from Marcos Mancilla writing in Brucella: Molecular Microbiology and Genomics:
The genomic islands (GIs) are DNA sequences of several kilobases (kb) that contain genes conferring adaptive advantages to the host bacteria. Despite the enclosed intracellular lifestyle, the sequence analysis of Brucella has revealed the presence of various GIs scattered through its genome, a fact that strongly suggests the acquisition of DNA by horizontal transfer events. In addition, the analysis of the genetic content of these regions indicates that they might represent a source of virulence factors. Recently, it has been demonstrated that some predicted GIs are unstable and can be excised from the chromosome by recombination. This experimental evidence points out the foreign origin of such loci and suggests an explanation for the polymorphism related to these large chromosomal regions exhibited by Brucellae.This chapter summarizes the advances in the identification and characterization of Brucella GIs. A detailed analysis of their genetic content and its relation to pathogenicity is also included. Recent data obtained for GI instability is discussed in the context of genome plasticity and virulence attenuation observed in smooth Brucellae.
Further reading: Brucella: Molecular Microbiology and Genomics