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

Abstract

The facultative intracellular bacterial pathogen Brucella infects a wide range of warm-blooded land and marine vertebrates and causes brucellosis. Currently, there are nine recognized Brucella species based on host preferences and phenotypic differences. The availability of 10 different genomes consisting of two chromosomes and representing six of the species allowed for a detailed comparison among themselves and relatives in the order Rhizobiales. Phylogenomic analysis of ortholog families shows limited divergence but distinct radiations, producing four clades as follows: Brucella abortus-Brucella melitensis, Brucella suis-Brucella canis, Brucella ovis, and Brucella ceti. In addition, Brucella phylogeny does not appear to reflect the phylogeny of Brucella species' preferred hosts. About 4.6% of protein-coding genes seem to be pseudogenes, which is a relatively large fraction. Only B. suis 1330 appears to have an intact ␤-ketoadipate pathway, responsible for utilization of plant-derived compounds. In contrast, this pathway in the other species is highly pseudogenized and consistent with the "domino theory" of gene death. There are distinct shared anomalous regions (SARs) found in both chromosomes as the result of horizontal gene transfer unique to Brucella and not shared with its closest relative Ochrobactrum, a soil bacterium, suggesting their acquisition occurred in spite of a predominantly intracellular lifestyle. In particular, SAR 2-5 appears to have been acquired by Brucella after it became intracellular. The SARs contain many genes, including those involved in O-polysaccharide synthesis and type IV secretion, which if mutated or absent significantly affect the ability of Brucella to survive intracellularly in the infected host.Brucellosis is a disease caused by bacteria of the genus Brucella. This disease is zoonotic and endemic in many areas throughout the world, causing chronic infections with common outcomes being abortion and sterility in infected animals. In humans, it is a severe acute febrile disease, producing focal lesions in bones, joints, the genitourinary tract, and other organs. Complications may include arthritis, sacroiliitis, spondylitis, and central nervous system effects. Brucella can cause abortions in women (as can other bacteria), mostly in the first and second trimesters of pregnancy (21, 27), and men can exhibit epididymo-orchitis (37).Currently, there are nine recognized species of Brucella, based on host preferences and phenotypic differences. Six classically recognized species are Brucella abortus (cattle), Brucella canis (dogs), Brucella melitensis (sheep and goats), Brucella neotomae (desert wood rats), Brucella ovis (sheep), and Brucella suis (pigs, reindeer, and hares). These six species have been subdivided into 18 biovars based on a panel of culture and biochemical characteristics (41). Recently, three additional species have been identified, namely Brucella microti from voles (49), "Brucella pinnipediae" from pinnipeds, and Brucella ceti from cetaceans (20).The genome from...

Brucella vulpis sp. nov., isolated from mandibular lymph nodes of red foxes (Vulpes vulpes)

“…83_13. Clustering within the classical Brucella species was similar to that of other studies (Wattam et al, 2009;Whatmore et al, 2014), demonstrating the close proximity of B. canis to B. suis bv. 4 and the separate position of B. suis bv.…”

“…Although genome similarities of these potential novel species of Brucella are still above 90 % compared with classical species (Wattam et al, 2009;this study), the majority of these novel candidates carries genetic information not found in classical species but similar to genetic information found in other soil-living bacteria, such as Ochrobactrum, Paracoccus denitrificans, Agrobacterium and Sinorhizobium. This suggests a different ecology and extended exchange of genetic material via horizontal gene transfer and/or loss of genetic information and genome reduction in the classical Brucella species.…”

The mglA gene and its flanking regions in Brucella: The role of mglA in tolerance to hostile environments, Fe-metabolism and in vivo persistence

“…abortus 9-941 ( Halling et al, 2005), B. suis ( Paulsen et al, 2002), B. canis ( Wattam et al, 2009), B.…”

“…ovis ( Wattam et al, 2009), Brucella sp. 83/13 (Broad Institute of MIT and Harvard, Cambridge, USA, http://www.broad.mit.edu/annotation/genome/brucella_group/GenomeDescriptions.html#Brucella_sp_ 83_13_v1), and B. microti CCM 4915 ( Audic et al, 2009) revealed various differences within these species.…”

Bartonella and Brucella--Weapons and Strategies for Stealth Attack

“…The Bartonella genus is composed of 24 species sharing a core genome and subdivided based on phylogenomic analysis in four phylogenetic lineages, lineage 1 being the most ancestral lineage with Bartonella bacilliformis as sole species (Saenz et al 2007;Engel and Dehio 2009;Engel et al 2011). The Brucella genus includes 10 species defined according to their preferential host and divided, based on phylogenomic analysis, in four clades: Brucella abortus -Brucella melitensis, Brucella suis -Brucella canis, Brucella ovis, and Brucella ceti (Wattam et al 2009), with Brucella ovis being a potential common ancestor (Foster et al 2009). …”