The presence of major world-wide clones for phage type 4 and 8 Salmonella enterica serovar Enteritidis and the evaluation of their virulence levels by invasiveness assays in vitro and in vivo

Seventy-seven animal isolates of Salmonella enterica serovar Enteritidis (S. Enteritidis) obtained from the United States were analyzed by phage typing and pulsed field gel electrophoresis (PFGE). Thirty-nine strains were found with phage types (PT) 4, 8, and 13a. When the chromosomal DNA of these 39 isolated strains with PT4, 8, and 13a were digested with XbaI, SpeI and NotI, followed by PFGE analysis, 28 strains were found with a pattern combination of X4S4N4, which was the major subtype. When PFGE patterns of the US isolates with PT 4 and 8 were compared with those of the Taiwanese and German isolates, pattern X3S3N3 was confirmed to be the world-wide subtype shared by PT 4 isolates, as previously reported, while pattern X4S4N4 was newly found to be the most common subtype shared by PT 8 strains. The presence of such major world-wide clones, however, does not necessarily mean that these clones are highly virulent, at least not according to the results of invasiveness assays using cultured human intestinal epithelium cell line Int-407 and living BALB/mice.     

稀疏效应下周期系数捕食-被捕食系统的全局渐近稳定性

研究一类稀疏效应下周期系数捕食-被捕食系统,得到了该系统存在唯一全局渐近稳定的正周期解的充分条件．     

Effect of ecological engineering on the nutrient content of surface sediments in Lake Taihu, China

Ecological engineering was carried out in Meiliang Bay of Lake Taihu beginning in 2003 in order to improve water quality. There were two main objectives: to improve the growth environment for macrophytes, and to restore macrophyte assemblages. We examined surface sediments once per month beginning in April 2005 to study the response of sediment nutrient content to the ecological engineering. Average total nitrogen (TN) and total phosphorus (TP) concentrations in the surface sediments were 7043 and 1370 mg kg⁻¹, respectively, in May 2005, while after 1 year, TN concentration was reduced to 2929 mg kg⁻¹ and TP concentration was reduced to 352 mg kg⁻¹. We conclude that ecological engineering can lower the nutrient content in surface sediments when it is used to improve water quality.     

Analysis of Pathotypic and Genotypic Diversity of Xanthomonas oryzae pv. oryzae in China

Virulence analysis and restriction fragment length polymorphism (RFLP) were used to evaluated the population structure of Xanthomonas oryzae pv . oryzae ( Xoo ) from the main rice-growing region in China. The pathotype of Xoo was determined for 103 strains by inoculating 13 near-isogenic rice lines using IR24 as the recurrent parent. Sixty-one pathotypes was shared by these strains, on the basis of the consensus of three clustering statistics, and four clusters for pathotype were formed. Cluster 2 consists of strains with high molecular polymorphorism and many pathotypes that are either virulent to a majority of the 13 major resistance ( R ) genes or avirulent only to Xa21 , and is geographically dispersed. The resistance gene Xa21 has broader resistance than others to the strains tested. A probe from a member of the avrBs3/pthA type III effector family, 1376 bp Sph I-digested fragment, was used to screen the genomes of 52 strains tested. Four common bands were found in the DNA fingerprint pattern of Xoo , suggesting basic patterns of evolutionary relationship for members of avrBs3/pthA family and/or the pathogen. Each distinct RFLP banding pattern of each strain was considered as a haplotype; 42 haplotypes were revealed by the probe and divided into four lineages by the same statistics method. It was observed that some isolates with different pathotypes shared the same haplotype and others with different haplotypes harboured identical pathotype. There was a weak correlation between virulent pathotypes and molecular haplotypes.     

RhoA/ROCK-mediated switching between Cdc42- and Rac1-dependent protrusion in MTLn3 carcinoma cells

Rho GTPases are versatile regulators of cell shape that act on the actin cytoskeleton. Studies using Rho GTPase mutants have shown that, in some cells, Rac1 and Cdc42 regulate the formation of lamellipodia and filopodia, respectively at the leading edge, whereas RhoA mediates contraction at the rear of moving cells. However, recent reports have described a zone of RhoA/ROCK activation at the front of cells undergoing motility. In this study, we use a FRET-based RhoA biosensor to show that RhoA activation localizes to the leading edge of EGF-stimulated cells. Inhibition of Rho or ROCK enhanced protrusion, yet markedly inhibited cell motility; these changes correlated with a marked activation of Rac-1 at the cell edge. Surprisingly, whereas EGF-stimulated protrusion in control MTLn3 cells is Rac-independent and Cdc42-dependent, the opposite pattern is observed in MTLn3 cells after inhibition of ROCK. Thus, Rho and ROCK suppress Rac-1 activation at the leading edge, and inhibition of ROCK causes a switch between Cdc42 and Rac-1 as the dominant Rho GTPase driving protrusion in carcinoma cells. These data describe a novel role for Rho in coordinating signaling by Rac and Cdc42.     

Utility of the trnH–psbA Intergenic Spacer Region and Its Combinations as Plant DNA Barcodes: A Meta-Analysis

Background

The trnH–psbA intergenic spacer region has been used in many DNA barcoding studies. However, a comprehensive evaluation with rigorous sequence preprocessing and statistical testing on the utility of trnH–psbA and its combinations as DNA barcodes is lacking.

Methodology/Principal Findings

Sequences were searched from GenBank for a meta-analysis on the usefulness of trnH–psbA and its combinations as DNA barcodes. After preprocessing, we constructed full and matching data sets that contained 17 983 trnH–psbA sequences and 2190 sets of trnH–psbA, matK, rbcL, and ITS2 sequences from the same sample, repectively. These datasets were used to analyze the ability of trnH–psbA and its combinations to discriminate species by the BLAST and BLAST+P methods. The Fisher''s exact test was used to evaluate the significance of performance differences. For the full data set, the identification success rates of trnH–psbA exceeded 70% in 18 families and 12 genera, respectively. For the matching data set, the identification rates of trnH–psbA were significantly higher than those of the other loci in two families and four genera. Similarly, the identification rates of trnH–psbA+ITS2 were significantly higher than those of matK+rbcL in 18 families and 21 genera.

Conclusion/Significane

This study provides valuable information on the higher utility of trnH–psbA and its combinations. We found that trnH–psbA+ITS2 combination performs better or equally well compared with other combinations in most taxonomic groups investigated. This information will guide the optimal usage of trnH–psbA and its combinations for species identification.     

BST-2抑制HIV-1病毒样颗粒释放的研究

BST-2是最近发现的可以抑制成熟HIV-1(human immunodeficiency virus,HIV)病毒颗粒从哺乳动物细胞表面释放的宿主因子,随之发现其也可以抑制多种包膜病毒的释放。本研究采用密码子优化的表达HIV-1 gag和gag-pol蛋白的质粒所形成的病毒样颗粒作为研究对象,观测BST-2对这两种病毒样颗粒(Virus-like particle,VLP)的释放抑制情况及其作用机制。结果发现,瞬时表达和稳定表达的BST-2均可以显著抑制病毒样颗粒从哺乳动物细胞释放,同时发现这两种病毒样颗粒(gag/gag-pol)的释放都可以被BST-2抑制;而且,HIV-1中Vpu蛋白可以拮抗BST-2抑制HIV病毒样颗粒释放的作用,另外,通过化学试剂和酶学方法处理,确证BST-2可以被包装进病毒样颗粒中。