HopW1 from <i>Pseudomonas syringae</i> Disrupts the Actin Cytoskeleton to Promote Virulence in Arabidopsis

A central mechanism of virulence of extracellular bacterial pathogens is the injection into host cells of effector proteins that modify host cellular functions. HopW1 is an effector injected by the type III secretion system that increases the growth of the plant pathogen Pseudomonas syringae on the Columbia accession of Arabidopsis. When delivered by P. syringae into plant cells, HopW1 causes a reduction in the filamentous actin (F-actin) network and the inhibition of endocytosis, a known actin-dependent process. When directly produced in plants, HopW1 forms complexes with actin, disrupts the actin cytoskeleton and inhibits endocytosis as well as the trafficking of certain proteins to vacuoles. The C-terminal region of HopW1 can reduce the length of actin filaments and therefore solubilize F-actin in vitro. Thus, HopW1 acts by disrupting the actin cytoskeleton and the cell biological processes that depend on actin, which in turn are needed for restricting P. syringae growth in Arabidopsis.</p

Passage of Heme-Iron Across the Envelope of Staphylococcus aureus

The cell wall envelope of Gram-positive pathogens functions as a scaffold for the attachment of virulence factors and as a sieve that prevents diffusion of molecules. Here the isdgenes (iron-regulated surface determinant) of Staphylococcus aureus were found to encode factors responsible for hemoglobin binding and passage of heme-iron to the cytoplasm, where it acts as an essential nutrient. Heme-iron passage required two sortases that tether Isd proteins to unique locations within the cell wall. Thus, Isd appears to act as an import apparatus that uses cell wall–anchored proteins to relay heme-iron across the bacterial envelope

Passage of Heme-Iron Across the Envelope of Staphylococcus aureus

The cell wall envelope of Gram-positive pathogens functions as a scaffold for the attachment of virulence factors and as a sieve that prevents diffusion of molecules. Here the isdgenes (iron-regulated surface determinant) of Staphylococcus aureus were found to encode factors responsible for hemoglobin binding and passage of heme-iron to the cytoplasm, where it acts as an essential nutrient. Heme-iron passage required two sortases that tether Isd proteins to unique locations within the cell wall. Thus, Isd appears to act as an import apparatus that uses cell wall–anchored proteins to relay heme-iron across the bacterial envelope

Genetic Analysis of the Individual Contribution to Virulence of the Type III Effector Inventory of Pseudomonas syringae pv. phaseolicola

Several reports have recently contributed to determine the effector inventory of the sequenced strain Pseudomonas syringae pv. phaseolicola (Pph) 1448a. However, the contribution to virulence of most of these effectors remains to be established. Genetic analysis of the contribution to virulence of individual P. syringae effectors has been traditionally hindered by the lack of phenotypes of the corresponding knockout mutants, largely attributed to a high degree of functional redundancy within their effector inventories. In support of this notion, effectors from Pseudomonas syringae pv. tomato (Pto) DC3000 have been classified into redundant effector groups (REGs), analysing virulence of polymutants in the model plant Nicotiana benthamiana. However, using competitive index (CI) as a virulence assay, we were able to establish the individual contribution of AvrPto1PtoDC3000 to Pto DC3000 virulence in tomato, its natural host, even though typically, contribution to virulence of AvrPto1 is only shown in strains also lacking AvrPtoB (also called HopAB2), a member of its REG. This report raised the possibility that even effectors targeting the same defence signalling pathway may have an individual contribution to virulence, and pointed out to CI assays as the means to establish such a contribution for individual effectors. In this work, we have analysed the individual contribution to virulence of the majority of previously uncharacterised Pph 1448a effectors, by monitoring the development of disease symptoms and determining the CI of single knockout mutants at different stages of growth within bean, its natural host. Despite their potential functional redundancy, we have found individual contributions to virulence for six out of the fifteen effectors analysed. In addition, we have analysed the functional relationships between effectors displaying individual contribution to virulence, highlighting the diversity that these relationships may present, and the interest of analysing their functions within the context of the infection

