are being revealed in nature (Fournier et al, 2003;Gevers et al, 2005).…”

Spotted fever group Rickettsia infecting ticks (Acari: Ixodidae) in the state of Santa Catarina, Brazil

“…Herein, we considered the Atlantic rainforest strain to belong to the species R. parkeri based on the gene sequence-based criteria recently proposed for identification of new Rickettsia isolates (Fournier et al 2003), as discussed by Spolidorio et al (2010). However, we are aware that the species definition for Rickettsia remains a controversial issue, without a major consensus among rickettsiologists (Walker & Ismail 2008, Fournier & Raoult 2009, Goddard 2009).…”

Tick- and flea-borne rickettsial emerging zoonoses

“…Between 1984 and 2004, nine more species or subspecies of tick-borne spotted fever rickettsiae were identified as emerging pathogens throughout the world, including, R. japonica in Japan [6,46,65,71,72,[82][83][84]146]; "R. conorii caspia" in Astrakhan [35,38,39,143], Africa [47] and Kosovo [48]; R. africae in sub-Saharan Africa and the West Indies [62,63]; R. honei in the Flinders Island, offshore of Australia [9,57,140,141], the Island of Tasmania, Australia [153], Thailand [73], and possibly in the USA [13]; R. slovaca in Europe [29,74,101,122]; "R. sibirica mongolotimonae" in China [157], Europe [44,118] and Africa [106,113]; R. heilongjiangensis in China [42,49]; R. aeschlimannii in Africa [11,112,121] and Europe [43]; and finally R. parkeri in the USA [104]. R. helvetica is also suspected to be a human pathogen in Europe [45] and Asia [46,61,107], but this needs c...…”

“…However, experts in the field of rickettsiology frequently disagree over species definitions. In this review we use currently accepted taxa, as well as names of species or subspecies proposed recently that are based on polyphasic taxonomic studies which integrate phenotypic and phylogenetic data [49].…”