Ehrlichia chaffeensis

 Genome sequencing

Dr. Yasuko Rikihisa (Ohio State University) is the Principal Investigator on NIH grant R01-AI47885, which supports the sequencing of the 1.2Mb genome of Ehrlichia chaffeensis strain Arkansas. This project is being done in collaboration with Dr. Robert Munson (Ohio State and the Columbus Children's Hospital Research Foundation), and Dr. David Dyer (OUHSC). Ehrlichiae are small gram-negative pleomorphic cocci that are obligate intracellular bacteria. These organisms replicate in membrane-bound parasitophorous vacuoles in the cytoplasm of specific host cells, chiefly granulocytes or monocytes. E. chaffeensis is typically monocytotropic. Ehrlichiae are vector-borne organisms, replicating in the tick or the trematode, and are horizontally transmitted from infected cells in the vector to the blood cells of animals or humans. Once thought only to be veterinary pathogens, several ehrlichiae have recently been recognized as emerging human pathogens. Human monocytic ehrlichiosis (HME), caused by E. chaffeensis, was discovered in 1986 by Maeda et al (New England Journal of Medicine, vol. 316, pp. 853-856). The data presented here is in the form of contigs assembled from a 6X-coverage shotgun sequence of the strain Arkansas genome.

 

 Data access

Download the E. chaffeensis contig collection at 6x coverage - echaff.fasta.screen.contigs

To BLAST the unfinished E. chaffeensis genome go here and choose "E. chaffeensis" from the Database menu.

 

 Statistics

Summary for E. chaffeensis as of Fri Jun 29 16:34:09 CDT 2001

Contig Size Total Number Total Length % of Cumulative
       
0 - 1 kb 89 53110 4.9%
1 - 2 kb 104 150750 13.8%
2 - 3 kb 39 94419 8.7%
3 - 4 kb 17 59027 5.4%
4 - 5 kb 14 62520 5.7%
5 - 10 kb 30 224291 20.6%
10 - 20 kb 18 241334 22.1%
20 - 30 kb 4 97254 8.9%
30 - 40 kb 2 66244 6.1%
40 - 50 kb 1 40915 3.8%
50 - 100 kb 0 0 0%
>100 kb 0 0 0%
       
Cumulative 318 1089864  
Cumulative > 1 kb 229 1036754  
Cumulative > 2 kb 125 886004  

Phrap Coverage: 6.3, Phrap Quality: 75.1, Phrap Avg. Confirmed Length: 641.5, Reads: 9637








The E. chaffeensis genome sequence has been made available in concordance with NIH/ NIAID regulations.

 

 Figure 1

Ehrlichiae, obligate intracellular bacteria first discovered to be pathogenic for humans in 1987, are the causative agents of human granulocytic ehrlichiosis (HGE) and human monocytic ehrlichiosis (HME). The effect of infection with these tick-borne agents may range from mild to fatal; the most common symptoms are fever, malaise, headache and myalgia. A number of the bacteria are seen above, clustered in a vacuole in an infected host cell. The gram negative ehrlichiae have an inner and an outer membrane represented by the arrows. (All bars represent 0.5 mm)

 

 Figure 2

Dense-core cells of E. chaffeensis are seen here exiting the host cell following rupture of the morula and the host cell cytoplasmic membrane. These ehrlichiae will now go on to infect additional host cells or they may be ingested by a feeding tick, thus spreading the infection.

 

 Figure 3

Ehrlichia sp. develop with host cell vacuoles first as reticulate cells (RC) and then as dense-core cells (DC). A vacuole containing an ehrlichial microcolony is called a morula. Several morulae are seen in this host cell, including one filled with what appear to be dead ehrlichiae (shown at the arrow).

 

 Figure 4

A cultured cell, experimentally infected with E. chaffeensis (causative agent of HME), shows morulae of different sizes. Small morulae (shown by arrows) contain few RC and are apparently in earlier stages of infection.