Ferredoxin containing bacteriocins suggest a novel mechanism of iron uptake in <i>Pectobacterium spp</i>

In order to kill competing strains of the same or closely related bacterial species, many bacteria produce potent narrow-spectrum protein antibiotics known as bacteriocins. Two sequenced strains of the phytopathogenic bacterium &lt;i&gt;Pectobacterium carotovorum&lt;/i&gt; carry genes encoding putative bacteriocins which have seemingly evolved through a recombination event to encode proteins containing an N-terminal domain with extensive similarity to a [2Fe-2S] plant ferredoxin and a C-terminal colicin M-like catalytic domain. In this work, we show that these genes encode active bacteriocins, pectocin M1 and M2, which target strains of &lt;i&gt;Pectobacterium carotovorum&lt;/i&gt; and &lt;i&gt;Pectobacterium atrosepticum&lt;/i&gt; with increased potency under iron limiting conditions. The activity of pectocin M1 and M2 can be inhibited by the addition of spinach ferredoxin, indicating that the ferredoxin domain of these proteins acts as a receptor binding domain. This effect is not observed with the mammalian ferredoxin protein adrenodoxin, indicating that &lt;i&gt;Pectobacterium spp.&lt;/i&gt; carries a specific receptor for plant ferredoxins and that these plant pathogens may acquire iron from the host through the uptake of ferredoxin. In further support of this hypothesis we show that the growth of strains of &lt;i&gt;Pectobacterium carotovorum&lt;/i&gt; and &lt;i&gt;atrosepticum&lt;/i&gt; that are not sensitive to the cytotoxic effects of pectocin M1 is enhanced in the presence of pectocin M1 and M2 under iron limiting conditions. A similar growth enhancement under iron limiting conditions is observed with spinach ferrodoxin, but not with adrenodoxin. Our data indicate that pectocin M1 and M2 have evolved to parasitise an existing iron uptake pathway by using a ferredoxin-containing receptor binding domain as a Trojan horse to gain entry into susceptible cells

Lectin-like bacteriocins from pseudomonas spp. utilise D-rhamnose containing lipopolysaccharide as a cellular receptor

Lectin-like bacteriocins consist of tandem monocot mannose-binding domains and display a genus-specific killing activity. Here we show that pyocin L1, a novel member of this family from Pseudomonas aeruginosa, targets susceptible strains of this species through recognition of the common polysaccharide antigen (CPA) of P. aeruginosa lipopolysaccharide that is predominantly a homopolymer of d-rhamnose. Structural and biophysical analyses show that recognition of CPA occurs through the C-terminal carbohydrate-binding domain of pyocin L1 and that this interaction is a prerequisite for bactericidal activity. Further to this, we show that the previously described lectin-like bacteriocin putidacin L1 shows a similar carbohydrate-binding specificity, indicating that oligosaccharides containing d-rhamnose and not d-mannose, as was previously thought, are the physiologically relevant ligands for this group of bacteriocins. The widespread inclusion of d-rhamnose in the lipopolysaccharide of members of the genus Pseudomonas explains the unusual genus-specific activity of the lectin-like bacteriocins

Detection of O3 and NH3 using hybrid tin dioxide/carbon nanotubes sensors: Influence of materials and processing on sensor's sensitivity

International audienceA tin oxide (SnO2)/arc-discharge single walled carbon nanotubes (SWNTs) hybrid material based sensor was developed for the detection of NH3 and O3 at room temperature. The gas sensitive composite thin films were prepared using sol gel and dip coating techniques, and characterized by transmission electron microscopy, atomic force microscopy and Raman spectroscopy. Overall, the hybrid material based sensor is found to have an enhanced sensitivity as compared to pure SnO2 or pure SWNTs based sensors. An optimum annealing temperature of the composite of 300 °C was determined. The detection limit at room temperature was evaluated at 1 ppm and lower than 20 ppb for NH3 and O3, respectively. Moreover, the hybrid sensor exhibited a fast response (few minutes), a good sensitivity and a full recovery at room temperature. The sensor efficiency has also been demonstrated to strongly depend on the SWNT source used for sensor fabrication (4 different commercial sources have been tested). These results open the way towards further optimized hybrid sensors

Structural Variability of EspG Chaperones from Mycobacterial ESX-1, ESX-3, and ESX-5 Type VII Secretion Systems

Type VII secretion systems (ESX) are responsible for transport of multiple proteins in mycobacteria. How different ESX systems achieve specific secretion of cognate substrates remains elusive. In the ESX systems, the cytoplasmic chaperone EspG forms complexes with heterodimeric PE–PPE substrates that are secreted from the cells or remain associated with the cell surface. Here we report the crystal structure of the EspG1 chaperone from the ESX-1 system determined using a fusion strategy with T4 lysozyme. EspG$_1$ adopts a quasi 2-fold symmetric structure that consists of a central β-sheet and two α-helical bundles. In addition, we describe the structures of EspG3 chaperones from four different crystal forms. Alternate conformations of the putative PE–PPE binding site are revealed by comparison of the available EspG$_3$ structures. Analysis of EspG$_1$, EspG$_3$, and EspG$_5$ chaperones using small-angle X-ray scattering reveals that EspG$_1$ and EspG$_3$ chaperones form dimers in solution, which we observed in several of our crystal forms. Finally, we propose a model of the ESX-3 specific EspG$_3$–PE5–PPE4 complex based on the small-angle X-ray scattering analysis

Cruelty and Other Dimensions of Exceptionality in Discourses about Violent Acts

This study analyzes concepts related to violence in discourses in circulation. It is based on an analysis of discourses about the homicide of a pregnant young woman committed by the staff member of a police department in a poor neighborhood of Buenos Aires, Argentina. The textual marks that allow accessing the meanings exposed and supported around the concept of violence are analyzed. Special attention is given to the factors that appear as indications of a violent act of greater degree. Revealing that which is considered excessive, with exception, can help in the understand of that which is normally considered as violence