A Functional and Phylogenetic Comparison of Quorum Sensing Related Genes in Brucella melitensis 16M

A quorum-sensing (QS) system is involved in Brucella melitensissurvival inside the host cell. Two transcriptional regulatorsidentified in B. melitensis, BlxR and VjbR, regulatethe expression of virB, an operon required for bacterial intracellularpersistence. In this work, 628 genes affected byVjbR and 124 by BlxR were analyzed to gain insights intotheir functional and taxonomical distributions among theBacteria and Archaea cellular domains. In this regard, theCluster of Orthologous Groups (COG) genes and orthologousgenes in 789 nonredundant bacterial and archaeal genomeswere obtained and compared against a group ofrandomly selected genes. From these analyses, we found 71coaffected genes between VjbR and BlxR. In the COG comparison,VjbR activated genes associated with intracellulartrafficking, secretion and vesicular transport and defensemechanisms, while BlxR affected genes related to energyproduction and conversion (with an equal effect) and translation,ribosomal structure and biogenesis, posttranslationalmodifications and carbohydrate and amino acid metabolism(with a negative effect). When the taxonomical distributionof orthologous genes was evaluated, the VjbR- and BlxRrelatedgenes presented more orthologous genes in Crenarchaeota(Archaea), Firmicutes, and Tenericutes and fewergenes in Proteobacteria than expected by chance. These findingssuggest that QS system exert a fine-tuning modulationof gene expression, by which VjbR activates genes relatedto infection persistence and defense, while BlxR repressesgeneral bacterial metabolism for intracellular adaptations. Finally, these affected genes present a degree of presenceamong Bacteria and Archaea genomes that is different fromthat expected by chance.