Identification of OtpR regulated sRNAs in Brucella melitensis expressed under acidic stress and their roles in pathogenesis and metabolism

Analysis of CenKR essentiality in Sinorhizobium meliloti and its activity at a target gene promoter in vivo

The two-component regulatory system CenK-CenR has recently emerged as a regulator of cell envelope and cell division processes in the alpha-proteobacteria. In Sinorhizobium meliloti, CenK-CenR regulates the expression of SrlA, a thioredoxin-domain protein of unknown function. Deletion of srlA causes sensitivity to salt and oxidizing agents on solid growth medium. In this work, we report that the response regulator CenR, but not the histidine kinase CenK, is essential for cell viability in S. meliloti. We also demonstrate that phosphorylation of the target residue D55 is not required for viability, suggesting that the unphosphorylated transcription factor sufficiently regulates expression of one or more essential genes in the genome. Using transcription assays and phenotype testing we examine CenK-CenR-dependent activation of the srlA promoter and demonstrate its absolute dependence on phosphoryl-CenR for activity and that the CenR substitution D55E acts as a phosphomimetic that partially restores activity at the srlA promoter in the absence of phosphorylation by CenK. Finally, we report a mutational analysis of the CenR binding site in the srlA promoter required for transcriptional activation.

Comparative Genome-Wide Transcriptome Analysis of Brucella suis and Brucella microti Under Acid Stress at pH 4.5: Cold Shock Protein CspA and Dps Are Associated With Acid Resistance of B. microti

Brucellae are facultative intracellular coccobacilli causing brucellosis, one of the most widespread bacterial zoonosis affecting wildlife animals, livestock and humans. The genus Brucella comprises classical and atypical species, such as Brucella suis and Brucella microti, respectively. The latter is characterized by increased metabolic activity, fast growth rates, and extreme acid resistance at pH 2.5, suggesting an advantage for environmental survival. In addition, B. microti is more acid-tolerant than B. suis at the intermediate pH of 4.5. This acid-resistant phenotype of B. microti may have major implications for fitness in soil, food products and macrophages. Our study focused on the identification and characterization of acid resistance determinants of B. suis and B. microti in Gerhardt's minimal medium at pH 4.5 and 7.0 for 20 min and 2 h by comparative RNA-Seq-based transcriptome analysis, validated by RT-qPCR. Results yielded a common core response in both species with a total of 150 differentially expressed genes, and acidic pH-dependent genes regulated specifically in each species. The identified core response mechanisms comprise proton neutralization or extrusion from the cytosol, participating in maintaining physiological intracellular pH values. Differential expression of 441 genes revealed species-specific mechanisms in B. microti with rapid physiological adaptation to acid stress, anticipating potential damage to cellular components and critical energy conditions. Acid stress-induced genes encoding cold shock protein CspA, pseudogene in B. suis, and stress protein Dps were associated with survival of B. microti at pH 4.5. B. suis response with 284 specifically regulated genes suggested increased acid stress-mediated protein misfolding or damaging, triggering the set-up of repair strategies countering the consequences rather than the origin of acid stress and leading to subsequent loss of viability. In conclusion, our work supports the hypothesis that increased acid stress resistance of B. microti is based on selective pressure for the maintenance of functionality of critical genes, and on specific differential gene expression, resulting in rapid adaptation.

Regulatory Networks of the T4SS Control: From Host Cell Sensing to the Biogenesis and the Activity during the Infection

Delivery of effectors, DNA or proteins, that hijack host cell processes to the benefit of bacteria is a mechanism widely used by bacterial pathogens. It is achieved by complex effector injection devices, the secretion systems, among which Type 4 Secretion Systems (T4SSs) play a key role in bacterial virulence of numerous animal and plant pathogens. Considerable progress has recently been made in the structure-function analyses of T4SSs. Nevertheless, the signals and processes that trigger machine assembly and activity during infection, as well as those involved in substrate recognition and transfer, are complex and still poorly understood. In this review, we aim at summarizing the last updates of the knowledge on signaling pathways that regulate the biogenesis and the activity of T4SSs in important bacterial pathogens.

Uncovering the Hidden Credentials of Brucella Virulence

Bacteria in the genus Brucella are important human and veterinary pathogens. The abortion and infertility they cause in food animals produce economic hardships in areas where the disease has not been controlled, and human brucellosis is one of the world's most common zoonoses. Brucella strains have also been isolated from wildlife, but we know much less about the pathobiology and epidemiology of these infections than we do about brucellosis in domestic animals. The brucellae maintain predominantly an intracellular lifestyle in their mammalian hosts, and their ability to subvert the host immune response and survive and replicate in macrophages and placental trophoblasts underlies their success as pathogens. We are just beginning to understand how these bacteria evolved from a progenitor alphaproteobacterium with an environmental niche and diverged to become highly host-adapted and host-specific pathogens. Two important virulence determinants played critical roles in this evolution: (i) a type IV secretion system that secretes effector molecules into the host cell cytoplasm that direct the intracellular trafficking of the brucellae and modulate host immune responses and (ii) a lipopolysaccharide moiety which poorly stimulates host inflammatory responses. This review highlights what we presently know about how these and other virulence determinants contribute to Brucella pathogenesis. Gaining a better understanding of how the brucellae produce disease will provide us with information that can be used to design better strategies for preventing brucellosis in animals and for preventing and treating this disease in humans.

Genomic insights into Brucella

Brucellosis is a zoonotic disease caused by certain species of Brucella. Each species has its preferred host animal, though it can infect other animals too. For a longer period, only six classical species were recognized in the genus Brucella. No vaccine is available for human brucellosis. Therefore, human brucellosis can be controlled only by controlling brucellosis in animals. The genus is now expanding with the newly isolated atypical strains from various animals, including marine mammals. Presently, 12 species of Brucella have been recognized. The first genome of Brucella was released in 2002, and today, we have more than 1500 genomes of Brucella spp. isolated worldwide. Multiple genome sequences are available for the major zoonotic species, B. abortus, B. melitensis, and B. suis. The Brucella genome has two chromosomes with the approximate sizes of 2.1 and 1.2 Mbp. The genome of Brucella is highly conserved across all the species at the nucleotide level. One of the unanswered questions is what makes host preference in different species of Brucella. Here, I summarize the recent advancements in the Brucella genomics research.