International Journal of Molecular Sciences Review Brucella Genomics: Macro and Micro Evolution Marcela Suárez-Esquivel 1 , Esteban Chaves-Olarte 2, Edgardo Moreno 1 and Caterina Guzmán-Verri 1,2,* 1 Programa de Investigación en Enfermedades Tropicales, Escuela de Medicina Veterinaria, Universidad Nacional, Heredia 3000, Costa Rica;
[email protected] (M.S.-E.);
[email protected] (E.M.) 2 Centro de Investigación en Enfermedades Tropicales, Facultad de Microbiología, Universidad de Costa Rica, San José 1180, Costa Rica;
[email protected] * Correspondence:
[email protected] Received: 1 September 2020; Accepted: 11 October 2020; Published: 20 October 2020 Abstract: Brucella organisms are responsible for one of the most widespread bacterial zoonoses, named brucellosis. The disease affects several species of animals, including humans. One of the most intriguing aspects of the brucellae is that the various species show a ~97% similarity at the genome level. Still, the distinct Brucella species display different host preferences, zoonotic risk, and virulence. After 133 years of research, there are many aspects of the Brucella biology that remain poorly understood, such as host adaptation and virulence mechanisms. A strategy to understand these characteristics focuses on the relationship between the genomic diversity and host preference of the various Brucella species. Pseudogenization, genome reduction, single nucleotide polymorphism variation, number of tandem repeats, and mobile genetic elements are unveiled markers for host adaptation and virulence. Understanding the mechanisms of genome variability in the Brucella genus is relevant to comprehend the emergence of pathogens. Keywords: Brucella; brucellosis; genome reduction; pseudogene; IS711; SNPs 1. Introduction The Proteobacteria phylum represents the most extensive bacteria domain known.