Dynamic Evolution of Pathogenicity Revealed by Sequencing and Comparative Genomics of 19 Pseudomonas syringae Isolates

Closely related pathogens may differ dramatically in host range, but the molecular, genetic, and evolutionary basis for these differences remains unclear. In many Gram- negative bacteria, including the phytopathogen Pseudomonas syringae, type III effectors (TTEs) are essential for pathogenicity, instrumental in structuring host range, and exhibit wide diversity between strains. To capture the dynamic nature of virulence gene repertoires across P. syringae, we screened 11 diverse strains for novel TTE families and coupled this nearly saturating screen with the sequencing and assembly of 14 phylogenetically diverse isolates from a broad collection of diseased host plants. TTE repertoires vary dramatically in size and content across all P. syringae clades; surprisingly few TTEs are conserved and present in all strains. Those that are likely provide basal requirements for pathogenicity. We demonstrate that functional divergence within one conserved locus, hopM1, leads to dramatic differences in pathogenicity, and we demonstrate that phylogenetics-informed mutagenesis can be used to identify functionally critical residues of TTEs. The dynamism of the TTE repertoire is mirrored by diversity in pathways affecting the synthesis of secreted phytotoxins, highlighting the likely role of both types of virulence factors in determination of host range. We used these 14 draft genome sequences, plus five additional genome sequences previously reported, to identify the core genome for P. syringae and we compared this core to that of two closely related non-pathogenic pseudomonad species. These data revealed the recent acquisition of a 1 Mb megaplasmid by a sub-clade of cucumber pathogens. This megaplasmid encodes a type IV secretion system and a diverse set of unknown proteins, which dramatically increases both the genomic content of these strains and the pan-genome of the species

Magnetometry as a tool to evaluate the environmental pollution

This paper presents the use of magnetometry to study pollution of soil and air. The magnetic method consists in determining the magnetic properties of pollution floating in the air and deposited in the soil, the leaves of trees or household dust in apartments. The method based on the fact that the magnetic particles present in the pollution are associated with heavy metals and toxic trace elements harmful to human health. The study of traffic pollution was focused on the spatial distribution of pollution in soils along roads in relation to the distance from the edge of road, the area topography and the factors affecting the speed of motor transport (traffic lights, traffic jams, road narrowing, etc.). The study of air pollution allowed to determine the seasonal correlation between pollution deposited on filters and meteorological parameters such as temperature, humidity and precipitation. Detailed analysis of magnetic susceptibility as an indicator of pollution revealed increasing trend with temperature and absolute humidity in the cold months of the year and the decreasing trend in the warm months. Similar correlations were not observed between the magnetic susceptibility and the precipitation. The second part presents a study of indoor air pollution based on measurements of dust collected in apartments in different districts of Warsaw. It was found that floor on which dust was taken did not affect the amount and composition of pollution in opposite to vehicle traffic, housing density and way of ventilation. Study shows that the most polluted apartments are in the Center, in the district of Praga Południe, Mokotów and Ursynów located close to the narrow streets with the large vehicle traffic and poor ventilation. Correlation of the magnetic susceptibility with the concentration of heavy metals in household dust is the base for use of susceptibility for monitoring indoor air pollution

Paleomagnetic study of upper carboniferous volcanics from Sudetes (Poland)

Upper Carboniferous and Permian volcanites from Sudetes were sampled in 11 localities (mean site coordinates: 50.8°N, 16.3°E). Thermal demagnetizations of the samples showed several magnetic components. But in one site, all high-temperature components are reversed. The interpretation of the results shows a first, primary magnetization acquired probably in the Upper Carboniferous before tilting (N = 8, D = 192°, I = -2°,&nbsp;k = 27, α95 = 11°, pole: 39°N, 181°E) and a remagnetization acquired later, during or after tilting (N = 5, D = 190°, I = -19°, k = 18, α95 = 18°, pole: 48°N, 181°E). &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ARK: https://n2t.net/ark:/88439/y097077 Permalink: https://geophysicsjournal.com/article/125 &nbsp

Re-aimantations des massifs Varisques et restitution de la paléosurface triasique en Europe

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