About Rickettsia

General information:
Gram-negative α-proteobacteria, small (0.3-0.5 X 0.8-1.0 μm).
Classified into four groups:
the ancestral group (R. bellii and R. canadensis, associated with ticks)
the typhus group (R. prowazekii and R. typhi, associated with fleas and lice)
the spotted fever group (SFG, R. aeschlimanii, R. africae, R. conorii, R. heilongjiangensis, R. helvetica, R. honei, R. japonica, R. massiliae, R. montanensis, R. parkeri, R. peacockii, R. rhipicephali, R. rickettsii, R. sibirica and R. slovaca, which are associated with ticks)
finally a transitional group (R. australis, R. akari and R. felis, associated with ticks, mites and fleas).
Obligate intracellular pathogen.
Zipper-induced entry mechanism.
Preferentially infect vascular endothelial cells.
All members of the genus Rickettsia possess the ability to invade host cells and quickly escape phagosomal vacuoles into host cell cytosol to evade phagosome-lysosome fusion, replication within the host cytoplasm, and exit from the host cell by actin-mediated motility (e.g., Spotted Fever Group rickettsiae) or lysis of host cells (e.g., TG rickettsiae).
A reduced genome (~1.3 Mbp), with high interstrain homology but very different degrees of virulence.
Spotted fever group rickettsiae including R. rickettsii (Rocky Mountain spotted fever, RMSF) and R. conorii (Mediterranean spotted fever, MSF) are pathogenic organisms transmitted to humans through tick salivary contents during the blood meal.
The TG rickettsiae include R. prowazekii, the etiologic agent of epidemic typhus, and R. typhi, the causative agent of murine typhus.
Selected genomes:comparative pathogenomics
R. africae ESF-5, 1278540 bp, NC_012633
R. akari str. Hartford, 1231060 bp, NC_009881
R. australis Cutlack, 1296670 bp, NC_017058
R. bellii OSU 85-389, 1528980 bp, NC_009883
R. bellii RML369-C, 1522076 bp, NC_007940
R. canadensis CA410, 1150228 bp, NC_016929
R. canadensis str. McKiel, 1159772 bp, NC_009879
R. conorii str. Malish 7, 1268755 bp, NC_003103
R. felis URRWXCal2, 1485148 bp, NC_007109
R. heilongjiangensis 054, 1278471 bp, NC_015866
R. japonica YH, 1283087 bp, NC_016050
R. massiliae AZT80, 1263719 bp, NC_016931
R. massiliae MTU5, 1360898 bp, NC_009900
R. parkeri Portsmouth, 1300386 bp, NC_017044
R. peacockii str. Rustic, 1288492 bp, NC_012730
R. philipii 364D, 1287740 bp, NC_016930
R. prowazekii Breinl, 1109301 bp, NC_020993
R. prowazekii BuV67-CWPP, 1111445 bp, NC_017056
R. prowazekii Chernikova, 1109804 bp, NC_017049
R. prowazekii Dachau, 1109051 bp, NC_017051
R. prowazekii GvV257, 1111969 bp, NC_017048
R. prowazekii Katsinyian, 1111454 bp, NC_017050
R. prowazekii NMRC Madrid E, 1111520 bp, NC_020992
R. prowazekii Rp22, 1111612 bp, NC_017560
R. prowazekii RpGvF24, 1112101 bp, NC_017057
R. prowazekii str. Madrid E, 1111523 bp, NC_000963
R. rhipicephali 3-7-female6-CWPP, 1290368 bp, NC_017042
R. rickettsii Arizona, 1267197 bp, NC_016909
R. rickettsii Brazil, 1255681 bp, NC_016913
R. rickettsii Colombia, 1270083 bp, NC_016908
R. rickettsii Hauke, 1269774 bp, NC_016911
R. rickettsii Hino, 1269837 bp, NC_016914
R. rickettsii Hlp#2, 1270751 bp, NC_016915
R. rickettsii str. Iowa, 1268188 bp, NC_010263
R. rickettsii str. Sheila Smith, 1257710 bp, NC_009882
R. slovaca 13-B , 1275089 bp, NC_016639
R. slovaca D-CWPP, 1275720 bp, NC_017065
R. typhi B9991CWPP, 1112957 bp, NC_017062
R. typhi str. Wilmington, 1111496 bp, NC_006142
R. typhi TH1527, 1112372 bp, NC_017066
Related publications:
Andersson SG, et al., 1998. The genome sequence of Rickettsia prowazekii and the origin of mitochondria. Nature 396(6707):133-40.
Ogata H, et al., 2001. Mechanisms of evolution in Rickettsia conorii and R. prowazekii. Science 293(5537):2093-8.
McLeod MP, et al., 2004. Complete genome sequence of Rickettsia typhi and comparison with sequences of other rickettsiae. J Bacteriol 186(17):5842-55.
Ogata H, et al., 2005. The genome sequence of Rickettsia felis identifies the first putative conjugative plasmid in an obligate intracellular parasite. PLoS Biol 3(8):e248.
Ogata H, et al., 2006. Genome sequence of Rickettsia bellii illuminates the role of amoebae in gene exchanges between intracellular pathogens. PLoS Genet 2(5):e76.
Blanc G, et al., 2007. Lateral gene transfer between obligate intracellular bacteria: evidence from the Rickettsia massiliae genome. Genome Res 17(11):1657-64.
Ellison DW, et al., 2008. Genomic comparison of virulent Rickettsia rickettsii Sheila Smith and avirulent Rickettsia rickettsii Iowa. Infect Immun 76(2):542-50.
Fournier PE, et al., 2009. Analysis of the Rickettsia africae genome reveals that virulence acquisition in Rickettsia species may be explained by genome reduction. BMC Genomics 10:166.
Felsheim RF, et al., 2009. Genome sequence of the endosymbiont Rickettsia peacockii and comparison with virulent Rickettsia rickettsii: identification of virulence factors. PLoS One 4(12):e8361.
Bechah Y, et al., 2010. Genomic, proteomic, and transcriptomic analysis of virulent and avirulent Rickettsia prowazekii reveals its adaptive mutation capabilities. Genome Res 20(5):655-63.
Duan C, et al., 2011. Complete genome sequence of Rickettsia heilongjiangensis, an emerging tick-transmitted human pathogen. J Bacteriol 193(19):5564-5.
Fournier PE, et al., 2012. Complete genome sequence of Rickettsia slovaca, the agent of tick-borne lymphadenitis. J Bacteriol 194(6):1612.
Model of the rickettsia-host cell interactions (From: Uchiyama T, 2012. Tropism and pathogenicity of rickettsiae. Front Microbiol 3:230.).

Major virulence factors in Rickettsia:
rOmpA/Sca0 (Surface cell antigen 0) - R. rickettsii
Sca1 (Surface cell antigen 1)
rOmpB/Sca5 (Surface cell antigen 5)
Effector delivery system
Rvh T4SS (Rickettsiales vir homolog (rvh) T4SS)
Rvh T4SS secreted effectors
RickA - R. conorii
Sca2 (Surface cell antigen 2)
Phospholipase A2
Immune modulation
Adr1 (Adhesion of Rickettsiae protein 1)
Adr2 (Adhesion of Rickettsiae protein 2)
Sca4 (Surface cell antigen 4)

Genomic location of virulence-related genes in Rickettsia:

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