A sensor histidine kinase from a plant-endosymbiont bacterium restores the virulence of a mammalian intracellular pathogen.

Alphaproteobacteria include organisms living in close association with plants or animals. This interaction relies partly on orthologous two-component regulatory systems (TCS), with sensor and regulator proteins modulating the expression of conserved genes related to symbiosis/virulence. We assessed the ability of the exoS+Sm gene, encoding a sensor protein from the plant endosymbiont Sinorhizobium meliloti to substitute its orthologous bvrS in the related animal/human pathogen Brucella abortus. ExoS phosphorylated the B. abortus regulator BvrR in vitro and in cultured bacteria, showing conserved biological function. Production of ExoS in a B. abortus bvrS mutant reestablished replication in host cells and the capacity to infect mice. Bacterial outer membrane properties, the production of the type IV secretion system VirB, and its transcriptional regulators VjbR and BvrR were restored as compared to parental B. abortus. These results indicate that conserved traits of orthologous TCS from bacteria living in and sensing different environments are sufficient to achieve phenotypic plasticity and support bacterial survival. The knowledge of bacterial genetic networks regulating host interactions allows for an understanding of the subtle differences between symbiosis and parasitism. Rewiring these networks could provide new alternatives to control and prevent bacterial infection.

Genome-Based Characterization of Listeria monocytogenes, Costa Rica.

Genomic data on the foodborne pathogen Listeria monocytogenes from Central America are scarce. We analyzed 92 isolates collected during 2009-2019 from different regions in Costa Rica, compared those to publicly available genomes, and identified unrecognized outbreaks. Our findings suggest mandatory reporting of listeriosis in Costa Rica would improve pathogen surveillance.

The Brucella abortus two-component system response regulator BvrR binds to three DNA regulatory boxes in the upstream region of omp25.

Brucella abortus is a facultative extracellular-intracellular bacterial zoonotic pathogen worldwide. It is also a major cause of abortion in bovines, generating economic losses. The two-component regulatory system BvrR/BvrS modulates the expression of genes required to transition from extracellular to intracellular lifestyles. However, few regulatory regions of BvrR direct target genes have been studied. In this study, we characterized the regulatory region of omp25, a gene encoding an outer membrane protein that is positively regulated by TCS BvrR/BvrS. By omp25-lacZ reporter fusions and ß-galactosidase activity assays, we found that the region between-262 and + 127 is necessary for transcriptional activity, particularly a 111-bp long fragment located from-262 to -152. In addition, we demonstrated the binding of P-BvrR to three sites within the -140 to +1 region. Two of these sites were delimited between -18 to +1 and - 99 to -76 by DNase I footprinting and called DNA regulatory boxes 1 and 2, respectively. The third binding site (box 3) was delimited from -140 to -122 by combining EMSA and fluorescence anisotropy results. A molecular docking analysis with HDOCK predicted BvrR-DNA interactions between 11, 13, and 12 amino acid residue-nucleotide pairs in boxes 1, 2, and 3, respectively. A manual sequence alignment of the three regulatory boxes revealed the presence of inverted and non-inverted repeats of five to eight nucleotides, partially matching DNA binding motifs previously described for BvrR. We propose that P-BvrR binds directly to up to three regulatory boxes and probably interacts with other transcription factors to regulate omp25 expression. This gene regulation model could apply to other BvrR target genes and to orthologs of the TCS BvrR/BvrS and Omp25 in phylogenetically closed Rhizobiales.

A bvrR/bvrS Non-Polar Brucella abortus Mutant Confirms the Role of the Two-Component System BvrR/BvrS in Virulence and Membrane Integrity.

Brucella abortus is a bacterial pathogen causing bovine brucellosis worldwide. This facultative extracellular-intracellular pathogen can be transmitted to humans, leading to a zoonotic disease. The disease remains a public health concern, particularly in regions where livestock farming is present. The two-component regulatory system BvrR/BvrS was described by isolating the attenuated transposition mutants bvrR::Tn5 and bvrS::Tn5, whose characterization led to the understanding of the role of the system in bacterial survival. However, a phenotypic comparison with deletion mutants has not been performed because their construction has been unsuccessful in brucellae and difficult in phylogenetically related Rhizobiales with BvrR/BvrS orthologs. Here, we used an unmarked gene excision strategy to generate a B. abortus mutant strain lacking both genes, called B. abortus ∆bvrRS. The deletion was verified through PCR, Southern blot, Western blot, Sanger sequencing, and whole-genome sequencing, confirming a clean mutation without further alterations at the genome level. B. abortus ∆bvrRS shared attenuated phenotypic traits with both transposition mutants, confirming the role of BvrR/BvrS in pathogenesis and membrane integrity. This B. abortus ∆bvrRS with a non-antimicrobial marker is an excellent tool for continuing studies on the role of BvrR/BvrS in the B. abortus lifestyle.

The regulon of Brucella abortus two-component system BvrR/BvrS reveals the coordination of metabolic pathways required for intracellular life.

Brucella abortus is a facultative intracellular pathogen causing a severe zoonotic disease worldwide. The two-component regulatory system (TCS) BvrR/BvrS of B. abortus is conserved in members of the Alphaproteobacteria class. It is related to the expression of genes required for host interaction and intracellular survival. Here we report that bvrR and bvrS are part of an operon composed of 16 genes encoding functions related to nitrogen metabolism, DNA repair and recombination, cell cycle arrest, and stress response. Synteny of this genomic region within close Alphaproteobacteria members suggests a conserved role in coordinating the expression of carbon and nitrogen metabolic pathways. In addition, we performed a ChIP-Seq analysis after exposure of bacteria to conditions that mimic the intracellular environment. Genes encoding enzymes at metabolic crossroads of the pentose phosphate shunt, gluconeogenesis, cell envelope homeostasis, nucleotide synthesis, cell division, and virulence are BvrR/BvrS direct targets. A 14 bp DNA BvrR binding motif was found and investigated in selected gene targets such as virB1, bvrR, pckA, omp25, and tamA. Understanding gene expression regulation is essential to elucidate how Brucella orchestrates a physiological response leading to a furtive pathogenic strategy.