Differential induction of symptoms in Arabidopsis by P6 of Cauliflower mosaic virus

The gene VI protein (P6) of Cauliflower mosaic virus (CaMV) functions as a virulence factor in crucifers by eliciting chlorotic symptoms in infected plants. The ability to induce chlorosis has been associated previously with P6 through gene-swapping experiments between strains and through the development of transgenic plants that express P6. The primary role that has been identified for P6 in the CaMV infection cycle is to modify the host translation machinery to facilitate the translation of the polycistronic CaMV 35S RNA. This function for P6 has been designated as the translational transactivator (TAV) function. In the present study, we have characterized an unusual variant of P6, derived from CaMV strain D4, that does not induce chlorosis upon transformation into Arabidopsis thaliana. The level of D4 P6 produced in transgenic Arabidopsis line D4-2 was comparable to the amount found in transgenic plants homozygous for W260 and CM1841 P6, two versions of P6 that induce strong chlorotic symptoms and stunting in Arabidopsis. A complementation assay proved that P6 expressed in the D4-2 line was functional, as it could support the systemic infection of a CM1841 mutant that contained a lethal frame-shift mutation within gene VI. This complementation assay allowed us to separately assess the contribution of CM1841 gene VI to symptom development versus the contribution of other CM1841 genes. Furthermore, a previous study had shown that the TAV activity of D4 P6 was comparable to that of W260 P6. That comparative analysis of TAV function, coupled with the characterization of the D4-2 transgenic line in the present paper, indicates that the TAV function of P6 may play only a minor role in the development of chlorotic symptoms.     

Characterization of an Enterotoxin Produced by Vibrio cholerae O139

A cholera-like enterotoxin was purified from Vibrio cholerae O139 strain AI-1841 isolated from a diarrheal patient in Bangladesh. Its characteristics were compared with that of cholera toxins (CTs) of classical strain 569B and El Tor strain KT25. Al-1841 produced as much toxin as O1 strains. The toxins were indistinguishable in terms of their migration profiles in conventional polyacrylamide gel disc electrophoresis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis and isoelectrofocusing as well as their affinity for hydroxyapatite. The skin permeability factor activity and the fluid accumulation induced in rabbit ileal loops of the toxin of AI-1841 were identical to those of the CTs. Three toxins equally reacted against anti-569B CT antiserum in Western blotting, and their B subunits formed a precipitin line against any anti-B subunit antiserum by double gel immunodiffusion. Anti-569B CTB antibody neutralized the three toxins in their PF activities and enterotoxicities. The amino acid sequence of 1841 toxin B subunit was identical with that of KT25 CTB, corresponding to the DNA sequence of ctxB from El Tor strains of the seventh pandemic. We concluded 1841 toxin was identical to CT of the seventh pandemic El Tor vibrios.     

Diversity of the fsr-gelE region of the Enterococcus faecalis genome but conservation in strains with partial deletions of the fsr operon

Most Enterococcus faecalis isolates carry gelE, but many are gelatinase nonproducers due to the lack of fsrC (EF_1820) to EF_1841 (fsrC-EF_1841; 23.9 kb in strain V583), including most of the locus encoding Fsr, which activates gelE expression. Analysis of 22 accessible E. faecalis genomes revealed the identity of the 53-amino-acid propeptide of fsrD across multiple MLSTs (multilocus sequence types), although 12 distinctly different variations were found in the EF_1814-to-EF_1902 region. Diversity was seen in fsrABC, in the region EF_1814 to EF_1902, and in a 700-kb region surrounding fsrC-EF_1841. However, analysis of five sequenced strains carrying the fsrC-EF_1841 deletion and the putative integrative conjugative element efaB5 showed almost identical single nucleotide polymorphisms (SNPs) in gelE and an identical junction sequence, despite their unrelated MLSTs, in contrast to those shown by strains without the deletion. Further analysis confirmed the conserved gelE SNPs in 6 additional strains (11 in total) with the deletion. While we were unable to detect evidence of spontaneous deletion using OG1RF and 8 other strains, we were able to engineer a deletion of the 37-kb fsrC-EF_1841 region of OG1RF without deleterious effects, and the 37-kb mutant showed changes in biofilm and chaining similar to those shown by fsr-gelE mutants. In conclusion, we describe the identity of fsrD despite high plasticity within the fsrC-EF_1841 region and the surrounding sequence. However, strains lacking the fsrC-EF_1841 region show a distinct conservation of the sequence surrounding this deletion and in gelE, suggesting that the deletion may result from horizontal transfer and recombination.     

Purification and characterization of Vibrio cholerae O139 fimbriae

Abstract A Vibrio cholerae O139 (strain Al-1841) isolated from a patient with a cholera-like disease in Bangladesh predominantly produced new curved, wavy fimbriae (Al-1841 fimbriae) and small numbers of previously reported V. cholerae non-O1 S7-like pili. The former was purified and characterized. The molecular mass of the Al-1841 fimbrial subunit was less than 2.5 kDa, and it was immunologically different from that of V. cholerae non-O1 S7 pili. This novel fimbrial antigen was detected in all 182 Gram-negative strains from five genera tested but was absent from the Gram-positive bacteria tested. The purified Al-1841 fimbriae did not agglutinate human or rabbit erythrocytes.     

