Curing of Plasmid pXO1 from Bacillus anthracis Using Plasmid Incompatibility

The large plasmid pXO1 encoding the anthrax toxin is important for the virulence of Bacillus anthracis. It is essential to cure pXO1 from B. anthracis to evaluate its role in the pathogenesis of anthrax infection. Because conventional methods for curing plasmids (e.g., curing agents or growth at elevated temperatures) can induce mutations in the host chromosomal DNA, we developed a specific and reliable method to eliminate pXO1 from B. anthracis using plasmid incompatibility. Three putative replication origins of pXO1 were inserted into a temperature-sensitive plasmid to generate three incompatible plasmids. One of the three plasmids successfully eliminated the large plasmid pXO1 from B. anthracis vaccine strain A16R and wild type strain A16. These findings provided additional information about the replication/partitioning of pXO1 and demonstrated that introducing a small incompatible plasmid can generate plasmid-cured strains of B. anthracis without inducing spontaneous mutations in the host chromosome

The origin of enhanced photocatalytic activities of hydrogenated TiO2 nanoparticles

The photocatalytic activity of semiconductors is largely governed by their light absorption, separation of photoinduced charge carriers and surface catalytically active sites, which are primarily controlled by the morphology, crystalline size, structure, and especially the electronic structure of photocatalysts. Black TiO 2 is recognized as one of the most promising visible-light photocatalysts, due to its significantly enhanced visible-light photocatalytic performance in comparison to intrinsic TiO 2 . In this work, black TiO 2 is synthesized through the hydrogenation process. The sample shows a TiO 2 @TiO 2-x core/shell structure which is attributed to hydrogenation. By using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and nuclear magnetic resonance (NMR) spectroscopy, we identified the featured midgap electronic states in black TiO 2 , which gave rise to the TiO 2-x shell layer. These states lead to the improvement of visible-light absorption and the separation of photoinduced charge carriers, which consequently result in remarkable enhanced photocatalytic activities in black TiO 2

Effects of temperature-induced variation of the second phase on the microstructure, texture and properties of Mg-RE-Zn alloys

In this paper, the Mg-9.32Gd-3.72Y-1.68Zn-0.72Zr (wt%) alloy has undergone three times of repetitive upsetting extrusion deformation. Alloys with different morphologies and distribution patterns of the second phase have been prepared by varying the deformation temperature in each pass. The effects of the second phase on microstructure, texture and mechanical properties are investigated. The results show that (i) the second phase, including Mg _5 Gd and LPSO phase, has an important effect on the dynamic recrystallization (DRX) behavior of the alloy. (ii) Appropriate lamella distance and block phase size can promote the activation of the slip system and effectively weaken the texture strength. (iii) The DT sample has an effective combination of fine grain strengthening and second phase strengthening due to the reasonable second phase distribution and size, which greatly improves the UTS and YS of the alloy

PCR analysis of pXO1 in <i>B. anthracis</i> vaccine strain A16R.

<p>PCR analysis of the vaccine strain A16R (1) and the putative pXO1-cured strain A16R (2) with 14 primer pairs specific for plasmid pXO1. M, DNA marker IV (Real-Times Biotechnology).</p

Three putative replicons of plasmid pXO1 (GenBank Accession no. AF065404).

<p>Each putative replicon of pXO1 is indicated in a different color, along with primer pairs used for amplification.</p

Western blot analysis of A16R and A16RO.

<p>The <i>B. anthracis</i> vaccine strain A16R (pX01⁺ pX02⁻) (left lane), A16RO (pX01⁻pX02⁻) (middle lane), and anthrax toxin protective antigen (PA) purified by affinity chromatography (right lane). The lines indicate the location of protein bands (Blue Plus Protein Marker, TransGen Biotechnology, Beijing, China).</p

Plasmids and bacterial strains used in this study.

<p>Plasmids and bacterial strains used in this study.</p

Elimination of exogenous plasmid pKS5K from A16R5K.

<p>Strains A16R5K (1), and A16RO (2) were analyzed with vector-specific primer pairs pKSV7P3_F/R and pKSV7P6_F/R. M, DNA marker IV (Real-Times Biotechnology).</p