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Comparative genomics in brucella suis : from intra-specific and inter-specific distinctive features to diagnostic molecular markers
Publication . Inácio, Ana Cristina Ribeiro Alves Ferreira, 1973-; Tenreiro, Rogério Paulo de Andrade, 1955-; Sá, Maria Inácia Aleixo Vacas de Carvalho Corrêa de
Brucella suis is divided into five biovars of which only biovars 1, 2 and 3 infect Suidae. Biovars 1 and 3 cause severe disease in humans and are mainly prevalent in South America and South-East Asia. In contrast, biovar 2 has been rarely isolated from humans, and its zoonotic role is questioned. Currently, B. suis biovar 2 is the unique biovar isolated in Portugal and Spain, representing an emerging disease in domestic swine throughout Europe, being associated with the increase of extensive pig farms and the high density of infected wild boars (Sus scrofa). In the present work the genetic structure of a collection of B. suis strains was characterized. Molecular fingerprinting with restriction enzymes and Variable Number Tandem Repeats (VNTR) showed differences between strains from Iberian Peninsula and others from Central Europe. The majority of strains isolated in Portugal and Spain share specific molecular characteristics establishing an Iberian clonal lineage. However, strains isolated from wild boars in the North-East region of Spain were similar to those isolated in other Central-European countries. In order to deeply understand genomic differences between Iberian and Central-European clones and further unveil B. suis pan-genome and evolutive history, the genomes of five B. suis biovar 2 strains isolated from wild boars and representative of both clonal lineages circulating in Iberian Peninsula were sequenced and compared with 18 publicly available sequenced genomes from eight of the 12 recognized Brucella species. This full genome comparative analysis showed that Brucella is a highly conserved genus with two chromosomes and apparently slow evolutionary rates at species level. Nevertheless, B. suis biovar 2 strains from Iberian clonal lineage can be differentiated from those from Central-European clonal lineage not only by the presence of one large inversion in Chromosome I but also by a number of specific SNPs, deletions and insertions. Furthermore, 10 different target-PCRs protocols were established and validated for the differentiation of strains from a specific clonal lineage, being useful to be used as epidemiological markers for future investigations. The mutational enrichment of Iberian lineage was associated to genes encoding membrane proteins described with potential of interaction with external stimulus, as well as to genes with impact on the metabolism of the pathogen. The genomic specialization and local adaptation of B. suis biovar 2 strains establish an Iberian ecovar, raising an important question regarding the mechanisms responsible for putative tropisms as response to adaptation to a specific host and/or pathobiological conditions. Future work should be done to better understand the consequences of these disarrangements and their impact in pathogenicity or virulence in wide range of hosts, including man.
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Fundação para a Ciência e a Tecnologia
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3599-PPCDT
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PTDC/CVT/104050/2008