Biodegradation of leuco derivatives of triphenylmethane dyes by <Emphasis Type="Italic">Sphingomonas</Emphasis> sp. CM9

A leuco derivatives of triphenylmethane dyes degrading bacterium, strain CM9, was isolated from an aquafarm field. Based on morphology, physiologic tests, 16S rDNA sequence, and phylogenetic characteristics, it was identified as Sphingomonas sp. This strain was capable of degrading leucomalachite green (LMG), leucocrystal violet and leucobasic fuchsin completely. The relationship between bacterium growth and LMG degradation suggested that strain CM9 could use LMG as the sole source of carbon. The most LMG degradation activity of CM9 crude extract was observed at pH 7.0 and at 30°C. Many metal ions had little inhibition effect on the degradation activity of the crude extract. CM9 also showed strong decolorization of triphenylmethane dyes to their leuco derivatives. GC/MS analysis detected two novel metabolic products, methylbenzene and 4-aminophenol, during the LMG degradation by CM9.     

鼠衣原体毒力基因的筛选和基因差异型菌株的建立

【目的】探讨鼠衣原体(Chlamydia muridarum,Cm)标准株与减毒株全基因组序列中存在的差异,筛选毒力基因并建立不同基因型的单克隆菌株,为后续致病机制的研究奠定基础。【方法】将Cm标准株G0和减毒株G28以高通量测序法进行全基因组测序,通过全基因组序列比对分析并筛选潜在的毒力相关基因;经空斑形成实验(Plaque assay)在混合菌G0和G28中大量挑取空斑,以毒力靶基因的PCR测序鉴定从G0和G28中筛选含有不同毒力基因型的单克隆菌株。【结果】全基因测序结果显示Cm G0与G28的TC0412、TC0237和TC0668基因明显不同。通过挑取空斑初步筛选了111个空斑样品,通过3个毒力基因的PCR测序鉴定最终获得了G0和G28来源的56个单克隆菌株,并根据TC0412蛋白型分成B3、D1和E1三组,每组中含有TC0237和TC0668基因差异性菌株。【结论】Cm的致病能力可能与TC0412、TC0237和TC0668基因有关,筛选获得的单克隆菌株通过分组匹配后可用于后续的毒力基因功能研究。     

Genome sequence of the Marine Janibacter Sp. Strain HTCC2649

Janibacter sp. strain HTCC2649 is a novel marine member of the Actinobacteria, family Intrasporangiaceae, and is closely related to Janibacter melonis CM2104(T) and Knoellia sinensis HKI 0119(T). The organism was isolated from a sample collected at Hydrostation S south of Bermuda by using high-throughput culturing techniques. Here we present the genome sequence of Janibacter sp. strain HTCC2649.     

Helicobacter pylori stimulates epithelial cell migration via CagA-mediated perturbation of host cell signaling

Helicobacter pylori CagA is delivered into gastric epithelial cells, where undergoes tyrosine phosphorylation at the Glu-Pro-Ile-Tyr-Ala (EPIYA) motif to interact with Src homology 2-containing protein tyrosine phosphatase-2 (SHP2) oncoprotein. CagA also binds to partitioning-defective 1 (PAR1) polarity-regulating kinase via the CagA multimerization (CM) sequence. To investigate pathophysiological role of CagA-SHP2 and/or CagA-PAR1 interaction in H. pylori infection, we generated H. pylori isogenic strains producing a phosphorylation-resistant CagA and a CagA without CM sequence. Infection studies revealed that deregulation of epithelial cell motility was more prominent in the wild-type strain than in the mutant strains. Thus, both CagA-SHP2 and CagA-PAR1 interactions are involved in the pathogenicity of cagA-positive H. pylori.     

Soluble di- and aminopeptidases in Escherichia K-12. Dispensible enzymes.

As part of a study of the peptidase content of Escherichia coli K-12, two peptidase-deficient amino acid auxotrophs isolated and characterized by Miller as pepD- (strain CM17) and pepD- pepN- pepA- pepB- pepQ- (strain CM89) were examined for the presence of several peptidases previously obtained from strain K-12 in this laboratory. The soluble fraction of each mutant was found to lack the broad-specificity strain K-12 dipeptidase DP and the strain CM89 fraction also lacked activity characteristic of the strain K-12 aminopeptidases AP, L, and OP; like strain CM17, strain CM89 contained the tripeptide-specific aminopeptidase TP. Strain CM89 (but not CM17) appeared to contain little if any activity attributable to the ribosome-bound aminopeptidase I of strain K-12. Whereas loss of DP, AP, OP, and aminopeptidase I activity may be attributed to the pepD-, pepB-, pepN-, and pepA- mutations, respectively, the reason for the loss of L activity remains uncertain. Grown responses of strain CM89 in liquid media containing di- or tripeptides were in accord with absence of enzymes catalyzing rapid hydrolysis of dipeptides. In synthetic liquid media supplemented with the required amino acids per se or with peptone, cultures of both CM strains grew more slowly than strain K-12 and produced smaller cell-yields than those produced by strain K-12.