Comparative Whole-Genome Hybridization Reveals Genomic Islands inBrucellaSpecies

Abstract

Brucella species are responsible for brucellosis, a worldwide zoonotic disease causing abortion in domestic animals and Malta fever in humans. Based on host preference, the genus is divided into six species. Brucella abortus, B. melitensis, and B. suis are pathogenic to humans, whereas B. ovis and B. neotomae are nonpathogenic to humans and B. canis human infections are rare. Limited genome diversity exists among Brucella species. Comparison of Brucella species whole genomes is, therefore, likely to identify factors responsible for differences in host preference and virulence restriction. To facilitate such studies, we used the complete genome sequence of B. melitensis 16M, the species highly pathogenic to humans, to construct a genomic microarray. Hybridization of labeled genomic DNA from Brucella species to this microarray revealed a total of 217 open reading frames (ORFs) altered in five Brucella species analyzed. These ORFs are often found in clusters (islands) in the 16M genome. Examination of the genomic context of these islands suggests that many are horizontally acquired. Deletions of genetic content identified in Brucella species are conserved in multiple strains of the same species, and genomic islands missing in a given species are often restricted to that particular species. These findings suggest that, whereas the loss or gain of genetic material may be related to the host range and virulence restriction of certain Brucella species for humans, independent mechanisms involving gene inactivation or altered expression of virulence determinants may also contribute to these differences.Brucellosis is a zoonotic disease endemic in many areas of the world and is characterized by chronic infections, abortion, and sterility (7). In humans, brucellosis is a systemic, febrile illness resulting in osteoarthritis, endocarditis, and several neurological disorders (7,53). Brucellosis is caused by many species belonging to the genus Brucella that are aerobic facultative intracellular bacteria. Brucella species are closely related to intracellular symbionts and pathogens of plants and animals and are classified as ␣ 2 -proteobacteria based on rRNA sequence comparison (36).The genus Brucella consists of six species, designated on the basis of host preference, antigenic and biochemical characteristics as Brucella melitensis (goats and sheep), B. abortus (cattle), B. suis (pigs), B. canis (dogs), B. ovis (sheep), and B. neotomae (wood rats) (6). B. abortus, B. melitensis, and B. suis can all infect humans with similar serious disease consequences (7). B. melitensis, originally isolated as a pathogen of goats and sheep, is highly pathogenic and a frequent cause of human brucellosis. In contrast, human infections of B. ovis and B. neotomae have not been reported, and B. canis rarely causes infection in humans. Human brucellosis occurs via contact with infected animals or animal products and is common in countries where the disease is endemic in domestic animals (13). Brucella also can be readily dispersed through aerosol...

Characterization of Genomic Island 3 and Genetic Variability of Chilean Field Strains of Brucella abortus

“…This might suggest that the island cannot be spontaneously separated from the genome. GI-3 is flanked by direct repeats of 18 bp (27), and the low number of base pairs might explain the low mobility of this genetic element in wild strains, despite the fact that this island displayed characteristics typical of GIs (12). The stability of GI-3 confirms, as reported by other authors, that the genomes of Brucella species are very stable and similar (37).…”

“…These islands can encode metabolic pathways and/or virulence factors, providing new features that can transform a nonpathogenic bacterium into a pathogenic bacterium (12). Nine GIs have been identified in B. melitensis, and two of them (GI-4 and GI-8) are missing in B. abortus (27). Subsequent studies reported that of these nine islands present in Brucella, GI-1, GI-5, and GI-6 do not contribute to Brucella virulence (26).…”

Analysis of TenBrucellaGenomes Reveals Evidence for Horizontal Gene Transfer Despite a Preferred Intracellular Lifestyle

“…Furthermore, they showed that BMEI0999, a hypothetical protein whose function is unknown, was necessary to restore a smooth LPS in rough strains. However, we have found that other (46,60). The B. ovis genome also has a truncated wzt; this gene encodes a protein that functions as a part of an ABC transporter, with its partner encoded by wzm.…”

Multiplex PCR Assay for the Identification and Differentiation of all Brucella Species and the Vaccine Strains Brucella abortus S19 and RB51 and Brucella melitensis Rev1

“…We used the following species-or strain-specific genetic differences to design PCR primers: (a) a 25-kb DNA deletion leading to the loss of omp31 gene in the reference strains of all B. abortus biovars (6, 7 ); (b) a 15-kb deletion comprising omp25b and wboAwboB genes in the Brucella ovis species (6, 7 ); (c) a wboA gene disruption by an IS711 element in the B. abortus vaccine strain RB51 (8 ); (d) a 702-bp deletion in the ery operon in the vaccine strain B. abortus S19 (9 ); (e) a specific mutation in the rpsL gene of the vaccine strain B. melitensis Rev1 that differentiates it from the B. melitensis reference strain (10 ); (f) a 976-bp deletion in chromosome I specific to Brucella canis (7 ); (g) a 2.2-kb deletion in chromosome II specific to Brucella neotomae (7 ); (h) a 2.6-kb fragment in B. suis, but not in B. abortus or B. melitensis (6,7 ); and (i) an IS711 element downstream of the bp26 gene in Brucella spp. isolated from marine mammals (11 ).…”