Obligate intracellular pathogen that causes heartwater disease in ruminants. Ehrlichia ruminantium str. Welgevonden

Ehrlichia ruminantium strain Welgevonden. This strain was isolated in mice from an infected tick. The most significant difference between the genome of E. ruminantium and those of the other Rickettsiales is the presence of a large number of repetitive sequences. These repeats make up 8.5% of the genome and consist of simple sequence repeats (SSRs), large tandem repeats, and dispersed repeats. These repeats are associated with 29 of the 32 pseudogenes which appear to have occured primarily through duplication events. In addition, it is thought that the SSRs may play a role in regulation or phase variation. Between 10-15% of the genes in free-living bacteria are thought to have been acquired by horizontal gene transfer. Intracellular bacteria have limited exposure to other bacteria and therefore a smaller portion of their genome is from other organisms. It is estimated that only 3% of the genome of E. ruminantium has been obtained by gene transfer. The existence of a large number of repeat elements may be a alternative strategy for increasing genetic diversity and improve the evolutionary fitness of E. ruminantium.