Comparative genomic analysis of three strains of Ehrlichia ruminantium reveals an active process of genome size plasticity.
Ehrlichia ruminantium is the causative agent of heartwater, a major tick-borne disease of livestock in Africa that has been introduced in the Caribbean and is threatening to emerge and spread on the American mainland. We sequenced the complete genomes of two strains of E. ruminantium of differing phenotypes, strains Gardel (Erga; 1,499,920 bp), from the island of Guadeloupe, and Welgevonden (Erwe; 1,512,977 bp), originating in South Africa and maintained in Guadeloupe in a different cell environment. Comparative genomic analysis of these two strains was performed with the recently published parent strain of Erwe (Erwo) and other Rickettsiales (Anaplasma, Wolbachia, and Rickettsia spp.). Gene order is highly conserved between the E. ruminantium strains and with A. marginale. In contrast, there is very little conservation of gene order with members of the Rickettsiaceae. However, gene order may be locally conserved, as illustrated by the tuf operons. Eighteen truncated protein-encoding sequences (CDSs) differentiate Erga from Erwe/Erwo, whereas four other truncated CDSs differentiate Erwe from Erwo. Moreover, E. ruminantium displays the lowest coding ratio observed among bacteria due to unusually long intergenic regions. This is related to an active process of genome expansion/contraction targeted at tandem repeats in noncoding regions and based on the addition or removal of ca. 150-bp tandem units. This process seems to be specific to E. ruminantium and is not observed in the other Rickettsiales.
Frutos
Roger
R
CIRAD TA30/G, Campus International de Baillarguet, 34398 Montpellier Cedex 5, France. roger.frutos@cirad.fr.
Viari
Alain
A
Ferraz
Conchita
C
Morgat
Anne
A
Eychenié
Sophie
S
Kandassamy
Yane
Y
Chantal
Isabelle
I
Bensaid
Albert
A
Coissac
Eric
E
Vachiery
Nathalie
N
Demaille
Jacques
J
Martinez
Dominique
D
D017124:Conserved Sequence; D016995:Ehrlichia ruminantium / Q000145:classification* / Q000235:genetics*; D019143:Evolution, Molecular; D023061:Gene Order; D014644:Genetic Variation / Q000235:genetics*; D016680:Genome, Bacterial; D008969:Molecular Sequence Data; D016296:Mutagenesis / Q000235:genetics*; D010641:Phenotype; D013045:Species Specificity; D020080:Tandem Repeat Sequences / Q000235:genetics