Genome sequencing of Brucella

Abstract

Sequencing of the 3.31 Mb genome of several strains of the intracellular pathogen Brucella suis has now been completed [1]. This pathogen is responsible for brucellosis, a zoonosis characterized by chronic infections in animals that can lead to abortion and infertility. In humans, brucellosis can cause a systemic, febrile illness. Several different strains have been used in genomic analysis, including B. suis strain 1330; this strain has two circular chromosomes of 2.1 Mb (Chr I) and 1.2 Mb (Chr II). Among strains of B. suis, however, there is variation in chromosome number and size. It has been suggested that Brucella strains might have evolved from a single ancestor that contained a single chromosome. Genome analysis also suggests that the two chromosomes have different evolutionary origins. Chr I resembles a classic bacterial circular chromosome with an origin of replication adjacent to a gene cluster containing the dnaA, dnaN and recF genes. Chr II, however, possesses a cluster of plasmid-like replication genes. There also appears to be separation of genes involved in specific functions; for example ChrI encodes the majority of the enzymes and machinery involved in metabolic processes, while Chr II encodes components involved in transport, energy metabolism and regulation.