Biomedical subjects

Qin Xiang

Publications and source records attributed to Qin Xiang.

5 recordsLinked to original sources

PubMed2006

Chromosome rearrangement and diversification of Francisella tularensis revealed by the type B (OSU18) genome sequence.

The gamma-proteobacterium Francisella tularensis is one of the most infectious human pathogens, and the highly virulent organism F. tularensis subsp. tularensis (type A) and less virulent organism F. tularensis subsp. holarctica (type B) are most commonly associated with significant disease in humans and animals. Here we report the complete genome sequence and annotation for a low-passage type B strain (OSU18) isolated from a dead beaver found near Red Rock, Okla., in 1978. A comparison of the F. tularensis subsp. holarctica sequence with that of F. tularensis subsp. tularensis strain Schu4 (P. Larsson et al., Nat. Genet. 37:153-159, 2005) highlighted genetic differences that may underlie different pathogenicity phenotypes and the evolutionary relationship between type A and type B strains. Despite extensive DNA sequence identity, the most significant difference between type A and type B isolates is the striking amount of genomic rearrangement that exists between the strains. All but two rearrangements can be attributed to homologous recombination occurring between two prominent insertion elements, ISFtu1 and ISFtu2. Numerous pseudogenes have been found in the genomes and are likely contributors to the difference in virulence between the strains. In contrast, no rearrangements have been observed between the OSU18 genome and the genome of the type B live vaccine strain (LVS), and only 448 polymorphisms have been found within non-transposase-coding sequences whose homologs are intact in OSU18. Nonconservative differences between the two strains likely include the LVS attenuating mutation(s).

Chromosomes, Bacterial↗

PubMed2004

Microfluidic PicoArray synthesis of oligodeoxynucleotides and simultaneous assembling of multiple DNA sequences.

Large DNA constructs of arbitrary sequences can currently be assembled with relative ease by joining short synthetic oligodeoxynucleotides (oligonucleotides). The ability to mass produce these synthetic genes readily will have a significant impact on research in biology and medicine. Presently, high-throughput gene synthesis is unlikely, due to the limits of oligonucleotide synthesis. We describe a microfluidic PicoArray method for the simultaneous synthesis and purification of oligonucleotides that are designed for multiplex gene synthesis. Given the demand for highly pure oligonucleotides in gene synthesis processes, we used a model to improve key reaction steps in DNA synthesis. The oligonucleotides obtained were successfully used in ligation under thermal cycling conditions to generate DNA constructs of several hundreds of base pairs. Protein expression using the gene thus synthesized was demonstrated. We used a DNA assembly strategy, i.e. ligation followed by fusion PCR, and achieved effective assembling of up to 10 kb DNA constructs. These results illustrate the potential of microfluidics-based ultra-fast oligonucleotide parallel synthesis as an enabling tool for modern synthetic biology applications, such as the construction of genome-scale molecular clones and cell-free large scale protein expression.

Base Sequence↗

PubMed2004

Comparison of the genome of the oral pathogen Treponema denticola with other spirochete genomes.

We present the complete 2,843,201-bp genome sequence of Treponema denticola (ATCC 35405) an oral spirochete associated with periodontal disease. Analysis of the T. denticola genome reveals factors mediating coaggregation, cell signaling, stress protection, and other competitive and cooperative measures, consistent with its pathogenic nature and lifestyle within the mixed-species environment of subgingival dental plaque. Comparisons with previously sequenced spirochete genomes revealed specific factors contributing to differences and similarities in spirochete physiology as well as pathogenic potential. The T. denticola genome is considerably larger in size than the genome of the related syphilis-causing spirochete Treponema pallidum. The differences in gene content appear to be attributable to a combination of three phenomena: genome reduction, lineage-specific expansions, and horizontal gene transfer. Genes lost due to reductive evolution appear to be largely involved in metabolism and transport, whereas some of the genes that have arisen due to lineage-specific expansions are implicated in various pathogenic interactions, and genes acquired via horizontal gene transfer are largely phage-related or of unknown function.

ATP-Binding Cassette Transporters↗

PubMed2002

Bi-1,10-phenanthrolines and their mononuclear Ru(II) complexes.

A series of four biphen (phen = 1,10-phenanthroline) ligands, 2,2'-biphen (1), 3,3'-biphen (2), 2,2'-dimethylene-3,3'-biphen (3), and 2,3'-dimethylene-3,2'-biphen (4), is prepared by coupling and Friedländer methodology. The corresponding mononuclear Ru(II) complexes, [Ru(1-4)(Mebpy)(2)](2+) where Mebpy = 4,4'-dimethyl-2,2'-bipyridine, are prepared. These complexes show long wavelength electronic absorptions at 441-452 nm and emissions at 622-641 nm. Metal-based oxidations occur in the range 1.18-1.21 V, and ligand-based reductions, at -1.20 to -1.30 V. The addition of Zn(2+), Cd(2+), or Hg(2+) ions results in a strong enhancement and red shift of the luminescence of complex Ru-3. Alkali and alkaline earth metal ions barely affect the luminescence of Ru-3 while transition metal ions such as Co(2+), Cu(2+), Ni(2+), and Mn(2+) lead to efficient quenching of the Ru-3 luminescence. The luminescence of Ru-2 and Ru-4 is quenched in the presence of Zn(2+) because of a conformationally induced reduction in electronic communication between the two phen halves of the ligand. The addition of Zn(2+) has only a slight effect on the luminescence of Ru-1 because of steric hindrance toward complexation.

Journal Article↗

PubMed2002

Evolution and kinetics of volatile organic compounds generated during low-temperature polymer degradation.

A method using direct flame ionization detector (FID) measurement was developed to study total volatile organic compound (VOC) emissions during thermal degradation of polymers. This method was used to estimate organic emissions from different polymers, such as low-density polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and commingled postconsumer streams, such as recycled carpet residue and auto shredder residue (ASR). The effects of process parameters, such as temperature, heating rate, and residence time, were also studied. Significant VOC emissions were observed at normal processing temperatures, particularly from recycled polymers. Each polymer showed a distinct evolution pattern during its thermal degradation. The kinetics of VOC emissions were also studied using a nonisothermal technique. The kinetic parameters were in agreement with data from the literature.

Air Pollutants↗