LsrR-Mediated Quorum Sensing Controls Invasiveness of Salmonella typhimurium by Regulating SPI-1 and Flagella Genes

Bacterial cell-to-cell communication, termed quorum sensing (QS), controls bacterial behavior by using various signal molecules. Despite the fact that the LuxS/autoinducer-2 (AI-2) QS system is necessary for normal expression of Salmonella pathogenicity island-1 (SPI-1), the mechanism remains unknown. Here, we report that the LsrR protein, a transcriptional regulator known to be involved in LuxS/AI-2-mediated QS, is also associated with the regulation of SPI-1-mediated Salmonella virulence. We determined that LsrR negatively controls SPI-1 and flagella gene expressions. As phosphorylated AI-2 binds to and inactivates LsrR, LsrR remains active and decreases expression of SPI-1 and flagella genes in the luxS mutant. The reduced expression of those genes resulted in impaired invasion of Salmonella into epithelial cells. Expression of SPI-1 and flagella genes was also reduced by overexpression of the LsrR regulator from a plasmid, but was relieved by exogenous AI-2, which binds to and inactivates LsrR. These results imply that LsrR plays an important role in selecting infectious niche of Salmonella in QS dependent mode

Localization of type 1 diabetes susceptibility to the MHC class I genes HLA-B and HLA-A

The major histocompatibility complex (MHC) on chromosome 6 is associated with susceptibility to more common diseases than any other region of the human genome, including almost all disorders classified as autoimmune. In type 1 diabetes the major genetic susceptibility determinants have been mapped to the MHC class II genes HLA-DQB1 and HLA-DRB1 (refs 1-3), but these genes cannot completely explain the association between type 1 diabetes and the MHC region. Owing to the region's extreme gene density, the multiplicity of disease-associated alleles, strong associations between alleles, limited genotyping capability, and inadequate statistical approaches and sample sizes, which, and how many, loci within the MHC determine susceptibility remains unclear. Here, in several large type 1 diabetes data sets, we analyse a combined total of 1,729 polymorphisms, and apply statistical methods - recursive partitioning and regression - to pinpoint disease susceptibility to the MHC class I genes HLA-B and HLA-A (risk ratios >1.5; Pcombined = 2.01 × 10-19 and 2.35 × 10-13, respectively) in addition to the established associations of the MHC class II genes. Other loci with smaller and/or rarer effects might also be involved, but to find these, future searches must take into account both the HLA class II and class I genes and use even larger samples. Taken together with previous studies, we conclude that MHC-class-I-mediated events, principally involving HLA-B*39, contribute to the aetiology of type 1 diabetes. ©2007 Nature Publishing Group

Overview of stress corrosion cracking of magnesium alloys

An overview is provided of current understanding of stress corrosion cracking (SCC) of Mg alloys. Nearly continuous second phases along grain boundaries (GBs) cause intergranular stress corrosion cracking (IGSCC). The second phase causes significant micro-galvanic acceleration of the corrosion of the adjacent matrix phase. The applied stress opens the stress corrosion crack and allows propagation through the alloy. IGSCC is expected in all creep resistant Mg alloys, whenever creep resistance is produced by a continuous second phase along GBs. Transganular SCC (TGSCC) is most probably caused by Hydrogen (H) so a detailed study of H-trap interactions is needed to understand this damage mechanism and to design alloys resistant to TGSCC. This is urgently needed if wrought alloys are to be used safely in service because prior research indicates that many Mg alloys have a SCC threshold stress of half the yield stress in common environments including high-purity water

Industrially-Relevant Multiscale Modelling of Hydrogen Assisted Degradation

The advancement of computational modelling methods, particularly atomistic techniques, provides new opportunities for the investigation of H-metal interactions. However, there remain numerous obstacles to the application of such methods to real industrial problems. Key among these are the inability of atomistic calculations to describe long range diffusion processes and the inherent uncertainty regarding the predominant H-assisted damage mechanism in real engineering systems. The EU-FP7 project MultiHy aims to develop a robust, transferrable multiscale modelling methodology for predicting the HE susceptibility of real materials and components under actual production/service conditions. This will be demonstrated by investigating the influence of microstructure on H diffusion and trapping in three contrasting industrial case studies: (i) pulse-plated Ni coatings used in EADSs Ariane satellite launch system; (ii) advanced high strength steels for future automobile bodies; and (ii) ultra-high-strength steels used for offshore wind turbine bearings. A summary of the results from the first year of the project are presented. We have performed accurate first-principles calculations based on density functional theory (DFT) of the H binding energies and diffusion barriers in Fe and Ni as a function of lattice strain. Semi-empirical tight-binding models have also been developed, which will facilitate the evaluation of H trapping at extended crystal defects such as grain boundaries and dislocations. The atomistically-derived results have been used in mesoscale kinetic Monte Carlo (K MC) simulations to evaluate the effective H diffusivities under different strain conditions and trap densities. At the macroscopic level, we have developed a framework for the evaluation of H distribution under rolling contact conditions using the finite element method (FEM). Such FEM models will be later extended to full component scale models and will incorporate diffusivities derived using the atomistic-KMC simulations. An overview of experimental work aimed at the validation of the models at all scales will also be presented

LuxS-dependent quorum sensing in Porphyromonas gingivalis modulates protease and haemagglutinin activities but is not essential for virulence.

Porphyromonas gingivalis is a Gram-negative black-pigmented obligate anaerobe implicated in the aetiology of human periodontal disease. The virulence of P. gingivalis is associated with the elaboration of the cysteine proteases Arg-gingipain (Rgp) and Lys-gingipain (Kgp), which are produced at high bacterial cell densities. To determine whether quorum sensing plays a role in the regulation of Rgp and Kgp, biosensors capable of detecting either N-acylhomoserine lactone (AHLs) or the luxS-dependent autoinducer (AI-2) quorum-sensing signalling molecules in spent culture supernatants were first employed. While no AHLs could be detected, the Vibrio harveyi BB170 biosensor was activated by spent P. gingivalis W50 culture supernatants. The P. gingivalis luxS gene was cloned and demonstrated to restore AI-2 production in the Escherichia coli luxS mutant DH5. Mutation of luxS abolished AI-2 production in P. gingivalis. Western blotting using antibodies raised against the recombinant protein revealed that LuxS levels increased throughout growth even though AI-2 activity was only maximally detected at the mid-exponential phase of growth and disappeared by the onset of stationary phase. Similar results were obtained with E. coli DH5 transformed with luxS, suggesting that AI-2 production is not limited by a lack of LuxS protein. Analysis of Rgp and Kgp protease activities revealed that the P. gingivalis luxS mutant produced around 45% less Rgp and 30% less Kgp activity than the parent strain. In addition, the luxS mutant exhibited a fourfold reduction in haemagglutinin titre. However, these reductions in virulence determinant levels were insufficient to attenuate the luxS mutant in a murine lesion model of P. gingivalis infection