The genome sequence of the facultative intracellular pathogen Brucella melitensis

Abstract

Brucella melitensis is a facultative intracellular bacterial pathogen that causes abortion in goats and sheep and Malta fever in humans. The genome of B. melitensis strain 16M was sequenced and found to contain 3,294,935 bp distributed over two circular chromosomes of 2,117,144 bp and 1,177,787 bp encoding 3,197 ORFs. By using the bioinformatics suite ERGO, 2,487 (78%) ORFs were assigned functions. The origins of replication of the two chromosomes are similar to those of other alpha-proteobacteria. Housekeeping genes, including those involved in DNA replication, transcription, translation, core metabolism, and cell wall biosynthesis, are distributed on both chromosomes. Type I, II, and III secretion systems are absent, but genes encoding sec-dependent, sec-independent, and flagella-specific type III, type IV, and type V secretion systems as well as adhesins, invasins, and hemolysins were identified. Several features of the B. melitensis genome are similar to those of the symbiotic Sinorhizobium meliloti.

Figure 1

The VirB operon of the type IV secretion system in B. melitensis is shown using the “pinned region” tool from ERGO, which exploits the occurrence of best paired bidirectional hits between ORFs among different organisms. The pinned region for VirB8 (red arrow) shows the type IV secretion cluster from Agrobacterium, Mesorhizobium, Yersinia, and Xylella sp. Identically colored arrows represent similar ORFs. Functions according to numbers are channel protein VirB8 homolog (no. 1), ATPase VirB11 homolog (no. 2), channel protein VirB10 homolog (no. 3), channel protein VirB9 homolog (no. 4), channel protein VirB6 homolog (5), attachment-mediating protein VirB5 homolog (no. 6), ATPase VirB4 homolog (no. 7), attachment-mediating protein VirB1 homolog (no. 8), hypothetical protein (no. 9), ATPase VirD4 homolog (no. 10), DNA recombination protein (no. 11), channel protein VirB3 protein (no. 12), and hypothetical exported protein (no. 13).

Figure 2

The erythritol uptake and utilization pathway in B. melitensis, reconstructed from the genome sequence. BME nos. in the boxes correspond to ORFs in the genome.

Figure 3

Reconstruction of possible anaerobic respiratory pathways in B. melitensis, based on the genome sequence. Red boxes indicate that these systems are absent from the genome.